Suchergebnisse

9 pages, 6 figures.-- PACS nrs.: 14.60.Pq; 97.60.Bw.-- ArXiv pre-print available at: http://arxiv.org/abs/0712.1137 ; 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 Vm and Vp refractive index. Including this ''mu-tau matter term'' provides a resonance at a density of P= 3 x 10(7) g cm-3 that typically causes significant modifications of the overall Ve and Ve survival probabilities. This effect is surprisingly sensitive to deviations from maximal 23-mixing, being different for each octant. ; We thank E. Akhmedov for an illuminating correspondence, A. Mirizzi for comments on the manuscript, and B. Dasgupta and A. Dighe for helpful comments and for making their manuscript [22] available before completion. This work was partly supported by the eutsche Forschungsgemeinschaft (Grant No. TR-27 ''Neutrinos and Beyond''), by the Cluster of Excellence ''Origin and Structure of the Universe'' (Garching and Munich), by the European Union (Contracts No. RII3-CT-2004-506222 and No. MRTN-CT-2004-503369), and by the Spanish Grants No. FPA2005-01269 (MEC) and No. ACOMP07-270 (Generalitat Valenciana). A. E. was supported by an FPU grant from the Spanish Government. S. P. and R. T. were supported by MEC contracts (Ramo´n y Cajal and Juan de la Cierva, respectively). ; Peer reviewed

16 pages, 12 figures.-- PACS nrs.: 14.60.Pq; 97.60.Bw.-- ISI Article Identifier: 000251987300100.-- ArXiv pre-print available at: http://arxiv.org/abs/0706.2498 ; 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 multiangle 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-[overline nu][sub e] > F-nu x = F-[overline nu][sub x] for the number fluxes. We define epsilon = (F-nu e - F-[overline nu][sub e])/(F-[overline nu][sub e] - F-[overline nu][sub x]) as a measure for the deleptonization flux which is the one crucial parameter. The transition between the quasi-single-angle behavior and multiangle decoherence is abrupt as a function of epsilon. For typical choices of other parameters, multiangle decoherence is suppressed for epsilon greater than or similar to 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 multiangle decoherence. ; This work was partly supported by the Deutsche Forschungsgemeinschaft under the Grant No. TR-27 "Neutrinos and Beyond", by The Cluster of Excellence for Fundamental Physics "Origin and Structure of the Universe" (Garching and Munich), by the European Union under the ILIAS project (Contract No. RII3-CT-2004-506222) and an RT Network (Contract No. MRTNCT-2004-503369), and by the Spanish grants FPA2005-01269 (MEC) and ACOMP07-270 (Generalitat Valenciana). A. E. has been supported by a FPU grant from the Spanish Government. S. P. and R. T. were supported by MEC contracts (Ramón y Cajal and Juan de la Cierva, respectively). ; Peer reviewed

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).

6 pages, 2 figures.-- PACS nrs.: 14.60.Pq; 97.60.Bw.-- ArXiv pre-print available at: http://arxiv.org/abs/0807.0659 ; For neutrinos streaming from a supernova core, dense matter suppresses self-induced flavor transformations if the electron density n(e) significantly exceeds the neutrino density n(nu) in the conversion region. If n(e) is comparable to n(nu), one finds multiangle decoherence, whereas the standard self-induced transformation behavior requires that in the transformation region n(nu) is safely above n(e). This condition need not be satisfied in the early phase after the supernova core bounce. Our new multiangle effect is a subtle consequence of neutrinos traveling on different trajectories when streaming from a source that is not pointlike. ; We acknowledge partial support by the DFG (Germany) under Grants No. TR-27 and No. SFB-676, by The Cluster of Excellence "Origin and Structure of the Universe", by the European Union under the ILIAS project (Contract No. RII3-CT-2004-506222) and an RT Network (Contract No. MRTN-CT-2004-503369), and by the Spanish Grant No. FPA2005-01269. A. E.-P. is supported by a FPU grant from the Spanish Government, A. M. by INFN (Italy), and P. S. by the U.S. Department of Energy and by NASA Grant No. NAG5-10842. Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. ; Peer reviewed