## SEMESTER 2020 - WINTER

__26.01.2021__

### Yannick Kluth

#### University of Sussex, Brighton

## Fixed Points of Quantum Gravity and the Dimensionality of the UV Critical Surface

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In this talk, I will start with a brief overview of the asymptotic safety scenario for quantum gravity and explain important concepts such as fixed points and the UV critical surface. After that, some recently obtained results for actions containing squares of the Riemann tensor will be presented. This includes a numerical scan for fixed points leading to three stable fixed points which have been analysed including up to 144 different curvature invariants. Properties such as UV critical surfaces, convergence and Gaussian scaling as well as their implications for asymptotically safe quantum gravity are discussed. Moreover, it is shown how eigenvectors can be used to understand how curvature invariants affect the number of relevant parameters at a fixed point.

__12.01.2021__

### Andrew Fowlie

#### Nanjing Normal University, Nanjing

## Evidence for axion-like particles from XENON1T and astrophysical data

The excess of electron recoil events seen by the XENON1T experiment has been interpreted as a potential signal of axion-like particles (ALPs), either produced in the Sun, or constituting part of the dark matter halo of the Milky Way. We consider the evidence for the solar and dark-matter ALP hypotheses from the combination of XENON1T data and multiple astrophysical probes, including horizontal branch stars, red giants, and white dwarfs. We discuss the pros and cons of different statistical approaches to quantify the evidence, including Bayesian and frequentist methods. Lastly, we describe the computational methods used in the analysis, including a recently development cross-check of Bayesian computation.

#### Slides

__15.12.2020__

### Michael Spannowsky

#### IPPP, Durham

## Novel (Quantum) Computational Methods for Quantum Field Theories

I will discuss novel approaches for the task of finding a solution to a quantum field theoretical problem, e.g. tunnelling, in terms of an optimisation problem that can be solved either classically using machine learning methods or through a quantum computational ansatz. The general method we use is a discretisation of the field theory problem into a general Ising model, with the continuous field values being encoded into Ising spin chains. To illustrate the method, and as a simple proof of principle, we have used a quantum annealer to recover the correct profile of various tunnelling solutions. I will discuss this as well as outlining future possibilities. These methods are applicable to many nonperturbative problems.

#### Slides

__01.12.2020__

### Antonio Enea Romano

#### CERN and ICRA, Pescara

## The MESS of the CMB

We analyze cosmic microwave background (CMB) data taking into account the effects of a momentum dependent effective sound speed (MESS). This approach allows to study the effects of primordial entropy perturbations in a model independent way, and its implementation requires a minimal modification of existing CMB fitting numerical codes developed for single scalar field models. We adopt a phenomenological approach, and study the effects of a local variation of the MESS around the scale where other analysis have shown some deviation from an approximately scale invariant curvature perturbation spectrum. We obtain a substantial improvement of the fit with respect to a model without MESS, showing that primordial entropy perturbations can be an explanation of these deviations.

__17.11.2020__

### Robert Szafron

#### CERN

## Wino Dark Matter and Sommerfeld effect at the next-to-leading order

I will discuss the computation of the Sommerfeld enhancement factor for the wino dark matter at the next-to-leading order. In the effective field theory approach, I will show how to calculate the correction to the Yukawa potential generated by the exchange of gauge bosons in the Standard Model. This effect leads to a sizeable modification of the annihilation cross-section, particularly near the resonance region, where it shifts the resonance position. I will also discuss how these corrections influence relic abundance.

#### Slides

__03.11.2020__

### Ivo de Medeiros Varzielas

#### Centro de Fisica Teorica de Particulas, Lisbon

## Modular symmetries and flavour

I will give a brief introduction of modular symmetries, in order to consider the finite modular symmetry groups as possible symmetries explaining the origin of flavour. I then discuss applications of modular symmetries to flavour model building, namely: 1. the use of multiple modular symmetries (based on https://arxiv.org/abs/1906.02208); 2. a method for systematically finding values of the modulus that stabilises specific subgroups of finite modular symmetries (based on https://arxiv.org/abs/2008.05329).

#### Slides

__20.10.2020__

### José Zurita

#### Institute for Theoretical Physics, Karlsruhe

## Exploring the Lifetime Frontier

While there are several theoretical motivations on why Physics Beyond the Standard Model (BSM) should be near the electroweak scale, there is no evidence in the current experimental data. One intriguing possibility is that this new Physics that might explain long-standing theoretical puzzles (e.g: hierarchy problem, dark matter, matter- antimatter asymmetry, neutrino mases, strong CP-problem) involves new BSM particles with macroscopic lifetimes, usually referred to as “Long-Lived Particles” (LLPs). While the LHC is in most cases a natural source of LLPs, it is also true that the current detectors are not built with LLPs as its primary physics target, and hence in the last few years several external detectors haven been proposed or even commissioned (MATHUSLA, FASER, CODEX-b, MoEDAL, AL3X, ANUBIS, MilliQan). Likewise existing experiments can have LLP capabilities (NA62, SeaQuest) In this talk I will motivate the existence of LLPs from theoretical considerations, briefly discuss the capabilities of the newly proposed experiments, and discuss several examples of the broad palette of the interesting and exciting signatures.