arXiv subjects

Tenta Tsuji

Publications and source records attributed to Tenta Tsuji.

4 recordsLinked to original sources

arXiv2026

Gravitational Waves from Reheating beyond Instantaneous Thermalization

We study gravitational-wave production during perturbative reheating without assuming instantaneous thermalization of the inflaton decay products. The injected energetic particles thermalize through an in-medium cascade of nearly collinear splittings subject to the Landau-Pomeranchuk-Migdal effect and are ultimately isotropized by elastic scatterings near the thermal scale. The non-thermal hard population present before complete thermalization produces an additional gravitational-wave component through hard-soft scatterings, with $Ω_{\mathrm{GW}}\propto f^{1/2}$ below the injection-scale turnover. The same isotropization erases the directional information underlying the vacuum $1/k$ bremsstrahlung soft pole, changing the deep-infrared spectrum from $Ω_{\mathrm{GW}}\propto f$ to $Ω_{\mathrm{GW}}\propto f^3$.

hep-ph↗

arXiv2026

Systematic derivation of the Boltzmann equation for electroweak baryogenesis

We derive the Boltzmann equation for electroweak baryogenesis within a field-theoretical framework. We first algebraically solve the Kadanoff--Baym equations by incorporating the effects of gradients of the CP-violating bubble-wall background order by order. We then apply approximations and assumptions appropriate for electroweak baryogenesis and identify the on-shell parts of the solutions, which describe quasiparticle states propagating in a plasma. Using these on-shell solutions, we derive the Boltzmann equations for flavor-diagonal quasiparticle modes, while neglecting the off-diagonal components describing quantum coherence between different flavor modes. Our derivation generalizes previous field-theoretical treatments by retaining self-energy corrections, and our results are consistent with the known Boltzmann equations when these corrections are neglected. This framework provides a systematic and transparent derivation applicable to multi-flavor bosonic and fermionic systems.

hep-ph↗

arXiv2026

Dark Matter Interpretation of the Super-Kamiokande Antineutrino Excess in $\mathrm{U}(1)_{L_μ-L_τ}$ model

Recent Super-Kamiokande analyses of the diffuse supernova neutrino background, based on data across all SK phases, indicate a mild preference over the zero-DSNB hypothesis at the level of about $2.3σ$ with electron-like antineutrino events at $E_{\barν_e} \simeq 20\,\mathrm{MeV}$. We investigate whether this excess can be explained by MeV-scale dark matter annihilation into neutrinos in a $\mathrm{U}(1)_{L_μ- L_τ}$ model. The dark matter is a Dirac fermion with $m_χ\simeq 22\,\mathrm{MeV}$ that annihilates via a light $Z'$ mediator into $ν_μ\barν_μ$ and $ν_τ\barν_τ$, which are partly converted into $\barν_e$ through flavor oscillations. We find that this scenario simultaneously accounts for the excess and the observed relic abundance via thermal freeze-out. We further discuss the relevant laboratory and cosmological constraints, including neutrino trident production, NA64-$μ$, Borexino, and the contribution to $ΔN_\mathrm{eff}$.

hep-ph↗

arXiv2025

Reheating after Axion Inflation

We investigate the reheating process in an axion inflation model where the inflaton couples to non-Abelian gauge fields via the Chern-Simons coupling. The Chern-Simons coupling leads to the efficient production of gauge fields via a tachyonic instability during inflation, whose implications have been actively studied in the literatures. Moreover, it has been recently pointed out that the produced gauge fields can be even thermalized during inflation, leading to warm inflation. Apparently, these findings seem to imply that the reheating is completed immediately after inflation because the tachyonic instability or the thermal friction induced by the Chern-Simons coupling cause the inflaton condensate to decay rapidly. Contrary to this naive expectation, however, we show that, in most of the parameter space, either the inflaton condensate, the inflaton particles, or the glueballs once dominate the Universe and their perturbative decay completes the reheating.

hep-ph↗