234 research outputs found

### Hartle-Hawking wave function and large-scale power suppression of CMB

In this presentation, we first describe the Hartle-Hawking wave function in
the Euclidean path integral approach. After we introduce perturbations to the
background instanton solution, following the formalism developed by
Halliwell-Hawking and Laflamme, one can obtain the scale-invariant power
spectrum for small-scales. We further emphasize that the Hartle-Hawking wave
function can explain the large-scale power suppression by choosing suitable
potential parameters, where this will be a possible window to confirm or
falsify models of quantum cosmology. Finally, we further comment on possible
future applications, e.g., Euclidean wormholes, which can result in distinct
signatures to the power spectrum.Comment: 5 pages, 1 figure; Proceedings of the 13th International Conference
on Gravitation, Astrophysics, and Cosmology & the 15th Italian-Korean
Symposium on Relativistic Astrophysics: A Joint Meeting. Talk on July 7,
2017, Seoul, Republic of Kore

### Semi-classical black holes with large N re-scaling and information loss problem

We consider semi-classical black holes and related re-scalings with N
massless fields. For a given semi-classical solution of an N = 1 universe, we
can find other solution of a large N universe by the re-scaling. After the
re-scaling, any curvature quantity takes a sufficiently small value without
changing its causal structure. Via the re-scaling, we argue that black hole
complementarity for semi-classical black holes cannot provide a fundamental
resolution of the information loss problem, and the violation of black hole
complementarity requires sufficiently reasonable amounts of N. Such N might be
realized from some string inspired models. Finally, we claim that any
fundamental resolution of the information loss problem should resolve the
problem of the singularity.Comment: 33 pages, 5 figure

### Fuzzy Euclidean wormholes in anti-de Sitter space

This paper is devoted to an investigation of Euclidean wormholes made by
fuzzy instantons. We investigate the Euclidean path integral in anti-de Sitter
space. In Einstein gravity, we introduce a scalar field with a potential.
Because of the analyticity, there is a contribution of complex-valued
instantons, so-called fuzzy instantons. If we have a massless scalar field,
then we obtain Euclidean wormholes, where the probabilities become smaller and
smaller as the size of the throat becomes larger and larger. If we introduce a
non-trivial potential, then in order to obtain a non-zero tunneling rate, we
need to tune the shape of the potential. With the $O(4)$ symmetry, after the
analytic continuation to the Lorentzian time, the wormhole throat should expand
to infinity. However, by adding mass, one may obtain an instant wormhole that
should eventually collapse to the event horizon. The existence of Euclidean
wormholes is related to the stability or unitarity issues of anti-de Sitter
space. We are not conclusive yet, but we carefully comment on these physical
problems.Comment: 20 pages, 9 figure

### Charged black holes in string-inspired gravity: I. Causal structures and responses of the Brans-Dicke field

We investigate gravitational collapses of charged black holes in
string-inspired gravity models, including dilaton gravity and braneworld model,
as well as f(R) gravity and the ghost limit. If we turn on gauge coupling, the
causal structures and the responses of the Brans-Dicke field depend on the
coupling between the charged matter and the Brans-Dicke field. For Type IIA
inspired models, a Cauchy horizon exists, while there is no Cauchy horizon for
Type I or Heterotic inspired models. For Type IIA inspired models, the no-hair
theorem is satisfied asymptotically, while it is biased to the weak coupling
limit for Type I or Heterotic inspired models. Apart from string theory, we
find that in the ghost limit, a gravitational collapse can induce inflation by
itself and create one-way traversable wormholes without the need of other
special initial conditions.Comment: 45 pages, 22 figure

### Tunneling from the past horizon

We investigate a tunneling and emission process of a thin-shell from a
Schwarzschild black hole, where the shell was initially located beyond the
Einstein-Rosen bridge and finally appears at the right side of the Penrose
diagram. In order to obtain such a solution, we should assume that the areal
radius of the black hole horizon increases after the tunneling. Hence, there is
a parameter range such that the tunneling rate is exponentially enhanced,
rather than suppressed. We may have two interpretations regarding this. First,
such a tunneling process from the past horizon is improbable by physical
reasons; second, such a tunneling is possible in principle, but in order to
obtain a stable Einstein-Rosen bridge, one needs to restrict the parameter
spaces. If such a process is allowed, this can be a non-perturbative
contribution to Einstein-Rosen bridges as well as eternal black holes.Comment: 13 pages, 6 figure

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