# Theoretical Physics Seminars

## Wednesday 11th May - Non-perturbative renormalisation with interpolating momentum schemes

Speaker: Nicolas Garron (Liverpool Hope University)

13: Room TP117 (plus on Zoom)

Abstract: Hadronic matrix elements evaluated on the lattice can be converted to a continuum scheme such as MS using intermediate non-perturbative renormalisation schemes. Discretisation eects on the lattice and convergence of the continuum perturbation theory are both scheme dependent and we explore this dependence in the framework of the Rome-Southampton method for generalised kinematics. In particular, we implement several non-exceptional interpolating momentum schemes, where the

momentum transfer is not restricted to the symmetric point dened in RI/SMOM. Using avour non-singlet quark bilinears, we compute the renormalisation factors of the quark mass and wave function for Nf = 3 avours of dynamical quarks. [https://arxiv.org/abs/2112.11140]

## Wednesday 23rd March 2022 - Gravitational waves from Feynman diagrams

Speaker: Andreas Maier (DESY, Zeuthen)

13:00 via Zoom

Abstract - An accurate understanding of binary black hole and neutron star systems is essential to interpret experimentally observed gravitational wave signals. I show how the early-inspiral dynamics can be predicted using well-known techniques from particle physics, namely a non-relativistic effective field theory and Feynman diagrams. I discuss recent results at fifth order in the post-Newtonian expansion in small velocities and weak gravitational coupling.

## Wednesday 16th February 2022 - Inhomogeneous Phases - From Toy Models To QCD

Fundamental Particle Physics

Speaker: Julian Lenz, University of Jena

13:00 via Zoom

Abstract: In this talk, I will review recent progress on the QCD phase diagram at non-vanishing baryon density from a particular family of toy models, namely four-Fermi theories. Various approaches find traces of inhomogeneities at low temperatures and intermediate chemical potentials which has inspired according conjectures for QCD. Starting from our MC simulations of 1+1D, I will highlight several such findings successively closer to QCD but also shed a light on open questions and problematic aspects in these investigations, which render the conclusions for QCD still disputed.

## Wednesday 11th November 2020 - The Semimetal-Mott Insulator Quantum Phase Transition of the Hubbard Model on the Honeycomb Lattice

Speaker: Evan Berkowitz (University of Maryland)

13:00 via Zoom

Abstract: I describe recent large-scale grand-canonical numerical studies of the fermionic Hubbard Model, a model of electrons with nearest-neighbor hopping and on-site interactions, formulated on a honeycomb lattice. In particular, I will focus on the quantum phase transition between the gapless semi-metal and gapped Mott-insulating phase, giving a sytematically controlled rst-principles determination of the critical coupling and associated critical exponents, after giving an introduction to the Hubbard Model and our rst-principles numerical approach. I will focus on results in 2005.11112 Ostmeyer, EB, Krieg, Lähde, Luu and Urbach but will also touch on some results in 1710.06213 EB, Körber, Krieg, Labus, Lähde, and Luu 1812.09268 Wynen, EB, Körber, Lähde, and Luu 2006.11221 Wynen, EB, Krieg, Luu, and Ostmeyer.

## Tuesday 10th November 2020 - Control issues of KKLT

String and Beyond the Standard Model Phenomenology

Speaker: Daniel Junghans (Harvard)

15:30 via Zoom

Abstract: We analyze to which extent the KKLT proposal for the construction of de Sitter vacua in string theory is quantitatively controlled. Our focus is on the quality of the 10d supergravity approximation. As our main finding, we uncover and quantify an issue which one may want to call the "singular-bulk problem". In particular, we show that, requiring the curvature to be small in the conifold region, one is generically forced into a regime where the warp factor becomes negative in a significant part of the Calabi-Yau orientifold. This implies true singularities, independent of the familiar, string-theoretically controlled singularities of this type in the vicinity of O-planes.

## Wednesday 4th November 2020 - Phenomenology of Z bosons and Minimal Models

Speaker: Juri Fiaschi (University of Liverpool)

13:00 via Zoom

Abstract: In this talk will be presented an overview of the phenomenology of BSM models featuring an extra heavy neutral resonance, usually called Z^{1}-boson, and of Minimal Models, a simple extension of the SM that can account for dark matter and explain the existence of neutrino masses, which are generated radiatively. Theoretically inspired BSM models featuring a Z^{1} boson will be introduced and their phenomenology will be explored in relation with the usual CMS and ATLAS experimental analysis. Some critical aspects of the latter will be discussed, motivating the introduction of extra observables to improve the sensitivity for both detection and diagnosis of Z^{1} signals, with particular focus on less conventional scenarios featuring resonance with large width and multiple resonant proles. General features of Minimal Models will be introduced and the phenomenology of two examples will be discussed. Their parameter space will be tested against recent results from collider, low energy and direct detection experiments, and in relation with cosmological observations.

## Tuesday 3rd November 2020 - Supersymmetric Protection and the Swampland

String and Beyond the Standard Model Phenomenology

Speaker: Eran Palti (Ben Gurion University)

13:30 via Zoom

Abstract: For certain terms in the action, supersymmetry can forbid an infinite number of possible contributions. We study whether such protection can occur in quantum gravity even without sufficient supersymmetry. We focus on whether the superpotential can vanish exactly in four-dimensional N=1 theories, and if the prepotential can be exactly cubic in N=2 theories. We investigate these questions in string theory and find that for almost all known string constructions the corrections allowed by supersymmetry do occur. However, we do find some special settings where all the corrections can be proven to vanish. These examples all share the common feature that they are related, through a certain orbifolding by a discrete gauged R-symmetry element, to a higher supersymmetric theory. Motivated by these results, we propose a Swampland criterion that any theory which enjoys such protection beyond its realised supersymmetry must have a direct connection to a higher supersymmetric theory.

The talk is based on the arXiv paper: arXiv:2003.10452

## Wednesday 28th October 2020 - Is the MiniBooNE Anomaly due to New Physics?

Speaker: Oliver Fischer (University of Liverpool)

13:00 via Zoom

Abstract: Recently the MiniBooNE collaboration consolidated the observation of an excess of electron-like events, which is generally referred to as the MiniBooNE anomaly. A natural explanation for this excess is neutrino oscillation, implying the existence of a fourth neutrino mass eigenstate with a mass around 1 eV, which is incompatible with the global neutrino data set. A number of New Physics models exist to explain this excess, all of which feature heavy neutrinos with masses around the MeV scale. In this talk I will show that it is possible to systematically test any new physics explanation of the MiniBooNE anomaly with dierent experiments. In particular the T2K near detector (but also many others) strongly disfavours most scenarios at the 3 sigma level with current data. Thus the conclusion of our systematic approach is that the observed excess of events by MiniBooNE is unlikely to be due to new physics.

## Wednesday 21st October 2020 - Three Pion Scattering from Lattice QCD

Speaker: Chris Culver (University of Liverpool)

13:00 via Zoom

Abstract: Three-body states are critical to the dynamics of many hadronic resonances. We show that lattice QCD calculations have reached a stage where these states can be accurately resolved. We perform a calculation over a wide range of parameters and find all states below inelastic threshold agree with predictions from a state-of-the-art phenomenological formalism. This also illustrates the reliability of the formalism used to connect lattice QCD results to infinite volume physics. Our calculation is performed using three positively charged pions, with different lattice geometries and quark masses.

## Tuesday 20th October 2020 - String Defects, Supersymmetry and the Swampland

String and Beyond the Standard Model Phenomenology

Speaker: Emilian Dudas (Ecole Polytechnique)

13:30 via Zoom

Abstract: We test Kim, Shiu and Vafa consistency conditions of six dimensional supergravity theories, coming from couplings to strings, in explicit orientifold models. Based on the perturbative data, we conjecture the existence of null charges Q·Q= 0 for models with at least one tensor multiplet, coupling to string of charge Q. We use the new constraint to exclude some six-dimensional supersymmetric anomaly-free examples that have currently no string or F-theory realization. We also investigate the constraints in case where supersymmetry is broken in tachyon free vacua, with the breaking localized on antibranes.

## Wednesday 14th October 2020 - New tool for old problems – Tensor network approach to spin models and gauge theories

Speaker: Raghav Jha (Perimeter Institute, Waterloo, Ontario)

13:00 via Zoom

Abstract: The tensor renormalization group approach has emerged as a useful numerical method to understand lower-dimensional statistical systems and gauge theories. I will discuss the problems we have studied using these techniques and mention some interesting future directions. The talk will be based on https://arxiv.org/abs/1901.11443 and https://arxiv.org/abs/2004.06314 and work in progress.

## Tuesday 6th October 2020 - Goldstino evaporation and de Sitter decay

String and Beyond the Standard Model Phenomenology

Speaker: Fotis Farakos (Padua)

13:30 via Zoom

Abstract: We study the restoration of supersymmetry within systems where it is intrinsically non-linearly realized and we discuss physical applications of such a procedure related to de Sitter vacua.

## Tuesday 29th September 2020 - Merging Swampland Conjectures using strings and membranes

String and Beyond the Standard Model Phenomenology

Speaker: Irene Valenzuela (Harvard)

12:30pm via Zoom

Abstract: In this talk I will discuss new relations that appear among the Swampland Conjectures when analysing the properties of low codimension BPS objects, in particular strings and membranes in N=1 4D EFTs. I will review the state of the art of the Swampland program and revisit some of the most important conjectures, namely the Weak Gravity Conjecture (WGC) and the Swampland Distance Conjecture (SDC). Then I will describe how to apply the WGC to low codimension BPS objects by interpreting the 4d backreaction of these objects as a classical RG flow of their couplings. Constraints on the UV charges and tensions get then translated to constraints on the axionic kinetic terms and scalar potential of the EFT, which uncovers new relations among the Swampland Conjectures. In particular, we show that the WGC for strings implies the SDC, by using that infinite distance limits can be realised as RG flow endpoints of fundamental axionic strings. Similarly, WGC-saturating membranes generate a scalar potential satisfying the de Sitter Conjecture.

