Particle theory

Abstract:

It is likely that ultrahigh energy cosmic rays contain a significant component of heavy or intermediate mass nuclei. The propagation of ultrahigh energy nuclei through cosmic radiation backgrounds is more complicated than that of protons and its study has required the use of Monte Carlo techniques. We present an analytic method for calculating the spectrum and the composition at Earth of ultrahigh energy cosmic rays which start out as heavy nuclei from their extragalactic sources. The results obtained are in good agreement with those obtained using numerical methods. © 2008 The American Physical Society.

Abstract:

We study the topological conditions for general Calabi-Yaus to get a non-supersymmetric AdS exponentially large volume minimum of the scalar potential in flux compactifications of IIB string theory. We show that negative Euler number and the existence of at least one blow-up mode resolving point-like singularities are necessary and sufficient conditions for moduli stabilisation with exponentially large volumes. We also analyse the general effects of string loop corrections on this scenario. While the combination of alpha' and nonperturbative corrections are sufficient to stabilise blow-up modes and the overall volume, quantum corrections are needed to stabilise other directions transverse to the overall volume. This allows exponentially large volume minima to be realised for fibration Calabi-Yaus, with the various moduli of the fibration all being stabilised at exponentially large values. String loop corrections may also play a role in stabilising 4-cycles which support chiral matter and cannot enter directly into the non-perturbative superpotential. We illustrate these ideas by studying the scalar potential for various Calabi-Yau three-folds including K3 fibrations and briefly discuss the potential phenomenological and cosmological implications of our results.