## 2023 - SUMMER SEMESTER

__07.03.2023__

### Ranjan Laha

#### Indian Institute of Science, Bangalore

## Detecting low-mass primordial black holes as the dark matter candidate

Primordial black holes (PBHs) are one of the oldest and well-motivated dark matter candidates. PBHs can have a wide range in masses and their detection techniques vary (depending on their masses). I will be concentrating on the low-mass end of PBH masses (masses ~ 10^{16} g to 10^{18} g). I will discuss how one can detect the Hawking radiation from these objects. I will discuss the current constraints using various astrophysical observables like low-energy Galactic positrons, gamma-rays, and other observables. I will also discuss how near-future gamma-ray telescopes can discover low-mass PBH dark matter.

#### Slides

__21.03.2023__

### Tobias Binder

#### TU Munich

## NLO Electric field correlators for the Dark Matter relic abundance

WIMPs at the TeV mass scale and above experience long-range force effects, which are known to play a crucial role for predicting the relic abundance precisely. One such effect is the existence of bound states in the spectrum. In the early Universe, they can form and subsequently decay through annihilation, leading to a further depletion of the total abundance. We review electroweakly charged dark matter and colored coannihilation scenarios as examples. To compute the formation of bound states at NLO (zero and finite temperature) in such scenarios, it turns out that the effort can be reduced to the evaluation of electric field correlators thanks to factorization. Our results for U(1) and SU(N) electric field correlators are presented, showing collinear finiteness and gauge invariance at NLO. Potential implications of enhanced bound-state formation rates due to the NLO effects are discussed.

#### Slides

__04.04.2023__

### Anish Ghoshal

#### University of Warsaw

## Complementary probes of weakly-coupled and high-scale BSM: Gravitational Waves versus Laboratory tests for Dark Matter and Leptogenesis

Leptogenesis usually involves high scales and it is hard to test in laboratories, Here we will discuss probing high scale and intermediate scale leptogenesis via primordial sources of Gravitational Waves from inflationary tensor perturbations, thermal phase transitions and domain walls. First we will show leptogenesis in the B−L symmetry breaking scenario associated with a strong first-order phase transition that gives rise to detectable gravitational waves (GWs) via bubble collision. And the possible future GW experiments can effectively probe leptogenesis over a wide range of the B−L symmetry-breaking scale. Second we propose a novel way of probing high-scale Dirac leptogenesis, a viable alternative to the canonical leptogenesis scenario where the total lepton number is conserved, keeping light standard model neutrinos purely Dirac. This leads to GW signals from collapsing domain walls. We find that most of the near-future GW observatories will be able to probe Dirac leptogenesis scales all the way up to 10ˆ11 GeV. Third we will show how inflationary tensor perturbations and its detectability may shed light upon high-scale leptogenesis and dark matter. Last we will show complementary tests for freeze-in DM via GW and long-lived particle searches. In particular, we show that freeze-in scenarios can be searched by various experiments such as DUNE, FASER, FASER-II, MATHUSLA, SHiP, etc. complementary observables for GW detectors such as LISA and u-DECIGO.

__18.04.2023__

### Anders Eller Thomsen

#### University of Bern

## New Developments in EFT Matching for BSM Physics

With the absence of new resonance discoveries at the LHC, the role of Effective Field Theories (EFTs) in Beyond the Standard Model (BSM) physics has become increasingly crucial. EFTs serve as indispensable tools in precision physics, offering the greatest potential to reveal indirect evidence of new phenomena. This talk will showcase cutting-edge methods for matching BSM models to EFTs and their integration into an automated matching tool, Matchete. Additionally, the treatment of evanescent operators within the matching procedure will be discussed. These advancements contribute to a more comprehensive exploration of BSM physics through the application of EFTs.

#### Slides

__25.04.2023__

### Richard Ruiz

#### Institute of Nuclear Physics, Kraków

## Life at a Multi-TeV Muon Collider

In this talk we present a picture of what life is like at a multi-TeV muon collider. We start by showing that beyond a few TeV electroweak (EW) boson fusion/scattering becomes the dominant roduction vehicle at lepton colliders for both the Standard Model and new physics. Motivated by this, we revisit the treatment of weak gauge bosons as constituents of high-energy leptons. In particular, using a new, public implementation of (polarized) W/Z parton distribution functions in the Monte Carlo event generator MadGraph5_aMC@NLO, we report the size of universal, i.e., process independent, corrections that spoil the accuracy of a (factorized) scattering formula for muon colliders. Guided by this insight, we give an outlook for polarized EW boson scattering at many TeVs.

#### Slides

__09.05.2023__

### Manuel Reichert

#### University of Sussex

## Asymptotically safe quantum gravity

Over the past decades, the asymptotic safety scenario has matured into a viable contender for a consistent theory of quantum gravity. The scenario is based on a non-perturbative quantisation via an interacting UV fixed point of the renormalisation group flow. The existence of the UV fixed point has been confirmed in increasingly elaborate truncations. These results open the door to working out observable consequences of the theory, for example, graviton-mediated scattering, black hole solutions, and constraints on low-energy matter couplings. I will give a detailed introduction to the topic and present some recent advances in the field, in particular, in the area of computations on a Lorentzian background and the connection to (beyond) Standard Model physics.

#### Slides

__30.05.2023__

### Rafael Robson Lino dos Santos

#### CP3-Originis, University of Southern Denmark

## Probing new physics and gravity across scales

Evidence for ultraviolet gravitational fixed points in asymptotic safety quantum gravity has been found over the past years. The non-trivial interplay of matter and gravity can either spoil fixed points or enhance predictive power in infrared scales. In the first part of the talk, I will summarize the status of the field and explore the “asymptotic safety landscape” by considering dark-universe-motivated models in the matter sectors. Besides, the field of gravitational waves has flourished over the past decade. The search for a gravitational wave background across different energy scales is a tantalizing probe of new physics as it is complementary to CMB. In the second part of the talk, I will summarize the status of searches and show that nHz PTA data are already competitive to constrain BSM and cosmology particle physics models.

#### Slides

__06.06.2023__

### Marco Hufnagel

#### ULB, Brussels

## Pandemics and Cannibals: Some intriguing ways of producing dark matter in the early Universe

In the first part of the talk, we propose a novel mechanism to generate sterile neutrinos in the early Universe, by converting ordinary neutrinos in scattering processes. After initial production by oscillations, this leads to an exponential growth in the sterile neutrino abundance. We show that such a production regime naturally occurs for self-interacting sterile neutrinos, and that this opens up significant new parameter space where they make up all of the observed dark matter. Our results provide strong motivation to further push the sensitivity of X-ray line searches, and to improve on constraints from structure formation. In the second part of the talk, we consider a scenario, in which the dark matter is alone in a hidden sector and consists of a real scalar particle in its spontaneously broken phase at a temperature which differs from the one of the visible sector. This is a particular case of a cannibal dark matter scenario, in which the relic abundance is sensitive to 3 to 2 and 4 to 2 processes. We study numerically and analytically the dark matter abundance both in the broken and the symmetric phases, while also reporting our results in the domain of thermal dark matter candidates.