4,406 research outputs found

    On the likely dominance of WIMP annihilation to fermion pair+W/Z (and implication for indirect detection)

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    Arguably, the most popular candidate for Dark Matter (DM) is a massive, stable, Majorana fermion. However, annihilation of Majorana DM to two fermions often features a helicity-suppressed s-wave rate. Radiating a gauge boson via electroweak (EW) and electromagnetic (EM) bremsstrahlung removes this s-wave suppression. The main purpose of this talk is to explain in some detail why the branching ratio to a fermion pair is likely suppressed while the decay to the pair plus a W/Z is not. In doing so, we investigate the general conditions for s-wave suppression and un-suppression using Fierz transformations and partial wave expansions. Suppression for the 2-to-2 process is sufficiently severe that the EW and EM bremsstrahlung are likely to be the dominant modes of gauge-singlet Majorana DM annihilation. We end this talk with a discussion of the challenge presented by space-based data for Majorana DM models, given that the enhanced rate to radiated W and Z gauge bosons and their dominant decay via hadronic channels tends to produce more anti-protons than are observed.Comment: 22 pages, including five sets of figures and two tables; expands upon talk presented at the CETUP* Dark Matter Workshop, Lead, South Dakota, July 201

    Extreme-Energy Cosmic Rays: Puzzles, Models, and Maybe Neutrinos

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    The observation of twenty cosmic-ray air-showers at and above 10^{20} eV poses fascinating problems for particle astrophysics: how the primary particles are accelerated to these energies, how the primaries get here through the 2.7K microwave background filling the Universe, and how the highest-energy events exhibit clustering on few-degree angular scales on the sky when charged particles are expected be bent by cosmic magnetic fields. An overview of the puzzles is presented, followed by a brief discussion of many of the models proposed to solve these puzzles. Emphasis is placed on (i) the signatures by which cosmic ray experiments in the near future will discriminate among the many proposed models, and (ii) the role neutrino primaries may play in resolving the observational issues. It is an exciting prospect that highest-energy cosmic rays may have already presented us with new physics not accessible in terrestrial accelerator searches.Comment: 12 pages, RevTeX, 4 figures, Expansion of talks given at NU2000 (Canada); Metepec, Mexico; RADHEP2000 (UCLA

    Neutrino flavor ratios as diagnostic of solar WIMP annihilation

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    We consider the neutrino (and antineutrino) flavors arriving at Earth for neutrinos produced in the annihilation of weakly interacting massive particles (WIMPs) in the Sun's core. Solar-matter effects on the flavor propagation of the resulting \agt GeV neutrinos are studied analytically within a density-matrix formalism. Matter effects, including mass-state level-crossings, influence the flavor fluxes considerably. The exposition herein is somewhat pedagogical, in that it starts with adiabatic evolution of single flavors from the Sun's center, with θ13\theta_{13} set to zero, and progresses to fully realistic processing of the flavor ratios expected in WIMP decay, from the Sun's core to the Earth. In the fully realistic calculation, non-adiabatic level-crossing is included, as are possible nonzero values for θ13\theta_{13} and the CP-violating phase δ\delta. Due to resonance enhancement in matter, nonzero values of θ13\theta_{13} even smaller than a degree can noticeably affect flavor propagation. Both normal and inverted neutrino-mass hierarchies are considered. Our main conclusion is that measuring flavor ratios (in addition to energy spectra) of \agt GeV solar neutrinos can provide discrinination between WIMP models. In particular, we demonstrate the flavor differences at Earth for neutrinos from the two main classes of WIMP final states, namely W+WW^+ W^- and 95% bbˉb \bar{b} + 5% τ+τ\tau^+\tau^-. Conversely, if WIMP properties were to be learned from production in future accelerators, then the flavor ratios of \agt GeV solar neutrinos might be useful for inferring θ13\theta_{13} and the mass hierarchy.Comment: 30 pages, including 10 figures and 4 appendice

    Absolute neutrino masses: physics beyond SM, double beta decay and cosmic rays

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    Absolute neutrino masses provide a key to physics beyond the standard model. We discuss the impact of absolute neutrinos masses on physics beyond the standard model, the experimental possibilities to determine absolute neutrinos masses, and the intriguing connection with the Z-burst model for extreme-energy cosmic rays.Comment: 11 pages, 4 figures. Talk given by H. Paes at the NOON2001 workshop, ICRR, University of Tokyo, Kashiwa, Japan; 2 references update