Mu-tau neutrino refraction and collective three-flavor transformations in supernovae

We study three-flavor collective neutrino transformations in the dense-neutrino region above the neutrino sphere of a supernova core. We find that two-flavor conversions driven by the atmospheric mass difference and the 13-mixing angle capture the full effect if one neglects the second-order difference between the muon and tau neutrino refractive index. Including this "mu-tau matter term" provides a resonance at a density of approximately 3 x 10^7 g cm^-3 that typically causes significant modifications of the overall electron neutrino and antineutrino survival probabilities. This effect is surprisingly sensitive to deviations from maximal 23-mixing, being different for each octant.Comment: 9 pages, 7 figures. New presentation of results, version to be published in PR

Decoherence in supernova neutrino transformations suppressed by deleptonization

In the dense-neutrino region at 50-400 km above the neutrino sphere in a supernova, neutrino-neutrino interactions cause large flavor transformations. We study when the multi-angle nature of the neutrino trajectories leads to flavor decoherence between different angular modes. We consider a two-flavor mixing scenario between nu_e and another flavor nu_x and assume the usual hierarchy F(nu_e)>F{antinu_e)>F(nu_x)=F(antinu_x) for the number fluxes. We define epsilon=(F(nu_e)-F(antinu_e))/(F(antinu_e)-F(antinu_x)) as a measure for the deleptonization flux which is the one crucial parameter. The transition between the quasi single-angle behavior and multi-angle decoherence is abrupt as a function of epsilon. For typical choices of other parameters, multi-angle decoherence is suppressed for epsilon>0.3, but a much smaller asymmetry suffices if the neutrino mass hierarchy is normal and the mixing angle small. The critical epsilon depends logarithmically on the neutrino luminosity. In a realistic supernova scenario, the deleptonization flux is probably enough to suppress multi-angle decoherence.Comment: 17 pages, 12 figures. Misprint in Eq (14) correcte

Collective flavor transitions of supernova neutrinos

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.This work was supported by the Deutsche Forschungsgemeinschaft (SFB 676 “Particles, Strings and the Early Universe: The Structure of Matter and Space-Time) and by the European Union (contracts No. RII3-CT-2004-506222)

Interplay between collective effects and nonstandard interactions of supernova neutrinos

We consider the effect of non-standard neutrino interactions (NSI, for short) on the propagation of neutrinos through the supernova (SN) envelope within a three-neutrino framework and taking into account the presence of a neutrino background. We find that for given NSI parameters, with strength generically denoted by εij, neutrino evolution exhibits a significant time dependence. For |εττ|≳ 10−3 the neutrino survival probability may become sensitive to the θ23 octant and the sign of εττ. In particular, if εττ≳10−2 an internal I-resonance may arise independently of the matter density. For typical values found in SN simulations this takes place in the same dense-neutrino region above the neutrinosphere where collective effects occur, in particular during the synchronization regime. This resonance may lead to an exchange of the neutrino fluxes entering the bipolar regime. The main consequences are (i) bipolar conversion taking place for normal neutrino mass hierarchy and (ii) a transformation of the flux of low-energy νe, instead of the usual spectral swap

Effect of Collective Neutrino Oscillations on the Neutrino Mechanism of Core-Collapse Supernovae

In the seconds after collapse of a massive star, the newborn proto-neutron star (PNS) radiates neutrinos of all flavors. The absorption of electron-type neutrinos below the radius of the stalled shockwave may drive explosions (the "neutrino mechanism"). Because the heating rate is proportional to the square of neutrino energy, flavor conversion of mu and tau neutrinos to electron-type neutrinos via collective neutrino oscillations (CnuO) may in principle increase the heating rate and drive explosions. In order to assess the potential importance of CnuO for the shock revival, we solve the steady-state boundary value problem of spherically-symmetric accretion between the PNS surface (r_nu) and the shock (r_S), including a scheme for flavor conversion via CnuO. For a given r_nu, PNS mass (M), accretion rate (Mdot), and assumed values of the neutrino energies from the PNS, we calculate the critical neutrino luminosity above which accretion is impossible and explosion results. We show that CnuO can decrease the critical luminosity by a factor of at most ~1.5, but only if the flavor conversion is fully completed inside r_S and if there is no matter suppression. The magnitude of the effect depends on the model parameters (M, Mdot, and r_nu) through the shock radius and the physical scale for flavor conversion. We quantify these dependencies and find that CnuO could lower the critical luminosity only for small M and Mdot, and large r_nu. However, for these parameter values CnuO are suppressed due to matter effects. By quantifying the importance of CnuO and matter suppression at the critical neutrino luminosity for explosion, we show in agreement with previous studies that CnuO are unlikely to affect the neutrino mechanism of core-collapse supernovae significantly.Comment: 8 pages, 3 figures, accepted to MNRA

Can OPERA help in constraining neutrino non-standard interactions?

