Primordial black holes (PBHs) have attracted significant attention from many aspects in recent years. In this seminar, I will review the basics and recent progress in the dynamics of PBH formation. I will begin with a brief review of the standard setup for PBH formation scenarios, followed by an analytical PBH formation model based on applying the Jeans criterion to a 3-zone model. I will then discuss spherically symmetric simulations of PBH formation in a radiation-dominated universe, covering numerical techniques, comparisons with threshold models using the compaction function, critical collapse, and the characteristics of Type I/II and Type A/B PBH formations. Furthermore, I will highlight recent developments in non-spherically symmetric PBH formation simulations. Finally, I will address our recent study on PBH formation during a matter-dominated era.

One of the major challenges in nuclear physics is to understand nuclear structure and reactions starting from the underlying interactions among nucleons. Over the past two decades, many efforts have been made to develop nuclear interactions based on chiral effective field theory and computationally efficient quantum many-body methods with polynomial scaling. With these systematically improvable frameworks, the range of applicability of nuclear ab initio calculations has rapidly expanded.
The neutron skin thickness of a nucleus is closely related to the density dependence of the nuclear symmetry energy, which is an important ingredient of the nuclear equation of state. Since neutrons are electrically neutral, determining their spatial distribution experimentally is challenging. Parity-violating electron scattering provides a powerful probe of neutron distributions, and the CREX and PREX collaborations have reported measurements of the neutron skins of 48Ca and 208Pb, respectively.
In this seminar, I will review recent progress in nuclear ab initio theory and discuss recent results on the neutron skin thicknesses of 48Ca and 208Pb.

Heavy-ion collisions exhibit distinctive phenomenological characteristics relative to pp collisions due to the formation of a considerably larger quark–gluon plasma (QGP). In the seminal work of Satz & Matsui, color screening effects of in-medium heavy-quark pairs were proposed, introducing the concept of quarkonium “melting”. Owing to its unusually large spatial extent and weak binding energy, the X(3872) provides a particularly compelling probe of the QGP, as its internal structure is compatible with a mixed configuration in turn very sensitive to the degree of separation of charm systems in the QGP. We employ simple theoretical arguments to quantify this separation, combining many experimental results by the LHC collaborations on the hidden-charm sector, including the X(3872).
This approach can be naturally extended to the bottomonia sector, and, leveraged together with the charmonia results, used to understand the distinction between in-medium and vacuum quarkonia production, incorporating results from the Belle II, CLEO and BESIII experiments.
Through this unified phenomenological study, we show how quarkonia measurements can provide insights into the spacial dependencies of hadronisation.

The Cabibbo–Kobayashi–Maskawa (CKM) matrix encodes the strengths of flavour-changing quark transitions mediated by the W boson. Its entries are fundamental parameters of the Standard Model, and their precise determination is a central goal of flavour physics. Within the Standard Model, decay rates of B and charm mesons can be predicted in terms of CKM matrix elements, including for leptonic decays such as B → ℓν and semileptonic channels like B → D(*)ℓν and B → πℓν. Experiments including Belle II at KEK then measure these rates to determine the corresponding CKM elements.
As pure-QCD predictions have reached sub-percent precision, electromagnetic corrections must now also be included. For heavy mesons, their internal structure plays an important role in radiative leptonic decays. In this talk, I will present our lattice-QCD approach to predicting decay rates for processes such as B → ℓνγ in terms of QCD form factors, and discuss ongoing analyses based on a set of JLQCD gauge ensembles. This type of lattice calculations begun only recently, and so I will explain why these decays can be studied in Euclidean space. I will also describe our strategy for controlling the leading systematic uncertainty from excited-state contamination. This approach also allows us to access a broad range of photon energies and several initial mesons, including D, Ds, B, and Bc. This work will provide a more complete understanding of the hadronic structure of these mesons and help construct infrared-safe observables, such as the radiation-inclusive decay B → ℓν[γ]. Ultimately, it will reduce theoretical systematic uncertainties in the extraction of CKM matrix elements.

