Motion in Brane World Models: The Bazanski Approach

Recently, path equations have been obtained for charged, spinning objects in brane world models, using a modified Bazanski Lagrangian. In this study, path deviation equations of extended objects are derived. The significance of moving extended objects in brane world models is examined. Motion in non- symmetric brane world models is also considered.Comment: A paper presented at the Thirteenth International Symposium on Particles, Strings and Cosmology PASCOS-07, held in London, 2-7 July 200

The dark matter as a light gravitino

We address the question of gravitino dark matter in the context of gauge mediated supersymmetry breaking models. A special emphasis is put on the role played by the MSSM singlet messenger in the case of SO(10) grand unification.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 2 eps figure

Distinguishing between w<−1w < -1 Dark Energy Models

Recent data and new data analysis methods show that most probably the parameter $w$ in the equation of state of the dark energy is smaller than -1 at low redshifts. We briefly review some of the models with such a property and without violating null energy condition. We investigate the difference between the observables and predictions of these models, and how they can be explored to single out or constrain the origin of dark energy and its properties.Comment: 4 papes, 2 figures. To appear in the proceedings of PASCOS-07 conference, Imperial College, London, UK, 2-7 July 200

A new non-perturbative time-dependent string configuration

A time-dependent bosonic string configuration is discussed, in graviton and dilaton backgrounds, leading to Weyl-symmetry beta-functions which are homogeneous in X^0, to any order in alpha'. As a consequence, a string reparametrization can always be implemented, such that beta functions can be cancelled, to any order in alpha'. This non-perturbative conformal invariance is valid for any target space dimension, and leads to a power law expanding Universe, for which the power vanishes if a specific relation between the dimension and dilaton amplitude holds. Finally, D=4 is the minimum dimension (in the case of a spherical world sheet) for which this configuration is consistent with a Wick rotation in a Minkowski target space.Comment: Talk given at PASCOS-0

Inflaton Decay in Supergravity and Gravitino Problem

We have recently shown that, if the inflaton has a nonzero vacuum expectation value, it generically couples to any matter fields that appear in the superpotential at the tree level, and to any gauge sectors through anomalies in the supergravity. Through these processes, the inflaton decays into the supersymmetry breaking sector, producing many gravitinos. The inflaton also directly decays into a pair of the gravitinos. Taking account of these processes, we derive constraints on both inflation models and supersymmetry breaking scenarios for avoiding overproduction of the gravitinos.Comment: Talk given at PASCOS-07, to appear in the proceedings. 4 page

O'Raifeartaigh models with spontaneous R-symmetry breaking

O'Raifeartaigh models with general R-charge assignments can have vacua where both supersymmetry and R-symmetry are spontaneously broken. Most of these vacua are metastable because the potential shows a runaway behaviour. We explain the relation between runaway directions and R-symmetry.Comment: Submitted for SUSY07 proceeding

Brane Decay and Defect Formation

Topological defects are generically expected to form in models of brane inflation. Brane-anti-brane annihilation provides a way to gracefully end inflation, and the dynamics of the tachyon field results in defect formation. The formation of defects has been studied mainly from the brane world-volume point of view, but the defects are themselves lower-dimensional branes, and as a result they couple to bulk fields. To investigate the impact of bulk fields on brane defect formation, we construct a toy model that captures the essential features of the tachyon condensation with bulk fields. In this toy model, we study the structure of defects and simulate their formation and evolution on a lattice. We find that while bulk fields do not have a significant effect on defect formation, they drastically influence the subsequent evolution of the defects, as they re-introduce long-range interactions between them.Comment: 4 pages, 3 figures. Contribution to the proceedings of PASCOS-07, 2-7 July 2007, Imperial College, Londo

NMSSM neutralino dark matter

We study the viability of the lightest neutralino as a dark matter candidate in the Next-to-Minimal Supersymmetric Standard Model. Taking into account accelerator constraints as well as bounds on low-energy observables, and imposing consistency with present bounds on the neutralino relic density, we address the prospects for the direct detection of neutralino dark matter. We find regions of the allowed parameter space where the neutralino detection cross section is within the reach of dark matter detectors, essentially owing to the presence of very light singlet-like Higgses, and to either singlino dominated or very light neutralinos.Comment: 4 pages, 2 figures. Presented at 13th International Symposium on Particles, Strings and Cosmology (PASCOS 07), London, England, 2-7 Jul 200

Emergent Quantum Mechanics and Emergent Symmetries

Quantum mechanics is 'emergent' if a statistical treatment of large scale phenomena in a locally deterministic theory requires the use of quantum operators. These quantum operators may allow for symmetry transformations that are not present in the underlying deterministic system. Such theories allow for a natural explanation of the existence of gauge equivalence classes (gauge orbits), including the equivalence classes generated by general coordinate transformations. Thus, local gauge symmetries and general coordinate invariance could be emergent symmetries, and this might lead to new alleys towards understanding the flatness problem of the Universe.Comment: 10 pages, 1 figure. Presented at PASCOS 13, Imperial College, London, July 6, 200

Solar System Constraints on Gauss-Bonnet Dark Energy

Quadratic curvature Gauss-Bonnet gravity may be the solution to the dark energy problem, but a large coupling strength is required. This can lead to conflict with laboratory and planetary tests of Newton's law, as well as light bending. The corresponding constraints are derived. If applied directly to cosmological scales, the resulting bound on the density fraction is |Omega_GB| < 3.6 x 10^-32.Comment: 4 pages, PASCOS-07 conference proceeding