Axions are one of the candidates for the unknown dark matter. Ultralight axions form a huge number of clouds in galactic halos. When such an axion cloud passes through the Earth, it interacts electromagnetically with the geomagnetic field and generates a monochromatic electromagnetic wave whose frequency corresponding to the axion mass. Recently we modeled the axion-induced electromagnetic wave signals by solving Maxwell’s equations under the appropriate boundary conditions of the ionosphere for geomagnetic fields and showed that Earth’s natural environment can serve as a powerful probe for ultralight axion dark matter with masses ranging from 10^{-15} eV — 10^{-13} eV. Based on the derived theoretical model, we searched for axion-induced magnetic field signals within the observational data of global geomagnetic field variations (Eskdalemuir Observatory, 2012–2022). In this talk, I report on the idea of the search, the data analysis mehtod, the results of the search having several tens of axion signal candidates.

The spectacular advances of deep learning in recent years have led to breakthroughs across a wide range of data analysis tasks. At the same time, the techniques used to boost model performance have become increasingly intricate, with ever larger parameter counts and training datasets. What, then, are the practical steps needed to harness these methods for fundamental science especially in the analysis of physics experiments? In this talk we first survey how machine learning and deep learning are being employed in international experimental collaborations. We then present, step by step, the workflow we have developed to tailor deep-learning models for the microscopic image analysis of nuclear emulsion detectors. Finally, we discuss several modern deep-learning ideas and how they might further benefit experimental data analysis.

The spectra of stable particles such as photons, positrons, antiprotons and neutrinos are one of the main ingredients to calculate the
fluxes of cosmic rays and radiation searched for in indirect detection experiments. The modeling of the whole process is however very complicated since after dark matter annihilation or decay, a number of phenomena occur including resonance decays, parton showering, hadronization and hadron decays. Therefore the modeling itself cannot be performed from first principles. I will discuss some progress in this direction and present CosmiXs which uses VINCIA to properly model electroweak corrections, and handles the polarization information. I will then move to the modeling of antideuterons and discuss briefly the associated theoretical uncertainties (The dataset can be found in this repo: https://github.com/ajueid/CosmiXs)
Talk is based on:
https://arxiv.org/abs/2411.04815
https://arxiv.org/abs/2312.01153
https://arxiv.org/abs/2303.11363
https://arxiv.org/abs/2202.11546

Quantum computing technology has been developing rapidly in recent years, and it is expected to speed up some kinds of computation that are highly time-consuming in classical computing, e.g., operations on extremely large matrices. Practical applications in various fields are being explored, and cosmology is one of them. In this talk, after an introduction to quantum computing, I explain its application in stochastic inflation, a formalism for analyzing the inflationary perturbation based on the probability theory. In this formalism, the perturbation is related to the Fokker-Planck equation, and its probability distribution is characterized by the eigenvalues of the differential operator. However, calculating them can be challenging, especially in multi-field cases, since it corresponds to finding eigenvalues of an exponentially large matrix. I explain a quantum algorithm to calculate the differential operator eigenvalues efficiently and share results from numerical demonstrations that suggest its applicability to the stochastic inflation problem.

The Weak Gravity Conjecture (WGC) plays an important role in the swampland program. While the WGC has been intensively studied and refined since its inception, most studies have been focused on formulating and testing the conjecture in Minkowski space. In this talk, I will discuss our proposal of a version of the Weak Gravity Conjecture that applies to AdS space. Adhering to one of the original motivations for the WGC by demanding extremal black holes to decay, the dynamics of black hole charged emission is analyzed, leading to an AdS WGC that is more stringent than the Minkowski version. The new AdS WGC bound can also be obtained from a black hole-particle repulsiveness condition and the near horizon Breitenlohner-Freedman (BF) instability of extremal black holes. I will discuss extensions and implications of the AdS WGC bound, including the convex hull version and consistency with supersymmetry, and comment on further steps to embed the AdS WGC into string theory settings.

https://www.rcnp.osaka-u.ac.jp/~suenaga/Hadron_Cafe/

Gravitational chiral anomaly connects the topological charge of spacetime and the chirality of fermions. It has been known that the chirality is carried by the particles (or the excited states) and also by vacuum. However, in the study of gravitational leptogenesis, for example, lepton asymmetry associated with the chiral gravitational waves sourced during inflation is conventionally evaluated only by integrating the anomaly equation. In this evaluation, no distinction between the excite states and vacuum contribution has been made. In this talk, I apply an analogy between U(1) electromagnetism and the weak gravity to the spacetime that resembles the one considered in the gravitational leptogenesis scenario. By assuming the emergence of Landau level-like dispersion relation in our setup, I suggest that level-crossing does not seem to be efficient while the charge accumulation in the vacuum likely takes place. Phenomenological implication is also discussed.

Ultralight bosonic (ULB) fields with mass m << 1 eV often arise in theories beyond the Standard Model (SM). If such fields exist, violent astrophysical events that result in emission of gravitational wave, photon, or neutrino signals could also produce bursts of high-density relativistic ULB fields. Detection of such ULB fields in terrestrial or space-based laboratories correlated with other signals from transient astrophysical events opens a novel avenue for multimessenger astronomy. This additionally provides a route for directly detected for fields that are otherwise very challenging to detect. I will discuss that quantum sensors are particularly well-suited to observe emitted scalar and pseudoscalar axion-like ULB fields coupled to SM, and demonstrate that multimessenger astronomy with ULB fields is possible even when accounting for matter screening effects.

Sterile neutrino with masses of the keV scale is a fascinating candidate for dark matter (DM). They can be produced via neutrino oscillations involving the Standard model neutrinos (“active” neutrinos), which are in thermal equilibrium in the early universe. Especially, in the presence of significant neutrino-antineutrino asymmetry, the production rate of the sterile neutrinos is resonantly enhanced and we can successfully account for all dark matter consistent with observational constraints.
In this seminar, we first present a comprehensive numerical analysis of the resonant production scenario and explore the consistency with current observations.Secondly, we examine a leptogenesis scenario that can naturally generate the neutrino-antineutrino asymmetry consistent with the resonant production of sterile neutrino DM. We demonstrate that this can be realized within the framework of Affleck Dine leptogenesis, based on the minimal supersymmetric Standard Model (MSSM). In our setup, spherical clumps of the slepton field—known as Q-balls—form and eventually decay into lepton asymmetric Standard model plasma.
Furthermore, in the above setup, Q-balls dominate the cosmic energy density and finally decay rapidly into radiation, triggering sudden reheating. This sudden reheating causes subhorizon modes of the gravitational potential to oscillate with large amplitudes, and then a significant amount of the gravitational waves (GWs) are produced by curvature perturbations at second order. Based on this idea, we discuss the testability of the scenario with the future GW observations.This presentation is mainly based on arXiv:2402.11902, but includes some updates on the analysis.

The QCD axion is currently the focus of intense experimental and theoretical research. A key feature of canonical QCD axion models is the fixed mass-coupling relation, which motivates experimental efforts to explore the so-called QCD axion band. But what if no axion is found within this range? Could a genuine QCD axion lie outside this band—and if so, at what theoretical cost? In this seminar, we will show that such a displacement can naturally arise if the axion propagates in extra dimensions, leading to distinctive patterns that motivates new regions of parameter space. We will discuss the theoretical framework, the associated experimental signatures, and the limitations of these constructions.