Showing papers by "Joaquim Gomis published in 2007"

General very special relativity is Finsler geometry

Abstract: We ask whether Cohen and Glashow's very special relativity model for Lorentz violation might be modified, perhaps by quantum corrections, possibly producing a curved space-time with a cosmological constant. We show that its symmetry group ISIM(2) does admit a 2-parameter family of continuous deformations, but none of these give rise to noncommutative translations analogous to those of the de Sitter deformation of the Poincar\'e group: space-time remains flat. Only a 1-parameter family ${\mathrm{DISIM}}_{b}(2)$ of deformations of SIM(2) is physically acceptable. Since this could arise through quantum corrections, its implications for tests of Lorentz violations via the Cohen-Glashow proposal should be taken into account. The Lorentz-violating point-particle action invariant under ${\mathrm{DISIM}}_{b}(2)$ is of Finsler type, for which the line element is homogeneous of degree 1 in displacements, but anisotropic. We derive ${\mathrm{DISIM}}_{b}(2)$-invariant wave equations for particles of spins 0, $\frac{1}{2}$, and 1. The experimental bound, $|b|l{10}^{\ensuremath{-}26}$, raises the question ``Why is the dimensionless constant $b$ so small in very special relativity?''

Kac-Moody Spectrum of (Half-)Maximal Supergravities

Abstract: We establish the correspondence between, on one side, the possible gaugings and massive deformations of half-maximal supergravity coupled to vector multiplets and, on the other side, certain generators of the associated very extended Kac-Moody algebras. The difference between generators associated to gaugings and to massive deformations is pointed out. Furthermore, we argue that another set of generators are related to the so-called quadratic constraints of the embedding tensor. Special emphasis is placed on a truncation of the Kac-Moody algebra that is related to the bosonic gauge transformations of supergravity. We give a separate discussion of this truncation when non-zero deformations are present. The new insights are also illustrated in the context of maximal supergravity.

Non-propagating degrees of freedom in supergravity and very extended G_2

Abstract: Recently a correspondence between non-propagating degrees of freedom in maximal supergravity and the very extended algebra E_11 has been found. We perform a similar analysis for a supergravity theory with eight supercharges and very extended G_2. In particular, in the context of d=5 minimal supergravity, we study whether supersymmetry can be realised on higher-rank tensors with no propagating degrees of freedom. We find that in this case the very extended algebra fails to capture these possibilities.

Non-propagating degrees of freedom in supergravity and very extended G2

Abstract: Recently a correspondence between non-propagating degrees of freedom in maximal supergravity and the very extended algebra E11 has been found. We perform a similar analysis for a supergravity theory with eight supercharges and very extended G2. In particular, in the context of d = 5 minimal supergravity, we study whether supersymmetry can be realised on higher-rank tensors with no propagating degrees of freedom. We find that in this case the very extended algebra fails to capture these possibilities.

(2+1)D Exotic Newton-Hooke Symmetry, Duality and Projective Phase

Abstract: A particle system with a (2+1)D exotic Newton-Hooke symmetry is constructed by the method of nonlinear realization. It has three essentially different phases depending on the values of the two central charges. The subcritical and supercritical phases (describing 2D isotropic ordinary and exotic oscillators) are separated by the critical phase (one-mode oscillator), and are related by a duality transformation. In the flat limit, the system transforms into a free Galilean exotic particle on the noncommutative plane. The wave equations carrying projective representations of the exotic Newton-Hooke symmetry are constructed.

Exotic nonrelativistic string

Abstract: We construct a classical nonrelativistic string model in 3+1 dimensions. The model contains a spurion tensor field that is responsible for the noncommutative structure of the model. Under double-dimensional reduction the model reduces to the exotic nonrelativistic particle in 2+1 dimensions.

Non-linear realizations, super branes and kappa symmetry

Abstract: Non-linearrealizationsplayedanimportantroleinparticlephysics.Ithasfirstbeendevelopedinconstructinglagrangianswithchiralsymmetries.Althoughtheoriginalpapers[1]ofCallan,Coleman,WessandZumino,andmuchofthesubsequentdevelopment,wereformulatedintermsofcosetrepresentativesitismoreelegantto reformulate the theory of non-linear realizations in terms of the group elements of

Non-Relativistic Strings in Expanding Spacetime

Abstract: We obtain a non-relativistic diffeomorphism invariant string action as a special limit of the Nambu-Goto action in an FLRW background. We use this action to study non-relativistic string dynamics in an expanding universe and construct an analytic model describing the macroscopic properties of non-relativistic string networks. The non-relativistic constraint equations allow arbitrarily small string velocities and thus a `frustrated' equation of state for non-interacting strings can be obtained without the need of a velocity damping mechanism. Assuming that colliding string segments reconnect by exchange of partners, non-relativistic string networks exhibit scaling behaviour, but with enhanced energy densities due to the reduced average string velocity. Non-relativistic string networks can be relevant in several contexts in condensed matter physics and cosmology.