Antioscillons

This proceeding is based on a talk I gave at the 13th Marcel Grossmann Meeting in Stockholm Sweden, on the role of topology on bubble collisions.Comment: 4 pgs., to appear in Proceedings of the 13th Marcel Grossmann Meeting, Stockholm, Swede

Cosmological Implications of the String Theory Landscape

Progress in string theory has resulted in a whole landscape of vacua solutions.In this talk I describe a proposal for exploring the cosmological implications of the landscape, based on the dynamics of the wavefunction of the universe propagating on it. The landscape is taken as the phase space of the initial conditions since every of its vacua can potentially give rise to a universe. A superselection rule on the landscape phase space emerges when we include the backreaction of massive long wavelengths and the quantum dynamics of gravitational and matter degrees of freedom. The quantum dynamics of the system selects only high energy patches which survive the collapse induced by the gravitational instability of massive perturbations.Comment: 7 pages, Talk given at 'The Dark Side of the Universe 2006', Madrid. To be published by AI

Back-reaction of the Hawking radiation flux on a gravitationally collapsing star II

A star collapsing gravitationally into a black hole emits a flux of radiation, known as Hawking radiation. When the initial state of a quantum field on the background of the star, is placed in the Unruh vacuum in the far past, then in the exterior Hawking radiation corresponds to a flux of positive energy radiation travelling outwards from near the surface to future infinity. Based on pair creation, the evaporation of the collapsing star can be equivalently described by the absorption of an ingoing negative energy flux of radiation travelling towards the center of the star. Here, we are interested in the evolution of the star during its collapse. Thus we include the backreaction of the negative energy Hawking flux in the interior geometry of the collapsing star when writing the full 4-dimensional Einstein and hydrodynamic equations. Hawking radiation emitted before the star passes through its Schwarzschild radius slows down and reverses the collapse of the star. The star evaporates without forming an horizon or a singularity. This study provides a more realistic investigation than the one first presented in [1], since the backreaction of Hawking radiation flux on the collapsing star is studied in the case when the initial state of the field is in Unruh's vacuum.Comment: 9 pages, 4 figures, a typo corrected, more detailed explanations added for clarit

Entropy of the Information Retrieved from Black Holes

The retrieval of black hole information was recently presented in two interesting proposals in the 'Hawking Radiation' conference: a revised version by G. 't Hooft of a proposal he initially suggested 20 years ago and, a new proposal by S. Hawking. Both proposals address the problem of black hole information loss at the classical level and derive an expression for the scattering matrix. The former uses gravitation back reaction of incoming particles that imprints its information on the outgoing modes. The latter uses supertranslation symmetry of horizons to relate a phase delay of the outgoing wave packet compared to their incoming wave partners. The difficulty in both proposals is that the entropy obtained from them appears to be infinite. By including quantum effects into the Hawking and 't Hooft's proposals, I show that a subtlety arising from the inescapable measurement process, the Quantum Zeno Effect, not only tames divergences but it actually recovers the correct $1/4$ of the area Bekenstein-Hawking entropy law of black holes.Comment: 9 pgs., 1 figur

Do We Have Evidence for New Physics in the Sky?

Predicting signatures of string theory on cosmological observables is not sufficient. Often the observable effects string theory may impact upon the cosmological arena may equally be predicted by features of inflationary physics. The question: what observable signatures are unique to new physics, is thus of crucial importance for claiming evidence for the theory. Here we discuss recent progress in addressing the above question. The evidence relies on identifying discrepancies between the source terms that give rise to large scale structure (LSS) and CMB, by cross-correlating the weak lensing potential maps LSS with the CMB spectra.Comment: Invited Review to appear in MPLA. Based on work done with Steen Hannesta

Birth of the Universe from the Multiverse, MG13

This proceeding is based on a talk I gave at the 13th Marcel Grossmann Meeting in Stockholm Sweden.Comment: to appear in Proceedings of the 13th Marcel Grossmann Meeting, Stockholm Swede

Wavefunction of the Universe on the Landscape

This talk reviews the proposal for dynamically selecting the most probable wavefunction of the universe propagating on the landscape of string theory, by means of quantum cosmology. Talk given at 'Albert Einstein Century International Conference'-UNESCO, Paris July 18-22 2005.Comment: 7 pgs., 1 fi

Backreaction of Hawking Radiation on a Gravitationally Collapsing Star I: Black Holes?

Particle creation leading to Hawking radiation is produced by the changing gravitational field of the collapsing star. The two main initial conditions in the far past placed on the quantum field from which particles arise, are the Hartle Hawking vacuum and the Unruh vacuum. The former leads to a time symmetric thermal bath of radiation, while the latter to a flux of radiation coming out of the collapsing star. The energy of Hawking radiation in the interior of the collapsing star is negative and equal in magnitude to its value at future infinity. This work investigates the backreaction of Hawking radiation on the interior of a gravitationally collapsing star, in a Hartle-Hawking initial vacuum. It shows that due to the negative energy Hawking radiation in the interior, the collapse of the star stops at a finite radius, before the singularity and the event horizon of a black hole have a chance to form. That is, the star bounces instead of collapsing to a black hole. A trapped surface near the last stage of the star's collapse to its minimum size may still exist temporarily. Its formation depends on the details of collapse. Results for the case of Hawking flux of radiation with the Unruh initial state, will be given in a companion paper II.Comment: 8 pg