229 research outputs found
Model Bond albedos of extrasolar giant planets
The atmospheres of extrasolar giant planets are modeled with various
effective temperatures and gravities, with and without clouds. Bond albedos are
computed by calculating the ratio of the flux reflected by a planet (integrated
over wavelength) to the total stellar flux incident on the planet. This
quantity is useful for estimating the effective temperature and evolution of a
planet. We find it is sensitive to the stellar type of the primary. For a 5
M_Jup planet the Bond albedo varies from 0.4 to 0.3 to 0.06 as the primary star
varies from A5V to G2V to M2V in spectral type. It is relatively insensitive to
the effective temperature and gravity for cloud--free planets. Water clouds
increase the reflectivity of the planet in the red, which increases the Bond
albedo. The Bond albedo increases by an order of magnitude for a 13 M_Jup
planet with an M2V primary when water clouds are present. Silicate clouds, on
the other hand, can either increase or decrease the Bond albedo, depending on
whether there are many small grains (the former) or few large grains (the
latter).Comment: 6 pages, 9 figures, uses egs.cls and epsfig.sty, submitted to Physics
and Chemistry of the Earth (proceedings of the April 1998 EGS meeting in
Nice, France
Is There Really a de Sitter/CFT Duality
In this paper a de Sitter Space version of Black Hole Complementarity is
formulated which states that an observer in de Sitter Space describes the
surrounding space as a sealed finite temperature cavity bounded by a horizon
which allows no loss of information. We then discuss the implications of this
for the existence of boundary correlators in the hypothesized dS/cft
correspondence. We find that dS complementarity precludes the existence of the
appropriate limits. We find that the limits exist only in approximations in
which the entropy of the de Sitter Space is infinite. The reason that the
correlators exist in quantum field theory in the de Sitter Space background is
traced to the fact that horizon entropy is infinite in QFT.Comment: 12 Figures, STIAS Workshop on Quantum Gravit
De Sitter Holography with a Finite Number of States
We investigate the possibility that, in a combined theory of quantum
mechanics and gravity, de Sitter space is described by finitely many states.
The notion of observer complementarity, which states that each observer has
complete but complementary information, implies that, for a single observer,
the complete Hilbert space describes one side of the horizon. Observer
complementarity is implemented by identifying antipodal states with outgoing
states. The de Sitter group acts on S-matrix elements. Despite the fact that
the de Sitter group has no nontrivial finite-dimensional unitary
representations, we show that it is possible to construct an S-matrix that is
finite-dimensional, unitary, and de Sitter-invariant. We present a class of
examples that realize this idea holographically in terms of spinor fields on
the boundary sphere. The finite dimensionality is due to Fermi statistics and
an `exclusion principle' that truncates the orthonormal basis in which the
spinor fields can be expanded.Comment: 23 pages, 1 eps figure, LaTe
New black holes in the brane-world?
It is known that the Einstein field equations in five dimensions admit more
general spherically symmetric black holes on the brane than four-dimensional
general relativity. We propose two families of analytic solutions (with
g_tt\not=-1/g_rr), parameterized by the ADM mass and the PPN parameter beta,
which reduce to Schwarzschild for beta=1. Agreement with observations requires
|\beta-1| |\eta|<<1. The sign of eta plays a key role in the global causal
structure, separating metrics which behave like Schwarzschild (eta<0) from
those similar to Reissner-Nordstroem (eta>0). In the latter case, we find a
family of black hole space-times completely regular.Comment: 4 pages, RevTeX, 3 eps figures, final version to appear in Phys. Rev.
Holographic Multiverse
We explore the idea that the dynamics of the inflationary multiverse is
encoded in its future boundary, where it is described by a lower dimensional
theory which is conformally invariant in the UV. We propose that a measure for
the multiverse, which is needed in order to extract quantitative probabilistic
predictions, can be derived in terms of the boundary theory by imposing a UV
cutoff. In the inflationary bulk, this is closely related (though not
identical) to the so-called scale factor cutoff measure.Comment: 23 pages, 4 figures. Replaced to match published versio
On the Origin of the Outgoing Black Hole Modes
The question of how to account for the outgoing black hole modes without
drawing upon a transplanckian reservoir at the horizon is addressed. It is
argued that the outgoing modes must arise via conversion from ingoing modes. It
is further argued that the back-reaction must be included to avoid the
conclusion that particle creation cannot occur in a strictly stationary
background. The process of ``mode conversion" is known in plasma physics by
this name and in condensed matter physics as ``Andreev reflection" or ``branch
conversion". It is illustrated here in a linear Lorentz non-invariant model
introduced by Unruh. The role of interactions and a physical short distance
cutoff is then examined in the sonic black hole formed with Helium-II.Comment: 12 pages, plain latex, 2 figures included using psfig; Analogy to
``Andreev reflection" in superfluid systems noted, references and
acknowledgment added, format changed to shorten tex
Dynamics near the critical point: the hot renormalization group in quantum field theory
The perturbative approach to the description of long wavelength excitations
at high temperature breaks down near the critical point of a second order phase
transition. We study the \emph{dynamics} of these excitations in a relativistic
scalar field theory at and near the critical point via a renormalization group
approach at high temperature and an expansion in
space-time dimensions. The long wavelength physics is determined by a
non-trivial fixed point of the renormalization group. At the critical point we
find that the dispersion relation and width of quasiparticles of momentum
is and respectively, the
group velocity of quasiparticles vanishes in the long
wavelength limit at the critical point. Away from the critical point for
we find and
with
the finite temperature correlation length . The
new \emph{dynamical} exponent results from anisotropic renormalization in
the spatial and time directions. For a theory with O(N) symmetry we find . Critical slowing down,
i.e, a vanishing width in the long-wavelength limit, and the validity of the
quasiparticle picture emerge naturally from this analysis.Comment: Discussion on new dynamical universality class. To appear in Phys.
Rev.
Theoretical description of deformed proton emitters: nonadiabatic coupled-channel method
The newly developed nonadiabatic method based on the coupled-channel
Schroedinger equation with Gamow states is used to study the phenomenon of
proton radioactivity. The new method, adopting the weak coupling regime of the
particle-plus-rotor model, allows for the inclusion of excitations in the
daughter nucleus. This can lead to rather different predictions for lifetimes
and branching ratios as compared to the standard adiabatic approximation
corresponding to the strong coupling scheme. Calculations are performed for
several experimentally seen, non-spherical nuclei beyond the proton dripline.
By comparing theory and experiment, we are able to characterize the angular
momentum content of the observed narrow resonance.Comment: 12 pages including 10 figure
Linking the trans-Planckian and the information loss problems in black hole physics
The trans-Planckian and information loss problems are usually discussed in
the literature as separate issues concerning the nature of Hawking radiation.
Here we instead argue that they are intimately linked, and can be understood as
"two sides of the same coin" once it is accepted that general relativity is an
effective field theory.Comment: 10 pages, 2 figures. Replaced with the version to be published in
General Relativity and Gravitatio
Production and Decay of D_1(2420)^0 and D_2^*(2460)^0
We have investigated and final states and
observed the two established charmed mesons, the with mass
MeV/c and width MeV/c and
the with mass MeV/c and width
MeV/c. Properties of these final states, including
their decay angular distributions and spin-parity assignments, have been
studied. We identify these two mesons as the doublet predicted
by HQET. We also obtain constraints on {\footnotesize } as a function of the cosine of the relative phase of the two
amplitudes in the decay.Comment: 15 pages in REVTEX format. hardcopies with figures can be obtained by
sending mail to: [email protected]
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