Flavor instabilities in the multiangle neutrino line model

Abstract

Neutrino flavor oscillations in the presence of ambient neutrinos is nonlinear in nature which leads to interesting phenomenology that has not been well understood. It was recently shown that, in the two-dimensional, two-beam neutrino Line model, the inhomogeneous neutrino oscillation modes on small distance scales can become unstable at larger neutrino densities than the homogeneous mode does. We develop a numerical code to solve neutrino oscillations in the multi-angle/beam Line model with a continuous neutrino angular distribution. We show that the inhomogeneous oscillation modes can occur at even higher neutrino densities in the multi-angle model than in the two-beam model. We also find that the inhomogeneous modes on sufficiently small scales can be unstable at smaller neutrino densities with ambient matter than without, although a larger matter density does shift the instability region of the homogeneous mode to higher neutrino densities in the Line model as it does in the one-dimensional supernova Bulb model. Our results suggest that the inhomogeneous neutrino oscillation modes can be difficult to treat numerically because the problem of spurious oscillations becomes more severe for oscillations on smaller scales.

Dynamic fast flavor oscillation waves in dense neutrino gases

“…We verified that the Fourier transform of P(t, z, u) has the same exponential growth rate as what is predicted by this analysis. Unlike stationary 2D models [34,35], however, there are no unstable spurious modes in this model. In Fig.…”

Effect of collisions on neutrino flavor inhomogeneity in a dense neutrino gas

“…Several recent studies, concerned primarily with anisotropic astrophysical environments, have demonstrated that the nonlinear neutrino self-coupling results in spatial instabilities [1][2][3][4]. These works indicate the importance of taking into account deviations from spherical symmetry in describing the evolution of, for example, the supernova neutrino flavor field.…”

“…In extreme environments with large neutrino number densities, such as the interior of a core-collapse supernovae (CCSN) and in the early universe, the nonlinearity associated with neutrino self-interactions lead to an array of interesting effects beyond the "standard" MSW [10,11]. These effects, which have their origin in the non-linear character of the neutrino evolution equations, include collective oscillations in an idealized model of supernova [12][13][14][15][16][17][18][19][20][21][22], matter-neutrino resonant behavior [23][24][25], spontaneous breaking of the axial symmetry [26,27], and Email addresses: cirigliano@lanl.gov (Vincenzo Cirigliano), mparis@lanl.gov (Mark W. Paris), shashank@lanl.gov (Shashank Shalgar) emergence of spatial inhomogeneity [1,2], to cite a few examples.…”

Fast neutrino flavor conversion modes in multidimensional core-collapse supernova models: The role of the asymmetric neutrino distributions

“…On the other hand, they can result in flavor conversions close to the surface of the proto-neutron star (PNS) where it can be more influential. This is important since (if fast modes are absent) calculations have shown so far that significant neutrino flavor conversions are not likely to occur close to the surface of the PNS, in spite of the existence of flavor instabilities therein [38][39][40][41][42]. In fact, the unstable modes can turn stable before growing significantly due to the rapid variations of the physical conditions during the neutrino propagation [39,43].…”