Collective neutrino flavor conversion: Recent developments

Abstract

Neutrino flavor evolution in core-collapse supernovae, neutron-star mergers, or the early universe is dominated by neutrino-neutrino refraction, often spawning "self-induced flavor conversion", i.e., shuffling of flavor among momentum modes. This effect is driven by collective run-away modes of the coupled "flavor oscillators" and can spontaneously break the initial symmetries such as axial symmetry, homogeneity, isotropy, and even stationarity. Moreover, the growth rates of unstable modes can be of the order of the neutrino-neutrino interaction energy instead of the much smaller vacuum oscillation frequency: self-induced flavor conversion does not always require neutrino masses. We illustrate these newly found phenomena in terms of simple toy models. What happens in realistic astrophysical settings is up to speculation at present

Flavor instabilities in the multiangle neutrino line model

“…We also thank A. Mirizzi for bringing several references including Ref. [18] to our attention. The work contained in this paper was developed independent of that in Ref.…”

“…The work contained in this paper was developed independent of that in Ref. [18]. We appreciate the hospitality of INT/UW where part of this work was done.…”

“…It was also shown that the axial symmetry around the radial direction in the Bulb model can be broken spontaneously during collective neutrino oscillations [12,13]. Some very recent work has shown that the spatial symmetries in the low-dimensional models such as the spherical symmetry in the Bulb model can be broken in multi-dimensional models [14][15][16][17][18].…”

Supernova Neutrinos: New Challenges and Future Directions

“…where the Hamiltonian contains vacuum, matter, and neutrino-neutrino terms; in particular, the latter is due to the fact that SNe are neutrino-rich environments and therefore ν-ν interactions cannot be neglected [3,4,19]. This term makes the equations non-linear and it depends on the angle between the momenta of the colliding neutrinos.…”

“…Since the last core-collapse supernova (SN), the only one detected in neutrinos, substantial progress has been made as for our understanding of the physics leading to the stellar explosion [1,2], the role of neutrinos in the star, and the flavor oscillations in neutrino-dense media [3,4]. Several large scale detectors are in place (or will be soon) to detect the next galactic burst [3,5,6].…”