Earth matter effects in supernova neutrinos: Optimal detector locations

A model-independent experimental signature for flavor oscillations in the neutrino signal from the next Galactic supernova (SN) would be the observation of Earth matter effects. We calculate the probability for observing a Galactic SN shadowed by the Earth as a function of the detector's geographic latitude. This probability depends only mildly on details of the Galactic SN distribution. A location at the North Pole would be optimal with a shadowing probability of about 60%, but a far-northern location such as Pyhasalmi in Finland, the proposed site for a large-volume scintillator detector, is almost equivalent (58%). We also consider several pairs of detector locations and calculate the probability that only one of them is shadowed, allowing a comparison between a shadowed and a direct signal. For the South Pole combined with Kamioka this probability is almost 75%, for the South Pole combined with Pyhasalmi it is almost 90%. One particular scenario consists of a large-volume scintillator detector located in Pyhasalmi to measure the geo-neutrino flux in a continental location and another such detector in Hawaii to measure it in an oceanic location. The probability that only one of them is shadowed exceeds 50% whereas the probability that at least one is shadowed is about 80%. We provide an online tool to calculate different shadowing probabilities for the one- and two-detector cases.Comment: v2: 17 pages, 6 eps figures. Typos removed, matches the published version. Online tool to calculate the Earth shadowing probabilities available at http://www.mppmu.mpg.de/supernova/shadowing . High-resolution color version of fig_2a and fig_2b available at http://www.mppmu.mpg.de/supernova/shadowing/ma

Probing supernova shock waves and neutrino flavor transitions in next-generation water-Cherenkov detectors

Several current projects aim at building a large water-Cherenkov detector, with a fiducial volume about 20 times larger than in the current Super-Kamiokande experiment. These projects include the Underground nucleon decay and Neutrino Observatory (UNO) in the Henderson Mine (Colorado), the Hyper-Kamiokande (HK) detector in the Tochibora Mine (Japan), and the MEgaton class PHYSics (MEMPHYS) detector in the Frejus site (Europe). We study the physics potential of a reference next-generation detector (0.4 Mton of fiducial mass) in providing information on supernova neutrino flavor transitions with unprecedented statistics. After discussing the ingredients of our calculations, we compute neutrino event rates from inverse beta decay ($\bar\nu_e p\to e^+ n$), elastic scattering on electrons, and scattering on oxygen, with emphasis on their time spectra, which may encode combined information on neutrino oscillation parameters and on supernova forward (and possibly reverse) shock waves. In particular, we show that an appropriate ratio of low-to-high energy events can faithfully monitor the time evolution of the neutrino crossing probability along the shock-wave profile. We also discuss some background issues related to the detection of supernova relic neutrinos, with and without the addition of gadolinium.Comment: Revised version (27 pages, 13 eps figures), to appear in JCAP. Includes revised numerical estimates and figures. In particular: calculations of inverse beta decay event rates improved by using the differential cross section by Vissani and Strumia (astro-ph/0302055); supernova relic neutrino flux calculations updated by using recent GALEX Mission data (astro-ph/0411424) on the star formation rate (SFR). References added. Conclusions unchange

Supernova neutrinos: Strong coupling effects of weak interactions

In core-collapse supernovae, neutrinos and antineutrinos are initially subject to significant self-interactions induced by weak neutral currents, which may induce strong-coupling effects on the flavor evolution (collective transitions). The interpretation of the effects is simplified when self-induced collective transitions are decoupled from ordinary matter oscillations, as for the matter density profile that we discuss. In this case, approximate analytical tools can be used (pendulum analogy, swap of energy spectra). For inverted neutrino mass hierarchy, the sequence of effects involves: synchronization, bipolar oscillations, and spectral split. Our simulations shows that the main features of these regimes are not altered when passing from simplified (angle-averaged) treatments to full, multi-angle numerical experiments.Comment: Proceedings of NO-VE 2008, IV International Workshop on "Neutrino Oscillations in Venice" (Venice, Italy, April 15-18, 2008), edited by M. Baldo Ceolin (University of Padova publication, Papergraf Editions, Padova, Italy, 2008), pages 233-24

Analysis of energy- and time-dependence of supernova shock effects on neutrino crossing probabilities

