## SEMESTER 2023/24 - WINTER

__06.10.2023__

### Shihwen Hor

#### University of Tokio

## Minimal Nambu-Goldstone-Higgs in Supersymmetric SU(5)

We revisit the minimal Nambu-Goldstone (NG) Higgs supersymmetric (SUSY) SU(5) grand unified model and study its phenomenological implications. The Higgs sector of the model possesses a global SU(6) symmetry, which is spontaneously broken and results in the Higgs doublets of the minimal SUSY Standard Model (MSSM) as NG chiral superfields. Therefore, the model naturally leads to light Higgs doublets and solves the doublet-triplet splitting problem. Because of the SU(6) symmetry, the couplings of the Higgs sector are tightly restricted, and thus the model is more predictive than the minimal SUSY SU(5). We determine all the grand-unified-theory parameters via the matching conditions of the gauge coupling constants at the unification scale and calculate proton lifetime, confronting this with current experimental bounds. We discuss that this model is incompatible with the constrained MSSM, whilst it has a large viable parameter space in the high-scale SUSY scenario. The perturbativity condition on the trilinear coupling of the adjoint Higgs field imposes an upper (lower) limit on the wino (gluino) mass, implying a hierarchical mass pattern for these gauginos. Future proton-decay searches can probe a large part of the parameter space, especially if the SUSY-breaking scale is <100 TeV.

__10.10.2023__

### Lei Zu

#### Purple Mountain Observatory, Nanjing

## Mirror Twin Higgs Cosmology

Cosmology and particle physics are two distinct branches of physics, but they are interconnected in several ways, and cosmological observations can provide valuable insights into particle physics. With the ever-advancing precision of astronomical cosmological observations, the classical LCDM model faces challenges posed by precise data points, including the Hubble tension, S_8 tension, and nHz gravitational waves. Mirror twin Higgs model has been put forward to explain the Higgs hierarchy problem from only particle physics side. Our research indicates that this model not only offers a particle physics solution but also has the potential to alleviate tensions observed in cosmological observations. The introduction of additional dark radiation during the early universe may alleviate the Hubble tension. Twin recombination mechanisms can help explain the S_8 tension. Furthermore, the potential occurrence of a first-order dQCD phase transition could provide an explanation for the nHz gravitational waves detected by Pulsar Timing Arrays. These findings show that cosmology serves as an ideal laboratory for exploring the particle physics.

#### Slides

__24.10.2023__

### Tom Steudtner

#### Technische Universitat Dortmund, Germany

## Weakly coupled asymptotic safety up to 4 loops

In this talk, I will report about the special role of the Litim-Sannino model for the Asymptotic Safety program, and present a high-precision estimate for the conformal window of its interacting UV fixed point. Four loop gauge, three loop Yukawa and three loop quartic beta functions are computed both by a direct loop calculation and by generalizing existing literature results. The UV fixed point and corresponding critical exponents are obtained at N3LO in the conformal expansion. Several approaches to estimate the conformal window are applied, and the phenomena behind the disappearance of the fixed point are discussed.

#### Slides

__31.10.2023__

### Motoko Fujiwara

#### Technical University of Munich

## Dark matter heating vs. vortex creep heating in old neutron stars

Dark matter can be captured in a neutron star and deposits its energy into a star. This dark matter heating effect, however, can be observed only if it dominates over other internal heating effects in neutron stars. In this work, as such a internal heating effect, we examine the frictional heating caused by the creep motion of neutron superfluid vortex lines in the neutron star crust. The luminosity of this heating effect is controlled by the strength of the interaction between the vortex lines and nuclei in the crust. We estimated this luminosity in two approaches; (1) the estimation through the temperature observation of old neutron stars and (2) the estimation from the many-body calculation of a high-density nuclear system. We find that both approaches suggest that the vortex creep heating dominates over the DM heating. The vortex-nuclei interaction must be smaller than the estimated values by several orders of magnitude to overturn this domination.

