4+4+3 pages; 4+4 figures; v2:minor changes, references added, comments welcome; v3: approx. identical to published version with supplemental material with analytical and numerical details
Flavor-dependent neutrino emission is critical to the evolution of a supernova and its neutrino signal. In the dense anisotropic interior of the star, neutrino-neutrino forward-scattering can lead to fast collective neutrino oscillations, which has striking consequences. We present a theory of fast flavor depolarization, explaining how neutrino flavor differences become smaller, i.e., depolarize, due to diffusion to smaller angular scales. We show that transverse relaxation determines the epoch of this irreversible depolarization. We give a method to compute the depolarized fluxes, presenting an explicit formula for simple initial conditions, which can be a crucial input for supernova theory and neutrino phenomenology.
We perform numerical simulations of fast collective neutrino flavor conversions in an one-dimensional box mimicking a system with the periodic boundary condition in one spatial direction and translation symmetry in the other two dimensions. We evolve the system over several thousands of the characteristic timescale (inverse of the interaction strength) with different initial $\barν_e$ to $ν_e$ number density ratios and different initial seed perturbations. We find that small scale structures are formed due to the interaction of the flavor waves. This results in nearly flavor depolarization in …
Dense clouds of neutrinos and antineutrinos can exhibit fast collective flavor oscillations. Previously, in Phys. Rev. Lett. 126 (2021) 061302, we proposed that such flavor oscillations lead to depolarization, i.e., an irreversible mixing of the flavors, whose extent depends on the initial momentum distributions of the different flavors. In this paper, we elaborate and extend this proposal, and compare it with related results in the literature. We present an accurate analytical estimate for the lower resting point of the fast flavor pendulum and underline the relaxation mechanisms, i.e., trans…
Neutrinos in a core-collapse supernova can undergo fast flavor conversions with a possible impact on the explosion mechanism and nucleosynthesis. We perform the first non-linear simulations of fast conversions in the presence of three neutrino flavors. The recent supernova simulations with muon production call for such an analysis, as they relax the standard $ν_{μ,τ}=\barν_{μ,τ}$ (two-flavor) assumption. Our results show the significance of muon and tau lepton number angular distributions, together with the traditional electron lepton number ones. Indeed, our three-flavor results are potential…
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…
The supernova neutrino flavor evolution in the presence of the non-trivial neutrino magnetic moment and strong magnetic field is numerically derived using the two-flavor and single-angle approximation. The novel properties of collective neutrino oscillations are studied and distinct patterns of flavor and spin-flavor spectral splits are presented. Finally we also discuss how the neutrino magnetic moment affects the observable supernova neutrino energy spectra.
We show that a self-interacting neutrino gas can spontaneously acquire a non-stationary pulsating component in its flavor content, with a frequency that can exactly cancel the "multi-angle" refractive effects of dense matter. This can then enable homogeneous and inhomogeneous flavor conversion instabilities to exist even at large neutrino and matter densities, where the system would have been stable if the evolution were strictly stationary. Large flavor conversions, especially close to a supernova core, are possible via this novel mechanism. This may have important consequences for the explos…
Neutrino flux streaming from a supernova can undergo rapid flavor conversions almost immediately above the core. Focusing on this region, we study these fast conversions using a linear stability analysis. We find that, for realistic angular distributions of neutrinos, fast conversions can occur within a few nanoseconds in regions just above the neutrinosphere. Our results also show that neutrinos travelling towards the core make fast conversions more rapid. These conversions, if they exist, can have significant implications for supernova explosion mechanism and nucleosynthesis.
