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Semiclassical dynamics of horizons in spherically symmetric collapse
Publication . Tavakoli, Yaser; Marto, João; Dapor, Andrea
In this work, we consider a semiclassical description of the spherically
symmetric gravitational collapse with a massless scalar field. In particular,
we employ an effective scenario provided by holonomy corrections from loop
quantum gravity, to the homogeneous interior spacetime. The singularity that
would arise at the final stage of the corresponding classical collapse, is
resolved in this context and is replaced by a bounce. Our main purpose is to
investigate the evolution of trapped surfaces during this semiclassical
collapse. Within this setting, we obtain a threshold radius for the collapsing
shells in order to have horizons formation. In addition, we study the final
state of the collapse by employing a suitable matching at the boundary shell
from which quantum gravity effects are carried to the exterior geometry.
Improved dynamics and gravitational collapse of tachyon field coupled with a barotropic fluid
Publication . Marto, João; Tavakoli, Yaser; Moniz, Paulo
We consider a spherically symmetric gravitational collapse of a tachyon field
with an inverse square potential, which is coupled with a barotropic fluid. By
employing an holonomy correction imported from loop quantum cosmology, we
analyse the dynamics of the collapse within a semiclassical description. Using
a dynamical system approach, we find that the stable fixed points given by the
standard general relativistic setting turn into saddle points in the present
context. This provides a new dynamics in contrast to the black hole and naked
singularities solutions appearing in the classical model. Our results suggest
that classical singularities can be avoided by quantum gravity effects and are
replaced by a bounce. By a thorough numerical studies we show that, depending
on the barotropic parameter $\gamma$, there exists a class of solutions
corresponding to either a fluid or a tachyon dominated regimes. Furthermore,
for the case $\gamma \sim 1$, we find an interesting tracking behaviour between
the tachyon and the fluid leading to a dust-like collapse. In addition, we show
that, there exists a threshold scale which determines when an outward energy
flux emerges, as a non-singular black hole is forming, at the corresponding
collapse final stages.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
COMPETE
Funding Award Number
CERN/FP/123609/2011