The Diffuse Supernova Neutrino Background

The Diffuse Supernova Neutrino Background (DSNB) is the weak glow of MeV neutrinos and antineutrinos from distant core-collapse supernovae. The DSNB has not been detected yet, but the Super-Kamiokande (SK) 2003 upper limit on the electron antineutrino flux is close to predictions, now quite precise, based on astrophysical data. If SK is modified with dissolved gadolinium to reduce detector backgrounds and increase the energy range for analysis, then it should detect the DSNB at a rate of a few events per year, providing a new probe of supernova neutrino emission and the cosmic core-collapse rate. If the DSNB is not detected, then new physics will be required. Neutrino astronomy, while uniquely powerful, has proven extremely difficult -- only the Sun and the nearby Supernova 1987A have been detected to date -- so the promise of detecting new sources soon is exciting indeed.Comment: Submitted to Annual Review of Nuclear and Particle Science, Volume 60. 25 pages with 7 figures

Supernova Neutrino Detection

World-wide, several detectors currently running or nearing completion are sensitive to a core collapse supernova neutrino signal in the Galaxy. I will briefly describe the nature of the neutrino signal and then survey current and future detection techniques. I will also explore what physics and astrophysics we can learn from the next Galactic core collapse.Comment: For the Proceedings of Neutrino 2000 - the X1X International Conference on Neutrino Physics and Astrophysics. 7 pages, 1 figur

Future galactic supernova neutrino signal: What can we learn?

The next supernova in our galaxy will be detected by a variety of neutrino detectors. In this lecture I discuss the set of observables needed to constrain the models of supernova neutrino emission. They are the flux normalizations, and average energies, of each of the three expected components of the neutrino flux: $\nu_e$, $\bar{\nu}_e$, and $\nu_x$ (all the other four flavors combined). I show how the existing, or soon to be operational, neutrino detectors will be able to determine the magnitude of these observables, and estimate the corresponding rates.Comment: 10 pages, 5 figures, Talk at the School `Neutrinos in Astro, Particle and Nuclear Physics', Erice, September 18-26, 200

TeV-Scale Thermal WIMPs: Unitarity and its Consequences

We re-examine unitarity bounds on the annihilation cross section of thermal-WIMP dark matter. For high-mass pointlike dark matter, it is generic to form WIMP bound states, which, together with Sommerfeld enhancement, affects the relic abundance. We show that these effects lower the unitarity bound from 139 TeV to below 100 TeV for non-self-conjugate dark matter and from 195 TeV (the oft-quoted value of 340 TeV assumes $\Omega_{DM} h^2 = 1$) to 140 TeV for the self-conjugate case. For composite dark matter, for which the unitarity limit on the radius was thought to be mass-independent, we show that the largest allowed mass is 1 PeV. In addition, we find important new effects for annihilation in the late universe. For example, while the production of high-energy light fermions in WIMP annihilation is suppressed by helicity, we show that bound-state formation changes this. Coupled with rapidly improving experimental sensitivity to TeV-range gamma rays, cosmic rays, and neutrinos, our results give new hope to attack the thermal-WIMP mass range from the high-mass end.Comment: Accepted in PRD. Gamma ray spectra from annihilation and bound-state formation added in FIG.

Revealing Type Ia supernova physics with cosmic rates and nuclear gamma rays

Type Ia supernovae (SNIa) remain mysterious despite their central importance in cosmology and their rapidly increasing discovery rate. The progenitors of SNIa can be probed by the delay time between progenitor birth and explosion as SNIa. The explosions and progenitors of SNIa can be probed by MeV nuclear gamma rays emitted in the decays of radioactive nickel and cobalt into iron. We compare the cosmic star formation and SNIa rates, finding that their different redshift evolution requires a large fraction of SNIa to have large delay times. A delay time distribution of the form t^{-1.0 +/- 0.3} provides a good fit, implying 50% of SNIa explode more than ~ 1 Gyr after progenitor birth. The extrapolation of the cosmic SNIa rate to z = 0 agrees with the rate we deduce from catalogs of local SNIa. We investigate prospects for gamma-ray telescopes to exploit the facts that escaping gamma rays directly reveal the power source of SNIa and uniquely provide tomography of the expanding ejecta. We find large improvements relative to earlier studies by Gehrels et al. in 1987 and Timmes & Woosley in 1997 due to larger and more certain SNIa rates and advances in gamma-ray detectors. The proposed Advanced Compton Telescope, with a narrow-line sensitivity ~ 60 times better than that of current satellites, would, on an annual basis, detect up to ~ 100 SNIa (3 sigma) and provide revolutionary model discrimination for SNIa within 20 Mpc, with gamma-ray light curves measured with ~ 10 sigma significance daily for ~ 100 days. Even more modest improvements in detector sensitivity would open a new and invaluable astronomy with frequent SNIa gamma-ray detections.Comment: 13 pages, 7 figures, 3 tables; accepted for publication in ApJ; published version with references update

Neutrino Properties from High Energy Astrophysical Neutrinos

It is shown that high energy neutrino beams from very distant sources can beutilized to learn about some properties fof neutrinos such as lifetimes and mass hierarchy etc. Furthermore, even mixing elements such as U-e3 and the CPV phase can be measured in principle. Pseudo-Dirac mass differences as small as 10^-18 eV^2 can be probed as well.Comment: 13 pages. Presented at the PASCOS'04 and Nath-Fest, august 16-22, 2004, Boston, to be published in the proceeding