124 research outputs found

### Causal Boundary Entropy From Horizon Conformal Field Theory

The quantum theory of near horizon regions of spacetimes with classical
spatially flat, homogeneous and isotropic Friedman-Robertson-Walker geometry
can be approximately described by a two dimensional conformal field theory. The
central charge of this theory and expectation value of its Hamiltonian are both
proportional to the horizon area in units of Newton's constant. The statistical
entropy of horizon states, which can be calculated using two dimensional state
counting methods, is proportional to the horizon area and depends on a
numerical constant of order unity which is determined by Planck scale physics.
This constant can be fixed such that the entropy is equal to a quarter of the
horizon area in units of Newton's constant, in agreement with thermodynamic
considerations.Comment: 11 pages, no figure

### Dark Matter in Models of String Cosmology

The origin of dark matter in the universe may be weakly interacting scalar
particles produced by amplification of quantum fluctuations during a period of
dilaton-driven inflation. We present two interesting cases, the case of small
fluctuations, and the resulting nonthermal spectrum, and the case of large
fluctuations of a field with a periodic potential, the QCD axion.Comment: 13 pages LaTeX, uses aipproc.sty, talk presented by R. Brustein at
COSMO 98, Asilomar, California, November 199

### Classical Corrections in String Cosmology

An important element in a model of non-singular string cosmology is a phase
in which classical corrections saturate the growth of curvature in a
deSitter-like phase with a linearly growing dilaton (an `algebraic fixed
point'). As the form of the classical corrections is not well known, here we
look for evidence, based on a suggested symmetry of the action, scale factor
duality and on conformal field theory considerations, that they can produce
this saturation. It has previously been observed that imposing scale factor
duality on the $O(\alpha')$ corrections is not compatible with fixed point
behavior. Here we present arguments that these problems persist to all orders
in $\alpha'$. We also present evidence for the form of a solution to the
equations of motion using conformal perturbation theory, examine its
implications for the form of the effective action and find novel fixed point
structure.Comment: 30 pages, Latex, epsfig, 6 figure

### Black hole entropy divergence and the uncertainty principle

Black hole entropy has been shown by 't Hooft to diverge at the horizon. The
region near the horizon is in a thermal state, so entropy is linear to energy
which consequently also diverges. We find a similar divergence for the energy
of the reduced density matrix of relativistic and non-relativistic field
theories, extending previous results in quantum mechanics. This divergence is
due to an infinitely sharp division between the observable and unobservable
regions of space, and it stems from the position/momentum uncertainty relation
in the same way that the momentum fluctuations of a precisely localized quantum
particle diverge. We show that when the boundary between the observable and
unobservable regions is smoothed the divergence is tamed. We argue that the
divergence of black hole entropy can also be interpreted as a consequence of
position/momentum uncertainty, and that 't Hooft's brick wall tames the
divergence in the same way, by smoothing the boundary.Comment: Added clarifications and explanation

### Small field models of inflation that predict a tensor-to-scalar ratio $r=0.03$

Future observations of the cosmic microwave background (CMB) polarization are
expected to set an improved upper bound on the tensor-to-scalar ratio of
$r\lesssim 0.03$. Recently, we showed that small field models of inflation can
produce a significant primordial gravitational wave signal. We constructed
viable small field models that predict a value of $r$ as high as $0.01$. Models
that predict higher values of $r$ are more tightly constrained and lead to
larger field excursions. This leads to an increase in tuning of the potential
parameters and requires higher levels of error control in the numerical
analysis. Here, we present viable small field models which predict $r=0.03$. We
further find the most likely candidate among these models which fit the most
recent Planck data while predicting $r= 0.03$. We thus demonstrate that this
class of small field models is an alternative to the class of large field
models. The BICEP3 experiment and the Euclid and SPHEREx missions are expected
to provide experimental evidence to support or refute our predictions.Comment: 10 pages, 5 figure

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