Primordial black holes (PBHs) are believed to form through the gravitational collapse of overdense regions in the early Universe. They may serve as seeds for galaxy formation and are also considered one of the important candidates for cold dark matter (DM).
In particular, I will focus on several representative toy models of single-field inflation. The enhanced primordial perturbations in these models can not only produce PBHs, but also generate gravitational waves through higher-order effects. I will further extend the discussion to the possibility of a PBH-dominated era, which could leave observable signatures if PBH evaporation produces stable relics.
These studies demonstrate the significant potential of PBHs as probes of the early Universe, naturally leading to the important question of how to accurately estimate the PBH abundance. In the latter part of the talk, I will introduce a method based on peaks theory for estimating the abundance of primordial black holes. Our approach works well for arbitrary forms of the power spectrum, and by incorporating more systematic statistical methods, we expect it to provide useful cross-checks in combination with future gravitational-wave observations and related cosmological probes.

Primordial black holes (PBHs) are a well-motivated dark-matter candidate that may have formed in the early Universe from the collapse of primordial density fluctuations. If PBHs constitute even a fraction of dark matter, they can be probed through gravitational microlensing. To test this possibility, we have been conducting microlensing observations of stars in the Andromeda galaxy (M31) with the Subaru Hyper Suprime-Cam (HSC).
In this talk, I will present the latest results from our Subaru HSC analysis, including both a reanalysis of previous observations and the analysis of newly acquired data, based on a new event-search pipeline designed to improve the sensitivity to PBH microlensing signals. The pipeline adopts a more flexible microlensing light-curve model, including finite-source effects, enabling improved fits to candidate events. I will also discuss how these candidates should be interpreted in the context of recent independent reanalyses of the Subaru HSC data and related microlensing results from other surveys.

Parity symmetric left-right models provide a viable solution to the strong CP problem. Spontaneous breaking of the Parity symmetric model results in heavy gauge bosons that are searched for at colliders, placing a lower bound on the Parity breaking scale close to 14 TeV. However, without an upper bound, the Parity breaking scale may be as large as the Planck scale. In this talk, I will discuss the minimal Parity symmetric left-right model and show that by embedding a WIMP dark matter candidate one obtains an upper bound on the Parity breaking scale that is far below the Planck scale. I will focus on three well-motivated embeddings of WIMP dark matter and demonstrate how an upper bound on the Parity breaking scale is obtained by requiring that the WIMP obtains the correct relic abundance. I will then discuss current constraints on the free parameters of the model— the Parity breaking scale and WIMP mass– and motivate future indirect detection experiments such as C.T.A. that can probe the entire parameter space for certain galactic center dark matter density profiles.

Primordial perturbations are born as quantum fluctuations during inflation and are believed to be the seeds of the (classical) cosmic structure observed today, such as the anisotropies in the cosmic microwave background (CMB). In order to shed light on the quantum-to-classical transition of primordial perturbations during single field inflation, we investigate the decoherence of superhorizon scalar curvature perturbations. These are considered as an open quantum system interacting with a time-dependent environment of deep subhorizon tensorial modes through the trilinear interactions predicted by General Relativity. We show that derivativeless interactions provide the dominant contribution to decoherence, while derivative interactions introduce significant non-Markovian effects that tend to slow it down. We introduce a modification to the quantum master equation to take into account the time dependence of the subhorizon environment induced by a time dependent environment of deep subhorizon tensorial modes. Finally, we compute the associated quantum corrections, due to the trilinear interactions, to cosmological correlators. We find a non-perturbative resummation of the quantum corrections to the power spectrum, and we extend this result to the bispectrum, where an analogous resummation structure emerges.
We then follow the evolution of primordial perturbations beyond inflation into the reheating era. Very little is known about this effectively matter dominated phase: it is only constrained to end before Big Bang Nucleosynthesis, at a temperature higher than O(1) MeV. We show that reheating can be long enough that structures, such as halos, can form, inflaton stars can condense inside the halos and eventually grow to collapse into PBH. By employing PBH constraints we are able to improve constraints on reheating temperature, depending on the scale of inflation, strengthening existing bounds by several orders of magnitude.

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.