522 research outputs found
Smooth horizons and quantum ripples
Black Holes are unique objects which allow for meaningful theoretical studies
of strong gravity and even quantum gravity effects. An infalling and a distant
observer would have very different views on the structure of the world.
However, a careful analysis has shown that it entails no genuine contradictions
for physics, and the paradigm of observer complementarity has been coined.
Recently this picture was put into doubt. In particular, it was argued that in
old Black Holes a firewall must form in order to protect the basic principles
of quantum mechanics. This AMPS paradox has already been discussed in a vast
number of papers with different attitudes and conclusions. Here we want to
argue that a possible source of confusion is neglection of quantum gravity
effects. Contrary to widespread perception, it does not necessarily mean that
effective field theory is inapplicable in rather smooth neighbourhoods of large
Black Hole horizons. The real offender might be an attempt to consistently use
it over the huge distances from the near-horizon zone of old Black Holes to the
early radiation. We give simple estimates to support this viewpoint and show
how the Page time and (somewhat more speculative) scrambling time do appear.Comment: 4 pages; minor changes, a few references adde
On non-perturbative analysis of massive and bimetric gravity
This is my contribution to Proceedings of II Russian-Spanish Congress on
Particle and Nuclear Physics at all Scales and Cosmology, Saint Petersburg,
Russia, October 1 - 4, 2013. We give a brief overview of the ghost-free massive
and bimetric gravity emphasising its non-perturbative aspects and ADM approach
to calculating the precise number of degrees of freedom. To the standard
material, we add some thoughts concerning existence and uniqueness problems of
matrix square roots in non-perturbative metric formulations of massive gravity.Comment: 5 pages; prepared for the Proceedings of II Russian-Spanish Congress
on Particle and Nuclear Physics at all Scales and Cosmolog
Beyond dRGT as Mimetic Massive
An interesting proposal has recently been made to extend massive gravity
models beyond dRGT by a disformal transformation of the metric. In this Letter
we want to note that it can be viewed as a mimetic extension of dRGT gravity
which enormously simplifies the Hamiltonian analysis. In particular, pure
gravity sector is equivalent to the usual dRGT gravity coupled to a constrained
scalar field. And we also give some comments about possible matter couplings.Comment: 7 pages; minor changes; final versio
Vector Field and Inflation
We have investigated if the vector field can give rise to an accelerating
phase in the early universe. We consider a timelike vector field with a general
quadratic kinetic term in order to preserve an isotropic background spacetime.
The vector field potential is required to satisfy the three minimal conditions
for successful inflation: i) , ii) and iii) the slow-roll
conditions. As an example, we consider the massive vector potential and small
field type potential as like in scalar driven inflation.Comment: 1+7pages, 3figures, To appear in the Proceedings of the CospA 2008,
Kore
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