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

Primordial black holes (PBHs) from Planck-mass to supermassive black holes produce a variety of interesting phenomena. I first present the PBH reformation process, where clouds of extremely light PBHs can recollapse into heavier PBHs before evaporating. By transitioning to a matter-dominated era, the formation probability of PBHs is greatly increased and does not therefore require any initial clustering. The larger reformed PBH population could survive to the present day, emitting high energy radiation potentially detectable by the next generation cosmic ray experiments. Chirping gravitational waves generated by O(10 M_sun) binary black hole mergers have been detected by the LIGO-VIRGO-KAGRA experiments, with speculation that some events are generated by PBH mergers. We show that the dark matter halo that accretes around PBHs can distinguish them from stellar evolution black holes, and gravitational lensing of chirping gravitational waves can reveal their extended structure and prove their primordial origin. I then present gas heating constraints on these dressed PBHs (PBH + dark halo) as well as other extended dark compact objects. In addition to modifying the point-mass dynamical friction formalism to include finite-size effects, the accretion disk emission sensitively depends on the object radius. Finally, I discuss a Friedberg-Lee-Sirlin Q-ball solution where the inclusion of a Yukawa force destabilizes the Q-ball at large charges. Surprisingly, the unstable Q-balls do not collapse under this attractive force but instead experience runaway expansion.

The statistical properties of the Cosmic Microwave Background (CMB) anisotropies, which reflect the curvature inhomogeneities of the early Universe, are well accounted for by assuming that these inhomogeneities emerged from amplified vacuum fluctuations. As they result from a genuine quantum process, it is natural to question which properties of these primordial inhomogeneities are inherently quantum and which, if any, have persisted until their observation despite interactions that induced decoherence, thereby rendering them classical. I will review the latest progress on these questions.

References:
Martin, J., Micheli, A., & Vennin, V. (2022). Discord and decoherence.
Journal of Cosmology and Astroparticle Physics, 2022(04), 051.
Micheli, A., & Peter, P. (2023). Quantum Cosmological Gravitational Waves? In C. Bambi, L. Modesto, & I. Shapiro (Eds), Handbook of Quantum Gravity (pp. 1-66).
Micheli, A., Oshima, Y., & Takahashi, T. (2025) Squeezing of cosmological perturbations in presence of decoherence, in preparation

Gravitational waves (GWs) from gravitational three-body decay (graviton Bremsstrahlung process) can leave an indelible signal at ultrahigh frequencies. We focus on a scenario where superheavy particles are produced gravitationally at a transition between the inflationary and kination phases and analyze the detectability of the signal in the presence of GWs generated from the vacuum fluctuations during inflation. We find that, in many cases, GWs from the graviton Bremsstrahlung are buried in the stochastic gravitational wave background originating from inflation. However, if the superheavy particles are as heavy as the Planck scale, the graviton Bremsstrahlung can produce a sizable amount of GWs, surpassing the inflationary ones.

Gravitational waves (GWs) may be produced by various mechanisms in the early universe. In particular, if parity is violated, it may lead to the production of parity-violating GWs. In this talk, we focus on GWs on the scale of the large-scale structure. Since GWs induce tidal deformations of the shape of galaxies, one can extract such GW signals by observing images of galaxies in galaxy surveys. Conventionally, the detection of such signals is discussed by considering the three-dimensional power spectra of the E/B-modes. Here, we develop a complementary new technique to estimate the contribution of GWs to the tidal force tensor field projected on the celestial sphere, which is a directly observable quantity. We introduce two two-dimensional vector fields constructed by taking the divergence and curl of the projected tidal field in three dimensions. Their auto-correlation functions naturally contain contributions of the scalar-type tidal field. However, we find that the divergence of the curl of the projected tidal field, which is a pseudo-scalar quantity, is free from the scalar contribution and thus enables us to extract GW signals. We also find that we can detect parity-violating signals in the GWs by observing the nonzero cross-correlation between the divergence of the projected tidal field and its curl. It roughly corresponds to measuring the cross-power spectrum of E and B-modes, but these are complementary to each other in the sense that our estimator can be naturally defined locally in position space. Finally, we present expressions of the correlation functions in the form of Fourier integrals and discuss the properties of the kernels specific to the GW case, namely the overlap reduction function.