## Tuesday 11th August 2020 - On the quantum origin of Lambda

String and Beyond the Standard Model Phenomenology

Speaker: Saurya Das (University of Lethbridge)

13:30 via Zoom

Abstract: Replacing perfect fluid geodesics by their quantal trajectories, we compute the quantum correction to the Raychaudhuri-Friedmann equation in cosmology. The correction term depends on the wavefunction of the fluid. Assuming that it is a Bose-Einstein condensate of light bosons described by a suitable wavefunction, we show that the density of the condensate can account for the observed Dark Matter while the quantum correction can account for the observed cosmological constant. We discuss its implications.

## Tuesday 4th August 2020 - Some comments on de Sitter horizons

String and Beyond the Standard Model Phenomenology

Speaker: Dionysios Anninos (King's College, London)

13:30 via Zoom

Abstract: We discuss properties of the cosmological horizon of a de Sitter universe, and compare to those of ordinary black holes. We consider both the Lorentzian and Euclidean picture. We discuss the relation to the sphere partition function and give a group-theoretic picture in terms of the de Sitter group. Time permitting we discuss some properties of three-dimensional de Sitter theories with higher spin particles.

## Tuesday 21st July 2020 - Tension between a vanishing cosmological constant and non-supersymmetric heterotic orbifolds

String and Beyond the Standard Model Phenomenology

Speaker: Stefan Groot Nibbelink (Rotterdam University)

13:30 via Zoom

Abstract: We investigate under which conditions the one-loop cosmological constant vanishes for heterotic strings on non-supersymmetric toroidal orbifolds. To obtain model-independent results, we require that each orbifold sector preserves at least a single Killing spinor, but not always the same one. The existence of such Killing spinors is related to the representation theory of the point groups that underly the orbifold geometries. Going through all inequivalent (Abelian and non-Abelian) point groups of six-dimensional toroidal orbifolds shows that this is never possible: For any non-supersymmetric orbifold there is always (at least) one sector, that does not admit any Killing spinor and hence gives a non-vanishing contribution to the partition function which most likely results in a too large cosmological constant. (The underlying reason for this can be phrased as a mathematical conjecture, which was tested for a much larger class of finite groups.) This result shows that it is very challenging to obtain a tiny cosmological constant on non-supersymmetric heterotic orbifolds.

## Wednesday 4th March 2020 - Color Conﬁnement, Bose-Einstein Condensation and Holographic Emergent Space

Speaker: Masanori Hasanada (University of Southampton)

13:00 MATH-117

Abstract: We propose a unified description of two important phenomena: color confinement in large-*N* gauge theory, and Bose-Einstein condensation (BEC). The key lies in relating standard criteria, based on off-diagonal long range order (ODLRO) for BEC and the Polyakov loop for gauge theory: the constant offset of the distribution of the phases of the Polyakov loop corresponds to ODLRO. Indistinguishability associated with the symmetry group - *SU(N)* or *O(N)* in gauge theory, and *S _{N}* permutations in the system of identical bosons - is crucial in either case. This viewpoint may have implications for confinement at finite

*N*, and for quantum gravity via gauge/gravity duality.

## Tuesday 11th February 2020 - Spacetime Geometry from the String Perspective

String and Beyond the Standard Model Phenomenology

Speaker: Severin Bunk (University of Hamburg)

13:30 MATH-117

Abstract: In this talk we present three very different, but related perspectives on the B-field and Chan-Paton bundles. First, we describe them as geometric objects on spacetime. This requires the language of bundle gerbes, twisted vector bundles, and higher structures, to which we will give a gentle introduction.

Second, we describe the B-field and Chan-Paton bundles using configuration spaces of strings, i.e. as bundles on loop and path spaces associated to the spacetime manifold. These bundles carry lifts of operations on paths, such as concatenation, which encode the string interactions.

Finally, we provide a worldsheet perspective on the B-field and Chan-Paton bundles, which leads to a formalisation of the Wess-Zumino term as a smooth TQFT. Showing that these perspectives are all equivalent is the subject of ongoing joint work with Konrad Waldorf.

## Wednesday 11th December 2019 - Gravitational waves from a strong electroweak phase transition

Speaker: David Weir (Helsinki University)

13:00 MATH-117

Abstract: In the Standard Model, the electroweak phase transition is a crossover. In many extensions, the phase transition can be of first order - even strongly so. The resulting phase transition results in collisions of bubbles of the new Higgs phase. These collisions, and the associated interactions of sound waves in the plasma, are substantial sources of gravitational waves. For a phase transition at or around the electroweak scale, these gravitational waves may be detectable by future or planned missions, such as LISA. This can indirectly provide a probe of particle physics beyond the Standard Model, complementary to future colliders. In this talk I will discuss the physics that will make this possible and present some new simulation results for strong phase transitions, showing how vorticity is generated.

## Wednesday 20th November 2019 - Exact saddle points and Lefschetz thimbles decomposition for lattice fermionic models.

Speaker: Maksim Ulybyshev (University of Würzburg)

13:00 MATH-117

Abstract: The sign problem represents one of the most significant challenges in modern computational physics. Quite often, the action in the functional integral is still complex even after the Wick rotation. It thus follows that one can not apply importance sampling in a straightforward fashion, since the computational complexity scales exponentially with system size and inverse temperature. Two the most prominent examples of the sign problem include lattice QCD and the Hubbard model at finite chemical potential, the latter is probably relevant to high temperature superconductors.

The recently proposed Lefschetz thimbles formalism provides firm mathematical ground to weaken the sign problem. In general, it relies on the shift of the integration manifold from real to complex space, where we can construct an optimal contour, which consists of so-called "thimbles": manifolds, attached to the saddle points of the action. However, there are still two major obstacles on the way. First of all, there might be many relevant saddle points and thus many thimbles, contributing to the optimal contour, all with different complex phases. The second potential difficulty is the fluctuations of the complex measure during the integration over the curved manifolds in complex space.

Here we present the study of the structure of Lefschetz thimbles decomposition for lattice fermionic models taking Hubbard models on square and hexagonal lattice as examples. We show how the complexity of the decomposition scales with the system size, working on large enough lattices to be able to trace the behaviour of the saddle points up to the thermodynamic and zero-temperature limits. The connections between the structure of the saddle points and the physics of the models is demonstrated. We also show that even in the thermodynamic limit, there can be only one important thimble contributing to the integration contour, depending on the details of the path integral representation of the model. In addition to the results outlined above, we present the algorithms used in thestudy, which are suitable not only for condensed matter systems, but also for lattice QCD.

## Wednesday 13th November 2019 - A falsifiable explanation of the MiniBooNE anomaly

Speaker: Oliver Fischer (Karlsruhe Institute of Technology)

13:00 MATH-107

Abstract: The MiniBooNE experiment was designed to test the LSND anomaly, and it found evidence for neutrino oscillations that contradict the global data set on short baseline experiments. In this talk I will give a non-standard explanation for the observed so-called "electron-like signal" that revolves around a BSM particle, a heavy neutrino with a mass of a few hundred MeV. This particle is produced from kaon decays after the proton beam-target interaction and decays inside the detector into a single photon and a light neutrino. Being heavy, the new neutrinos arrive later than the light ones, such that their decays give rise to electron-like events with a very characteristic time spectrum that cannot be mimicked by the light neutrinos.

## Tuesday 5th November 2019 - Hasse Diagrams for Higgs Branches

String and Beyond the Standard Model Phenomenology

Speaker: Julius Grimminger (Imperial College, London)

13:30 MATH-117

Abstract: In my talk I will review some facts about the Higgs effect and Higgs branches of gauge theories with 8 supercharges and then explain the recent progress in analysing the Higgs branch both classically and at UV fixed points of certain theories in 5 and 6 dimensions. The partial order of partial Higgsings of a gauge theory with 8 supercharges matches the partial order of inclusion of closures of the symplectic leaves that make up its Higgs branch. The Hasse diagram is a graphical depiction of a partial ordering and as such a central tool in studying Moduli spaces of quantum field theories with 8 supercharges.

## Wednesday 30th October 2019 - CP violation in Kaons and an emerging anomaly

Fundamental Particle Physics

Speaker: Maria Cerda-Sevilla (Technische Universität München)

13:00 MATH-117

Abstract: Novel lattice results reveal a tension between the measured direct CP violation in K → ππ decays and the standard model theory prediction, with the theoretical uncertainty dominating. This inconsistency could have several sources, one of which could be the missing contribution of new particles in the theory predictions. However, a reliable standard model prediction is needed to disentangle possible new physics effects from the standard model background. As rapid progress on the lattice is bringing non-perturbative long-distance eects under control, a more precise knowledge of short-distance contributions is essential. We describe the first NNLO calculation for this observable and discuss future prospects, as well as issues of scheme dependence and the separation of perturbative and non-perturbative effects.

## Tuesday 29th October 2019 - The symplectic structure and Dirac quantization of string effective actions

String and Beyond the Standard Model Phenomenology

Speaker: Carlos Shahbazi (University of Hamburg)

13:30 MATH-117

Abstract: String theory compactified on a Calabi-Yau three-fold or a balanced Hermitian complex manifold is effectively described by a supergravity theory in four dimensions. Whereas the local structure, couplings, and phenomenology of four-dimensional supergravity have all been extensively studied in the literature, its global geometric structure remains to be elucidated. Understanding the global structure of string effective actions is of utmost importance in order to understand the U-fold structure of its physical solutions and the global geometry and moduli of its supersymmetric solutions. In this talk a will give a pedagogical introduction to recent developments on the geometric theory of four-dimensional supergravity, focusing on the description of its symplectic structure, which governs the couplings between scalars and gauge fields, and its Dirac quantization, which is based on a bundle of polarized abelian varieties over the scalar manifold of the theory and determines the notion of gauge field in the theory. Work in collaboration with C. Lazaroiu.

