Basudeb Dasgupta

Collective three-flavor oscillations of supernova neutrinos

We present a formalism to study three-flavor effects in flavor conversions of dense neutrino ensembles. The main idea is to use the smallness of Δm2⊙Δm2atm and θ13. The formalism has immediate applications to neutrinos from supernovae or the early Universe. We outline some consequences for supernova neutrino phenomenology, e.g hierarchy determination at extremely small θ13.

The effect of collective flavor oscillations on the diffuse supernova neutrino background

Collective flavor oscillations driven by neutrino-neutrino self interaction inside core-collapse supernovae have now been shown to bring drastic changes in the resultant neutrino fluxes. This would in turn significantly affect the diffuse supernova neutrino background (DSNB), created by all core-collapse supernovae that have exploded in the past. In view of these collective effects, we re-analyze the potential of detecting the DSNB in currently running and planned large-scale detectors meant for detecting both electron neutrinos and antineutrinos. The next generation detectors should be able to observe DSNB fluxes. Under certain conducive conditions, one could learn about neutrino parameters. For instance, it might be possible to determine the neutrino mass hierarchy, even if theta_{13} is almost zero.

Fast neutrino flavor conversions near the supernova core with realistic flavor-dependent angular distributions

It has been recently pointed out that neutrino fluxes from a supernova can show substantial flavor conversions almost immediately above the core. Using linear stability analyses and numerical solutions of the fully nonlinear equations of motion, we perform a detailed study of these fast conversions, focussing on the region just above the supernova core. We carefully specify the instabilities for evolution in space or time, andfind that neutrinos travelling towards the core make fast conversions more generic, i.e., possible for a wider range of flux ratios and angular asymmetries that produce a crossing between the zenith-angle spectra of

Self-induced temporal instability from a neutrino antenna

\nu_e

Spectral split in a prompt supernova neutrino burst : Analytic three-flavor treatment

and

Collective neutrino oscillations in nonspherical geometry

{\bar\nu_e}

Photons, photon jets, and dark photons at 750 GeV and beyond

. Using fluxes and angular distributions predicted by supernova simulations, we find that fast conversions can occur within tens of nanoseconds, only a few meters away from the putative neutrinospheres. If these fast flavor conversions indeed take place, they would have important implications for the supernova explosion mechanism and nucleosynthesis.

Sterile neutrinos with secret interactions — lasting friendship with cosmology

It has been recently shown that the flavor composition of a self-interacting neutrino gas can spontaneously acquire a time-dependent pulsating component during its flavor evolution. In this work, we perform a more detailed study of this effect in a model where neutrinos are assumed to be emitted in a two-dimensional plane from an infinite line that acts as a neutrino antenna. We consider several examples with varying matter and neutrino densities and find that temporal instabilities with various frequencies are excited in a cascade. We compare the numerical calculations of the flavor evolution with the predictions of linearized stability analysis of the equations of motion. The results obtained with these two approaches are in good agreement in the linear regime, while a dramatic speed-up of the flavor conversions occurs in the non-linear regime due to the interactions among the different pulsating modes. We show that large flavor conversions can take place if some of the temporal modes are unstable for long enough, and that this can happen even if the matter and neutrino densities are changing, as long as they vary slowly.