0000000000906487
AUTHOR
Teguayco Pinto
Relic density of neutrinos with primordial asymmetries.
We study flavor oscillations in the early Universe, assuming primordial neutrino-antineutrino asymmetries. Including collisions and pair processes in the kinetic equations, we not only estimate the degree of flavor equilibration, but for the first time also kinetic equilibration among neutrinos and with the ambient plasma. Typically, the restrictive big-bang nucleosynthesis bound on the nu(e)(nu) over bar (e) asymmetry indeed applies to all flavors as claimed in the previous literature, but fine-tuned initial asymmetries always allow for a large surviving neutrino excess radiation that may show up in precision cosmological data.
Upper limit on the diffuse flux of UHE tau neutrinos from the Pierre Auger Observatory
The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth¿s crust. Tau leptons from ντ charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of ντ at EeV energies. Assuming an E−2ν differential energy spectrum the limit set at 90% C.L. is E2νdNντ/dEν<1.3×10−7 GeV cm−2 s−1 sr−1 in the energy range 2×1017 eV<Eν<2×1019 eV.