We study how much the unique ability of the OPERA experiment to directly detect \nu_\tau can help in probing new, non-standard contact interactions of the third family of neutrinos. We perform a combined analysis of future, high-statistics MINOS and OPERA data. For the case of non-standard interactions in \nu_\mu to \nu_e transitions we also include the impact of possible DoubleCHOOZ data. In all cases we find that the \nu_\tau sample of OPERA is too small to be statistically significant, even if one doubles the nominal exposure of OPERA to 4.5E20 pot. OPERA's real benefit for this measurement lies in its very high neutrino energy and hence very different L/E compared to MINOS.Comment: 8 pages, 2 figures, 3 table

S_3-flavour symmetry as realized in lepton flavour violating processes

A variety of lepton flavour violating effects related to the recent discovery of neutrino oscillations and mixings is here systematically discussed in terms of an S_3-flavour permutational symmetry. After a brief review of some relevant results on lepton masses and mixings, that had been derived in the framework of a Minimal S_3-Invariant Extension of the Standard Model, we derive explicit analytical expressions for the matrices of the Yukawa couplings and compute the branching ratios of some selected flavour changing neutral current (FCNC) processes, as well as, the contribution of the exchange of neutral flavour changing scalars to the anomaly of the muon's magnetic moment as functions of the masses of the charged leptons and the neutral Higgs bosons. We find that the S_3 x Z_2 flavour symmetry and the strong mass hierarchy of the charged leptons strongly suppress the FCNC processes in the leptonic sector well below the present experimental upper bounds by many orders of magnitude. The contribution of FCNC to the anomaly of the muon's magnetic moment is small but non-negligible.Comment: 23 pages, one figure. To appear in J. Phys A: Mathematical and Theoretical (SPE QTS5

Physics potential of future supernova neutrino observations

We point out possible features of neutrino spectra from a future galactic core collapse supernova that will enhance our understanding of neutrino mixing as well as supernova astrophysics. We describe the neutrino flavor conversions inside the star, emphasizing the role of "collective effects" that has been appreciated and understood only very recently. These collective effects change the traditional predictions of flavor conversion substantially, and enable the identification of neutrino mixing scenarios through signatures like Earth matter effects.Comment: 8 pages, uses jpconf.cls. Talk given at Neutrino 2008, Christchurch, NZ. Some entries in Table 2 have been correcte

Collective neutrino flavor transitions in supernovae and the role of trajectory averaging

Non-linear effects on supernova neutrino oscillations, associated with neutrino self-interactions, are known to induce collective flavor transitions near the supernova core for theta_13 \neq 0. In scenarios with very shallow electron density profiles, these transformations have been shown to couple with ordinary matter effects, jointly producing spectral distortions both in normal and inverted hierarchy. In this work we consider a complementary scenario, characterized by higher electron density, as indicated by post-bounce shock-wave simulations. In this case, early collective flavor transitions are decoupled from later, ordinary matter effects. Moreover, such transitions become more amenable to both numerical computations and analytical interpretations in inverted hierarchy, while they basically vanish in normal hierarchy. We numerically evolve the neutrino density matrix in the region relevant for self-interaction effects. In the approximation of averaged intersection angle between neutrino trajectories, our simulations neatly show the collective phenomena of synchronization, bipolar oscillations, and spectral split, recently discussed in the literature. In the more realistic (but computationally demanding) case of non-averaged neutrino trajectories, our simulations do not show new significant features, apart from the smearing of ``fine structures'' such as bipolar nutations. Our results seem to suggest that, at least for non-shallow matter density profiles, averaging over neutrino trajectories plays a minor role in the final outcome. In this case, the swap of nu_e and nu_{\mu,\tau} spectra above a critical energy may represent an unmistakable signature of the inverted hierarchy, especially for theta_{13} small enough to render further matter effects irrelevant.Comment: v2 (27 pages, including 9 eps figures). Typos removed, references updated. Minor comments added. Corrected numerical errors in Eq.(6). Matches the published versio

Testing matter effects in propagation of atmospheric and long-baseline neutrinos

We quantify our current knowledge of the size and flavor structure of the matter effects in the evolution of atmospheric and long-baseline neutrinos based solely on the analysis of the corresponding neutrino data. To this aim we generalize the matter potential of the Standard Model by rescaling its strength, rotating it away from the e-e sector, and rephasing it with respect to the vacuum term. This phenomenological parametrization can be easily translated in terms of non-standard neutrino interactions in matter. We show that in the most general case, the strength of the potential cannot be determined solely by atmospheric and long-baseline data. However its flavor composition is very much constrained and the present determination of the neutrino masses and mixing is robust under its presence. We also present an update of the constraints arising from this analysis in the particular case in which no potential is present in the e-mu and e-tau sectors. Finally we quantify to what degree in this scenario it is possible to alleviate the tension between the oscillation results for neutrinos and antineutrinos in the MINOS experiment and show the relevance of the high energy part of the spectrum measured at MINOS.Comment: PDFLaTeX file using JHEP3 class, 25 pages, 7 figures included. Accepted for publication in JHE