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In this paper we consider photon-photon scattering due to self-induced gravitational perturbations on a Minkowski background. We focus on four-wave interaction between plane waves with weakly space and time dependent amplitudes, since…

Motivated by the severity of the bounds on Lorentz violation in the presence of ordinary gravity, we study frameworks in which Lorentz violation does not affect the spacetime geometry. We show that there are at least two inequivalent…

We study cosmological implications of a Lorentz invariance violating DGP-inspired braneworld scenario. A minimally coupled scalar field and a single, fixed-norm, Lorentz-violating timelike vector field within an interactive picture provide…

In this work we continue the systematic study of observable effects emerging from modified dispersion relations. We study the motion of test particles subject to a general first order modification of the general relativistic dispersion…

A very small dispersion in the speed of light may be observable in Fermi time- and energy-tagged data on variable sources, such as gamma-ray bursts (GRB) and active galactic nuclei (AGN). We describe a method to compute the size of this…

We consider the effect on the propagation of light of inhomogeneities with sizes of order 10 Mpc or larger. The Universe is approximated through a variation of the Swiss-cheese model. The spherical inhomogeneities are void-like, with…

Lorentz Invariance Violation (LIV) may be a good observational window on Quantum Gravity physics. Within last few years, all major Gamma-ray experiments have published results from the search for LIV with variable astrophysical sources:…

Several recent studies have concerned the faith of classical symmetries in quantum space-time. In particular, it appears likely that quantum (discretized, noncommutative,...) versions of Minkowski space-time would not enjoy the classical…

Superluminal particles are not excluded by particle physics. The apparent Lorentz invariance of the laws of physics does not imply that space-time is indeed minkowskian. Matter made of solutions of Lorentz-invariant equations would feel a…

Within the setting of a recently proposed model of quantum fields on noncommutative Minkowski spacetime, the consequences of the consistent application of the proper, untwisted Poincare group as the symmetry group are investigated. The…

Supersymmetry and Lorentz invariance are closely related as both are spacetime symmetries. Terms can be added to Lagrangians that explicitly break either supersymmetry or Lorentz invariance. It is possible to include terms which violate…

This paper presents an attempt to come to a natural field model of individual photons considered as finite entities and propagating along some distinguished direction in space in a consistent translational-rotational manner. The starting…

The parity violation at the level of weak interactions and other similar discrete symmetries breaking show that the invariance of laws under the full group of Lorentz transformations can not be taken granted. We examine the principle of…

The hypothesis that the Lorentz transformations may be modified at Planck scale energies is further explored. We present a general formalism for theories which preserve the relativity of inertial frames with a non-linear action of the…

We extend previous analyses of the violation of Lorentz invariance induced in a non-critical string model of quantum space-time foam, discussing the propagation of low-energy particles through a distribution of non-relativistic…

In a recent paper we demonstrated how the simplest model for varying alpha may be interpreted as the effect of a dielectric material, generalized to be consistent with Lorentz invariance. Unlike normal dielectrics, such a medium cannot…

The quantum lightcone fluctuations in flat spacetimes with compactified spatial dimensions or with boundaries are examined. The discussion is based upon a model in which the source of the underlying metric fluctuations is taken to be…

Astroparticle physics has recently reached a new status of precision due to the construction of new observatories, operating innovative technologies and the detection of large numbers of events and sources. The precise measurements of…

The difference between Lorentz invariance and Lorentz covariance is discussed in detail. A covariant formalism is developed for the internal space-time symmetry of extended particles, especially in connection with the insightful…

We consider the phenomenology of a dimension-four operator that violates electromagnetic gauge invariance. Its magnitude is severely constrained by the lack of scattering of very low energy electromagnetic radiation off of the Cosmic…