Light dark matter from inflaton decay

We propose a simple mechanism of light dark matter (DM) production from the decay of the oscillating inflaton condensation. If the reheating temperature after inflation is higher than the inflaton mass, which is of the same order of the momentum of the DM at the time of the production, the DM momentum can be suppressed compared to the temperature of the thermal plasma if the interaction of the DM is weak enough. Consequently, the DM can be cold enough to avoid the observational constraints on the warm DM, like the Lyman-α bound even if the DM mass is small. We study the bosonic and fermionic DM production from the inflaton decay, taking into account the effect of the stimulated emission and Pauli blocking, respectively. In both cases, the DM can be cold and abundant enough to be a viable candidate of the DM. We also apply our mechanism to the production of isocurvature-problem-free axion DM and Dirac sea DM of right-handed neutrino consistent the seesaw relation for the active neutrino masses.

Gamow-Teller transitions of neutron-rich N = 82, 81 nuclei by shell-model calculations

β-decay half-lives of neutron-rich nuclei around N = 82 are key data to understand the r-process nucleosynthesis. We performed large-scale shell-model calculations in this region using a newly constructed shell-model Hamiltonian, and successfully described the low-lying spectra and half-lives of neutron-rich N = 82 and N = 81 isotones with Z = 42 − 49 in a unified way. We found that their Gamow-Teller strength distributions have a peak in the low-excitation energies, which significantly contributes to the half-lives. This peak, dominated by ν0g7/2 → π0g9/2 transitions, is enhanced on the proton deficient side because the Pauli-blocking effect caused by occupying the valence proton 0g9/2 orbit is weakened.

Thermal conductivity of an ultracold Fermi gas in the BCS-BEC crossover

Recent experiments on sound waves in a unitary Fermi gas reveal many transport properties about strongly interacting fermions. Sound propagates through the coupling of momentum and heat transport, and attenuates strongly with the presence of a phase transition. In this work, focusing on the temperature regimes near and below the superfluid critical temperature $$T_c$$ T c in the BCS-BEC crossover, we present a Kubo-based microscopic calculation of thermal conductivity $$\kappa$$ κ , which has not attracted much attention compared to the shear viscosity. Our approach primarily addresses the contributions of the fermionic quasiparticles to thermal transport and our results return to the kinetic descriptions at high temperatures. $$\kappa$$ κ drops upon crossing the pseudogap temperature $$T^*$$ T ∗ , and its temperature dependence changes below $$T_c$$ T c . The drops become more pronounced on the weakly coupled BCS side, where the Pauli blocking causes the upturn of $$\kappa$$ κ above $$T^*$$ T ∗ . Our calculations fit well with the sound measurement on the damping rate.