Shih-Jie Huang | Searcharxiv

arXiv2026

Collective neutrino-antineutrino pair oscillations

In dense neutrino gas, pairing correlations between neutrinos and antineutrinos with opposite momenta can be nonzero in generalized neutrino quantum kinetic equations at the mean-field level. In this Letter, we investigate for the first time the condition under which collective neutrino-antineutrino ($ν\barν$) pairing instabilities can occur, using simplified toy models consisting of discretized $ν\barν$ pairs in a homogeneous neutrino gas. We find that, in ansiotropic systems, $ν\barν$ pairing instabilities generally emerge when the phase space distribution of the excessive pair-occupation number, defined as the sum of the neutrino and antineutrino occupation numbers of a pair minus 1, changes signs. The associated instability growth rate is set by the forward scattering potential and is comparable to that of collective fast neutrino flavor instabilities. The instabilities can result in pair conversions of $ν\barν$ occupation numbers between different momentum modes. Our results motivate further studies to assess the relevance of $ν\barν$ pairing effects in realistic astrophysical and cosmological environments.

hep-ph↗

arXiv2023

R-process beta-decay neutrino flux from binary neutron star mergers and collapsars

This study investigates the antineutrinos production by $β$-decay of $r$-process nuclei in two astrophysical sites that are capable of producing gamma-ray bursts (GRBs): binary neutron star mergers (BNSMs) and collapsars, which are promising sites for heavy element nucleosynthesis. We employ a simplified method to compute the $β$-decay $\barν_e$ energy spectrum and consider a number of different representative thermodynamic trajectories for $r$-process simulations, each with four sets of $Y_e$ distribution. The time evolution of the $\barν_e$ spectrum is derived for both the dynamical ejecta and the disk wind for BNSMs and collapsar outflow, based on approximated mass outflow rates. Our results show that the $\barν_e$ has an average energy of approximately 3 to 9~MeV, with a high energy tail of up to 20 MeV. The $\barν_e$ flux evolution is primarily determined by the outflow duration, and can thus remain large for $\mathcal{O}(10)$~s and $\mathcal{O}(100)$~s for BNSMs and collapsars, respectively. For a single merger or collapsar at 40~Mpc, the $\barν_e$ flux is $\mathcal{O}(10-100)$~cm$^{-2}$~s$^{-1}$, indicating a possible detection horizon up to $0.1-1$~Mpc for Hyper-Kamiokande. We also estimate their contributions to the diffuse $\barν_e$ background, and find that both sources should only contribute subdominantly to the diffuse background when compared to that expected from core-collapse supernovae.

astro-ph.HE↗