Systematic study of the resonancelike structure in the collisional flavor instability of neutrinos

Investigations on the resonancelike phenomenon in the collisional flavor instability (CFI) of neutrinos, which were observed in the linear phase recently, are reported. We show that it occurs not only for the isotropy-preserving modes as pointed out in the previous work but also for the isotropy-breaking modes and that it enhances the linear growth rate of the CFI. Employing linear analysis and nonlinear numerical simulations in the two-flavor scheme and under the relaxation approximation for the collision term, we discuss the criterion for the resonancelike phenomenon observed in the linear phase, its effect on the subsequent nonlinear evolution as well as the influences of homogeneity-breaking (k & NOTEQUAL; 0) perturbations and of anisotropy in the background on the resonancelike structure. We will also touch on idea the cohabitation of the resonancelike structure with the fast-flavor conversion.