104 research outputs found
Isolated, slowly evolving, and dynamical trapping horizons: geometry and mechanics from surface deformations
We study the geometry and dynamics of both isolated and dynamical trapping
horizons by considering the allowed variations of their foliating two-surfaces.
This provides a common framework that may be used to consider both their
possible evolutions and their deformations as well as derive the well-known
flux laws. Using this framework, we unify much of what is already known about
these objects as well as derive some new results. In particular we characterize
and study the "almost-isolated" trapping horizons known as slowly evolving
horizons. It is for these horizons that a dynamical first law holds and this is
analogous and closely related to the Hawking-Hartle formula for event horizons.Comment: 39 pages, 6 figures, version to appear in PRD : a few minor changes
and many typos corrected in equation
Constraints on the anisotropy of dark energy
If the equation of state of dark energy is anisotropic there will be
additional quadrupole anisotropy in the cosmic microwave background induced by
the time dependent anisotropic stress quantified in terms of .
Assuming that the entire amplitude of the observed quadrupole is due to this
anisotropy, we conservatively impose a limit of for any value of assuming that . This is
considerably tighter than that which comes from SNe. Stronger limits, upto a
factor of 10, are possible for specific values of and .
Since we assume this component is uncorrelated with the stochastic component
from inflation, we find that both the expectation value and the sample variance
are increased. There no improvement in the likelihood of an anomalously low
quadrupole as suggested by previous work on an elliptical universe
Pair Creation of Black Holes During Inflation
Black holes came into existence together with the universe through the
quantum process of pair creation in the inflationary era. We present the
instantons responsible for this process and calculate the pair creation rate
from the no boundary proposal for the wave function of the universe. We find
that this proposal leads to physically sensible results, which fit in with
other descriptions of pair creation, while the tunnelling proposal makes
unphysical predictions. We then describe how the pair created black holes
evolve during inflation. In the classical solution, they grow with the horizon
scale during the slow roll-down of the inflaton field; this is shown to
correspond to the flux of field energy across the horizon according to the
First Law of black hole mechanics. When quantum effects are taken into account,
however, it is found that most black holes evaporate before the end of
inflation. Finally, we consider the pair creation of magnetically charged black
holes, which cannot evaporate. In standard Einstein-Maxwell theory we find that
their number in the presently observable universe is exponentially small. We
speculate how this conclusion may change if dilatonic theories are applied.Comment: 29 pages, LaTeX, 3 figures, submitted to Phys. Rev. D; minor typos
corrected, missing minus sign in Eq. (3.11) inserte
Thermal gravity, black holes and cosmological entropy
Taking seriously the interpretation of black hole entropy as the logarithm of
the number of microstates, we argue that thermal gravitons may undergo a phase
transition to a kind of black hole condensate. The phase transition proceeds
via nucleation of black holes at a rate governed by a saddlepoint configuration
whose free energy is of order the inverse temperature in Planck units. Whether
the universe remains in a low entropy state as opposed to the high entropy
black hole condensate depends sensitively on its thermal history. Our results
may clarify an old observation of Penrose regarding the very low entropy state
of the universe.Comment: 5 pages, 2 figures, RevTex. v4: to appear in Phys. Rev.
(Anti-)Evaporation of Schwarzschild-de Sitter Black Holes
We study the quantum evolution of black holes immersed in a de Sitter
background space. For black holes whose size is comparable to that of the
cosmological horizon, this process differs significantly from the evaporation
of asymptotically flat black holes. Our model includes the one-loop effective
action in the s-wave and large N approximation. Black holes of the maximal mass
are in equilibrium. Unexpectedly, we find that nearly maximal quantum
Schwarzschild-de Sitter black holes anti-evaporate. However, there is a
different perturbative mode that leads to evaporation. We show that this mode
will always be excited when a pair of cosmological holes nucleates.Comment: 16 pages, LaTeX2e; submitted to Phys. Rev.
Trace Anomaly of Dilaton Coupled Scalars in Two Dimensions
Conformal scalar fields coupled to the dilaton appear naturally in
two-dimensional models of black hole evaporation. We calculate their trace
anomaly. It follows that an RST-type counterterm appears naturally in the
one-loop effective action.Comment: 11 pages, LaTeX2e; submitted to Phys. Rev. Lett., minor change
Lightcone reference for total gravitational energy
We give an explicit expression for gravitational energy, written solely in
terms of physical spacetime geometry, which in suitable limits agrees with the
total Arnowitt-Deser-Misner and Trautman-Bondi-Sachs energies for
asymptotically flat spacetimes and with the Abbot-Deser energy for
asymptotically anti-de Sitter spacetimes. Our expression is a boundary value of
the standard gravitational Hamiltonian. Moreover, although it stands alone as
such, we derive the expression by picking the zero-point of energy via a
``lightcone reference.''Comment: latex, 7 pages, no figures. Uses an amstex symbo
Horizon energy and angular momentum from a Hamiltonian perspective
Classical black holes and event horizons are highly non-local objects,
defined in terms of the causal past of future null infinity. Alternative,
(quasi)local definitions are often used in mathematical, quantum, and numerical
relativity. These include apparent, trapping, isolated, and dynamical horizons,
all of which are closely associated to two-surfaces of zero outward null
expansion. In this paper we show that three-surfaces which can be foliated with
such two-surfaces are suitable boundaries in both a quasilocal action and a
phase space formulation of general relativity. The resulting formalism provides
expressions for the quasilocal energy and angular momentum associated with the
horizon. The values of the energy and angular momentum are in agreement with
those derived from the isolated and dynamical horizon frameworks.Comment: 39 pages, 3 figures, Final Version : content essentially unchanged
but many small improvements made in response to referees, a few references
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