Particle theory

Abstract:

The Pierre Auger Collaboration has reported evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies E > Eth= 5.5 × 1019eV. These show a correlation with the distribution of nearby extragalactic objects, including an apparent excess around the direction of Centaurus A. If the particles responsible for these excesses at E > Ethare heavy nuclei with charge Z, the proton component of the sources shouldłead to excesses in the same regions at energies E/Z. We here report thełack of anisotropies in these directions at energies above Eth/Z (for illustrative values of Z = 6,13,26). If the anisotropies above Ethare due to nuclei with charge Z, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at thełower energies. © 2011 IOP Publishing Ltd and SISSA.

Abstract:

We propose a scenario to stabilize all geometric moduli-that is, the complex structure, Kähler moduli, and the dilaton-in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with nonperturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized-in the most restrictive case, leaving only one combination of Kähler moduli and the dilaton as a flat direction. At this stage, the remaining moduli space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate nonperturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous U(1) symmetries, which arise from the required bundle constructions. We present a specific example, with a consistent choice of nonperturbative effects, where all remaining flat directions are stabilized in an anti-de Sitter vacuum. © 2011 American Physical Society.

Abstract:

We report on a search for extremely-high energy neutrinos with energies greater than 106GeV using the data taken with the IceCube detector at the South Pole. The data was collected between April 2008 and May 2009 with the half-completed IceCube array. The absence of signal candidate events in the sample of 333.5 days of live time significantly improves model-independent limits from previous searches and allows to place a limit on the diffuse flux of cosmic neutrinos with an E-2 spectrum in the energy range 2.0×106-6.3×109GeV to a level of E2φ≤3.6×10 -8GeVcm-2sec-1sr-1. © 2011 American Physical Society.

Abstract:

DAMA observes an annual modulation in their event rate, as might be expected from dark matter scatterings, while CoGeNT has reported evidence for a similar modulation. The simplest interpretation of these findings in terms of dark matter-nucleus scatterings is excluded by other direct detection experiments. We consider the robustness of these exclusions with respect to assumptions regarding the scattering and find that isospin-violating inelastic dark matter helps alleviate this tension and allows marginal compatibility between experiments. Isospin-violation can significantly weaken the XENON constraints, while inelasticity enhances the annual modulation fraction of the signal, bringing the CoGeNT and CDMS results into better agreement.