The early universe is regarded as an ideal laboratory for the generation of all kinds of elementary particles (Standard Model (SM) and beyond the Standard Model (BSM)), populating the present universe. An intermediate phase, which bridges the gap in energy and time scales between the end of inflation and the beginning of the hot Big Bang, is the post-inflationary reheating phase. The absence of direct observational evidence has left this important phase of the early universe poorly constrained, both at present and in the foreseeable future. However, the distinct imprints of this phase on cosmic relics offer us a promising avenue for its indirect probe through various cosmological observables.
The early inflation and post-inflationary reheating phases are an important playground for investigating various non-perturbative, non-equilibrium phenomena. Parametric resonance and tachyonic instability are some distinctive features of the non-perturbative phenomena in the early era. For instance, in the early reheating era (Preheating), plenty of elementary particles were produced within a very short period through the mechanism of parametric resonance instability, when the interaction strength between the inflaton and the daughter particles is appropriate. Another notable aspect where non-perturbative effects become instrumental is the Cosmological Gravitational Particle Production (CGPP). This CGPP is the quantum mechanical particle production in a time-dependent dynamical background. Unlike Preheating, in CGPP, the background dynamics during reheating itself causes particle production without any direct coupling to the inflaton. These particles can play an important role in cosmic history, being possible candidates for dark matter, gravitational wave radiation, dark radiation, etc. This talk sheds light on various non-perturbative signatures of gravitational particle production, both in minimalistic (no coupling to gravity) and non-minimalistic (non-zero coupling to gravity) scenarios.
We have made unprecedented progress in observational cosmology after the detection of gravitational waves. In this talk, one of the prime objectives is to decipher various non-perturbative signatures of different early universe phenomena through their discernible imprint on gravitational waves. These ideas present the main theme of my presentation.

Light minicharged particles are well-motivated targets in searches for physics beyond the Standard Model, but their masses are often introduced as free parameters. In this talk, I will discuss a chiral hidden-sector framework in which the light masses are protected by a spontaneously broken gauge symmetry. Requiring quantum consistency then imposes anomaly cancellation conditions on the chiral charge assignments. I will show that these conditions are exactly equivalent to the degree-three Prouhet–Tarry–Escott problem in number theory. This correspondence turns anomaly cancellation into a predictive organizing principle for the particle spectrum: the minimal consistent sector contains at least four minicharged mass eigenstates, and minimal solutions typically contain partner states with the same minicharge and nearby masses. I will explain the origin of this structure and discuss its implications for laboratory, astrophysical, and cosmological searches.

We delineate the maximal parameter space of sterile neutrino dark matter in the presence of lepton flavor asymmetries. We focus on large flavor asymmetries with vanishing total lepton asymmetry, which are washed out by neutrino oscillations at MeV temperatures and hence are consistent with BBN and CMB constraints. We derive a semi-classical Boltzmann equation for sterile neutrinos applicable in this regime and validate it against quantum kinetic equations. For sterile neutrino masses up to 60 keV, the viable range of mixing angles extends by up to two orders of magnitude, with broad prospects for tests in forthcoming X-ray, CMB, and structure formation observations. We will also discuss some related topics: the origin of lepton flavor asymmetries and baryon asymmetry, and so on.

Nuclear Lattice Effective Field Theory (NLEFT) is a robust framework that integrates lattice techniques, effective field theory, and quantum Monte Carlo (QMC) algorithms to provide ab initio solutions to the nuclear many-body Schrödinger equation. This talk will introduce the fundamental principles of NLEFT and highlight recent advancements, including a novel solution to the Monte Carlo sign problem in nuclei, the renormalization group (RG) evolution of lattice-regulated nuclear EFT, and various applications for computing key nuclear observables. These developments demonstrate the framework’s efficiency and versatility in tackling complex challenges in nuclear many-body physics.

https://www-conf.kek.jp/kincha/

Several low energy observables such as the muon g-2, the proton radius or parity-violating electron scattering are pushing the intensity frontier of particle physics, demanding precise control of the scattering processes behind them. McMule is a Monte Carlo framework built to meet this challenge. By combining automated tools with effective field theory techniques, it delivers NNLO predictions in QED and has recently been extended to systematically include electroweak and non-perturbative effects. This makes McMule a powerful tool for the most ambitious precision experiments at lepton facilities, such as KEK. I will highlight our biggest challenges, the underlying methods, and the path forward.

Radiative transfer is a fundamental tool in astrophysics for understanding physical states and formation processes of various objects. In this talk, I will demonstrate how similar principles can be applied to a distant field—medical diagnostics using near-infrared light. Biological tissues are highly scattering media, analogous in some respects to dusty astrophysical systems, where photons undergo complex trajectories before reaching the observer. By adapting the techniques in the astrophysics research, we have developed a new radiative transfer code, TRINITY, that can simulate time-resolved photon transport in the human head and enables us to address the associated inverse problem. I will present our simulation results and their integration with machine learning, which enables rapid identification of bleeding sites. Our AI-based diagnostic model achieves an accuracy of over 90% in detecting bleeding sites. Finally, I will discuss ongoing efforts toward practical applications, including early-stage detection of brain hemorrhage, and future directions for interdisciplinary research connecting physics and medicine.

State-of-the-art atomic clocks achieved fractional uncertainties below 10^-18. In these clocks, effects of conventional external fields, such as electric and magnetic fields, are suppressed for the high accuracy. Under this condition, the system can potentially be sensitive to tiny energy shifts caused by hypothetical fields weakly coupled to ordinary matter or by effects mediated by massive particles. Based on this idea, various searches for new particles and fields are performed using precision spectroscopy.
In this seminar, starting from the overview of precision spectroscopy of atoms and its applications to fundamental physics searches, I will describe some major recent progress in the field. Particularly, I focus on the topics related to the new clock transition at 431 nm in ytterbium that has high sensitivity to variation of the fine structure constant and fifth forces between a neutron and an electron.

We ask the question of how angular momentum is conserved in a number of related processes, from elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon; to scattering of a fully relativistic spin-1/2 particle by a central potential; to inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus, where the final spin is in a different direction than that of the neutrino – an apparent change of angular momentum.

The seeming non-conservation of angular momentum arises, in fact, in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in direction in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physical insights into angular and helicity distributions in these reactions.

Primordial black holes (PBHs), hypothesized to have largely been produced in the early Universe, span a broad mass range and offer rich cosmological and astrophysical implications. Among them, there has been a recent growing interest in the evaporating PBHs, looking for the cosmological consequences of their past existence and observable signatures. In this talk, I will provide a brief overview of PBHs and the physics of their evaporation. Then, I will introduce my works on evaporating PBHs, about their reformation, isocurvature generation, and dark matter and hotspots. These examples are just a fraction of the phenomenological side of the rich physics of PBHs.