## Wednesday 16th October 2019 - Modelling lattice gluon propagators using gluon mass and Gribov copies

Speaker: Prof John Gracey (University of Liverpool)

13:00 MATH-117

Abstract: We report on a two loop computation of the gluon and ghost propagators in the Landau gauge which quantitatively fits lattice data over all momenta. The background to achieve this is reviewed first which is an extension of the usual QCD Lagrangian but where the effect of averaging over Gribov copies is included. The additional structure means that in the replica limit the influence of Gribov copies in the infrared is correctly included. While it is known that this generalized theory is equivalent to the Curci-Ferrari model the novel feature of these recent developments is that the associated gluon mass parameter derives from the copies and in effect acts as a second gauge parameter. Previous one loop results using the Curci-Ferrari model gave qualitative agreement with the lattice. The technical aspects of computing the two loop gluon and ghost propagators exactly with a non-zero gluon mass are also discussed.

## Tuesday 15th October 2019 - Gravitational waves and fundamental physics

String and Beyond Standard Model Phenomenology

Speaker: Cyril Lagger (University of Liverpool)

13:00 MATH-117

Abstract: The detection of gravitational waves (GWs) by LIGO/Virgo offers promising opportunities to probe the fundamental laws of the Universe. GW physics is not only relevant to our understanding of gravity but can also shed light on the interplay between particle physics and cosmology. I discuss here both aspects. First, I show how the waveforms observed by LIGO/Virgo allow us to constrain theories of gravity beyond general relativity, such as the idea of noncommutative space-time. Second, I discuss how the potential detection of GWs produced from first-order phase transitions during the early Universe may provide valuable information for particle physics beyond the Standard Model.

## Wednesday 11th September 2019 - Real time gauge theory dynamics: Programing gauge theory on quantum computers

Speaker: David Berenstein (University of California at Santa Barbara)

13:00 MATH-117

Abstract: I will address why a quantum computing device can in principle solve real time gauge theory problems. I will then address how to implement such a setup and what the challenges are. In particular, I show how truncations of an electric representation of the Kogut-Susskind lattice Hamiltonian can be implemented into qubit machines.

## Wednesday 15th May 2019 - Lattice field theory with worldlines and worldsheets

Speaker: Christof Gattringer (University of Graz, Austria)

13:00 MATH-117

Abstract: In recent years many lattice field theories were exactly rewritten in terms of worldlines and worldsheets. Such a change of the degrees of freedom puts emphasis on different aspects of the theory. In particular some quantities such as the particle number or also theta terms appear as topological invariants (winding numbers) of the new degrees of freedom, and in several cases the transformation solves the complex action problem from such terms. In the talk we give an introduction to the newly developed techniques and discuss several examples of physical systems in the worldline/worldsheet representation.

## Tuesday 14th May 2019 - KKLT de Sitter vacua in the swampland era

String and Beyond the Standard Model Phenomenology

Speaker: Pablo Soler (Heidelberg)

12:30 MATH-117

Abstract: A series of conjectures have been recently proposed to distinguish effective field theories that can be consistently coupled to quantum gravity from those which cannot. The latter do not arise as low energy limits of string compactifications and are said to live in the Swampland. The most recent of the swampland conjectures argues that theories of quantum gravity with de Sitter (dS) minima are inconsistent. If correct, it would imply that well known dS constructions in string theory (e.g. the KKLT and the Large Volume Scenarios) are secretly pathological. I will review some motivations behind the no-dS swampland conjecture and discuss recent insights on the consistency of the KKLT scenario.

## Wednesday 8th May 2019 - Application of large-N resummations to the a-theorem

Speaker: Nicola Dondi (CP^{3}, Odense, Denmark)

13:00 Math-117

Abstract: In recent years there has been a revival of large-*N* methods in gauge theories, with *N* being the number of gauged fermion fields. I will present the explicit diagram resummation approach for calculating leading order large-*N* contributions to renormalisation group functions in the appropriate 't Hooft coupling. This method is flexible enough to access various quantities in the local renormalisation group framework as well. In particular, my focus will be on the calculation of the Zamolodchikov metric for four-dimensional gauge theories. The leading order large-*N* contribution shows a finite radius of convergence in coupling space, as well as positivity violation for coupling values well within such radius, making it reachable by ordinary perturbation theory at sufficient high order. I will then discuss implications for the *a*-theorem as well as extensions in which vector current operators are included in the formalism.

## Wednesday 3rd April 2019 - The Tower of Effective Field Theories for Dark Matter Direct Detection

Speaker: Fady Bishara (DESY, Hamburg)

13:00 MATH-117

Abstract: The existence of Dark Matter (DM) is observationally well established due to its gravitational interactions. If, in addition, DM is a particle which has interactions with the SM, complementarity (i.e. direct, indirect, and collider searches together) will play a crucial role in identifying its putative particle nature and perhaps in unraveling the underlying model. However, complementarity between different search strategies also entails the comparison of experimental results obtained at different energy scales. Further, in direct detection, which is the topic of this talk, the scale of interaction between the DM and atomic nuclei is widely separated from the scales of the DM model itself in a large class of models.

In this talk, I will describe our work to write down a consistent tower of effective field theories (EFTs) to connect all relevant intervening energy scales down to the nuclear scale. In particular, I will discuss the role of meson exchanges and operator mixing due to renormalization group running above the electroweak scale and will show a few examples to illustrate their effect on direct detection scattering rates which can be sizeable. Finally, I will present a Mathematica and python package 'DirectDM' which performs all the required matching and running automatically.

## Tuesday 2nd April 2019 - Unraveling the Hubble constant tension

String and Beyond the Standard Model Phenomenology

Speaker: Eleonora Di Valentino (University of Manchester)

MATH-117 12:30

Abstract: The Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the Planck mission have provided a strong confirmation of the LCDM model of structure formation. However, there are a few interesting tensions that leave the door open to possible extensions to LCDM, like the Hubble constant one. I will review some interesting extended cosmological scenarios, in order to find a new concordance model that could explain and relieve tensions in current cosmological data.

## Wednesday 27th March 2019 - Fixed points and universality classes for graphene

Speaker: Prof John Gracey (University of Liverpool)

13:00 MATH-117

Abstract: The Gross-Neveu (GN) and Gross-Neveu-Yukawa (GNY) theories have recently seen a resurgence in interest due to a potential connection with a phase transition in graphene. In order to improve our understanding of the associated critical exponents perturbative and large N methods are used to compute these to high precision. Recent results and methods are discussed and are shown to be competitive with other analytic methods. In addition the coupling of GN and GNY to QED will also be covered. At some fixed points there is an emergent symmetry where the theory is critically equivalent to another with a larger symmetry group. Several cases of these are mentioned and an example in scalar ø^{3} theory in six dimensions is also discussed.

## Tuesday 26th March 2019 - Remaining Positive

String and Beyond the Standard Model Phenomenology

Speaker: Claudia de Rham (Imperial College, London)

12:30 MATH-117

Abstract: I will review different classes of effective field theories that have played significant roles for cosmology. They come with a set of signatures which has already allowed to distinguish them with current observations and I will discuss the interplay between observational and theoretical constraints. I will also develop some “positivity bounds” diagnoses which allows us to establish if and when effective field theories could enjoy a standard high energy completion.

## Wednesday 20th March 2019 - Axions and X-ray polarimetry

Speaker: Francesca Day (University of Cambridge)

MATH-117 13:00

Abstract: Axions are one of the best motivated extensions to the Standard Model, both solving the strong CP problem and providing a natural dark matter candidate. X-Ray telescope observations have already placed world leading bounds on the axion-photon coupling by searching for axion-photon interconversion in the magnetic fields of galaxy clusters. However, current X-ray telescopes are unable to exploit one of the most striking features of this effect: only photons polarised parallel to the background magnetic field mix with axions. This leads to distinctive polarisation signatures from astrophysical sources. The next generation of polarising X-ray telescopes could detect these signatures. I will discuss the opportunities and diffculties of

detecting axions with X-ray polarimetry.

## Wednesday 13th March 2019 - Effective field theory and the electroweak sector

Speaker: Veronica Sanz (University of Sussex)

13:00 MATH-117

Abstract: I will give a pedagogical introduction to the use of EFTs in characterising data from the LHC and other colliders. I will explain how this framework allows us to systematically improve predictions and also make a connection to models of new physics at multi-TeV scales. I will also explain how experiments are adopting EFTs as a way to communicate with theorists and preserve data. I will finish with a look up on future directions on this area.

## Wednesday 6th March 2019 - Bounds and Prospects for Stable Multiply Charged Particles at the LHC

Speaker: Sandra Kvedaraite (University of Sussex)

13:00 MATH-117

Abstract: Colored and colorless particles that are stable on collider scales and carry exotic electric charges exist in extensions of the Standard Model, and can include top partners in solutions of the hierarchy problem. In this talk, I will present our recast of two production channels of such particles: the "open" channel - where particles are pair-produced above threshold, and are detectable in dedicated LHC searches for stable multiply charged leptons, and the "closed" channel - where a particle-antiparticle pair is produced as a bound state, detectable in searches for a diphoton resonance. We obtain current and projected bounds on the masses of the multiply charged particles. Moreover, we show how a joint observation in the open and the closed channels would allow us to determine the mass, spin, color, and electric charge of the particle. The talk is based on arxiv:1812.03182.

## Tuesday 5th March 2019 - Non-geometric Calabi-Yau backgrounds in String Theory

String and Beyond the Standard Model Phenomenology

Speaker: Chris Hull (Imperial College, London)

13:00 MATH-117

Abstract: String theory duality symmetries can be used to glue together different patches of a solution to construct what have been called ‘non-geometric spaces’; these can be good solutions of string theory even though they would not be allowed in supergravity. In this talk, some recent work with Israel and Sarti will be described that constructs non-geometric analogues of Calabi-Yau manifolds in which patches are glued together with mirror symmetry transformations to construct a ‘mirrorfold'. These solutions preserve the same amount of supersymmetry as Calabi-Yau spaces, but typically have far fewer light moduli and so lead to models with far fewer light particles.

