175 research outputs found
The Number of States of Two Dimensional Critical String Theory
We discuss string theory vacua which have the wrong number of spacetime
dimensions, and give a crude argument that vacua with more than four large
dimensions are improbable. We then turn to two dimensional vacua, which naively
appear to violate Bekenstein's entropy principle. A classical analysis shows
that the naive perturbative counting of states is unjustified. All excited
states of the system have strong coupling singularities which prevent us from
concluding that they really exist. A speculative interpretation of the
classical solutions suggests only a finite number of states will be found in
regions bounded by a finite area. We also argue that the vacuum degeneracy of
two dimensional classical string theory is removed in quantum mechanics. The
system appears to be in a Kosterlitz-Thouless phase. This leads to the
conclusion that it is also improbable to have only two large spacetime
dimensions in string theory. However, we note that, unlike our argument for
high dimensions, our conclusions about the ground state have neglected two
dimensional quantum gravitational effects, and are at best incomplete.Comment: 12 pages, harvma
The Trouble with de Sitter Space
In this paper we assume the de Sitter Space version of Black Hole
Complementarity which states that a single causal patch of de Sitter space is
described as an isolated finite temperature cavity bounded by a horizon which
allows no loss of information. We discuss the how the symmetries of de Sitter
space should be implemented. Then we prove a no go theorem for implementing the
symmetries if the entropy is finite. Thus we must either give up the finiteness
of the de Sitter entropy or the exact symmetry of the classical space. Each has
interesting implications for the very long time behavior. We argue that the
lifetime of a de Sitter phase can not exceed the Poincare recurrence time. This
is supported by recent results of Kachru, Kallosh, Linde and Trivedi.Comment: 15 pages, 1 figure. v2: added fifth section with comments on long
time stability of de Sitter space, in which we argue that the lifetime can
not exceed the Poincare recurrence time. v3: corrected a minor error in the
appendi
Semi-infinite Throat as the End-state Geometry of two-dimensional Black Hole Evaporation
We study a modified two-dimensional dilaton gravity theory which is exactly
solvable in the semiclassical approximation including back-reaction. The vacuum
solutions of this modified theory are asymptotically flat static space-times.
Infalling matter forms a black hole if its energy is above a certain threshold.
The black hole singularity is initially hidden behind a timelike apparent
horizon. As the black hole evaporates by emitting Hawking radiation, the
singularity meets the shrinking horizon in finite retarded time to become
naked. A natural boundary condition exists at the naked singularity such that
for general infalling matter-configuration the evaporating black hole
geometries can be matched continuously to a unique static end-state geometry.
This end-state geometry is asymptotically flat at its right spatial infinity,
while its left spatial infinity is a semi-infinite throat extending into the
strong coupling region.Comment: Tex + compressed uuencoded ps version with one figure included, 11
Disturbing Implications of a Cosmological Constant
In this paper we consider the implications of a cosmological constant for the
evolution of the universe, under a set of assumptions motivated by the
holographic and horizon complementarity principles. We discuss the ``causal
patch" description of spacetime required by this framework, and present some
simple examples of cosmologies described this way. We argue that these
assumptions inevitably lead to very deep paradoxes, which seem to require major
revisions of our usual assumptions.Comment: 26 pages, 7 figures v2: references added v3: reference adde
Synergistic effects of the invasive Chinese tallow (Triadica sebifera) and climate change on aquatic amphibian survival
Changes in climate and the introduction of invasive species are two major stressors to amphibians, although little is known about the interaction between these two factors with regard to impacts on amphibians. We focused our study on an invasive tree species, the Chinese tallow (Triadica sebifera), that annually sheds its leaves and produces leaf litter that is known to negatively impact aquatic amphibian survival. The purpose of our research was to determine whether the timing of leaf fall from Chinese tallow and the timing of amphibian breeding (determined by weather) influence survival of amphibian larvae. We simulated a range of winter weather scenarios, ranging from cold to warm, by altering the relative timing of when leaf litter and amphibian larvae were introduced into aquatic mesocosms. Our results indicate that amphibian larvae survival was greatly affected by the length of time Chinese tallow leaf litter decomposes in water prior to the introduction of the larvae. Larvae in treatments simulating warm winters (early amphibian breeding) were introduced to the mesocosms early in the aquatic decomposition process of the leaf litter and had significantly lower survival compared with cold winters (late amphibian breeding), likely due to significantly lower dissolved oxygen levels. Shifts to earlier breeding phenology, linked to warming climate, have already been observed in many amphibian taxa, and with most climate models predicting a significant warming trend over the next century, the trend toward earlier breeding should continue if not increase. Our results strongly suggest that a warming climate can interact with the effects of invasive plant species, in ways we have not previously considered, to reduce the survival of an already declining group of organisms
Initial Conditions for Inflation
Free scalar fields in de Sitter space have a one-parameter family of states
invariant under the de Sitter group, including the standard thermal vacuum. We
show that, except for the thermal vacuum, these states are unphysical when
gravitational interactions are included. We apply these observations to the
quantum state of the inflaton, and find that, at best, dramatic fine tuning is
required for states other than the thermal vacuum to lead to observable
features in the CMBR anisotropy.Comment: 31 pages, 4 figure
Information Loss and Anomalous Scattering
The approach of 't Hooft to the puzzles of black hole evaporation can be
applied to a simpler system with analogous features. The system is
dimensional electrodynamics in a linear dilaton background. Analogues of black
holes, Hawking radiation and evaporation exist in this system. In perturbation
theory there appears to be an information paradox but this gets resolved in the
full quantum theory and there exists an exact -matrix, which is fully
unitary and information conserving. 't Hooft's method gives the leading terms
in a systematic approximation to the exact result.Comment: 18 pages, 3 figures (postscript files available soon on request),
(earlier version got corrupted by mail system
Tachyon Hair on Two-Dimensional Black Holes
Static black holes in two-dimensional string theory can carry tachyon hair.
Configurations which are non-singular at the event horizon have non-vanishing
asymptotic energy density. Such solutions can be smoothly extended through the
event horizon and have non-vanishing energy flux emerging from the past
singularity. Dynamical processes will not change the amount of tachyon hair on
a black hole. In particular, there will be no tachyon hair on a black hole
formed in gravitational collapse if the initial geometry is the linear dilaton
vacuum. There also exist static solutions with finite total energy, which have
singular event horizons. Simple dynamical arguments suggest that black holes
formed in gravitational collapse will not have tachyon hair of this type.Comment: 11 pages, 1 figure (not included), uses phyzzx, SU-ITP-93-1
The Stretched Horizon and Black Hole Complementarity
Three postulates asserting the validity of conventional quantum theory,
semi-classical general relativity and the statistical basis for thermodynamics
are introduced as a foundation for the study of black hole evolution. We
explain how these postulates may be implemented in a ``stretched horizon'' or
membrane description of the black hole, appropriate to a distant observer. The
technical analysis is illustrated in the simplified context of 1+1 dimensional
dilaton gravity. Our postulates imply that the dissipative properties of the
stretched horizon arise from a course graining of microphysical degrees of
freedom that the horizon must possess. A principle of black hole
complementarity is advocated. The overall viewpoint is similar to that
pioneered by 't~Hooft but the detailed implementation is different.Comment: (some misprints in equations have been fixed), 48 pages (including
figures), SU-ITP-93-1
July 2004 Report of Progress
Progress of each ALS-NSCORT project given by each project lead. 10 pages
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