Inclusive semileptonic decays of $B_{(s)}$ mesons provide an important avenue for the determination of the CKM matrix element $|V_{cb}|$ and play a central role in understanding the long-standing tension between its inclusive and exclusive determinations.
In this talk, I will discuss how inclusive semileptonic decay observables can be accessed from lattice QCD through suitably constructed four-point correlation functions and spectral reconstruction techniques. I will introduce the basic strategy and discuss the treatment of the inverse problem. I will then present recent results for inclusive semileptonic $B_s\to X_c\ell\nu$ decays, with particular emphasis on systematic uncertainties and the steps towards a controlled continuum limit.
Finally, I will discuss ongoing developments and future directions, including connections to continuum OPE calculations and the heavy-quark expansion.

We propose a new avenue for understanding the cosmological singularity. The standard cosmological model contains a generic initial singularity usually referred to as the big bang. Herein, we present a novel idea to extend the description of our Universe beyond this limit. The proposal relies on rewriting physics in a purely Riemannian, i.e. locally Euclidean, 4-dimensional space and the emergence of Lorentzian patches owing to the interaction of all matter fields to a clock field that is responsible for a signature change. If our universe is contained within one of these patches, the initial singularity is replaced by a smooth boundary on which the signature of the physical metric flips. In this talk, we first define the model and draw the necessary conditions on its arbitrary functions for solutions to exist. Next, we prove the existence of solutions that lead to an emergent universe with a primordial (almost) de Sitter phase. To finish, we discuss the consequences of this construction for the universe on scales much larger than our observable universe: a large “Euclidean sea” in which Lorentzian islands locally emerge and host an expanding universe potentially similar to ours. While speculative, this scenario has specific features that can be tested, and this talk sets the basis for further phenomenological investigations.

Superconducting sensors are a cornerstone of modern frontier physics, driving discoveries from the early universe to the quantum world. In this talk, I will discuss the diverse applications and synergistic development of superconducting detector technologies, highlighting how advances in one discipline frequently drive progress in others. The extensive R&D and industry partnerships established for CMB-S4 detector fabrication have opened new pathways for fabricating superconducting sensors, which are now enabling highly sensitive detector arrays for line intensity mapping, dark matter detection and quantum computing. This talk will illustrate the feedback loop between astrophysics, particle physics, and quantum science, showing how detectors built to observe the sky simultaneously advance quantum technology.

An interesting proposal suggests that a QCD axion (a)coupling to the up quark, down quark, and electron remains viable for an axion mass near 10~MeV. In this paper, this possibility is reexamined by deriving new bounds from kaon decays. In particular, we perform a detailed analysis of the KL -> pi0 pi0 e+ e- measurement reported by the KTeV experiment, and reinterpret K+ decay measurements at the E949 and NA62 experiments to constrain both the diphoton decay and effectively invisible decay modes of the axion. We find that, combined with the previously known bounds, the viable window for the MeV-scale QCD axion is excluded, primarily due to the KTeV bound. Uncertainties associated with the chiral Lagrangian are further examined, and the scenario remains excluded even after accounting for these uncertainties, except for a tiny region of parameter space where higher-order corrections must finely cancel the leading-order contribution, suppressing the branching ratio of KL->pi0 pi0 a by three orders of magnitude.

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

3-form dark energy shows a similar behavior to but distinguishable one from that of a scalar field in an expanding universe, and its tensorial structure allows for unique couplings that cannot be experienced by canonical scalars. We here explore the possibility that 3-form dark energy can explain the cosmic birefringence angle β~0.3°, as suggested by observations of the CMB polarization. We consider two EFT-inspired couplings between the 3-form and the photon, finding a dimension-4 operator is a candidate explanation, moreover predicting a photon mass around the Hubble scale. The profiles for β(z) from the model can mimic those from ALP dark energy or ALP dark matter, or be distinguishable, depending on the field configuration in the early universe, which may be tested by precise measurements of CMB polarization or radio galaxies.