## Tuesday 26th February 2019 - Double Field Theory on Para-Hermitian Manifolds

String and Beyond the Standard Model Phenomenology

Speaker: Richard Szabo (University of Edinburgh)

13:00 MATH-117

Abstract: We briefly review the arguments that T-duality leads to doubled geometry and non-geometry in string theory, and how these notions are partially captured by generalized geometry and double field theory. We then describe how the latter two descriptions can be unified into a global and rigorous formulation of doubled target spaces as para-Hermitian manifolds. We will work through the main ideas and definitions of para-Hermitian geometry, together with many examples, and how they reduce to generalized geometry and double field theory on flat space as special instances.

## Tuesday 19th February 2019 - From Static to Cosmological Solutions of N = 2 Supergravity

Speaker: Giacomo Pope (University of Liverpool)

13:00 MATH-117

Abstract: I will talk about the construction of a family of solutions to theories of $\N=2$ vector multiplets coupled to supergravity, which interpolate between the Nernst brane solutions of gauged supergravity and planar horizon solutions of the gauged and ungauged STU-model. While the latter initially appear to be black holes with planar horizons, I will show by analytic extension that they are actually cosmological solutions. The planar Killing horizon is sourced by the presence of repulsive brane sources. These solutions are related to, for special choices of the parameters and in the ungauged case, to brane cosmologies discussed previously in the literature. I will outline the various uplifts to five, six, ten and eleven dimensions for the ungauged solution, comparing the string/M-theory embeddings to their spherically symmetric counterparts. By taking the extremal limit in six dimensions we obtain a BPS solution by fine tuning the integration parameters.

## Wednesday 13th February 2019 - The Implications of Decoupling New Physics

Speaker: Tevong You (University of Cambridge)

13:00 MATH-117

Abstract: The Higgs boson appears to be Standard-Model-like to a first approximation with no accompanying particles close to the weak scale. New physics must therefore be decoupled to heavier scales. However, signs of deviations from the Standard Model may be appearing in precision measurements of B meson decays. In this context, I will discuss the implications of decoupling new physics to heavier scales for phenomenology, model-building, and future colliders.

## Wednesday 6th February 2019 - Quantum chaos, thermalization and entanglement generation in matrix quantum mechanics

Speaker: Pavel Buividovich (University of Regensburg)

13:00 MATH-117

Abstract: We study numerically the onset of chaos and thermalization in the Banks-Fischler-Shenker-Susskind (BFSS) matrix model, which is holographically dual to a higher-dimensional black hole. We approximate the real-time dynamics in terms of the most general Gaussian density matrices with parameters which obey self-consistent equations of motion, extending the applicability of real-time simulations beyond the classical limit. Thus attempting to bridge between the low-energy regime with a calculable holographic description and the classical regime at high energies, we find that quantum corrections to classical dynamics tend to decrease the Lyapunov exponents, which is essential for consistency with the Maldacena-Shenker-Stanford (MSS) "bound on chaos" at low temperatures. The entanglement entropy is found to exhibit an expected "scrambling" behavior - rapid initial growth followed by saturation. Decay of quasinormal modes is found to be characterized by the shortest time scale of all. We also find that while the bosonic matrix model becomes non-chaotic in the low-temperature confining regime, the full supersymmetric BFSS model remains chaotic and dissipative down to the lowest temperatures, in full accord with the expected dual black hole picture.

## Tuesday 5th February 2019 - Toward machine learning in the classification of Z2xZ2 orbifolds

String and Beyond the Standard Model Phenomenology

Speaker: Prof Alon Faraggi (University of Liverpool)

13:00 MATH-117

Abstract: Systematic classification of Z2xZ2 orbifold compactifications of the heterotic-string was pursued by using its free fermion formulation. The method entails random generation of string vacua and analysis of their entire spectra, and led to discovery of spinor-vector duality and three generation exophobic string vacua. The classification was performed for string vacua with unbroken SO(10) GUT symmetry, and progressively extended to models in which the SO(10) symmetry is broken to the SO(6)xSO(4), SU(5)xU(1), SU(3)xSU(2)xU(1)^2 and SU(3)xU(1)xSU(2)^2 subgroups. Obtaining sizeable number of phenomenologically viable vacua in the last two cases requires identification of fertility conditions. Adaptation of machine learning tools to identify the fertility conditions will be useful when the frequency of viable models becomes exceedingly small in the total space of vacua.

## Wednesday 30th January 2019 - Integration-by-parts reductions from computational algebraic geometry

Speaker: Kasper Larsen (University of Southampton)

13:00 Room MATH TP-117

Abstract: Integration-by-parts (IBP) reductions form the very core of computations of multi-loop scattering amplitudes in QCD and the electroweak theory, which are crucial for precision LHC physics. In this talk I discuss a new and highly efficient approach for generating the IBP reductions. The approach makes use of ideas from modern unitarity and from algebraic geometry, which I will explain. I then demonstrate the power of the approach by performing fully analytically IBP reduction relevant for two-loop five-gluon scattering in QCD which are well beyond the capabilities of publicly available IBP solvers.

## Tuesday 29th January 2019 - Dai-Freed anomalies in particle physics

String and Beyond the Standard Model Phenomenology

Speaker: Iñaki Garcia-Etxebarria (Durham University)

13:00 Room MATH TP-117

Abstract: Anomalies can be elegantly analyzed by means of the Dai-Freed theorem. In this framework it is natural to consider a refinement of traditional anomaly cancellation conditions, which sometimes leads to nontrivial extra constraints in the fermion spectrum. After an explanation of how to compute these anomalies from the Dai-Freed viewpoint, I will describe some beautiful results that follow from cancellation of these anomalies in phenomenologically interesting models, such as the standard model, SU(5) and Spin(10) GUTs or the MSSM.

## Wednesday 12th December 2018 - Emergent phenomena and critical behaviour of Dirac fermions

Speaker: Michael Scherer (University of Köln)

13:00 Room MATH TP-117

Abstract: Interacting two-dimensional Dirac fermions appear in various condensed-matter scenarios as for example in graphene and related materials, but also in the dual description of the deconfined quantum critical point between Neel and valence bond solid orders in frustrated quantum magnets. The precise determination of the critical behavior of Dirac fermions defines a prime benchmark for complementary theoretical approaches and moreover will allow us to test conjectures based on duality arguments. In my talk, I present a comprehensive analysis of the Gross-Neveu universality classes based on the recently achieved four-loop renormalization group calculations and compare to Monte Carlo and the conformal bootstrap. Further, I will show a study of deconfined criticality from the dual QED3-Gross-Neveu model and discuss the implications of the estimates for the critical exponents for nontrivial scaling relations which follow from the emergent SO(5) symmetry implied by a duality conjecture. Eventually, I will also discuss the physical implications of the presence of dangerously irrelevant parameters for such Dirac systems, including the emergence of two length scales and the generation of mass hierarchies.

## Tuesday 4th December 2018 - Non-geometric Calabi-Yau backgrounds

String and Beyond the Standard Model Phenomenology

Speaker: Dan Israel (Paris)

13:30 Room MATH TP-117

Abstract: Non-geometric compactifications are believed to be rather generic in string theory, and promising for phenomenology at the same time, yet explicit constructions are rare. In this talk I will present recent and ongoing work about non-geometric type II models based on Calabi-Yau compactifications, that can be understood as mirror-folds with K3 fibers. I'll present them from different viewpoints, worldsheet, algebraic geometry, gauged supergravity and finally from the S-dual heterotic description.

## Wednesday 28th November 2018 - Lattice studies of maximally supersymmetric Yang–Mills theories

Speaker: David Schaich (University of Bern)

13:00 Room MATH TP-117

Abstract: Supersymmetry plays prominent roles in the study of quantum field theory and in many proposals for potential new physics beyond the standard model, while lattice field theory provides a non-perturbative regularisation suitable for strongly interacting systems. Lattice investigations of supersymmetric field theories have a long history but often struggle due to the interplay of supersymmetry with the lattice discretisation of space-time. I will discuss a way around these difficulties for maximally supersymmetric Yang-Mills theories, which are a cornerstone of holographic duality. After reviewing some highlights of the lattice formulation, I will present a selection of results from ongoing numerical studies, including tests of holography.

## Tuesday 27th November 2018 - Gravitational Generation of Dark Matter

String and Beyond the Standard Model Phenomenology

Speaker: Tommi Markkanen (Imperial College)

13:30 Room MATH TP-117

Abstract: In this talk I will discuss several working models for producing dark matter (DM), which require no couplings between the visible sector and DM besides (classical) gravity. In particular, I will show that contrary to common wisdom the current observational bounds do not substantially limit the parameter space nor cosmological history, but rather that gravitational particle production can quite naturally lead to a DM abundance in agreement with observations. Based on arXiv:1808.08236 and arXiv:1811.02586.

## Wednesday 21st November 2018 - Exploring the tension between nature and the Standard Model: the muon g-2

Speaker: Marina Marinkovic (Trinity College, Dublin)

13:00 Room MATH TP-117

Abstract: The anomalous magnetic moment of the muon (muon g-2) is one of the most pre- cisely measured quantities in particle physics. At the same time, it can be evaluated in the Standard Model with an unprecedented accuracy. The Muon g-2 experiment at Fermilab has started major data collection and the aimed four-fold increase in precision will shed light on the current discrepancy between the theory prediction and the measured value. This renders a comparable improvement of the precision in the SM theory an essential ingredient in order to fully exploit the expected increase of precision in experimental results. For all these reasons, the muon g-2 is considered to be a great testing ground for new physics.

