53681182
Triggering collective oscillations by three-flavor effects
Collective flavor transformations in supernovae, caused by neutrino-neutrino interactions, are essentially a two-flavor phenomenon driven by the atmospheric mass difference and the small mixing angle {theta}{sub 13}. In the two-flavor approximation, the initial evolution depends logarithmically on {theta}{sub 13} and the system remains trapped in an unstable fixed point for {theta}{sub 13}=0. However, any effect breaking exact {nu}{sub {mu}-{nu}{tau}}equivalence triggers the conversion. Such three-flavor perturbations include radiative corrections to weak interactions, small differences between the {nu}{sub {mu}}and {nu}{sub {tau}}fluxes, or nonstandard interactions. Therefore, extremely small values of {theta}{sub 13} are in practice equivalent, the fate of the system depending only on the neutrino spectra and their mass ordering.
5467110
Galactic center radio constraints on gamma-ray lines from dark matter annihilation
Recent evidence for one or more gamma-ray lines at ~ 130 GeV in the Fermi-LAT data from the Galactic Center has been interpreted as a hint for dark matter annihilation to Z{\gamma} or H{\gamma} with an annihilation cross section, ~ 10^{-27} cm^3 s^{-1} . We test this hypothesis by comparing synchrotron fluxes due to the electrons and positrons from the decay of the Z or the H boson only in the Galactic Center against radio data from the same region in the Galactic Center. We find that the radio data from single dish telescopes marginally constrain this interpretation of the claimed gamma lines for a contracted NFW profile. Already-operational radio telescopes such as LWA, VLA-Low and LOFAR, and future radio telescopes like SKA, which are sensitive to annihilation cross sections as small as 10^{-28} cm^3 s^{-1}, can confirm or rule out this scenario very soon. We discuss the assumptions on the dark matter profile, magnetic fields, and background radiation density profiles, and show that the constraints are relatively robust for any reasonable assumptions. Independent of the above said recent developments, we emphasize that our radio constraints apply to all models where dark matter annihilates to Z{\gamma} or H{\gamma}.
118571843
Effect of collective neutrino oscillations on the neutrino mechanism of core-collapse supernovae
In the seconds after collapse of a massive star, the newborn protoneutron star (PNS) radiates neutrinos of all flavours. 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, flavour conversion of μ and τ neutrinos to electron-type neutrinos via collective neutrino oscillations (CνO) may in principle increase the heating rate and drive explosions. In order to assess the potential importance of CνO for the shock revival, we solve the steady-state boundary value problem of spherically symmetric accretion between the PNS surface (rν) and the shock (rS), including a scheme for flavour conversion via CνO. For a given rν, PNS mass (M), accretion rate () 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 CνO can decrease the critical luminosity by a factor of at most ∼1.5, but only if the flavour conversion is fully completed inside rS and if there is no matter suppression. The magnitude of the effect depends on the model parameters (M, and rν) through the shock radius and the physical scale for flavour conversion. We quantify these dependencies and find that CνO could lower the critical luminosity only for small M and , and large rν. However, for these parameter values CνO are suppressed due to matter effects. By quantifying the importance of CνO and matter suppression at the critical neutrino luminosity for explosion, we show in agreement with previous studies that CνO are unlikely to affect the neutrino mechanism of core-collapse supernovae significantly.
822603
Adiabatic Faraday effect in a two-level Hamiltonian formalism
The helicity of a photon traversing a magnetized plasma can flip when the B field along the trajectory slowly reverses. Broderick and Blandford have recently shown that this intriguing effect can profoundly change the usual Faraday effect for radio waves. We study this phenomenon in a formalism analogous to neutrino flavor oscillations: the evolution is governed by a Schrodinger equation for a two-level system consisting of the two photon helicities. Our treatment allows for a transparent physical understanding of this system and its dynamics. In particular, it allows us to investigate the nature of transitions at intermediate adiabaticities.
