Field Configurations and their Instability Induced by Higher Dimensions of Spacetime: An Example

We use the model of L. Randall et al to investigate the stability of allowed quantum field configurations. Firstly, we find that due to the topology of this 5 dimensional model, there are 2 possible configurations of the scalar field, untwisted and twisted. Secondly, when allowed to interact the untwisted field is shown to be unstable even if it is at the true vacuum groundstate as a result of one-loop corrections that arise from coupling with the twisted field. The twisted field can make the two 3-branes (that are otherwise identical in their properties and geometry) distinguishable. That is due to the antiperiodicity of the twisted fields, when rotating with $\pi$ to go from one 3-brane to the other. This toy model is simple enough to use to illustrate a point that can be important for the general case of any high dimension model, namely: higher dimensions, besides many other effects can also induce more than one field configuration and that can have consequences (e.g. instabilities) even after reducing the problem to 4 dimensions

Why the Universe Started from a Low Entropy State

We show that the inclusion of backreaction of massive long wavelengths imposes dynamical constraints on the allowed phase space of initial conditions for inflation, which results in a superselection rule for the initial conditions. Only high energy inflation is stable against collapse due to the gravitational instability of massive perturbations. We present arguments to the effect that the initial conditions problem {\it cannot} be meaningfully addressed by thermostatistics as far as the gravitational degrees of freedom are concerned. Rather, the choice of the initial conditions for the universe in the phase space and the emergence of an arrow of time have to be treated as a dynamic selection.Comment: 12 pages, 2 figs. Final version; agrees with accepted version in Phys. Rev.

Kinematical solution of the UHE-cosmic-ray puzzle without a preferred class of inertial observers

Among the possible explanations for the puzzling observations of cosmic rays above the GZK cutoff there is growing interest in the ones that represent kinematical solutions, based either on general formulations of particle physics with small violations of Lorentz symmetry or on a quantum-gravity-motivated scheme for the breakup of Lorentz symmetry. An unappealing aspect of these cosmic-ray-puzzle solutions is that they require the existence of a preferred class of inertial observers. Here I propose a new kinematical solution of the cosmic-ray puzzle, which does not require the existence of a preferred class of inertial observers. My proposal is a new example of a type of relativistic theories, the so-called "doubly-special-relativity" theories, which have already been studied extensively over the last two years. The core ingredient of the proposal is a deformation of Lorentz transformations in which also the Planck scale $E_p$ (in addition to the speed-of-light scale $c$) is described as an invariant. Just like the introduction of the invariant $c$ requires a deformation of the Galileian transformations into the Lorentz transformations, the introduction of the invariant $E_p$ requires a deformation of the Lorentz transformations, but there is no special class of inertial observers. The Pierre Auger Observatory and the GLAST space telescope should play a key role in future developments of these investigations. I also emphasize that the doubly-special-relativity theory here proposed, besides being the first one to provide a solution for the cosmic-ray puzzle, is also the first one in which a natural description of macroscopic bodies is achieved, and may find applications in the context of a recently-proposed dark-energy scenario.Comment: LaTex (revtex), 9 page