Electrons and electron neutrinos in the inner core of the core-collapse supernova are highly degenerate and therefore numerous during a few seconds of explosion. In contrast, leptons of other flavors are non-degenerate and therefore relatively scarce. This is due to lepton flavor conservation. If this conservation law is broken by some non-standard interactions, electron neutrinos are converted to muon and tau-neutrinos, and electrons - to muons. This affects the supernova dynamics and the supernova neutrino signal. We consider lepton flavor violating interactions mediated by scalar bileptons,…
We calculate the effects of random density fluctuations on two-neutrino flavor transformations ($ν_{τ(μ)} \rightleftharpoons ν_e$) in the post-core-bounce supernova environment. In particular, we follow numerically the flavor evolution of neutrino states propagating through a stochastic field of density fluctuations. We examine the approach to neutrino flavor depolarization, and study the effects of this phenomenon in both the early shock reheating epoch and the later r-process nucleosynthesis epoch. Our results suggest that significant fluctuation-induced neutrino flavor depolarization effect…
Electrons and electron neutrinos in the inner core of the core-collapse supernova are highly degenerate and therefore numerous during a few seconds of explosion. In contrast, leptons of other flavors are non-degenerate and therefore relatively scarce. This is due to lepton flavor conservation. If this conservation law is broken by some non-standard interactions, electron neutrinos are converted to muon and tau-neutrinos, and electrons -- to muons. This affects the supernova dynamics and the supernova neutrino signal in several ways. In particular, the total neutrino luminosity in the first sec…
Neutrino self-interactions are known to lead to non-linear collective flavor oscillations in a core-collapse supernova. We point out new possible effects of non-standard self-interactions (NSSI) of neutrinos on flavor conversions in a two-flavor framework. We show that, for a single-energy neutrino-antineutrino ensemble, a flavor instability is generated even in normal hierarchy for large enough NSSI. Using a toy model for the neutrino spectra, we show that flavor-preserving NSSI lead to pinching of spectral swaps, while flavor-violating NSSI cause swaps to develop away from a spectral crossin…
Neutrinos emitted from a supernova may undergo flavor conversions almost immediately above the core, with possible consequences for supernova dynamics and nucleosynthesis. However, the precise conditions for such fast conversions can be difficult to compute and require knowledge of the full angular distribution of the flavor-dependent neutrino fluxes, that is not available in typical supernova simulations. In this paper, we show that the overall flavor evolution is qualitatively similar to the growth of a so-called `zero mode', determined by the background matter and neutrino densities, which …
Fast flavor conversions of supernova neutrinos, possible near the neutrinosphere, depends on an interesting interplay of collisions and neutrino oscillations. Contrary to naive expectations, the rate of self-induced neutrino oscillations, due to neutrino-neutrino forward scattering, comfortably exceeds the rate of collisions even deep inside the supernova core. Consistently accounting for collisions and oscillations, we present the first calculations to show that collisions can create the conditions for fast flavor conversions of neutrinos, but oscillations can continue without significant dam…
Neutrinos in a core-collapse supernova undergo coherent flavor transformations in their own background. We explore this phenomenon during the cooling stage of the explosion. Our three-flavor calculations reveal qualitatively new effects compared to a two-flavor analysis. These effects are especially clearly seen for the inverted mass hierarchy: we find a different pattern of spectral "swaps" in the neutrino spectrum and a novel "mixed" spectrum for the antineutrinos. A brief discussion of the relevant physics is presented, including the instability of the two-flavor evolution trajectory, the 3…
It is becoming ever clearer that the neutrino signal from the next supernova in our Galaxy can reveal missing information about the neutrino as well as allowing us to probe the explosion of the star by decoding the temporal and spectral evolution of the flavor composition of the signal. But this information may be lost if turbulence in the supernova `depolarizes' the neutrinos so that the observed flux for each flavor is an equal mixture of the initial - unencoded - spectra. Determining if depolarization occurs is one of the most pressing issues of this field. The most difficult aspect of stud…
We show that the bump in the electron number density profile at the base of the hydrogen envelope in O-Ne-Mg core-collapse supernovae causes an interesting interplay between neutrino-electron and neutrino-neutrino forward scattering effects in the flavor evolution of low-energy nu_e in the neutronization burst. The bump allows a significant fraction of the low-energy nu_e to survive by rendering their flavor evolution nonadiabatic. Increasing the luminosity of the neutronization burst shifts the bump-affected nu_e to lower energy with reduced survival probability. Similarly, lowering the lumin…
We apply a linearized stability analysis to simplified models of accretion-phase neutrino fluxes streaming from a supernova. We compare the results with recent numerical studies and find excellent agreement. This provides confidence that a linearized stability analysis can be further applied to more realistic models.
