Supernova neutrinos: Flavor-dependent fluxes and spectra

Transporting nu_mu and nu_tau in a supernova (SN) core involves several processes that have been neglected in traditional simulations. Based on a Monte Carlo study we find that the flavor-dependent spectral differences are much smaller than is often stated in the literature. A full-scale SN simulation using a Boltzmann solver and including all relevant neutrino reactions confirms these results. The flavor-dependent flux differences are largest during the initial accretion phase.Comment: Proceedings NOON 03, Kanazawa, 10-14 Feb 200

Hydromagnetic instabilities in protoneutron stars

The stability properties of newly born neutron stars, or proto--neutron stars, are considered. We take into account dissipative processes, such as neutrino transport and viscosity, in the presence of a magnetic field. In order to find the regions of the star subject to different sorts of instability, we derive the general instability criteria and apply it to evolutionary models of PNSs. The influence of the magnetic field on instabilities is analyzed and the critical magnetic field stabilizing the star is obtained. In the light of our results, we estimate of the maximum poloidal magnetic field that might be present in young pulsars or magnetars.Comment: 18 pages, 4 figures, to appear in Astrophysical Journa

Electron Neutrino Pair Annihilation: A New Source for Muon and Tau Neutrinos in Supernovae

We show that in a supernova core the annihilation process nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar is always more important than the traditional reaction e^+ e^- -> nu_{mu,tau} nu_{mu,tau}-bar as a source for muon and tau neutrino pairs. We study the impact of the new process by means of a Monte Carlo transport code with a static stellar background model and by means of a self-consistent hydrodynamical simulation with Boltzmann neutrino transport. Nucleon bremsstrahlung NN -> NN nu_{mu,tau} nu_{mu,tau}-bar is also included as another important source term. Taking into account nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar increases the nu_mu and nu_tau luminosities by as much as 20% while the spectra remain almost unaffected. In our hydrodynamical simulation the shock was somewhat weakened. Elastic nu_{mu,tau} nu_e and nu_{mu,tau} nu_e scattering is not negligible but less important than nu_{mu,tau} e^+ or e^- scattering. Its influence on the nu_{mu,tau} fluxes and spectra is small after all other processes have been included.Comment: 11 pages, 9 eps-figs, submitted to Ap

XMM-Newton observations of the BL Lac MS 0737+7441

We report on the XMM-Newton observations of the BL Lac object MS 0737.9+7441 during the performance verification phase. A simple power-law fit provides an adequate description of the integrated spectrum in the 0.2-10 keV energy band. The photon index is slightly steeper in the EPIC pn data with 2.38+-0.01 compared to the EPIC MOS data (2.28+-0.01). The difference is most probably due to the present uncertainties in the calibration of the EPIC MOS and EPIC pn data sets. We report evidence for intrinsic absorption in the distant BL Lac above the Galactic column N_H,Gal=3.2*10^20 cm^-2 which is N_H,fit(z=0.315)= (2.70+-0.20)*10^20cm^-2 in the EPIC pn data and N_H,fit(z=0.315)= (3.25+-0.25)*10^20cm^-2 in the EPIC MOS data assuming neutral gas and solar abundances. The flux variations are found to be of the order of 10 %.Comment: 4 pages, 4 Figures, accepted for publication in the special A&A Letters issue for XMM-Newto

Neutrino Coherent Scattering Rates at Direct Dark Matter Detectors

Neutrino-induced recoil events may constitute a background to direct dark matter searches, particularly for those detectors that strive to reach the ton-scale and beyond. This paper discusses the expected neutrino-induced background spectrum due to several of the most important sources, including solar, atmospheric, and diffuse supernova neutrinos. The largest rate arises from $^8$B produced solar neutrinos, providing upwards of $\sim 10^3$ events per ton-year over all recoil energies for the heaviest nuclear targets. However the majority of these $^8$B events are expected to be below the recoil threshold of modern detectors. The remaining neutrino sources are found to constitute a background to the WIMP-induced recoil rate only if the WIMP-nucleon cross section is less than $10^{-12}$ pb. Finally the sensitivity to diffuse supernova neutrino flux for non-electron neutrino flavors is discussed, and projected flux limits are compared with existing flux limits