The axion remains one of the most compelling candidates for new physics, offering solutions to both the strong CP problem and the nature of dark matter. This talk charts a journey with the axion, beginning with its fundamental theoretical description and later talk in new frontiers for its detection. The first part of this talk details axion low-energy phenomenology. We present a consistent derivation of the complete Wess-Zumino-Witten (WZW) interactions of axion by treating the 1-form axion derivative as a background field to ensure the physical consistency of the theory. We then expand this to construct a complete Lagrangian for axion interactions with both gauge bosons and the full spectrum of pseudoscalar and (axial-)vector mesons. This comprehensive framework, incorporating the chiral Lagrangian and the WZW term, provides a consistent basis for calculating physical observables, such as the decay widths of axions into hadronic final states. The second part of talk shifts from theory to detection, focusing on the search for ultralight axion dark matter. We explore the untapped potential of higher dimensional quantum systems, moving beyond standard qubits to a universal qutrit framework. We demonstrate how spin-1 NV-center qutrits can enhance the search for the axion-electron coupling by an order of magnitude, establishing higher-dimensional quantum sensing as a powerful new tool for probing fundamental physics.

The existence of the relic neutrino background is a strong prediction of the Big Bang cosmology. But because of their extremely small kinetic energy today, the direct detection of relic neutrinos remains elusive. On the other hand, we know very little about the nature of dark matter. In this work, we propose heavy decaying neutrinophilic dark matter (DM) as a new probe of the cosmic neutrino background. Including the contribution of neutrinos resulting from DM-decay along with the measured astrophysical and predicted cosmogenic neutrino fluxes, we study the scattering of ultra high energy (UHE) neutrinos with the relic neutrino background via standard weak interactions mediated by the Z-boson and calculate the expected spectrum of this UHE neutrino flux at future neutrino telescopes, such as IceCube-Gen2 Radio. Observations of such scattered UHE neutrino flux can be used to probe the Cosmic neutrino background properties, and specifically, its local clustering. We find that, depending on the absolute neutrino mass and the DM mass and lifetime, a local relic neutrino overdensity around 1e6 can be probed at IceCube-Gen2 Radio within 10 years of data taking.

The correlation functions of primordial cosmological perturbations encode valuable information about the early universe. In particular, higher-order correlations, known as non-Gaussianities, can reveal additional insights, including the mass and spin of heavy particles, through characteristic oscillatory signatures. Remarkably, such particles can have masses as large as the Hubble scale during inflation, far beyond the reach of terrestrial experiments. This approach to uncovering new particles through primordial non-Gaussianity is known as the cosmological collider program, and it has emerged as a promising avenue for probing physics beyond the Standard Model. In this talk, I will briefly outline the cosmological collider framework, comment on some recent developments, and discuss my own contributions to this growing field.

量子コンピュータは，従来のコンピューターとは全く異なる仕組みで計算を行うコンピューターである．近年，古典力学系シミュレーションの一部が量子コンピュータによって計算加速されることが理論的に示されたことから，その実用化や理論拡張に注目が集まっている．
本講演では，古典力学系シミュレーションを計算加速する様々な量子アルゴリズムを体系的に紹介する．

The IKKT matrix model is an example of holography where all spacetime dimensions are emergent. It is a simply a multi-matrix integral but conjectured to non-perturbatively describe type IIB string theory. Being a regular matrix integral, as opposed to path integrals, it is technically very tractable. However, the holographic dictionary remains poorly understood due to conceptual difficulties. In this talk, I will discuss a mass deformation of the original matrix integral, the polarised IKKT model, in which some entries of the dictionary can be established. In particular, I will describe how various large N limits of this model capture different bulk gravity phenomena. These include brane polarisation in the presence of background fluxes, backreaction of the polarised branes into bubbling geometries, and the dissolution of branes into D-instantons through a phase transition.