Combining collective, MSW, and turbulence effects in supernova neutrino flavor evolution

Abstract

In order to decode the neutrino burst signal from a Galactic core-collapse supernova (ccSN) and reveal the complicated inner workings of the explosion we need a thorough understanding of the neutrino flavor evolution from the proto-neutron star outwards. The flavor content of the signal evolves due to both neutrino collective effects and matter effects which can lead to a highly interesting interplay and distinctive spectral features. In this paper we investigate the supernova neutrino flavor evolution in three different progenitors and include collective flavor effects, the evolution of the Mikheyev, Smirnov & Wolfenstein (MSW) conversion due to the shock wave passage through the star, and the impact of turbulence. We consider both normal and inverted neutrino mass hierarchies and a value of θ13 close to the current experimental measurements. In the Oxygen-Neon-Magnesium (ONeMg) supernova we find that the impact of turbulence is both brief and slight during a window of 1-2 seconds post bounce. This is because the shock races through the star extremely quickly and the turbulence amplitude is expected to be small, less than 10%, since these stars do not require multi-dimensional physics to explode. Thus the spectral features of collective and shock effects in the neutrino signals from Oxygen-Neon-Magnesium supernovae may be almost turbulence free making them the easiest to interpret. For the more massive progenitors we again find that small amplitude turbulence, up to 10%, leads to a minimal modification of the signal, and the emerging neutrino spectra retain both collective and MSW features. However, when larger amounts of turbulence is added, 30% and 50%, which is justified by the requirement of multi-dimensional physics in order to make these stars explode, the features of collective and shock wave effects in the high (H) density resonance channel are almost completely obscured at late times. Yet at the same time we find the other mixing channels -the low (L) density resonance channel and the non-resonant channels -begin to develop turbulence signatures. Large amplitude turbulent motions in the outer layers of more massive, iron core-collapse supernovae may obscure the most obvious fingerprints of collective and shock wave effects in the neutrino signal but cannot remove them completely, and additionally bring about new features in the signal.

Stimulated neutrino transformation through turbulence on a changing density profile and application to supernovae

“…The amount of turbulence in the SN progenitor has been reported as C rms ∼ 10 −5 , providing a lower limit to the turbulence in the explosion [42]. Upper limits in SN turbulence reach up to C rms ∼ 0.3 − 0.5, justified from the multidimensional physics required for a large star to actually explode in simulations [28]. Given the variety of values for C rms reported, we study how these changes alter the neutrino propagation.…”

“…The cutoff wavelengths used in previous work have varied from tens of kilometers [25] to thousands or tens of thousands of kilometers [16,17,21,28,29,41]. From the work in [38], we know that long wavelength modes can have a suppressive effect on the neutrino transformations, so a change in cutoff wavelength could make a drastic difference in the resulting transitions.…”

“…For example, if λ cut is increased from 300 km to 3000 km while holding C rms constant, the amplitudes for modes with wavelengths ∼10 km will decrease. Previous work has used cutoff wavelengths that vary by orders of magnitude from one study to the next [16,17,21,25,28,29,41]. This wide range and our knowledge of the wavelengths which most affect neutrino transformations necessitates an investigation into how these different cutoff scales change the neutrino propagation in the SN model.…”

“…Due to the inverse power law nature of the spectrum, longer wavelength modes will have more power and thus larger amplitudes. The amplitudes and frequencies for the N k modes are chosen using the Randomization Method described in [28,29,41].…”

“…For example, the small fluctuations in the Sun and Earth have been investigated [13][14][15][16][17], as well as the large fluctuations in SN [18][19][20][21][22][23][24]. Recently, collective effects in SN have been studied in the presence of density fluctuations [25][26][27] and the synthesis of collective, MSW effects and turbulence was investigated in [28] where it was shown that features in the neutrino spectrum indicating the effects of self-interactions and/or MSW transitions may be partially or completely erased .…”