13930790
Issues on 3D noncommutative electromagnetic duality
We extend the ordinary 3D electromagnetic duality to the noncommutative (NC) space-time through a Seiberg-Witten map to second order in the noncommutativity parameter {theta}, defining a new scalar field model. There are similarities with the 4D NC duality; these are exploited to clarify properties of both cases. Up to second order in {theta}, we find that duality interchanges the 2-form {theta} with its 1-form Hodge dual *{theta} times the gauge coupling constant, i.e., {theta}{yields}*{theta}g{sup 2} (similar to the 4D NC electromagnetic duality). We directly prove that this property is false in the third order expansion in both 3D and 4D space-times, unless the slowly varying fields limit is imposed. Outside this limit, starting from the third order expansion, {theta} cannot be rescaled to attain an S-duality. In addition to possible applications on effective models, the 3D space-time is useful for studying general properties of NC theories. In particular, in this dimension, we deduce an expression that significantly simplifies the Seiberg-Witten mapped Lagrangian to all orders in {theta}.
119244636
Auxiliary fields representation for modified gravity models
We consider tensor-multiscalar representations for several types of modified gravity actions. The first example is the theory with the action representing an arbitrary smooth function of the scalar curvature R and {open_square}R, the integrand of the Gauss-Bonnet term and the square of the Weyl tensor. We present a simple procedure leading to an equivalent theory of a space-time metric and four auxiliary scalars and especially discuss the calibration of a cosmological constant and the condition of the existence of de Sitter-like solutions in the case of an empty universe. The condition for obtaining a smaller number of independent scalar fields is derived. The second example is the Eddington-like gravity action. In this case we show, in particular, the equivalence of the theory to general relativity with the cosmological constant term, with or without use of the first-order formalism, and also discuss some possible generalizations.
119208390
Evolution of the phase-space density and the Jeans scale for dark matter derived from the Vlasov-Einstein equation
We discuss solutions of Vlasov-Einstein equation for collisionless dark matter particles in the context of a flat Friedmann universe. We show that, after decoupling from the primordial plasma, the dark matter phase-space density indicator Q = ρ/(σ1D2)3/2 remains constant during the expansion of the universe, prior to structure formation. This well known result is valid for non-relativistic particles and is not ``observer dependent'' as in solutions derived from the Vlasov-Poisson system. In the linear regime, the inclusion of velocity dispersion effects permits to define a physical Jeans length for collisionless matter as function of the primordial phase-space density indicator: λJ = (5π/G)1/2Q−1/3ρdm−1/6. The comoving Jeans wavenumber at matter-radiation equality is smaller by a factor of 2-3 than the comoving wavenumber due to free-streaming, contributing to the cut-off of the density fluctuation power spectrum at the lowest scales. We discuss the physical differences between these two scales. For dark matter particles of mass equal to 200 GeV, the derived Jeans mass is 4.3 × 10−6M⊙.
118986738
Conflict between symmetries: a classical example
We have found a (classical) competition between duality and gauge symmetries when trying to obtain an explicit dual to the non-nonabelian version of the self-dual model proposed by Townsend, Pilch and van Nieuwenhuizen\cite{TPvN} (NASD) either through gauge embedding procedures or gauge invariant master approach. We found that the theory dual to NASD {\it is not} the Yang-Mills-Chern-Simons model. We then proved that a model gauge invariant and dual equivalent to NASD cannot be achieved because of this conflict. Other nonabelian self-dual formulation proposed in \cite{KLRvN} was studied and its dual obtained. We discuss the consequences of the dual equivalence found here in the context of 3D non-abelian bosonization.
119554025
3D and 4D noncommutative electromagnetic duality and the role of the slowly varying fields limit
We study classical noncommutative (NC) electromagnetic duality in both 3D and 4D space-times through the Seiberg-Witten (SW) map to all orders in θ . We evaluate the role of space-time dimensions, of the gauge coupling constant g 2 inversion, of the slowly varying fields (SVF) limit and of the rule θ duality −→ ˜ θ = g 2 ⋆ θ (where ⋆ is the Hodge duality operator), which was originally found in the 4D space-time. Among our results, a new scalar picture for NC electromagnetism to second order in θ is established, a formula which simplifies considerably the application of the SW map in 3D is presented and we show that the SVF limit has a crucial role in this duality starting from the third order in θ for any dimension: outside this limit the symmetry between θ and ˜ θ is lost.
118406707
Evolution of Anisotropies in Eddington-Born-Infeld Cosmology
Recently a Born-Infeld action for dark energy and dark matter that uses additional affine connections was proposed. At the background level, it was shown that the new proposal can mimic the standard cosmological evolution. In Bianchi cosmologies, contrary to the scalar field approach (e.g., Chaplygin gas), the new approach leads to anisotropic pressure, raising the issues of stability of the isotropic solution under anisotropic perturbations and, being stable, how the anisotropies evolve. In this work, the Eddington-Born-Infeld proposal is extended to a Bianchi type I scenario and residual post-inflationary anisotropies are shown to decay in time. Moreover, it is shown that the shears decay following a damped oscillatory pattern, instead of the standard exponential-like decay. Allowing for some fine-tuning on the initial conditions, standard theoretical bounds on the shears can be avoided.
53389884
Monitoring the efficiency of user jobs
Instrumentation of jobs throughout its life-cycle is not obvious, as they are quite independent after being submitted, crossing multiple environments and locations until landing on a worker node. In order to measure correctly the resources used at each step, and to compare it with the view from a Fabric Infrastructure, a solution is proposed using Messaging System for the Grids (MSG) for integrating information coming from different sources.