Hadronic contributions are the dominant sources of uncertainty in the theoretical prediction of the muon g-2. I will outline several promising approaches for a precise determination of the leading hadronic contribution to the muon g-2 using lattice gauge theories. I will then proceed with a discussion of a reciprocal eort to directly measure the hadronic contributions to the running of the ne structure constant proposed by the MUonE experiment, which is part of the Physics Beyond Colliders program at CERN. A hybrid strategy including both experimental and lattice data sets is expected to give an independent check of the dispersive results from e+e- annihilation, which dominate the current world average.

## Tuesday 20th November 2018 - Classical de Sitter solutions and the swampland

String and Beyond the Standard Model Phenomenology

Speaker: David Andriot (CERN)

13:30 Room MATH TP-117

Abstract: I will first give a brief overview of the difficulties in getting controlled de Sitter vacua from string theory. This motivated the recent proposal of a swampland criterion forbidding de Sitter solutions. I will discuss consequences and further refinements of this criterion. I will finally present the most recent constraints on classical de Sitter solutions in 10d type II supergravities.

## Wednesday 14th November 2018 - Density-of-States Approach to dense matter systems

Speaker: Professor Kurt Langfeld (University of Liverpool)

13:00 Room MATH TP-117

Abstract: Dense matter Quantum Field Theories are generically hampered by a complex Gibbs factor invalidating Markov Chain Monte-Carlo simulations. The density-of-states method is based upon a stochastic process based upon the positivity of the entropy factor and, hence, offers first principles numerical access to theories with sign problems. The recently proposed LLR method features an exponential error suppression, and is ideally placed for the simulation of rare events. In my talk, I will highlight the approach for the Z3 gauge theory at nite density and Heavy-dense QCD. I will also present first results for a numerical solution of the Hubbard model on the hexagonal lattice, i.e., Graphene.

## Tuesday 13th November 2018 - Tensionless Strings and Quantum Gravity Conjectures

String and Beyond the Standard Model Phenomenology

Speaker: Seung-Joo Lee (CERN)

13:30 Room MATH TP-117

Abstract: We test various conjectures on quantum gravity for general 6d string compactifications in the framework of F-theory. Starting with a gauge theory coupled to gravity, we first analyze the limit in Kähler moduli space where the gauge coupling tends to zero while gravity is kept dynamical. A key observation is made about the appearance of a tensionless string in such a limit. For a more quantitative analysis, we focus on a U(1) gauge symmetry and determine the elliptic genus of this string in terms of certain meromorphic weak Jacobi forms, of which modular properties allow us to determine the charge-to-mass ratios of certain string excitations. A tower of these asymptotically massless charged states are then confirmed to satisfy the (sub-)Lattice Weak Gravity Conjecture, the Completeness Conjecture, and the Swampland Distance Conjecture. If time permits, we interpret their charge-to-mass ratios in two a priori independent perspectives. All of this is then generalized to theories with multiple U(1)s.

## Tuesday 6th November 2018 - Holography for Super Yang-Mills Theories on Spheres

String and Beyond the Standard Model Phenomenology

Speaker: Fridrik Gautason (Leuven)

13:30 Room MATH TP-117

Abstract: I will describe the construction of the holographic duals to Euclidean Yang-Mills theories in d dimensions placed on S^d preserving some amount of supersymmetry. The resulting geometries can be used to compute observables such as the supersymmetric free energy and Wilson loop VEVs. In some cases these observables have been computed exactly using the technique of supersymmetric localisation and we find agreement with these exact results using holography.

## Wednesday 31st October 2018 - Heavy Flavour physics with domain wall fermions

Speaker: Tobi Tsang (University of Edinburgh)

13:00 Room MATH TP-117

Abstract: After a short motivation, I will outline our domain wall charm physics program. I will briefly recall our Pilot study, used to find a sweet spot in the parameter space. I will then present our results for the decay constants fD and fDs. In the second part of my talk I will present the current status of our Domain Wall heavy quark physics program, including preliminary results for the charm quark mass, fDs/fD, fBs/fB and the BBbar mixing parameter ξ. Time permitting I will outline our complementary efforts for semi-leptonic B_{s}-decays using the Relativistic Heavy Quark action.

## Tuesday 30th October 2018 - Extracting and constraining scalar-only couplings in generic BSM theories

String and Beyond the Standard Model Phenomenology

Speaker: Mark Goodsell (Laboratory of Theoretical Physics and High Energies, Paris)

13:30 Room MATH TP-117

Abstract: We extract the Higgs cubic and quartic couplings of the Standard Model (SM) from the Higgs mass. Calculating the Higgs mass in generic SM extensions can thus be used to extract new cubic or quartic couplings, which can then be used to study vacuum stability or the scale of landau poles. On the other hand, unitarity gives us a different way to constrain how large these couplings can be at low energies. I will review the latest developments in calculating these quantities, and the implementations in the package SARAH.

## Wednesday 24th October 2018 - Mellin Approximants to Hadronic Vacuum Polarization

Speaker: David Greynat

13:00 Room MATH TP-117

Abstract: It is shown that with a precise determination of a few derivatives of the hadronic vacuum polarization (HVP) self-energy function at the origin, from lattice QCD or from a dedicated low-energy experiment, one can obtain an evaluation of the lowest order HVP contribution to the anomalous magnetic moment of the muon with an accuracy comparable to the one reached using the *e*^{+}*e*^{-} annihilation cross section into hadrons. We will show how the technique of Mellin-Barnes approximants that we propose can be applied to the first few moments of the hadronic spectral function obtained from experiment and and how the resulting evaluations converge.

## Wednesday 17th October 2018 - Consistent perturbative fixed point calculations in gauge theories

Speaker: Thomas Ryttov (CP3, University of Odense)

13:00 Room MATH TP-117

Abstract: In order to obtain a better understanding of non supersymmetric as well as supersymmetric gauge theories in the the non-Abliean Coulomb phase it is important that we can reliably calculate scaling dimensions of composite operators. We show how to consistently calculate scaling dimensions order by order in perturbation theory in a fully scheme independent and unambiguous manner. In supersymmetric gauge theories we find that the scaling dimension of all gauge invariant chiral operators as well as central charges a, b and c are astonishingly well be approximated by a few loops computation throughout the entire conformal window. We also study how electric-magnetic duality emerges order by order within the conformal window. Finally we study scaling dimensions in non-supersymmetric gauge theories (including QCD) to the maximum known order and provide evidence that a similar precision is achieved here.

## Wednesday 10th October 2018 - Heavy physics contributions to neutrinoless double beta decay from QCD

Speaker: Nicolas Garron (University of Liverpool)

13:00 Room MATH TP-117

Abstract: If observed, neutrinoless double beta decay would reveal violations of symmetries fundamental to the Standard Model, and would guarantee that neutrinos have nonzero Majorana mass. Relating nuclear decay rates to beyond the Standard Model (BSM) theories requires detailed knowledge of non-perturbative QCD effects. Using lattice QCD and taking advantage of effective field theory methods, we compute the model-independent leading-order matrix elements of short-range operators, which arise due to heavy BSM mediators, that contribute to this decay. Contributions from short-range operators may prove to be equally important to those from long-range Majorana neutrino exchange.

## Tuesday 9th October 2018 - Counting String Theory Standard Models

String and Beyond the Standard Model Phenomenology

Speaker: Andrei Constantin (Oxford)

13:00 Room MATH TP-117

Abstract: I will discuss various aspects of heterotic string compactifications on smooth Calabi-Yau threefolds with abelian internal fluxes. This set-up allows for a systematic construction of a large number of N=1 supersymmetric compactifications. I will present an approximate analytic relation between the number of consistent heterotic Calabi-Yau compactifications of string theory with the exact charged matter content of the standard model of particle physics and the topological data of the internal manifold: the former scaling exponentially with the number of Kahler parameters. This is done by an estimate of the number of solutions to a set of Diophantine equations representing constraints satisfied by any consistent heterotic string vacuum with three chiral massless families, and has been computationally checked to hold for complete intersection Calabi-Yau threefolds (CICYs) with up to seven Kahler parameters. When extrapolated to the entire CICY list, the relation gives about 10^23 string theory standard models; for the class of Calabi-Yau hypersurfaces in toric varieties, it gives about 10^723 standard models.

## Tuesday 26th June 2018 - Lattice theory at the physics frontier: Towards the understanding of (exotic) matter through advanced spectroscopy

Speaker: Anthony Francis (CERN)

09:30 Room MATH-117

Abstract: In a time of precision experiments the low-energy, hadronic effects to the predictions of the standard model of particle physics become dominant uncertainties. This has become particularly clear in the anomalous magnetic moment of the muon. In addition, the physics of matter at energies beyond confinement, actively being probed by heavy-ion collision experiments, remains elusive due to the strong non-perturbative effects arising. Finally, for many years the existence of the heavy X,Y,Z (tetraquark)-states has puzzled theory and experiment. Approaching these frontiers, the unique structure of QCD itself prevents its solution through currently available analytic methods. Lacking these, lattice QCD provides the rigorous means to solve QCD numerically. Today, modern lattice QCD studies have reached an era of precision with the main systematic uncertainties under control. To illustrate, we will briefly comment on the spectroscopy of ordinary hadrons with a view of (g - 2)_{μ} and will then focus on how we use lattice QCD towards the goal of a first principles understanding of exotic, tetraquark states. Through direct and indirect calculations we find unambiguous signals for J^{P} = 1+ tetraquarks with binding energies 189(10) and 98(7) MeV with flavor content *udbb *as well as *lsbb*. Further evidence for binding is found in the *udcb* channel. Highlighting the interplay between theory, phenomenology, computing and experiments, in this presentation we show how lattice calculations can serve as benchmarks for model calculations, what the implications for experimental searches are and comment on how lattice methods can contribute to extending the frontiers of fundamental particle theory.