We give a very brief overview of collective effects in neutrino oscillations in core collapse supernovae where refractive effects of neutrinos on themselves can considerably modify flavor oscillations, with possible repercussions for future supernova neutrino detection. We discuss synchronized and bipolar oscillations, the role of energy and angular neutrino modes, as well as three-flavor effects. We close with a short summary and some open questions.
We explore the possibility of probing the nonstandard interactions between the neutrino and a hypothetical massive scalar or pseudoscalar via neutrino flavor transformation in supernovae. We find that in the ultrarelativistic limit, the effective interaction between the neutrinos vanishes if neutrinos are Dirac fermions but not if they are Majorana fermions. The impact of the new neutrino interaction upon the flavor transformation above the neutrinosphere is calculated in the context of the multi-angle "neutrino bulb model". We find that the addition of the nonstandard neutrino self-interactio…
We study the effects of non-standard self-interactions (NSSI) of neutrinos streaming out of a core-collapse supernova. We show that with NSSI, the standard linear stability analysis gives rise to linearly as well as exponentially growing solutions. For a two-box spectrum, we demonstrate analytically that flavor-preserving NSSI lead to a suppression of bipolar collective oscillations. In the intersecting four-beam model, we show that flavor-violating NSSI can lead to fast oscillations even when the angle between the neutrino and antineutrino beams is obtuse, which is forbidden in the Standard M…
Measuring core-collapse supernova neutrinos, both from individual supernovae within the Milky Way and from past core collapses throughout the Universe (the diffuse supernova neutrino background, or DSNB), is one of the main goals of current and next generation neutrino experiments. Detecting the heavy-lepton flavor (muon and tau types, collectively $ν_x$) component of the flux is particularly challenging due to small statistics and large backgrounds. While the next galactic neutrino burst will be observed in a plethora of neutrino channels, allowing to measure a small number of $ν_x$ events, o…
Neutrino-neutrino interactions can lead to collective flavor conversion in the dense parts of a core collapse supernova. Growing instabilities that lead to collective conversions have been studied intensely in the limit of two-neutrino species and occur for inverted mass ordering in the case of a perfectly spherical supernova. We examine two simple models of colliding and intersecting neutrino beams and show, that for three neutrino species instabilities exist also for normal mass ordering even in the case of a fully symmetric system. Whereas the instability for inverted mass ordering is assoc…
We argue that the small fraction of neutrinos that undergo direction-changing scattering outside of the neutrinosphere could have significant influence on neutrino flavor transformation in core-collapse supernova environments. We show that the standard treatment for collective neutrino flavor transformation is adequate at late times, but could be inadequate in the crucial shock revival/explosion epoch of core-collapse supernovae, where the potentials that govern neutrino flavor evolution are affected by the scattered neutrinos. Taking account of this effect, and the way it couples to entropy a…
Neutrinos propagating in dense neutrino media such as core-collapse supernovae and neutron star merger remnants can experience the so-called fast flavor conversions on scales much shorter than those expected in vacuum. A very generic class of fast flavor instabilities is the ones which are produced by the backward scattering of neutrinos off the nuclei at relatively large distances from the supernova core. In this study we demonstrate that despite their ubiquity, such fast instabilities are unlikely to cause significant flavor conversions if the population of neutrinos in the backward directio…