It has recently been realized that supernova neutrino signals may be affected by shock propagation over a time interval of a few seconds after bounce. In the standard three-neutrino oscillation scenario, such effects crucially depend on the neutrino level crossing probability P_H in the 1-3 sector. By using a simplified parametrization of the time-dependent supernova radial density profile, we explicitly show that simple analytical expressions for P_H accurately reproduce the phase-averaged results of numerical calculations in the relevant parameter space. Such expressions are then used to study the structure of P_H as a function of energy and time, with particular attention to cases involving multiple crossing along the shock profile. Illustrative applications are given in terms of positron spectra generated by supernova electron antineutrinos through inverse beta decay.Comment: Major changes both in the text and in the figures in order to include the effect of a step-like shock front density profile; final version to appear in Physical Review

Axion hot dark matter bounds

We derive cosmological limits on two-component hot dark matter consisting of neutrinos and axions. We restrict the large-scale structure data to the safely linear regime, excluding the Lyman-alpha forest. We derive Bayesian credible regions in the two-parameter space consisting of m_a and sum(m_nu). Marginalizing over sum(m_nu) provides m_a<1.02 eV (95% CL). In the absence of axions the same data and methods give sum(m_nu)< 0.63 eV (95% CL).Comment: Contribution to Proc. 4th Patras Workshop on Axions, WIMPs and WISPs (18-21 June 2008, DESY

Revisiting cosmological bounds on radiative neutrino lifetime

Neutrino oscillation experiments and direct bounds on absolute masses constrain neutrino mass differences to fall into the microwave energy range, for most of the allowed parameter space. As a consequence of these recent phenomenological advances, older constraints on radiative neutrino decays based on diffuse background radiations and assuming strongly hierarchical masses in the eV range are now outdated. We thus derive new bounds on the radiative neutrino lifetime using the high precision cosmic microwave background spectral data collected by the Far Infrared Absolute Spectrophotometer instrument on board of Cosmic Background Explorer. The lower bound on the lifetime is between a few x 10^19 s and 5 x 10^20 s, depending on the neutrino mass ordering and on the absolute mass scale. However, due to phase space limitations, the upper bound in terms of the effective magnetic moment mediating the decay is not better than ~ 10^-8 Bohr magnetons. We also comment about possible improvements of these limits, by means of recent diffuse infrared photon background data. We compare these bounds with pre-existing limits coming from laboratory or astrophysical arguments. We emphasize the complementarity of our results with others available in the literature.Comment: 7 pages, 3 figures. Minor changes in the text, few references added. Matches the published versio

Signatures of axion-like particles in the spectra of TeV gamma-ray sources

One interpretation of the unexplained signature observed in the PVLAS experiment invokes a new axion-like particle (ALP) with a two-photon vertex, allowing for photon-ALP oscillations in the presence of magnetic fields. In the range of masses and couplings suggested by PVLAS, the same effect would lead to a peculiar dimming of high-energy photon sources. For typical parameters of the turbulent magnetic field in the galaxy, the effect sets in at E_gamma >~ 10 TeV, providing an ALP signature in the spectra of TeV gamma sources that can be probed with Cherenkov telescopes. A dedicated search will be strongly motivated if the ongoing photon regeneration experiments confirm the PVLAS particle interpretation.Comment: 8 pages, 1 eps figure; typos corrected, matches published versio

Cosmological axion bounds

We discuss current cosmological constraints on axions, as well as future sensitivities. Bounds on axion hot dark matter are discussed first, and subsequently we discuss both current and future sensitivity to models in which axions play the role as cold dark matter, but where the Peccei-Quinn symmetry is not restored during reheating.Comment: 4 pages, 2 figures, To appear in the proceedings of 5th Patras Workshop on Axions, WIMPs and WISPs, Durham 13-17 July 200

New analysis of the SN 1987A neutrinos with a flexible spectral shape

We analyze the neutrino events from the supernova (SN) 1987A detected by the Kamiokande II (KII) and Irvine-Michigan-Brookhaven (IMB) experiments. For the time-integrated flux we assume a quasi-thermal spectrum of the form $(E/E_0)^\alpha e^{-(\alpha+1)E/E_0}$ where $\alpha$ plays the role of a spectral index. This simple representation not only allows one to fit the total energy $E_{\rm tot}$ emitted in $\bar\nu_e$ and the average energy , but also accommodates a wide range of shapes, notably anti-pinched spectra that are broader than a thermal distribution. We find that the pile-up of low-energy events near threshold in KII forces the best-fit value for $\alpha$ to the lowest value of any assumed prior range. This applies to the KII events alone as well as to a common analysis of the two data sets. The preference of the data for an ``unphysical'' spectral shape implies that one can extract meaningful values for and $E_{\rm tot}$ only if one fixes a prior value for $\alpha$. The tension between the KII and IMB data sets and theoretical expectations for $$ is not resolved by an anti-pinched spectrum.Comment: to appear in PRD (6 pages, 6 eps figures