996 research outputs found
Spherically symmetric trapping horizons, the Misner-Sharp mass and black hole evaporation
Understood in terms of pure states evolving into mixed states, the
possibility of information loss in black holes is closely related to the global
causal structure of spacetime, as is the existence of event horizons. However,
black holes need not be defined by event horizons, and in fact we argue that in
order to have a fully unitary evolution for black holes, they should be defined
in terms of something else, such as a trapping horizon. The Misner-Sharp mass
in spherical symmetry shows very simply how trapping horizons can give rise to
black hole thermodynamics, Hawking radiation and singularities. We show how the
Misner-Sharp mass can also be used to give insights into the process of
collapse and evaporation of locally defined black holes.Comment: 9 pages, 10 figure
Tunneling decay of false vortices
We consider the decay of vortices trapped in the false vacuum of a theory of
scalar electrodynamics in 2+1 dimensions. The potential is inspired by models
with intermediate symmetry breaking to a metastable vacuum that completely
breaks a U(1) symmetry, while in the true vacuum the symmetry is unbroken. The
false vacuum is unstable through the formation of true vacuum bubbles; however,
the rate of decay can be extremely long. On the other hand, the false vacuum
can contain metastable vortex solutions. These vortices contain the true vacuum
inside in addition to a unit of magnetic flux and the appropriate topologically
nontrivial false vacuum outside. We numerically establish the existence of
vortex solutions which are classically stable; however, they can decay via
tunneling. In general terms, they tunnel to a configuration which is a large,
thin-walled vortex configuration that is now classically unstable to the
expansion of its radius. We compute an estimate for the tunneling amplitude in
the semi-classical approximation. We believe our analysis would be relevant to
superconducting thin films or superfluids.Comment: 27 pages, 9 figure
The causal structure of dynamical charged black holes
We study the causal structure of dynamical charged black holes, with a
sufficient number of massless fields, using numerical simulations. Neglecting
Hawking radiation, the inner horizon is a null Cauchy horizon and a curvature
singularity due to mass inflation. When we include Hawking radiation, the inner
horizon becomes space-like and is separated from the Cauchy horizon, which is
parallel to the out-going null direction. Since a charged black hole must
eventually transit to a neutral black hole, we studied the neutralization of
the black hole and observed that the inner horizon evolves into a space-like
singularity, generating a Cauchy horizon which is parallel to the in-going null
direction. Since the mass function is finite around the inner horizon, the
inner horizon is regular and penetrable in a general relativistic sense.
However, since the curvature functions become trans-Planckian, we cannot
saymore about the region beyond the inner horizon, and it is natural to say
that there is a 'physical' space-like singularity. However, if we assume an
exponentially large number of massless scalar fields, our results can be
extended beyond the inner horizon. In this case, strong cosmic censorship and
black hole complementarity can be violated.Comment: 23 pages, 23 figure
The Battle of the Bulge: Decay of the Thin, False Cosmic String
We consider the decay of cosmic strings that are trapped in the false vacuum
in a theory of scalar electrodynamics in 3+1 dimensions. We restrict our
analysis to the case of thin-walled cosmic strings which occur when large
magnetic flux trapped inside the string. Thus the string looks like a tube of
fixed radius, at which it is classically stable. The core of the string
contains magnetic flux in the true vacuum, while outside the string, separated
by a thin wall, is the false vacuum. The string decays by tunnelling to a
configuration which is represented by a bulge, where the region of true vacuum
within, is ostensibly enlarged. The bulge can be described as the meeting, of a
kink soliton anti-soliton pair, along the length of the string. It can be
described as a bulge appearing in the initial string, starting from the string
of small, classically stable radius, expanding to a fat string of large,
classically unstable (to expansion) radius and then returning back to the
string of small radius along its length. This configuration is the bounce point
of a corresponding O(2) symmetric instanton, which we can determine
numerically. Once the bulge appears it explodes in real time. The kink soliton
anti-soliton pair recede from each other along the length of the string with a
velocity that quickly approaches the speed of light, leaving behind a fat tube.
At the same time the radius of the fat tube that is being formed, expands
(transversely) as it is no longer classically stable, converting false vacuum
to the true vacuum with ever diluting magnetic field within. The rate of this
expansion is determined by the energy difference between the true vacuum and
the false vacuum. Our analysis could be applied to a network, of cosmic strings
formed in the very early universe or vortex lines in a superheated
superconductor.Comment: 13 pages, 4 figure
Dynamics of false vacuum bubbles: beyond the thin shell approximation
We numerically study the dynamics of false vacuum bubbles which are inside an
almost flat background; we assumed spherical symmetry and the size of the
bubble is smaller than the size of the background horizon. According to the
thin shell approximation and the null energy condition, if the bubble is
outside of a Schwarzschild black hole, unless we assume Farhi-Guth-Guven
tunneling, expanding and inflating solutions are impossible. In this paper, we
extend our method to beyond the thin shell approximation: we include the
dynamics of fields and assume that the transition layer between a true vacuum
and a false vacuum has non-zero thickness. If a shell has sufficiently low
energy, as expected from the thin shell approximation, it collapses (Type 1).
However, if the shell has sufficiently large energy, it tends to expand. Here,
via the field dynamics, field values of inside of the shell slowly roll down to
the true vacuum and hence the shell does not inflate (Type 2). If we add
sufficient exotic matters to regularize the curvature near the shell, inflation
may be possible without assuming Farhi-Guth-Guven tunneling. In this case, a
wormhole is dynamically generated around the shell (Type 3). By tuning our
simulation parameters, we could find transitions between Type 1 and Type 2, as
well as between Type 2 and Type 3. Between Type 2 and Type 3, we could find
another class of solutions (Type 4). Finally, we discuss the generation of a
bubble universe and the violation of unitarity. We conclude that the existence
of a certain combination of exotic matter fields violates unitarity.Comment: 40 pages, 41 figure
No-boundary measure and preference for large e-foldings in multi-field inflation
The no-boundary wave function of quantum gravity usually assigns only very
small probability to long periods of inflation. This was a reason to doubt
about the no-boundary wave function to explain the observational universe. We
study the no-boundary proposal in the context of multi-field inflation to see
whether the number of fields changes the situation. For a simple model, we find
that indeed the no-boundary wave function can give higher probability for
sufficient inflation, but the number of fields involved has to be very high.Comment: 16 pages, 2 figure
Dynamics of false vacuum bubbles in Brans-Dicke theory
We study the dynamics of false vacuum bubbles in the Brans-Dicke theory of
gravity by using the thin shell or thin wall approximation. We consider a false
vacuum bubble that has a different value for the Brans-Dicke field between the
inside false vacuum region and the outside true vacuum region. Within a certain
limit of field values, the difference of field values makes the effective
tension of the shell negative. This allows new expanding false vacuum bubbles
to be seen by the outside observer, which are disallowed in Einstein gravity.Comment: 29 pages, 20 figure
The horizon-entropy increase law for causal and quasi-local horizons and conformal field redefinitions
We explicitly prove the horizon-entropy increase law for both causal and
quasi-locally defined horizons in scalar-tensor and gravity theories.
Contrary to causal event horizons, future outer trapping horizons are not
conformally invariant and we provide a modification of trapping horizons to
complete the proof, using the idea of generalised entropy. This modification
means they are no longer foliated by marginally outer trapped surfaces but
fixes the location of the horizon under a conformal transformation. We also
discuss the behaviour of horizons in "veiled" general relativity and show,
using this new definition, how to locate cosmological horizons in flat
Minkowski space with varying units, which is physically identified with a
spatially flat FLRW spacetime.Comment: 23 page
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