__14.11.2023__

### Toni Mäkelä

#### National Centre for Nuclear Research, Warsaw

## Investigating the reach of LHC neutrino experiments

The recent obbservation of neutrinos produced at the Large Hadron Collider (LHC), reported by the FASER$\nu$ and SND@LHC experiments, has given rise to a novel neutrino physics program for the LHC. In particular, the proposal of a purpose-built Forward Physics Facility (FPF) motivates studies of the discovery potential of these searches. This requires resolving degeneracies between new predictions and uncertainties in modeling neutrino production in the forward kinematic region. Based on a broad selection of existing predictions for the parent hadron spectra at FASER$\nu$ and the FPF, we parametrize the expected correlations in the spectra of neutrinos produced in their decays, and use a Fisher information approach to determine the highest achievable precision for their observation. This allows for constraining various physics processes within and beyond the Standard Model, including neutrino non-standard interactions. We also illustrate how combining multiple neutrino observables could lead to experimental confirmation of the enhanced-strangeness scenario proposed to resolve the cosmic-ray muon puzzle during LHC Run 3.

#### Slides

__28.11.2023__

### Gregory Patellis

#### Technical University of Lisbon

## Reduction of Couplings in the Type-II 2HDM

The idea of reduction of couplings consists in the search for relations between seemingly independent couplings of a renormalizable theory that are renormalization group invariant. In this article, we demonstrate the existence of such 1-loop relations among the top Yukawa, the Higgs quartic and the gauge colour couplings of the Type-II Two Higgs Doublet Model at a high-energy boundary. The phenomenological viability of the reduced theory suggests the value of tanβ and the scale in which new physics may appear.

#### Slides

__05.12.2023__

### Peter Athron

#### Nanjing Normal University

## From first order cosmological phase transitions to gravitational waves

The 2015 observation of gravitational waves opened up a new window into particle physics. First order cosmological phase transitions are predicted in many extensions of the standard model of particle physics and can generate gravitational wave signatures. Exciting recent results mean that we have now entered an era where data from gravitational wave experiments may be used as possible signals or constraints on particle physics theories. I will discuss these and show how to determine gravitational wave constraints, signals and future discovery projections using the state-of-the-art methods. I will critically evaluate many approximations used in the literature and discuss substantial sources of uncertainty and unknowns.

#### Slides

__12.01.2024__

### Hiroki Kawai

#### University of Tokyo

## Cosmological structure formation with fuzzy dark matter

Dark matter is one of the major components in our universe and plays an important role in structure formation. In the standard cosmology, the nature of the dark matter is generally thought that it is cold, and interacts with other matter only through gravity. The so-called Λ Cold Dark Matter (ΛCDM) model can successfully explain a broad range of observations at large length scales. However, there are several discrepancies at small scales, known as small-scale problems. To alleviate these problems, alternative dark matter models such as fuzzy dark matter (FDM) are considered. FDM is a scalar particle coupled to a gravitational field without self-interaction whose mass is around 10E-22 eV. Due to the small mass of the FDM, the de Broglie wavelength becomes large and wave nature can be seen on a cosmological scale. The wave nature can be seen inside halos, where two unique features can be observed, soliton core and granular structures. In this talk, I first review the standard ΛCDM cosmology and the small-scale problems and introduce the FDM model. Then I show the structures in FDM halos in detail with our studies.

__30.01.2024__

### Camilo Garcia-Cely

#### University of Valencia

## Insights from Axion Dark Matter for the Field of Gravitational Wave Physics

A decade ago, the discovery of gravitational waves marked a crucial milestone in our understanding of the universe. While ongoing efforts primarily focus on detecting gravitational waves at frequencies below a few kHz, a growing interest in exploring higher frequencies is emerging, driven by the potential to observe signals of cosmological origin. In the first segment of my talk, I will delve into the backgrounds for such signals within the Standard Model, with a particular emphasis on the dominant source on Earth: the high-temperature plasma in the Sun. I will highlight the strong parallel with solar axions. Shifting focus in the second part, the discussion will center on experimental proposals for detecting high-frequency gravitational waves. Specifically, I will discuss the potential of axion haloscopes to probe gravitational waves in the 100 kHz-100 MHz range.