68 research outputs found
Cosmological Signature of New Parity-Violating Interactions
Does Nature yield any manifestations of parity violation other than those
observed in weak interactions? A map of the cosmic microwave background (CMB)
temperature and polarization will provide a new signature of P violation. We
give two examples of new P violating interactions, which may have something to
do with Planck-scale physics, inflation, and/or quintessence, that would give
rise to such a signature. Although these effects would most likely elude
detection by MAP and the Planck Surveyor, they may be detectable with a future
dedicated CMB polarization experiment.Comment: 4 pages, 2 figures. Origin of new terms clarified, to be published in
Physical Review Letter
Probing Newton's Constant on Vast Scales: DGP Gravity, Cosmic Acceleration and Large Scale Structure
The nature of the fuel that drives today's cosmic acceleration is an open and
tantalizing mystery. The braneworld theory of Dvali, Gabadadze, and Porrati
(DGP) provides a context where late-time acceleration is driven not by some
energy-momentum component (dark energy), but rather is the manifestation of the
excruciatingly slow leakage of gravity off our four-dimensional world into an
extra dimension. At the same time, DGP gravity alters the gravitational force
law in a specific and dramatic way at cosmologically accessible scales. We
derive the DGP gravitational force law in a cosmological setting for spherical
perturbations at subhorizon scales and compute the growth of large-scale
structure. We find that a residual repulsive force at large distances gives
rise to a suppression of the growth of density and velocity perturbations.
Explaining the cosmic acceleration in this framework leads to a present day
fluctuation power spectrum normalization sigma_8 <= 0.8 at about the two-sigma
level, in contrast with observations. We discuss further theoretical work
necessary to go beyond our approximations to confirm these results.Comment: 21 pages, 3 figures. References adde
Monopoles and the Emergence of Black Hole Entropy
One of the remarkable features of black holes is that they possess a
thermodynamic description, even though they do not appear to be statistical
systems. We use self-gravitating magnetic monopole solutions as tools for
understanding the emergence of this description as one goes from an ordinary
spacetime to one containing a black hole. We describe how causally distinct
regions emerge as a monopole solution develops a horizon. We define an entropy
that is naturally associated with these regions and that has a clear connection
with the Hawking-Bekenstein entropy in the critical black hole limit.Comment: 6 pages, one figure RevTe
Probing Newton's constant on vast scales: Dvali-Gabadadze-Porrati gravity, cosmic acceleration, and large scale structure
The nature of the fuel that drives today's cosmic acceleration is an open and tantalizing mystery. The brane-world theory of Dvali, Gabadadze, and Porrati (DGP) provides a context where late-time acceleration is driven not by some energy-momentum component (dark energy), but rather is the manifestation of the excruciatingly slow leakage of gravity off our four-dimensional world into an extra dimension. At the same time, DGP gravity alters the gravitational force law in a specific and dramatic way at cosmologically accessible scales. We derive the DGP gravitational force law in a cosmological setting for spherical perturbations at subhorizon scales and compute the growth of large-scale structures. We find that a residual repulsive force at large distances gives rise to a suppression of the growth of density and velocity perturbations. Explaining the cosmic acceleration in this framework leads to a present day fluctuation power spectrum normalization sigma8<=0.8 at about the two-sigma level, in contrast with observations. We discuss further theoretical work necessary to go beyond our approximations to confirm these results
Gravitational Properties of Monopole Spacetimes Near the Black Hole Threshold
Although nonsingular spacetimes and those containing black holes are
qualitatively quite different, there are continuous families of configurations
that connect the two. In this paper we use self-gravitating monopole solutions
as tools for investigating the transition between these two types of
spacetimes. We show how causally distinct regions emerge as the black hole
limit is achieved, even though the measurements made by an external observer
vary continuously. We find that near-critical solutions have a naturally
defined entropy, despite the absence of a true horizon, and that this has a
clear connection with the Hawking-Bekenstein entropy. We find that certain
classes of near-critical solutions display naked black hole behavior, although
they are not truly black holes at all. Finally, we present a numerical
simulation illustrating how an incident pulse of matter can induce the
dynamical collapse of a monopole into an extremal black hole. We discuss the
implications of this process for the third law of black hole thermodynamics.Comment: 23 pages, 4 figures RevTe
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