Detecting the Neutrino Mass Hierarchy with a Supernova at IceCube

IceCube, a future km^3 antarctic ice Cherenkov neutrino telescope, is highly sensitive to a galactic supernova (SN) neutrino burst. The Cherenkov light corresponding to the total energy deposited by the SN neutrinos in the ice can be measured relative to background fluctuations with a statistical precision much better than 1%. If the SN is viewed through the Earth, the matter effect on neutrino oscillations can change the signal by more than 5%, depending on the flavor-dependent source spectra and the neutrino mixing parameters. Therefore, IceCube together with another high-statistics experiment like Hyper-Kamiokande can detect the Earth effect, an observation that would identify specific neutrino mixing scenarios that are difficult to pin down with long-baseline experiments. In particular, the normal mass hierarchy can be clearly detected if the third mixing angle is not too small, sin^2 theta_13 < 10^-3. The small flavor-dependent differences of the SN neutrino fluxes and spectra that are found in state-of-the-art simulations suffice for this purpose. Although the absolute calibration uncertainty at IceCube may exceed 5%, the Earth effect would typically vary by a large amount over the duration of the SN signal, obviating the need for a precise calibration. Therefore, IceCube with its unique geographic location and expected longevity can play a decisive role as a "co-detector" to measure SN neutrino oscillations. It is also a powerful stand-alone SN detector that can verify the delayed-explosion scenario.Comment: 19 pages, 6 Figs, final version accepted by JCAP, some references adde

Anti-Kaon Induced Reactions on the Nucleon

Using a previously established effective Lagrangian model we describe anti-kaon induced reactions on the nucleon. The dominantly contributing channels in the cm-energy region from threshold up to 1.72 GeV are included (K N, \pi \Sigma, \pi \Lambda). We solve the Bethe-Salpeter equation in an unitary $K$-matrix approximation.Comment: 21 pages, 13 figures, minor typos corrected, accepted for publication in Phys. Rev.

A Fresh Look at Axions and SN 1987A

We re-examine the very stringent limits on the axion mass based on the strength and duration of the neutrino signal from SN 1987A, in the light of new measurements of the axial-vector coupling strength of nucleons, possible suppression of axion emission due to many-body effects, and additional emission processes involving pions. The suppression of axion emission due to nucleon spin fluctuations induced by many-body effects degrades previous limits by a factor of about 2. Emission processes involving thermal pions can strengthen the limits by a factor of 3-4 within a perturbative treatment that neglects saturation of nucleon spin fluctuations. Inclusion of saturation effects, however, tends to make the limits less dependent on pion abundances. The resulting axion mass limit also depends on the precise couplings of the axion and ranges from 0.5x10**(-3) eV to 6x10**(-3) eV.Comment: 32 latex pages, 13 postscript figures included, uses revtex.sty, submitted to Physical Review

Nucleon Spin Fluctuations and the Supernova Emission of Neutrinos and Axions

In the hot and dense medium of a supernova (SN) core, the nucleon spins fluctuate so fast that the axial-vector neutrino opacity and the axion emissivity are expected to be significantly modified. Axions with m_a\alt10^{-2}\,{\rm eV} are not excluded by SN~1987A. A substantial transfer of energy in neutrino-nucleon ($\nu N$) collisions is enabled which may alter the spectra of SN neutrinos relative to calculations where energy-conserving $\nu N$ collisions had been assumed near the neutrinosphere.Comment: 8 pages. REVTeX. 2 postscript figures, can be included with epsf. Small modifications of the text, a new "Note Added", and three new references. To be published in Phys. Rev. Let

Two-dimensional hydrodynamic core-collapse supernova simulations with spectral neutrino transport. I. Numerical method and results for a 15 M_sun star

Supernova models with a full spectral treatment of the neutrino transport are presented, employing the Prometheus/Vertex neutrino-hydrodynamics code with a ``ray-by-ray plus'' approximation for treating two- (or three-) dimensional problems. The method is described in detail and critically assessed with respect to its capabilities, limitations, and inaccuracies in the context of supernova simulations. In this first paper of a series, 1D and 2D core-collapse calculations for a (nonrotating) 15 M_sun star are discussed, uncertainties in the treatment of the equation of state -- numerical and physical -- are tested, Newtonian results are compared with simulations using a general relativistic potential, bremsstrahlung and interactions of neutrinos of different flavors are investigated, and the standard approximation in neutrino-nucleon interactions with zero energy transfer is replaced by rates that include corrections due to nucleon recoil, thermal motions, weak magnetism, and nucleon correlations. Models with the full implementation of the ``ray-by-ray plus'' spectral transport were found not to explode, neither in spherical symmetry nor in 2D with a 90 degree lateral wedge. The success of previous 2D simulations with grey, flux-limited neutrino diffusion can therefore not be confirmed. Omitting the radial velocity terms in the neutrino momentum equation leads to ``artificial'' explosions by increasing the neutrino energy density in the convective gain layer by about 20--30% and thus the integral neutrino energy deposition in this region by about a factor of two. (abbreviated)Comment: 46 pages plus 13 pages online material; 49 figures; referee's comments included, version accepted by Astronomy & Astrophysic