H. Vucetich

Lorentz Invariance and Quantum Gravity: An Additional Fine-Tuning Problem?

Trying to combine standard quantum field theories with gravity leads to a breakdown of the usual structure of space time at around the Planck length, 1.6x10(-35) m, with possible violations of Lorentz invariance. Calculations of preferred-frame effects in quantum gravity have further motivated high precision searches for Lorentz violation. Here, we explain that combining known elementary particle interactions with a Planck-scale preferred frame gives rise to Lorentz violation at the percent level, some 20 orders of magnitude higher than earlier estimates, unless the bare parameters of the theory are unnaturally strongly fine tuned. Therefore an important task is not just the improvement of the precision of searches for violations of Lorentz invariance, but also the search for theoretical mechanisms for automatically preserving Lorentz invariance.

Early universe test of nonextensive statistics

Within an early Universe scenario, nonextensive thermostatistics is investigated on the basis of data concerning primordial helium abundance. We obtain first order corrections to the energy densities and weak interaction rates, and use them to compute the deviation in the primordial helium abundance. After comparing with observational results, we get

Observational bounds on quantum gravity signals using existing data.

|q\ensuremath{-}1|l2.08\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}

Gravitational instabilities in Kerr spacetimes

as a bound for the nonextensive parameter.

Strange matter, detonations and supernovae

We consider a new set of effects arising from the quantum gravity corrections to the propagation of fields, associated with fluctuations of the spacetime geometry. Using already existing experimental data, we can put bounds on these effects that are more stringent by several orders of magnitude than those expected to be obtained in astrophysical observations. In fact these results can be already interpreted as questioning the whole scenario of linear (in

Primordial Nucleosynthesis with Varying Fundamental Constants: A Semianalytical Approach

l_P

Testing Theories That Predict Time Variation of Fundamental Constants

) corrections to the dispersion relations for free fields in Lorentz violating theories.

Early universe constraints on time variation of fundamental constants

In this paper we consider the possible existence of unstable axisymmetric modes in Kerr spacetimes, resulting from exponentially growing solutions of the Teukolsky equation. We describe a transformation that casts the radial equation that results upon separation of variables in the Teukolsky equation, in the form of a Schrodinger equation, and combine the properties of the solutions of this equations with some recent results on the asymptotic behaviour of spin weighted spheroidal harmonics to prove the existence of an infinite family of unstable modes. Thus we prove that the stationary region beyond a Kerr black hole inner horizon is unstable under gravitational linear perturbations. We also prove that Kerr spacetime with angular momentum larger than its square mass, which has a naked singularity, is unstable.

Cosmology, oscillating physics, and oscillating biology.

We present a possible scenario driven by QCD deconfinement in a high density nuclear matter medium. Some expected consequences for type II supernovae explosions are also given, particularly, the output energy that might be enough to account for the observed events.

Bounds on stringy quantum gravity from low energy existing data

Using the semianalytic method proposed by Esmailzadeh and coworkers we calculate the abundances of the light elements produced during primordial nucleosynthesis assuming that the gauge coupling constants of the fundamental interactions may vary. We analyze the dependence of the nucleon masses, nuclear binding energies, and cross sections involved in the calculation of the abundances with the fundamental constants assuming the chiral limit of QCD. We obtain the abundances of light elements as a function of the fundamental constants. Finally, using the observational data of D, 3He, 4He, and 7Li, we estimate constraints on the variation of the fundamental constants between the time of primordial nucleosynthesis and the present. All observational abundances and the WMAP estimate of the baryon density can be fitted to the theoretical predictions with varying coupling constants. The possible systematic errors in the observational data preclude stronger conclusions.