We revisit several minimal extensions of the Standard Model for dark matter. Depending on time, we discuss some or all of the following: (i) a scalar dark matter with higher-dimensional operators, where thermal misalignment provides a viable production mechanism; (ii) sterile neutrino dark matter in the presence of lepton flavor asymmetries; (iii) Majorana fermion dark matter with a coannihilating scalar, with the bino-slepton scenario in supersymmetry as a concrete benchmark; (iv) Majoron dark matter arising from a minimal extension of the seesaw mechanism. We present recent updates on each topic in light of current experimental constraints.
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Major improvements in the theoretical understanding of LSS have been possible due to the effective field theory approach. After an overview of the perturbation theory applications for LSS, I will discuss how to go beyond the one-loop calculation, presenting novel two-loop results and their information content (both for clustering and lensing). I will also show how to extract information from higher-loop orders using renormalization group equations.

Big Bang Nucleosynthesis (BBN) provides a powerful probe of hadronic injection from new physics that modifies the neutron-to-proton ratio, thanks to the precisely measured primordial helium-4 abundance. In this talk, I apply this probe to long-lived particles, specifically heavy QCD axions which are well-motivated candidates that can address the strong CP problem and predominantly decay into hadrons. We compute the axion-induced modification of the neutron-to-proton ratio and derive robust upper bounds on the axion lifetime, as short as 0.017 seconds, well before 1 second, the onset of BBN. While motivated by the axion study, we also make several significant and broadly applicable advances in the treatment of hadronic injection during BBN. These include new or updated hadronic cross sections, scattering processes involving energetic neutral kaons (KL), and the effects of secondary hadrons. Neglecting these effects can lead to significant misestimates of the primordial helium-4 abundance. In addition, we derive a semi-analytic solution that allows us to estimate theoretical uncertainties and demonstrate the robustness of our bounds.

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.

Black holes pose sharp consistency questions at the interface of gravity, quantum mechanics, and thermodynamics. It is widely believed that resolving problems such as providing a microscopic account of Bekenstein–Hawking entropy, understanding the origin of black hole thermodynamics, and resolving the information paradox posed by Hawking radiation will provide valuable insights to the construction of the theory of quantum gravity. In this talk, I discuss a recent proposal [1,2] of a quantum mechanics of quantized space as a model of quantum black hole and quantum gravity in 4-dimensions. Our construction was motivated by the bottom-up approach [3,4]. As a system of quantum bits of quantum space, our model reproduces not only the needed macroscopic properties of the Schwarzschild black hole [1] and the rotating Kerr black hole [2], it also provides a microscopic counting of the Bekenstein-Hawking entropy of black hole [1,2] and explains the origin of Hawking radiation in terms of a tunneling process of emission of monopole in the quantum mechanics [5]. As application, I discuss how the well-known membrane paradigm of black hole is modified by quantum gravity effects [6]. In classical general relativity, the black hole membrane is an electrical conductor with a constant vacuum resistivity. We identify new quantum gravity effects and show that the quantum black hole membrane has also a frequency dependent inductance and a chiral Hall conductance. We propose to test these new effects with the observation of quasi-normal modes.

1. Matrix model proposal for quantum gravity and the quantum mechanics of black holes, Phys.Rev.D 112 (2025) 6, 066001, Chong-Sun Chu
2. Quantum Kerr black hole from matrix theory of quantum gravity, Phys.Rev.D 112 (2025) 4, 046014, Chong-Sun Chu
3. Fermi model of a quantum black hole, Phys.Rev.D 110 (2024) 4, 046001, Chong-Sun Chu
4. Tunneling of Bell particles, page curve and black hole information, Phys.Lett.B 865 (2025) 139486, Chong-Sun Chu
5. Hawking Radiation from Tunneling in Black Hole Quantum Mechanics, e- Print: 2603.12199 [hep-th], Chong-Sun Chu
6. Membrane Paradigm for Quantum Black Hole, to appear, Chong-Sun Chu

There have been growing interests in quantum states of photons (and gravitons) produced, say, from conversion of axion dark matter (and binary black holes). With high luminosity (or large occupation number), they are well described as classical waves. On the other hand, as luminosity decreases, quantum nature gets more significant. A half century ago, Roy Glauber showed that photons produced by a classical source follow the coherent state. We generalize this notion of Glauber including quadratic non-linearity and show that photons follow the displaced squeezed state. We compare our full treatment with a simplified treatment found in the literature.