## Tuesday 22nd May 2018 - Applied Top-Down Holographic Large-N Thermal QCD and G-Structures via Delocalized SYZ Mirrors

String and Beyond the Standard Model Phenomenology

Speaker: Aalok Misra (IIT, India)

13:30 126 Mount Pleasant Room 113

Abstract: In the context of a top-down non-conformal holographic type II dual of large-N thermal QCD at finite coupling, there are three sets of issues we will be discussing. One, having to do with the Mathematical aspect of the setup will include a discussion on the SU(3)-structure torsion classes of the type IIB dual and its delocalized SYZ type IIA mirror as well as a discussion on the G_2-structure torsion classes of the M-theory uplift - both in the "MQGP" limit. The second has to do with holographic evaluation of transport coefficients like electrical/thermal conductivity, Wiedemann-Franz law, speed of sound, eta/s, diffusion coefficient, Buchel's bound inclusive of non-conformal corrections to some. The third has to do with non-conformal holographic phenomenology wherein we will be discussing obtaining glueball and mesonic spectra and comparing with available lattice results.

## Wednesday 16th May 2018 - D-brane Scalar-Tensor Theories, Thermal Dark Matter and Inflation

String and Beyond the Standard Model Phenomenology

Speaker: Ivonne Zavala (University of Swansea)

13:30 Room TP-117

Abstract: I will discuss modifications of pre-BBN cosmology due to scalar-tensor theories, which arise naturally in modified theories of gravity such as string theory. In particular, I will discuss the implications for the thermal dark matter abundances due to conformal and disformal couplings between the scalar field and matter, which arise generically in these theories modifying the early universe evolution. I will also discuss the effect of these modifications on the number of e-foldings between horizon exit of CMB modes and the end of inflation with relevant implications for the inflationary predictions of some models.

## Wednesday 9th May 2018 - Constructing Scattering Amplitudes from their Singular Structure

Speaker: David Dunbar (University of Swansea)

13:00 Room TP-117

Abstract: We review progress in computing amplitudes from an understanding of their symmetries and singular structure. In particular it is shown how amplitudes may be computed using factorisation and generalised unitarity rather than conventional techniques. Finally recent progress in computing QCD amplitudes in analytic form at two-loop using these techniques is presented.

## Tuesday 8th May 2018 - From complex inflationary physics to simple observations

String and Beyond the Standard Model Phenomenology

Speaker: Malfada Dias (DESY)

14:45 Room TP-117

Abstract: The most striking characteristic of the primordial curvature perturbation is its simple statistics. These statistics are well described to high accuracy by only two parameters — the amplitude and tilt of the power spectrum. Whatever the physical origin of inflation might be, it must predict this observation. Yet, an ultraviolet-complete description of inflation may not be simple, and string theory points towards the possibility of highly complex low-energy models for the early universe. In this talk I will describe how complex models can give rise to emergent simple observations, in a phenomenon which can be understood as an information bottleneck. I will also present a strategy to compute such predictions while encompassing the inherent complexity of the underlying model.

## Wednesday 2nd May 2018 - Mixing and Lifetimes

Speaker: Alexander Lenz (University of Durham)

13:00 Room TP-117

Abstract: We review the current status of theory predictions for mixing and lifetimes of heavy mesons. In particular we show rst evidence for a convergence of the Heavy Quark Expansion in the charm system. Taking the most recent lattice inputs we find a slight discrepancy between experiment and theory for the *B* mixing observables, leading to extremely severe constraints for BSM models that try to explain the flavour anomalies.

## Tuesday 1st May 2018 - Holographic Descriptions of Dynamical Symmetry Breaking

String and Beyond the Standard Model Phenomenology

Speaker: Nick Evans (University of Southampton)

14:45 Room TP-117

Abstract: Holography provides a very simple dual description of dynamical symmetry breaking mechansims including chiral symmetry breaking in QCD-like gauge theories, the NJL model and superconductivity. I will summarize the basic instability mechanisms - a radially dependent scalar mass that violates the BF bound in AdS as a result of running or a chemical potential, or through UV boundary terms. I will then discuss some phenomenological examples from QCD to the gauged NJL model to colour superconductivity.

## Wednesday 25th April 2018 - Flavored Axion Models

Speaker: Robert Ziegler (CERN)

13:00 Room TP-117

Abstract: I will discuss two scenarios that give rise to QCD axions with large flavor-violating couplings at tree-level. The first scenario is a class of generalized DFSZ models with PQ charges compatible with a 2+1 flavor structure, in which the flavor misalignment are treated as free parameters and control both diagonal and flavor-violating axion couplings. This structure allows to construct axion models that have suppressed couplings to nucleons and electrons, thus relaxing the most stringent astrophysical constraints. The axion can be as heavy as 0.2 eV and therefore be tested at the next generation of helioscopes. In the second scenario the PQ symmetry is identified with a U(1) Froggatt-Nielsen symmetry, so that axion couplings to fermions and photons are related to fermion masses and mixings. Both scenarios can be tested by precision flavor experiments like NA62.

## Monday 23rd April 2018 - On the Cosmological Quantum Frame Problem in Multi-field Inflation

String and Beyond the Standard Model Phenomenology

Speaker: Apostolos Pilaftsis (Manchester University)

14:45 Room TP-117

Abstract: Predictions for cosmological observables, such as the scalar and tensor power spectra, their spectral indices and their higher order runnings, suffer from the so-called frame problem. They depend on whether the computation has been performed in the Jordan or Einstein frame. In this talk, I will present a frame-covariant formalism which enables one to address the frame problem in the context of general scalar-curvature multi-field theories. The formalism makes use of notions and techniques known from differential geometry, and can be extended beyond the tree approximation in the Vilkovisky-De Witt framework which needs to be generalized appropriately. I will show how frame-invariant predictions for cosmological observables can be obtained in simple two-field models, motivated by Higgs inflation.

## Wednesday 18th April 2018 - QCD-like theories at finite density

Speaker: Lorenz von Smekal (University of Giessen)

13:00 Room TP-117

Abstract: Studies of QCD-like theories without a fermion sign problem at finite density by now have a rather long history already. I will report results from two-color QCD, with two instead of the usual three colors, and G_{2}-QCD, with gauge group G_{2} instead of *SU*(3). The physics of the bosonic diquark baryons in these theories is believed to be fairly well understood and qualitatively resembles QCD at finite isospin density with pion condensation. There is good guidance from effective field theory predictions and model studies of the BEC-BCS crossover inside the condensed phase. In the last part I will present a condensed matter system that we have studied at finite spin density instead of charge density as another analogy of studying QCD at finite isospin density.

## Tuesday 17th April 2018 - Amplitudes and form factors from N=4 super Yang-Mills to QCD

String and Beyond the Standard Model Phenomenology

Speaker: Gabriele Travaglini (Queen Mary's, London)

14:45 Room TP-117

Abstract: I will review some recent (and less recent) results on the calculation of form factors in N=4 super Yang-Mills. Surprisingly, some of these form factors are intimately connected to certain QCD amplitudes describing Higgs + multi-gluon processes (without any supersymmetry). After describing this connection, I will discuss the calculation of form factors of protected and non-protected operators in N=4 super Yang-Mills. A notion a universality seems to emerge in the results that will be described. I will comment on this as well as on possible further connections to processes in QCD involving the Higgs boson.

## Wednesday 11th April 2018 - On The Four-Loop Form Factors Of Massless QCD

Speaker: Robert Schabinger (Michigan State University)

13:00 Room TP-117

Abstract: In this talk, we discuss an ongoing calculation of the four-loop form factors in massless QCD. We begin by discussing our novel approach to the calculation in detail. Of particular interest are a new polynomial-time integration by parts reduction algorithm and a new method to algebraically resolve the IR and UV singularities of dimensionally-regulated bare perturbative scattering amplitudes. Although not all integral topologies are analytically calculable for the more non-trivial color structures, we show that it is nevertheless feasible to obtain accurate numerical results for the finite parts of the complete four-loop form factors using publicly available sector decomposition programs and bases of finite integrals. Although these techniques were developed for the problem at hand, we explain that they are also relevant to other cutting-edge higher-order perturbative computations of current phenomenological interest.

## Tuesday 10th April 2018 - Axion Cosmology and the Lightest Possible Dark Matter Candidate

String and Beyond the Standard Model Phenomenology

Speaker: David Marsh (Goettingen)

14:45 Room TP-117

Abstract: If axions are particularly light, and compose a significant fraction of the dark matter then there are interesting and potentially observable effects on the acoustic peaks and gravitational lensing of the CMB power spectrum, and on galaxy formation. These effects can be used to search for axions in cosmological and astrophysical data. Current constraints from Planck limit axions over eight orders of magnitude in mass to compose less than a few percent of the total dark matter. Upcoming "CMB Stage IV” polarization and lensing data will probe ten orders of magnitude in mass and could detect a percent level presence of axion dark matter at high statistical significance (5 sigma). This represents a precision test of the single-component standard cold DM model. Constraints from high redshift structure formation with axion DM place the current best lower bound on DM particle mass, m>1e-22 eV. This "fuzzy DM" model has certain desirable and interesting galactic-scale properties that could allow for its detection using astrometry. Given time, I will discuss the ideas and challenges to detect axion DM in this mass window, the origins of light axions in models of the string landscape, and aspects related to black hole physics.

## Tuesday 20th February 2018 - Gravity and the explicit breaking of global symmetries: from theoretical aspects to phenomenological applications

String and Beyond the Standard Model Phenomenology

Speaker: Alfredo Urbano (CERN)

14:45 Room TP-117

Abstract: What does gravity do with global symmetries? The common lore — supported by a number of “folk” theorems — is that gravity breaks explicitly all global symmetries. In this talk, I will show that the explicit breaking induced by gravity can be computed already in the context of General Relativity. Furthermore, I will discuss possible phenomenological applications, focusing on the case of the QCD axion and, more generally, on axion-like particles.

