95 research outputs found
Ion and neutral temperature distributions in the E-region observed by the EISCAT Tromsø and Svalbard radars
Electromagnetic energy deposition rate in the polar upper thermosphere derived from the EISCAT Svalbard radar and CUTLASS Finland radar observations
Black-hole dynamics in BHT massive gravity
Using an exact Vaidya-type null-dust solution, we study the area and entropy
laws for dynamical black holes defined by a future outer trapping horizon in
(2+1)-dimensional Bergshoeff-Hohm-Townsend (BHT) massive gravity. We consider
the theory admitting a degenerate (anti-)de Sitter vacuum and pure BHT gravity.
It is shown that, while the area of a black hole decreases by the injection of
a null dust with positive energy density in several cases, the Wald-Kodama
dynamical entropy always increases.Comment: 7 pages, 1 figur
Hamiltonian Formulation of Scalar Field Collapse in Einstein Gauss Bonnet Gravity
We compute the Hamiltonian for spherically symmetric scalar field collapse in
Einstein-Gauss-Bonnet gravity in D dimensions using slicings that are regular
across future horizons. We first reduce the Lagrangian to two dimensions using
spherical symmetry. We then show that choosing the spatial coordinate to be a
function of the areal radius leads to a relatively simple Hamiltonian
constraint whose gravitational part is the gradient of the generalized mass
function. Next we complete the gauge fixing such that the metric is the
Einstein-Gauss-Bonnet generalization of non-static Painleve-Gullstrand
coordinates. Finally, we derive the resultant reduced equations of motion for
the scalar field. These equations are suitable for use in numerical simulations
of spherically symmetric scalar field collapse in Gauss-Bonnet gravity and can
readily be generalized to other matter fields minimally coupled to gravity.Comment: 14 pages, 0 figure
The Peculiar Type Ib Supernova 2006jc: A WCO Wolf-Rayet Star Explosion
We present a theoretical model for Type Ib supernova (SN) 2006jc. We
calculate the evolution of the progenitor star, hydrodynamics and
nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC).
The synthetic bolometric LC is compared with the observed bolometric LC
constructed by integrating the UV, optical, near-infrared (NIR), and
mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as
on the zero-age main-sequence. The star undergoes extensive mass
loss to reduce its mass down to as small as , thus becoming a WCO
Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which
amorphous carbon grains can be formed. This could explain the NIR brightening
and the dust feature seen in the MIR spectrum. We suggest that the progenitor
of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and
such massive stars are the important sites of dust formation. We derive the
parameters of the explosion model in order to reproduce the bolometric LC of SN
2006jc by the radioactive decays: the ejecta mass , hypernova-like
explosion energy ergs, and ejected Ni mass . We
also calculate the circumstellar interaction and find that a CSM with a flat
density structure is required to reproduce the X-ray LC of SN 2006jc. This
suggests a drastic change of the mass-loss rate and/or the wind velocity that
is consistent with the past luminous blue variable (LBV)-like event.Comment: 12 pages, 11 figures. Accepted for publication in the Astrophysical
Journa
Entropy Bound and Causality Violation in Higher Curvature Gravity
In any quantum theory of gravity we do expect corrections to Einstein gravity
to occur. Yet, at fundamental level, it is not apparent what the most relevant
corrections are. We argue that the generic curvature square corrections present
in lower dimensional actions of various compactified string theories provide a
natural passage between the classical and quantum realms of gravity. The
Gauss-Bonnet and gravities, in particular, provide concrete
examples in which inconsistency of a theory, such as, a violation of
microcausality, and a classical limit on black hole entropy are correlated. In
such theories the ratio of the shear viscosity to the entropy density,
, can be smaller than for a boundary conformal field theory with
Einstein gravity dual. This result is interesting from the viewpoint that the
nuclear matter or quark-gluon plasma produced (such as at RHIC) under extreme
densities and temperatures may violate the conjectured bound , {\it albeit} marginally so.Comment: 23 pages, several eps figures; minor changes, references added,
published versio
Deformation of Codimension-2 Surface and Horizon Thermodynamics
The deformation equation of a spacelike submanifold with an arbitrary
codimension is given by a general construction without using local frames. In
the case of codimension-1, this equation reduces to the evolution equation of
the extrinsic curvature of a spacelike hypersurface. In the more interesting
case of codimension-2, after selecting a local null frame, this deformation
equation reduces to the well known (cross) focusing equations. We show how the
thermodynamics of trapping horizons is related to these deformation equations
in two different formalisms: with and without introducing quasilocal energy. In
the formalism with the quasilocal energy, the Hawking mass in four dimension is
generalized to higher dimension, and it is found that the deformation of this
energy inside a marginal surface can be also decomposed into the contributions
from matter fields and gravitational radiation as in the four dimension. In the
formalism without the quasilocal energy, we generalize the definition of slowly
evolving future outer trapping horizons proposed by Booth to past trapping
horizons. The dynamics of the trapping horizons in FLRW universe is given as an
example. Especially, the slowly evolving past trapping horizon in the FLRW
universe has close relation to the scenario of slow-roll inflation. Up to the
second order of the slowly evolving parameter in this generalization, the
temperature (surface gravity) associated with the slowly evolving trapping
horizon in the FLRW universe is essentially the same as the one defined by
using the quasilocal energy.Comment: Latex, 61 pages, no figures; v2, type errors corrected; v3,
references and comments are added, English is improved, to appear in JHE
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