The stress tensor of a quantized field undergoes fluctuations which can in principle give rise to observable effects. These effects include the Brownian motion of test particles moving in the fluctuating gravitational field generated by the stress tensor fluctuations. On a flat background, the fluctuations are strongly anticorrelated so as to cause the net effect on a test particle to average to zero. It will be argued that this cancellation need not occur on curved backgrounds. During an inflationary phase in the universe, for example, the effects of the stress tensor fluctuations can grow and have the potential to lead to a non-Gaussian component in the subsequent density perturbations.
This talk consists of two parts. The first part establishes certain astrophysical bounds on the smoothness of classical spacetime. The second part discusses theoretical implications for the possible structure of a hypothetical quantum spacetime foam.
This model is an effective field theory including dimension five operators to describe the phenomenology of Lorentz invariance violation produced by a preferred reference frame. Theories incorporating higher time derivatives suffer from well known quantization problems, among which one finds Hamiltonians not bounded from below together with an increase in the number of degrees of freedom. The point of view taken here is that the Lorentz violating part of the action is to be considered as a perturbation over the dynamics described by the standard lowest order theory. In order to cope with the problems mentioned above, it is necessary to deal with a modified perturbation theory which is well described in the literature. We apply such methods to this specific model and calculate the corresponding one-loop self-energies, having an eye on the renormalization properties of the effective model which are connected to the fine?tunning problems reported previously in this and related models.
In this work I consider the effects of assuming noncommutaivity among the variables of the mini superspace and also the deformation of the Poisson structure in the framework of the Scalar Tensor Theories of gravity.
The application of Statistical Mechanics to the phenomenology of some quantum gravity models is analyzed. The possibility of finding astrophysical systems which could provide us with bounds to some parameters, emerging in quantum gravity theories, is studied. The consequences, at the bulk level, of these models is also a topic of the talk.
I present the fundamentals of geometrothermodynamics, an approach to study the properties of thermodynamic systems in terms of differential geometric concepts. It is based, on the one hand, upon the well-known contact structure of the thermodynamic phase space and, on the other hand, on the metric structure of the space of thermodynamic equilibrium states. In order to make these two structures compatible we introduce a Legendre invariant set of metrics in the phase space, and demand that their pullback generates metrics on the space of equilibrium states. The formalism is applied to several thermodynamic systems to show a relationship between curvature singularities and phase transitions. The thermodynamics of black holes is analyzed and compared with previous works.
Last update: 29 de mayo de 2007