## Wednesday 14th February 2018 - DNA of asymptotic safety

Speaker: Daniel Litim (University of Sussex)

13:00 Room TP-117

Abstract: Asymptotic safety ensures that quantum field theories are fundamental and predictive even beyond the confines of asymptotic freedom. The recent discovery of asymptotic safety in particle physics has, therefore, raised substantial interest. In this talk, I explain the origin for asymptotic safety, and show how and why it arises in particle theories with and without supersymmetry. Intriguingly, asymptotic freedom and asymptotic safety are two sides of one and the same medal. We illustrate our findings at the example of weakly-coupled simple and semi-simple gauge theories. First implications for BSM model building and phenomenological signatures for asymptotic safety at colliders are also indicated.

## Wednesday 7th February 2018 - Renormalization of the energy-momentum tensor using the Wilson flow

Speaker: Luigi Del Debbio (University of Edinburgh)

13:00 Room TP-117

Abstract: The non-perturbative computation of the energy-momentum tensor can be used to study the scaling behaviour of strongly coupled quantum field theories. The Wilson flow is an essential tool to formulate a nonperturbative renormalization of the energy-momentum tensor on the lattice. We extend recent studies of the renormalization of the energy-momentum tensor in four-dimensional gauge theory to the case of a three-dimensional scalar theory to investigate its intrinsic structure and numerical feasibility in a simpler framework. In this seminar, we discuss translation Ward identities, introduce the Wilson flow for scalar theory, and present preliminary results for the renormalization constants of the scalar energy-momentum tensor.

## Tuesday 6th February 2018 - Axion strings and domain walls

String and Beyond the Standard Model Phenomenology

Speaker: Ed Hardy (University of Liverpool)

14:15 Room TP-117

Abstract: I will discuss the calculation of the axion dark matter relic abundance produced by strings and domain walls in the early universe. These objects appear if the global symmetry that the axion is associated with is unbroken at the end of inflation, and in this scenario there is, in principle, a unique prediction for the axion dark matter mass. I will present results from numerical simulations that indicate that the density of strings may be significantly larger than previously thought, leading to a corresponding change in the required axion dark matter mass. I will also discuss the difficulties in computing the energy spectrum of axions produced in the physically relevant regime, and the remaining uncertainties and challenges.

## Wednesday 31st January 2018 - The a-theorem, scheme invariants and Hopf algebras

Speaker: Professor Ian Jack (University of Liverpool)

13:00 Room TP-117

Abstract: We show how the existence of an a-theorem imposes constraints on the beta-functions which may be expressed in terms of renormalisation-scheme-invariant combinations of the beta-function coefficients. This motivates a general discussion of scheme-invariance; we show that the structure of scheme transformations implies significantly more scheme-invariants than might be naively expected. Finally we show that the language of Hopf algebras provides a convenient means to describe the requirements of scheme invariance.

## Tuesday 30th January 2018 - Integrability and AdS3/CFT2

String and Beyond the Standard Model Phenomenology

Speaker: Bogdan Stefanski (City University London)

11:30 Room TP-117

Abstract: I will review the recent progress in computing the exact spectrum of closed strings in AdS3/CFT2 using integrability. The spectrum is determined through a set of all-loop Bethe Equations, from which one can find, for example, the protected closed string states and compare with supergravity results. Exact agreement is found in the case of AdS3xS3xT4. For AdS3xS3xS3xS1 past supergravity calculations predicted too many BPS states, many of which are not protected in string theory. I will discuss the current status of these states.

## Wednesday 13th December 2017 - Long-lived charged particles to constrain dark matter: asymptotically safe Standard Model extensions

Speaker: Alexi Plascencia (University of Durham)

13:00 Room TP-117

Abstract: In the first part of my talk I will discuss a new set of simplified models that include the effect of co-annihilation and are constrained by searches for long-lived charged states at the LHC. In the second part of my talk I will present models beyond the Standard Model where all the couplings reach an ultraviolet fixed point, which can be interacting (asymptotic safety) or non-interacting (asymptotic freedom).

## Wednesday 29th November 2017 - QED Corrections to Hadronic Processes in Lattice QCD

Speaker: Chris Sachrajda (University of Southampton)

13:00 Room TP-117

Abstract: In recent years, many important quantities in flavour physics have been computed to a precision approaching 1%. In order to make further progress therefore, isospin-breaking effects, including electromagnetism, must be included. This is now being increasingly done for the spectrum, where there are no infrared divergences to consider. I will review the method, proposed in the papers below for computing electromagnetic corrections to weak decay processes in lattice simulations, including the treatment of infrared divergences. The first results for the isospin-breaking corrections to leptonic decays of pions and kaons will be presented.

## Wednesday 22nd November 2017 - The S-matrix bootstrap

Speaker: Balt van Rees (University of Durham)

13:00 Room TP-117

Abstract: We take a fresh look at the S-matrix bootstrap program using modern tools inspired by the revived conformal bootstrap. There exist various approaches to taming the landscape of S-matrices. We will discuss two different methods and show that they both lead to the same universal bound for the interaction strength in 2-dimensional QFTs. We propose a specific numerical algorithm for higher-dimensional QFTs and present some initial results.

## Tuesday 21st November 2017 - Interactions in the dark sector mediated by dark energy

Speaker: Carsten Van de Bruck (University of Sheffield)

11:45 Room TP-117

Abstract: A fifth force between the standard model particles mediated by new degrees of freedom is highly constrained. On the other hand, dark matter particles could interact for example via a force mediated by dark energy scalar field. Such interactions are currently constrained only by cosmological observations. In this talk I will discuss scalar-tensor theories of interacting dark matter-dark energy, allowing for both conformal and disformal couplings. I will present the cosmological consequences and constraints on these theories. At the end of my talk I will also comment on how more general theories of modified gravity, such as Gauss—Bonnet gravity, are constrained by the latest LIGO/VIRGO observations.

## Tuesday 14th November 2017 - Constraining Particle Physics from Quantum Gravity Conjectures

Speaker: Irene Valenzuela (Utrecht)

11:45 Room TP-117

Abstract: Consistency with quantum gravity can have significant consequences on low energy physics. Using the Weak Gravity Conjecture, it has been recently argued by Ooguri and Vafa that non supersymmetric stable AdS vacua are incompatible with quantum gravity. However, it is known that AdS vacua can appear from compactifying the Standard Model to 2 or 3 dimensions. By requiring the absence of these vacua we can put constraints on the SM and BSM spectra, obtaining a lower bound for the cosmological constant in terms of the neutrino masses. This can also be translated into an upper bound for the EW scale around the TeV range, bringing a new perspective into the issue of the EW hierarchy.

## Wednesday 8th November 2017 - Recent four- and five-loop results in QCD

Speaker: Andreas Vogt (University of Liverpool)

13:00 Room TP-117

## Tuesday 31st October 2017 - Primordial Black Hole Cosmology

Speaker: Kazunori Kohri (KEK/Oxford)

12:00 Room TP-117

Abstract: After aLIGO detected the gravitational wave events produced by mergers of binary black holes (BHs), researchers have aggressively studied the origin of the BHs with masses of the order of O(10) M_solar. In additional to astrophysical origins through evolutions of Pop.II and/or Pop.III stars, one of the attractive candidates of those BHs would be Primordial Black Holes (PBHs). The PBHs were produced in the early radiation dominated Universe due to spherical collapses of regions which have a large density perturbation at the horizon scale at that time.

I will review the current status of cosmological and astrophysical constraints on PBHs with introducing my own recent bounds on PBHs in terms of gamma-ray observations (arXiv:1604.05349 [astro-ph.CO]), CMB (arXiv:1707.04206 [astro-ph.CO]), BBN (arXiv:0912.5297 [astro-ph.CO]), and Higgs phenomenology (arXiv:1708.02138 [hep-ph]). I also introduce some theoretical models to produce PBHs in the inflationary Universe. In addition, I will discuss a new production mechanism in the early matter dominated Universe and its application to cosmology, which had not been considered in detail (arXiv:1707.03595 [gr-qc]).

## Wednesday 18th October 2017 - Exotic RG Flows from Holography

Speaker: Leandro Silva Pimenta (University of Paris 7)

13:00 Room TP-117

Abstract: The AdS/CFT correspondence, a useful tool in the study of strongly coupled physics, relates elds, including gravity, in a d+1 dimensional asymptotically AdS space-time to operators in a d-dimensional Conformal Field Theory (CFT), in a one-to-one correspondence. The extra spatial dimension appearing in the gravitational side of the duality, the holographic dimension, is in correspondence with an energy scale on the QFT side : elds evolving along the holographic dimension are dual to renormalisation group ows of couplings at the dual QFT. In this talk I will present some classes of solutions on the gravitational side which are associated with exotic RG ows in QFT. These exotic RG ows are non-perturbative and may suggest that there is more in QFT than we currently believe.

## Wednesday 11th October 2017 - PUse and limitations of SUSY simplified model results from the LHC

Speaker: Sabine Kraml (University of Grenoble)

13:00 Room TP-117

Abstract: The ATLAS and CMS experiments at the LHC are searching for new physics in many different channels. The results of the searches are often communicated by the experimental collaborations in terms of simplifed models, assuming the presence of just a few new particles with fixed decay branching ratios - typically 100% into a specific final state. I will discuss how such simplified model results from searches in final states with large missing energy, targeting supersymmetric particles, can be used to constrain full models. In particular, I will present SModelS, an automatised tool for decomposing the signatures of models with a Z2 symmetry into simplified model topologies and comparing the theoretical predictions against a large database of SUSY simplified model results. The procedure being much faster than event + detector simulation, it is particularly convenient for a fast assessment of existing constraints and parameter scans. Experimental signatures which are currently not constrained can also easily be identied. I will explain the assumptions made and show examples of applications to non-minimal SUSY and extra quark models. Finally, I will discuss to what extent the currently available simplified model results cover a complete model like the phenomenological MSSM with 19 parameters, and how this coverage might be improved.