31519375
Multiple spectral splits of supernova neutrinos.
Collective oscillations of supernova neutrinos swap the spectra f(nu(e))(E) and f(nu[over ](e))(E) with those of another flavor in certain energy intervals bounded by sharp spectral splits. This phenomenon is far more general than previously appreciated: typically one finds one or more swaps and accompanying splits in the nu and nu[over ] channels for both inverted and normal neutrino mass hierarchies. Depending on an instability condition, swaps develop around spectral crossings (energies where f(nu(e))=f(nu(x)), f(nu[over ](e))=f(nu[over ](x)) as well as E-->infinity where all fluxes vanish), and the widths of swaps are determined by the spectra and fluxes. Washout by multiangle decoherence varies across the spectrum and splits can survive as sharp spectral features.
18322845
Quasithermal neutrinos from rotating protoneutron stars born during core collapse of massive stars
Rotating and magnetized protoneutron stars (PNSs) may drive relativistic magneto-centrifugally accelerated winds as they cool immediately after core collapse. The wind fluid near the star is composed of neutrons and protons, and the neutrons become relativistic while collisionally coupled with the ions. Here, we argue that the neutrons in the flow eventually undergo inelastic collisions around the termination shock inside the stellar material, producing ~0.1-1 GeV neutrinos, without relying on cosmic-ray acceleration mechanisms. Even higher-energy neutrinos may be produced via particle acceleration mechanisms. We show that PINGU and Hyper-Kamiokande can detect such neutrinos from nearby core-collapse supernovae, by reducing the atmospheric neutrino background via coincident detection of MeV neutrinos or gravitational waves and optical observations. Detection of these GeV and/or higher-energy neutrinos would provide important clues to the physics of magnetic acceleration, nucleosynthesis, the relation between supernovae and gamma-ray bursts, and the properties of newly born neutron stars.
18721076
A practical approach to coronal magnetic field extrapolation based on the principle of minimum dissipation rate
We present a newly developed approach to solar coronal magnetic field extrapolation from vector magnetograms, based on the principle of minimum dissipation rate (MDR). The MDR system was derived from a variational problem that is more suitable for an open and externally driven system, like the solar corona. The resulting magnetic field equation is more general than force-free. Its solution can be expressed as the superposition of two linear (constant-α) force-free fields (LFFFs) with distinct α parameters, and one potential field. Thus, the original extrapolation problem is decomposed into three LFFF extrapolations, utilizing boundary data. The full MDR-based approach requires two layers of vector magnetograph measurements on the solar surface, while a slightly modified practical approach only requires one. We test both approaches against three-dimensional MHD simulation data in a finite volume. Both yield quantitatively good results. The errors in the magnetic energy estimate are within a few percent. In particular, the main features of relatively strong perpendicular current density structures, representative of the non-force-freeness of the solution, are well recovered.
32178161
Exclusion of Tiny Interstellar Dust Grains From the Heliosphere
The distribution of interstellar dust grains (ISDG) observed in the Solar System depends on the nature of the interstellar medium‐solar wind interaction. The charge of the grains couples them to the interstellar magnetic field (ISMF) resulting in some fraction of grains being excluded from the heliosphere while grains on the larger end of the size distribution, with gyroradii comparable to the size of the heliosphere, penetrate the termination shock. This results in a skewing the size distribution detected in the Solar System. 
 
We present new calculations of grain trajectories and the resultant grain density distribution for small ISDGs propagating through the heliosphere. We make use of detailed heliosphere model results, using three‐dimensional (3‐D) magnetohydrodynamic/kinetic models designed to match data on the shape of the termination shock and the relative deflection of interstellar H° and He° flowing into the heliosphere. We find that the necessary inclination of the ISMF relative to the inflow direction results in an asymmetry in the distribution of the larger grains (0.1 μm) that penetrate the heliopause. Smaller grains (0.01 μm) are completely excluded from the Solar System at the heliopause.