Self-induced flavor conversion of supernova (SN) neutrinos is a generic feature of neutrino-neutrino dispersion. The corresponding run-away modes in flavor space can spontaneously break the original symmetries of the neutrino flux and in particular can spontaneously produce small-scale features as shown in recent schematic studies. However, the unavoidable "multi-angle matter effect" shifts these small-scale instabilities into regions of matter and neutrino density which are not encountered on the way out from a SN. The traditional modes which are uniform on the largest scales are most prone f…
Self-induced flavor conversions of supernova (SN) neutrinos can strongly modify the flavor dependent fluxes. We perform a linearized flavor stability analysis with accretion-phase matter profiles of a 15 M_sun spherically symmetric model and corresponding neutrino fluxes. We use realistic energy and angle distributions, the latter deviating strongly from quasi-isotropic emission, thus accounting for both multi-angle and multi-energy effects. For our matter and neutrino density profile we always find stable conditions: flavor conversions are limited to the usual MSW effect. In this case one may…
In environments with high dense neutrino gases, such as in core-collapse supernovae, the neutrinos can experience collective neutrino oscillation due to their self-interactions. In particular, fast flavor conversion driven by the crossings in the neutrino angular distribution can affect explosion mechanism, nucleosynthesis, and neutrino observation. We perform the numerical computation of nonlinear flavor evolution on the neutrino angular distribution with tiny crossings expected to be generated in the preshock region. We demonstrate that the fast instability is triggered and a cascade develop…
It was recently realized that three-flavor effects could peculiarly modify the development of spectral splits induced by collective oscillations, for supernova neutrinos emitted during the cooling phase of a protoneutron star. We systematically explore this case, explaining how the impact of these three-flavor effects depends on the ordering of the neutrino masses. In inverted mass hierarchy, the solar mass splitting gives rise to instabilities in regions of the (anti)neutrino energy spectra that were otherwise stable under the leading two-flavor evolution governed by the atmospheric mass spli…
Matter-enhanced antineutrino flavor transformation between $\barν_e$ and $\barν_{μ(τ)}$ can occur in supernovae if the vacuum masses for these species satisfy $m_{\barν_e}>m_{\barν_{μ(τ)}}$. For $δm^2> 1$ eV$^2$, such flavor transformation can affect the electron fraction $Y_e$ in the neutrino-heated supernova ejecta. We point out that such flavor transformation will not drive $Y_e>0.5$ at the $r$-process nucleosynthesis epoch in the best available supernova model for such nucleosynthesis. Consequently, there is no obvious conflict between matter-enhanced antineutrino flavor transformation $\b…
A dense neutrino medium such as that inside a core-collapse supernova can experience collective flavor conversion or oscillations because of the neutral-current weak interaction among the neutrinos. This phenomenon has been studied in a restricted, stationary supernova model which possesses the (spatial) spherical symmetry about the center of the supernova and the (directional) axial symmetry around the radial direction. Recently it has been shown that these spatial and directional symmetries can be broken spontaneously by collective neutrino oscillations. In this paper we analyze the neutrino…
Although Galactic core-collapse supernovae (SNe) only happen a few times per century, every hour a vast number of explosions happen in the whole universe, emitting energy in the form of neutrinos, resulting in the diffuse supernova neutrino background (DSNB). The DSNB has not yet been detected, but Super-Kamiokande doped with gadolinium is expected to yield the first statistically significant observation within the next several years. Since the neutrinos produced at the core collapse undergo mixing during their propagation to Earth, the flavor content at detection is a test of oscillation phys…
These conference proceedings cover various aspects of neutrino propagation through the high matter and neutrino densities near the proto-neutron star in a core-collapse supernova. A significant feature of this regime is the impact of neutrino-neutrino interactions. Properties of this non-linear many-neutrino system are discussed with a particular emphasis on its symmetries.