## Tuesday 10th October 2017 - Progress in Strings without Supersymmetry

Speaker: Steve Abel (University of Durham)

12:00 Noon Room TP-117

Abstract: I describe recent work towards formulating non-supersymmetric string theory as a phenomenological framework in which to embed the Standard Model. Chief among the issues that one has to solve in the absence of supersymmetry are stability and naturalness. I describe how they can be tackled using a Scherk-Schwarz compactification that allows supersymmetry to be parametrically broken (and the theory to be parametrically badly behaved). Generic phenomenological patterns are deduced including “Entwined SUSY” - a cousin of neutral naturalness - and GUT precursors.

## Tuesday 3rd October 2017 - A Riemann-Hilbert approach to rotating attractors

Speaker: Thomas Mohaupt

12:00 Noon Room TP-117

Abstract: Stationary axisymmetric solutions of gravity are related to integrable systems. We discuss how this allows to obtain explicit solutions of the field equations from solutions of a factorisation problems for matrix valued functions on the complex plane.

## Tuesday 2nd May 2017 - Searches for dark matter and new physics with GAMBIT

Speaker: Pat Scott (Imperial)

12:00 Noon Fröelich Library

Abstract: I will give an introduction to GAMBIT, the Global and Modular Beyond-the-Standard Inference Tool, focussing on the Beyond-the-Standard-Model science programme currently being pursued with it. This includes indirect searches for dark matter annihilation and decay with gamma-rays and neutrinos, direct searches with a range of underground experiments, cosmological constraints, associated searches for new particles at the LHC and in flavour experiments, and precision tests of the Standard Model. I will present the latest combined constraints on various supersymmetric and Higgs-portal dark matter candidates, and briefly discuss extensions on the near horizon.

## Tuesday 25th April 2017 - Aspects of Berry phase in QFT

Speaker: Vasilis Niarchos (Durham)

12:00 Noon Fröelich Library

Abstract: Berry phase is a well-known feature of quantum mechanics. In this talk I will describe several new results about Berry phase in quantum field theory. We will see that even simple quantum field theories can exhibit non-trivial Berry phases and will discuss an explicit example in axion electrodynamics. We will also discuss a general relation between the Berry connection in conformal field theories and the connections on conformal manifolds considered previously by several authors in conformal perturbation theory. The implementation of this relation in 2d N=(2,2) and 4d N=2 superconformal field theories leads to a useful re-derivation of the tt* equations. The latter have important implications on the non-perturbative structure of certain correlation functions in supersymmetric theories, which I will briefly review.

## Tuesday 7th February 2017 - Recent progresses in modern string phenomenology

Speaker: Miguel Crispin Romao (Southampton University)

12:00 Noon MATH-106

Abstract: In this communication we'll report on recent developments on model building and phenomenological consequences of non-perturbative formulations of string theory, such as M- and F-Theory. From SO(10) SUSY GUTs realisations from M-Theory compactified on G2-manifolds, to single-coupling RPV interactions arising from F-Theory, we argue that these corners of String Theory hold a rich and exciting area of research in String Phenomenology.

## Wednesday 30th November 2016 - Renormalization of phi^4 theory at six loops

Speaker: Erik Panzer (Oxford University)

1:00PM Chris Michael Seminar Room TP-117

Abstract: I will discuss some new techniques used in a recent perturbative calculation of phi^4 theory in dimensional regularization and minimal subtraction. In particular I will focus on methods to extract divergences of Feynman integrals, such that their epsilon expansion is expressed in terms of convergent integrals (suitable for exact and numerical evaluation).

## Wednesday 23rd November 2016 - Screening of fifth forces and spontaneous symmetry breaking

Speaker: Peter Millington (Nottingham University)

1:00PM Chris Michael Seminar Room TP-117

Abstract: Scalar-tensor theories of gravity provide a potential explanation for dark energy. However, any associated scalar fifth forces have not been observed to date in local tests of gravity. The coupling to matter must therefore be fine-tuned, or the scalar fifth force itself must somehow be screened in the local environment. In this talk, we focus on so-called symmetron models, wherein spontaneous symmetry breaking leads to density-dependent modifications of the matter coupling. In addition, we discuss the potential implications of the symmetron mechanism for astrophysical observations, illustrating that it is capable of describing observed galactic rotation curves without the need for particle dark matter.

## Wednesday 16th November 2016 - On branes and (non-linear) instantons

Speaker: Ruben Minasian (Saclay, Paris)

1:00PM Chris Michael Seminar Room TP-117

Abstract: I will describe some aspects of gauge theories as seen by supersymmetric D-branes, ranging from the non-linear deformations of instanton equations to the globally supersymmetric theories on curved manifolds.

## Wednesday 9th November 2016 - Tachyonic antibranes and the landscape

Speaker: Iosif Bena (Saclay, Paris)

1:00PM Chris Michael Seminar Room TP-117

Abstract: Antibranes in backgrounds that have charge dissolved in fluxes are a key ingredient in constructing a landscape (Multiverse) of deSitter vacua in String Theory, and also of constructing microstate solutions corresponding to non-supersymmetric near-extremal black holes. There are several regimes of parameters in which one can study the physics of these antibranes, and I will show that in the regime of parameters where their gravitational backreaction is important, antibranes have a naked singularity that cannot be resolved either by brane polarization or by cloaking with a black hole horizon, and that signals a tachyonic instability. I will also present recent evidence that the theory on the wordvolume of anti-D3 branes is finite to all loops. I will conclude by discussing the implications of these results for the Multiverse paradigm and for the Fuzzball proposal.

## Wednesday 2nd November 2016 - Probing the astrophysics and particle physics of WIMPs with direct detection experiments

Speaker: Anne Green (Nottingham University)

1:00PM Chris Michael Seminar Room TP-117

Abstract: Diverse astrophysical and cosmological observations indicate that most of the matter in the Universe is cold, dark and non-baryonic. Weakly Interactive Massive Particles (WIMPs) are generically a good dark matter candidate and particle physics provides us with a well-motivated WIMP candidate in the form of the lightest neutralino. WIMPs can be detected indirectly (via the products of their annihilation) or directly (via elastic scattering in underground detectors). After an overview of WIMPs and the status of attempts to detect them, I will focus on what we could learn from direct detection experiments about the astrophysics and particle physics of WIMPs.

## Wednesday 26th October 2016 - The top quark and its mass

Speaker: Peter Marquard (DESY Zeuthen)

1:00PM Chris Michael Seminar Room TP-117

Abstract: The top quark is the heaviest particle in the Standard Model and plays an important role for precision observables. I will discuss recent results for the translation between different mass renormalization schemes and the possibilities to measure the mass of the top quark at a future linear collider.

## Wednesday 19th October 2016 - Hidden Sectors and the Dark Glueball Problem

Speaker: Fabian Ruehle (University of Oxford)

1:00PM Chris Michael Seminar Room TP-117

Abstract: We discuss cosmological constraints on glueballs arising from hidden Yang-Mills sectors. These are well-motivated from UV physics such as string theory. As it turns out, dark glueballs are overproduced for large regions of ultraviolet parameter space. After explaining this dark glueball problem we address several ways in which the problem can be alleviated, e.g. via preferential reheating of the visible sector or glueball decay into lighter particles. Furthermore, we discuss the constraints placed on these alleviation mechanisms from experimental bounds.

## Wednesday 12th October 2016 - Asymptotically safe quantum gravity and matter

Speaker: Astrid Eichhorn (University of Heidelberg)

1:00PM Room MATH-106

Abstract: I will introduce the asymptotic safety scenario as a potential candidate for a model of quantum gravity. I will review the basic idea of the approach and highlight recent progress that provides intriguing hints that quantum gravity might be asymptotically safe. I will then focus on the interactions of quantum gravity with matter, and explain why matter matters in quantum gravity. Finally, I will discuss quantum-gravity effects on matter and show how these can be used to devise observational consistency tests for this model of quantum gravity.

## Tuesday 4th October 2016 - Holgraphy inspired stringy hadrons

Speaker: Cobi Sonnenschein (University of Tel Aviv)

11:45AM Chris Michael Seminar Room TP-117

Abstract: Holography inspired stringy hadrons (HISH) is a set of models that describe hadrons: mesons, baryons, glueballs and exotic hadrons as strings in four dimensional at space-time. The models are based on a "map" from stringy hadrons of curved holographic conning backgrounds. In the first part of the talk I will review the "derivation" of the models. I will start with a brief reminder of the passage from the original AdS=CFT correspondence to the string/gauge duality of certain favored confining holographic models. I will then describe the string configurations in these holographic backgrounds that correspond to Wilson lines, mesons, baryons, glueballs and exotics. Key ingredients of the four dimensional picture of hadrons are the "string end-point mass" and the "baryonic string vertex".

I will determine the classical trajectories of the HISH spectra. I will review the current understanding of the quantization of these hadronic strings. The computation of HISH decay width of hadrons will be described. In the last part of the talk I will summarize the comparison of the outcome of the HISH models with the PDG data about mesons and baryons. I will present the values of the tension, masses and intercepts extracted from best fits to hadron spectra and write down certain predictions for higher excited hadrons. I will present attempts to identify glueballs. The decay width of certain hadrons will be compared with the theoretical calculation. I will suggest a window to the landscape of tetra-quarks and other exotic hadrons.

## Wednesday 28th September 2016 - The gauge coupling field and effective super-Yang-Mills actions

Speaker: Jean Pierre Derendinger (University of Bern)

1:00PM Chris Michael Seminar Room TP-117

Abstract: Promoting couplings to (background) fields is a useful and powerful technique to study all-order or nonperturbative properties of supersymmetric field theories. The case of the gauge coupling in N=1 supersymmetric gauge theories requires a non-standard treatment using a linear superfield. The corresponding current structure and anomaly matching or cancellation in effective lagrangian formulations lead then to a simple algebraic understanding of the all-order running of the gauge coupling (J / NSVZ beta function), while chiral currents respect the Adler-Bardeen theorem. (This talk is based on papers 1607.08646, 1609.00164 and earlier literature).