https://www.rcnp.osaka-u.ac.jp/~suenaga/Hadron_Cafe/

Gravitational chiral anomaly connects the topological charge of spacetime and the chirality of fermions. It has been known that the chirality is carried by the particles (or the excited states) and also by vacuum. However, in the study of gravitational leptogenesis, for example, lepton asymmetry associated with the chiral gravitational waves sourced during inflation is conventionally evaluated only by integrating the anomaly equation. In this evaluation, no distinction between the excite states and vacuum contribution has been made. In this talk, I apply an analogy between U(1) electromagnetism and the weak gravity to the spacetime that resembles the one considered in the gravitational leptogenesis scenario. By assuming the emergence of Landau level-like dispersion relation in our setup, I suggest that level-crossing does not seem to be efficient while the charge accumulation in the vacuum likely takes place. Phenomenological implication is also discussed.

Ultralight bosonic (ULB) fields with mass m << 1 eV often arise in theories beyond the Standard Model (SM). If such fields exist, violent astrophysical events that result in emission of gravitational wave, photon, or neutrino signals could also produce bursts of high-density relativistic ULB fields. Detection of such ULB fields in terrestrial or space-based laboratories correlated with other signals from transient astrophysical events opens a novel avenue for multimessenger astronomy. This additionally provides a route for directly detected for fields that are otherwise very challenging to detect. I will discuss that quantum sensors are particularly well-suited to observe emitted scalar and pseudoscalar axion-like ULB fields coupled to SM, and demonstrate that multimessenger astronomy with ULB fields is possible even when accounting for matter screening effects.

Sterile neutrino with masses of the keV scale is a fascinating candidate for dark matter (DM). They can be produced via neutrino oscillations involving the Standard model neutrinos (“active” neutrinos), which are in thermal equilibrium in the early universe. Especially, in the presence of significant neutrino-antineutrino asymmetry, the production rate of the sterile neutrinos is resonantly enhanced and we can successfully account for all dark matter consistent with observational constraints.
In this seminar, we first present a comprehensive numerical analysis of the resonant production scenario and explore the consistency with current observations.Secondly, we examine a leptogenesis scenario that can naturally generate the neutrino-antineutrino asymmetry consistent with the resonant production of sterile neutrino DM. We demonstrate that this can be realized within the framework of Affleck Dine leptogenesis, based on the minimal supersymmetric Standard Model (MSSM). In our setup, spherical clumps of the slepton field—known as Q-balls—form and eventually decay into lepton asymmetric Standard model plasma.
Furthermore, in the above setup, Q-balls dominate the cosmic energy density and finally decay rapidly into radiation, triggering sudden reheating. This sudden reheating causes subhorizon modes of the gravitational potential to oscillate with large amplitudes, and then a significant amount of the gravitational waves (GWs) are produced by curvature perturbations at second order. Based on this idea, we discuss the testability of the scenario with the future GW observations.This presentation is mainly based on arXiv:2402.11902, but includes some updates on the analysis.

The QCD axion is currently the focus of intense experimental and theoretical research. A key feature of canonical QCD axion models is the fixed mass-coupling relation, which motivates experimental efforts to explore the so-called QCD axion band. But what if no axion is found within this range? Could a genuine QCD axion lie outside this band—and if so, at what theoretical cost? In this seminar, we will show that such a displacement can naturally arise if the axion propagates in extra dimensions, leading to distinctive patterns that motivates new regions of parameter space. We will discuss the theoretical framework, the associated experimental signatures, and the limitations of these constructions.

In the path-integral formalism, significant progress has been made in understanding chiral symmetry on the lattice using overlap fermions, which are constructed from Dirac operators satisfying the Ginsparg–Wilson relation. A corresponding formulation and understanding in the Hamiltonian formalism are also desirable yet remains under active investigation. Recently, A. Chatterjee, S. D. Pace, and S.-H. Shao proposed a novel construction of both vector and axial charge operators in a $1+1$ D staggered fermion system, which not only commute with the Hamiltonian but also possess quantized eigenvalues. The axial charge operator acts locally and generates a $\mathrm{U}(1)_A$ symmetry that can be gauged. These features provide a promising framework for the precise definition of chiral fermions.