QCD is an SU(3) gauge theory and forms a part of the Standard Model of particle physics that describes the strong interaction. Despite its importance, perturbative calculations based on Feynman diagrams cannot directly describe nonperturbative phenomena such as confinement, and quantitative calculations in the strong-coupling regime are known to be difficult. Lattice gauge theory provides a powerful framework for formulating quantum field theories on a spacetime lattice and numerically investigating nonperturbative quantum effects. In the first part of this talk, I will start from basic ideas such as lattice field theory, gauge fields, and Monte Carlo sampling, and give an overview of how lattice QCD computes the physics of the strong interaction. In the second part, I will introduce the development of JuliaQCD / LatticeQCD.jl, a lattice QCD simulation framework written in Julia, together with recent research examples using it. I will also discuss how modern computational techniques, including machine learning, may contribute to calculations in lattice field theory. This talk is based in part on J. Phys. Soc. Jpn. 94, 031006 (2025), arXiv:2602.20516, and related work.

The anthropic principle is often criticized as lying outside science, since we cannot experimentally produce universes with different fundamental laws. In this talk, I will take a different viewpoint: instead of asking whether the anthropic principle is a final explanation, I will ask whether the conditions for complex structures can be mapped as a concrete problem in physics. The aim is to formulate an "Atlas Anthropica": a map of the theory and parameter space in which matter, stars, heavy elements, large-scale structure, and possibly living systems can exist. Such a map requires input from particle physics, nuclear physics, astrophysics, cosmology, and condensed-matter-like reasoning. I will first review known bottlenecks, including the Hoyle state, supernova explosions, the weak scale, and Weinberg’s argument for the cosmological constant. I will then illustrate how even a simple deformation, such as replacing SU(3)_c by an SU(4)_c-type color sector, leads to a branching network of questions involving anomalies, charge assignments, confinement, bosonic baryons, nuclear matter, stellar burning, heavy-element production, and baryon stability. The main message is that the anthropic principle should not be treated as a slogan, but as an unexplored atlas of physical bottlenecks. Recent advances in artificial intelligence and scientific computing may finally make it possible to explore this terra incognita systematically.

Hermiticity is a fundamental requirement for Hamiltonians in closed quantum systems. Nevertheless, non-Hermitian Hamiltonians arise ubiquitously in physics as effective descriptions, ranging from nuclear physics [1] and condensed-matter physics [2] to classical optics [3]. In this talk, I will discuss two routes by which non-Hermitian Hamiltonians appear. The first is as an effective theory for open quantum systems—quantum systems that interact with a surrounding environment. By tracing out the environmental degrees of freedom, one obtains an effective description of the system alone, which can become non-Hermitian. The second route is to reconstruct a consistent quantum theory by introducing a modified inner product, as in pseudo-Hermitian (or quasi-Hermitian) quantum mechanics [4].
As a simple example of the open-system setting, I will consider a qubit coupled to a Dirac Hamiltonian. I will also introduce the concept of non-Markovianity in open quantum systems, which manifests as a time-nonlocal (memory) effect in the reduced dynamics. I will discuss the connection between non-Markovianity and the survival probability of the qubit and also the wave function emitted by the qubit into the Dirac environment. I will show that in the Markovian limit, the wave function converges to a time-evolving resonant state [5]. As an example in the closed-system setting, I will discuss the Swanson model (a non-Hermitian harmonic oscillator) and show that even a non-Hermitian Hamiltonian that is not pseudo-Hermitian can exhibit a real energy spectrum when appropriate time-dependent boundary conditions are imposed [6]. From this viewpoint, a non-Hermitian (open-system) description can effectively behave as a closed system when suitable boundary conditions are enforced.

[1] Gamow, G. (1928). Zur Quantentheorie des Atomkernes. Zeitschrift für Physik, 51(3), 204–212.
[2] Ashida, Y., Gong, Z., & Ueda, M. (2020). Non-Hermitian physics. Advances in Physics, 69(3), 249–435.
[3] Rüter, C. E., Makris, K. G., El-Ganainy, R., Christodoulides, D. N., Segev, M., & Kip, D. (2010). Observation of parity–time symmetry in optics. Nature Physics, 6(3), 192–195.
[4] Scholtz, F. G., Geyer, H. B., & Hahne, F. J. W. (1992). Quasi-Hermitian operators in quantum mechanics and the variational principle. Annals of Physics, 213(1), 74–101.
[5] Taira, T., Hatano, N., & Nishino, A. (2024). Markovianity and non-Markovianity of a particle bath with a Dirac dispersion relation. arXiv preprint arXiv:2406.17436.
[6] Fring, A., & Taira, T. (2023). Non-Hermitian quantum Fermi accelerator. Physical Review A, 108(1), 012222.

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