During the accretion phase of a core-collapse supernova (SN), the deleptonization flux has recently been found to develop a global dipole pattern (LESA---Lepton Emission Self-sustained Asymmetry). The $ν_e$ minus $\barν_e$ flux essentially vanishes in one direction, potentially facilitating self-induced flavor conversion. On the other hand, below the stalled shock wave, self-induced flavor conversion is typically suppressed by multi-angle matter effects, preventing any impact of flavor conversion on SN explosion dynamics. In a schematic model of SN neutrino fluxes, we study the impact of modif…
Core collapse supernovae are unique laboratories to study many aspects of neutrino physics. The vicinity of the proto-neutron star in a core-collapse supernova is characterized by large matter and neutrino densities. A salient feature of this region is the impact of neutrino-neutrino interactions. Properties of the ensuing non-linear many-neutrino system are examined with a particular emphasis on its collective behavior and its symmetries. The impact of neutrino properties and interactions on the r-process nucleosynthesis that may take place in the supernova environment is discussed.
Mounting evidence indicates that neutrinos likely undergo fast flavor conversion (FFC) in at least some core-collapse supernovae. Outcomes of FFC, however, remain highly uncertain. Here we study the cascade of flavor-field power from large angular scales in momentum space down to small ones, showing that FFC enhances this process and thereby hastens relaxation. Cascade also poses a computational challenge, which is present even if the flavor field is stable: When power reaches the smallest angular scale of the calculation, error from truncating the angular-moment expansion propagates back to l…
Neutrinos streaming from a supernova (SN) core occasionally scatter in the envelope, producing a small "neutrino halo" with a much broader angle distribution than the primary flux originating directly from the core. Cherry et al. (2012) have recently pointed out that, during the accretion phase, the halo actually dominates neutrino-neutrino refraction at distances exceeding some 100 km. However, the multiangle matter effect (which increases if the angle distribution is broader) still appears to suppress self-induced flavor conversion during the accretion phase.
Self induced neutrino flavor conversions in the dense regions of stellar core collapse are almost exclusively studied in the standard two flavor scenario. Linear stability analysis has been successfully used to understand these flavor conversions. This is the first linearized study of $\textit{three flavor}$ fast instabilities. The `fast' conversions are fascinating distinctions of the dense neutrino systems. In the fast modes the collective oscillation dynamics are independent of the neutrino mass, growing at the scale of the large neutrino-neutrino interaction strength ($10^5$ km$^{-1}$) of …
Neutrino-neutrino refraction causes self-induced flavor conversion in dense neutrino fluxes. For the first time, we include the azimuth angle of neutrino propagation as an explicit variable and find a new generic multi-azimuth-angle (MAA) instability which, for simple spectra, occurs in the normal neutrino mass hierarchy. Matter suppression of this instability in supernovae requires larger densities than the traditional bimodal case. The new instability shows explicitly that solutions of the equations for collective flavor oscillations need not inherit the symmetries of initial or boundary con…
Numerical simulations of the supernova (SN) neutrino self-induced flavor conversions, associated with the neutrino-neutrino interactions in the deepest stellar regions, have been typically carried out assuming the "bulb-model". In this approximation, neutrinos are taken to be emitted half-isotropically by a common neutrinosphere. In the recent Ref. \cite{Mirizzi:2011tu} we have removed this assumption by introducing flavor-dependent angular distributions for SN neutrinos, as suggested by core-collapse simulations. We have found that in this case a novel multi-angle instability in the self-indu…
We investigate the multi-azimuthal angle (MAA) effect on collective neutrino oscillation by considering the three-dimensional neutrino momentum distribution in a realistic electron-capture supernova model with an $8.8 M_{\odot}$ progenitor. We find that the MAA effect induces collective flavor conversions at epochs when it is completely suppressed under the axial-symmetric approximation. This novel activity is switched on/off by the growth of the MAA instability and imprints additional time evolution in the expected neutrino event rate. We validate our results by extending the linear stability…
Neutrino and antineutrino fluxes from a core-collapse galactic supernova are studied, within a representative three-flavor scenario with inverted mass hierarchy and tiny 1-3 mixing. The initial flavor evolution is dominated by collective self-interaction effects, which are computed in a full three-family framework along an averaged radial trajectory. During the whole time span considered (t=1-20 s), neutrino and antineutrino spectral splits emerge as dominant features in the energy domain for the final, observable fluxes. Some minor or unobservable three-family features (e.g., related to the m…
We show that the supernova neutrino signal in terrestrial detectors could give characteristic signatures as the shock propagates through the regions where matter-enhanced neutrino flavor transformation takes place. This effect could allow existing and proposed supernova neutrino detectors to provide new insights into the problem of shock re-generation and propagation. Alternatively, such observations could allow unique insights into the neutrino mass and mixing matrix.