In this work, we focus on the fact that the Hamiltonian of the $1+1$D staggered fermion system can be smoothly deformed into that of Wilson fermions. We reinterpret the structure of the axial charge operator proposed above using Wilson fermions. The eigenstates of the axial charge are expressed as linear combinations of positive-energy creation and negative-energy annihilation operators. Consequently, the corresponding Hamiltonian includes terms that violate particle number conservation. Interestingly, by applying the insights of Chatterjee et al., it can be shown that even such Hamiltonians admit a conserved charge operator associated with the vector $\mathrm{U}(1)$ symmetry in the continuum limit. Since this operator does not commute with the axial charge, the construction is consistent with the Nielsen–Ninomiya theorem.

The resulting $1+1$D Hamiltonian formulation is expected to be useful in constructing chiral gauge theories based on the symmetric mass generation (SMG) mechanism. SMG refers to a mechanism by which gapless systems can be gapped without fermion bilinears, purely through appropriate interactions, while preserving symmetries. To demonstrate this, we examine the feasibility of realizing SMG while maintaining the $\mathrm{U}(1)_A$ gauge symmetry generated by the axial charge operator $Q_A$, using the $1^4(-1)^4$ and 3-4-5-0 models as examples.

After a brief review of our current models of the early universe I will argue that the usual effective field theory techniques
which are currently employed inevitably break down, and we need a non-perturbative starting point. Matrix models such as the BFSS and IKKT models provide a promising starting point, and I will indicate a way to obtain an emergent spacetime and early universe cosmology from these models.

I will discuss the impact of highly excited bound states on the evolution of number densities of new physics particles, focusing on dark matter, in the early Universe. In case of non-Abelian gauge interactions, which source dipole interactions between fundamental particles, highly excited states can prevent the particles from freezing, supporting a continuous depletion in the regime consistent with perturbativity and unitarity. Unitarity violation does in fact arise systematically, that is even for arbitrary small interaction strengths, once sufficiently highly excited states become relevant at low velocities. Novel analytic expressions for bound state formation, which we found recently, allow to accurately compute the freeze-out dynamics down to very low temperatures. I will highlight the importance of bound states to dark SU(N) sectors. For a more concrete dark matter model, I will focus on a colored and charged t-channel mediator model in the regime of superWIMP production. Here, excited states render the mediator depletion efficient all the way until its decay, introducing a dependence of the dark matter density on the mediator lifetime as a novel feature. Refrence: [arXiv: 2308.01336, 2411.08737]

In this talk, I discuss the Hamiltonian formulation of lattice gauge theory using the uniform matrix product state and its application to the single flavor Schwinger model. We perform simulations based on the variational uniform matrix product state (VUMPS) algorithm with a gauge-invariant matrix product ansatz that locally enforces the Gauss law constraint. Both the continuum and lattice versions of the Schwinger model with θ = π are known to exhibit first-order phase transitions for fermion masses above a critical value, at which a second-order phase transition occurs. Our algorithm enables a precise determination of the critical point in the continuum theory.

Recently, resonance-like signals for 4n system were reported in experiment. By confining finite 3n and 4n systems in external potential, we use tensor-optimized antisymmetrized molecular dynamics and inverse analytical continuation in the coupling constant method to study the possibility of the resonances. Consistent results are obtained, however, evident dependence on external attraction is observed. Besides, we also study the infinite nuclear matter with unitary correlation operator method and high-momentum pairs.
The former is employed to treat the short-range nucleon-nucleon correlation, while the latter is for the tensor correlation. The equations of state for both neutron matter and symmetric nuclear matter are obtained as well as the Hamiltonian components. Calculations by adding hyperons into these systems in the future are also discussed.
References:
[1] Niu Wan, Takayuki Myo, Hiroki Takemoto, Mengjiao Lyu, Qing Zhao, Hisashi Horiuchi, Masahiro Isaka, and Akinobu Dote, under review.
[2] Niu Wan, Takayuki Myo, Hiroki Takemoto, Hiroshi Toki, Chang Xu, Hisashi Horiuchi, Masahiro Isaka, Mengjiao Lyu, and Qing Zhao, Physical Review C 106, 034308 (2022).
[3] Niu Wan, Takayuki Myo, Chang Xu, Hiroshi Toki, Hisashi Horiuchi, and Mengjiao Lyu, Chinese Physics C 44, 124104 (2020).
[4] Takayuki Myo, Hiroki Takemoto, Mengjiao Lyu, Niu Wan, Chang Xu, Hiroshi Toki, Hisashi Horiuchi, Taiichi Yamada, and Kiyomi Ikeda, Physical Review C 99, 024312 (2019).
*Remark:
This seminar is included in KEK Theory Center one-day workshop “Nuclear Physics with Strangeness and Clusters”.
(https://kds.kek.jp/event/53383/)”