362 research outputs found
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
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 of the area Bekenstein-Hawking entropy law of black holes.Comment: 9 pgs., 1 figur
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
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
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
- …