Even tiny lepton flavor violation (LFV) due to some New Physics is able to alter the conditions inside a collapsing supernova core and probably to facilitate the explosion. LFV emerges naturally in a See-Saw type II model of neutrino mass generation. Experimentally LFV is constrained by rare lepton decay searches. In particular, strong bounds are imposed on the mu->eee branching ratio and on the mu-e conversion probability in muonic gold. Currently the mu->e gamma decay is under investigation in the MEG experiment which aims at dramatic increase of sensitivity in the next three years. We searc…
We explore the effects of collective neutrino flavor oscillations due to neutrino-neutrino interactions on the neutrino heating behind a stalled core-collapse supernova shock. We carry out axisymmetric (2D) radiation-hydrodynamic core-collapse supernova simulations, tracking the first 400 ms of the post-core-bounce evolution in 11.2 solar mass and 15 solar mass progenitor stars. Using inputs from these 2D simulations, we perform neutrino flavor oscillation calculations in multi-energy single-angle and multi-angle single-energy approximations. Our results show that flavor conversions do not set…
The neutrinos from galactic supernovae can be detected by the Sudbury Neutrino Observatory and the Super-Kamiokande. The effect of neutrino mass can show up in the observed neutrino signal by (i) delay in the time of flight and (ii) distortion of the neutrino energy spectrum due to flavor mixing. We discuss a combination of the two effects for both charged and neutral current processes in the detectors for realistic three flavor scenarios and show that neutrino flavor mixing can lead to non-trivial changes in the event rate as a function of time.
Using moment equations we analyze collective flavor transformation of supernova neutrinos. We study the convergence of moment equations and find that numerical results using a few moment converge quite fast. We study effects of emission angle distribution of neutrinos on neutrino sphere. We study scaling law of the amplitude of neutrino self-interaction Hamiltonian and find that it depends on model of emission angle distribution of neutrinos. Dependence of neutrino oscillation on different models of emission angle distribution is studied.
If neutrinos have mass, they can also decay. Decay lifetimes of cosmological interest can be probed, in principle, through the detection of the redshifted, diffuse neutrino flux produced by all past supernovae--the so-called supernova relic neutrino (SRN) flux. In this work, we solve the SRN kinetic equations in the general case of three-generation flavor transitions followed by invisible (nonradiative) two-body decays. We then use the general solution to calculate observable SRN spectra in some representative decay scenarios. It is shown that, in the presence of decay, the SRN event rate can …
A new mechanism of supernova shock revival is proposed, which involves resonant spin--flavor precession of neutrinos with a transition magnetic moment in the magnetic field of the supernova. The mechanism can be operative in supernovae for transition magnetic moments as small as $10^{-14}μ_B$ provided the neutrino mass squared difference is in the range $Δm^2 \sim (3 \;{\rm eV})^2-(600 \;{\rm eV})^2$. It is shown that this mechanism can increase the neutrino--induced shock reheating energy by about 60\%.
We calculate coherent neutrino and antineutrino flavor transformation in the supernova environment, for the first time including a self-consistent treatment of forward scattering-induced coupling and entanglement of intersecting neutrino/antineutrino trajectories. For the atmospheric neutrino mass-squared difference we find that in the normal (inverted) mass hierarchy the more tangentially-propagating (radially-propagating) neutrinos and antineutrinos can initiate collective, simultaneous medium-enhanced flavor conversion of these particles across broad ranges of energy and propagation directi…
