51 research outputs found
A global picture of quantum de Sitter space
Perturbative gravity about a de Sitter background motivates a global picture
of quantum dynamics in `eternal de Sitter space,' the theory of states which
are asymptotically de Sitter to both future and past. Eternal de Sitter physics
is described by a finite dimensional Hilbert space in which each state is
precisely invariant under the full de Sitter group. This resolves a
previously-noted tension between de Sitter symmetry and finite entropy.
Observables, implications for Boltzmann brains, and Poincare recurrences are
briefly discussed.Comment: 17 pages, 1 figure. v2: minor changes, references added. v3: minor
changes to correspond to PRD versio
Is string theory a theory of quantum gravity?
Some problems in finding a complete quantum theory incorporating gravity are
discussed. One is that of giving a consistent unitary description of
high-energy scattering. Another is that of giving a consistent quantum
description of cosmology, with appropriate observables. While string theory
addresses some problems of quantum gravity, its ability to resolve these
remains unclear. Answers may require new mechanisms and constructs, whether
within string theory, or in another framework.Comment: Invited contribution for "Forty Years of String Theory: Reflecting on
the Foundations," a special issue of Found. Phys., ed. by G 't Hooft, E.
Verlinde, D. Dieks, S. de Haro. 32 pages, 5 figs., harvmac. v2: final version
to appear in journal (small revisions
Spacetime Embedding Diagrams for Black Holes
We show that the 1+1 dimensional reduction (i.e., the radial plane) of the
Kruskal black hole can be embedded in 2+1 Minkowski spacetime and discuss how
features of this spacetime can be seen from the embedding diagram. The purpose
of this work is educational: The associated embedding diagrams may be useful
for explaining aspects of black holes to students who are familiar with special
relativity, but not general relativity.Comment: 22 pages, 21 figures, RevTex. To be submitted to the American Journal
of Physics. Experts will wish only to skim appendix A and to look at the
pictures. Suggested Maple code is now compatible with MapleV4r
Comments on Microcausality, Chaos, and Gravitational Observables
Observables in gravitational systems must be non-local so as to be invariant
under diffeomorphism gauge transformations. But at the classical level some
such observables can nevertheless satisfy an exact form of microcausality. This
property is conjectured to remain true at all orders in the semiclassical
expansion, though with limitations at finite or . We
also discuss related issues concerning observables in black hole spacetimes and
comment on the senses in which they do and do not experience the form of chaos
identified by Shenker and Stanford. In particular, in contrast to the situation
in a reflecting cavity, this chaos does not afflict observables naturally
associated with Hawking radiation for evaporating black holes.Comment: 16 pages, 1 figure; references adde
Soft branes in supersymmetry-breaking backgrounds
We revisit the analysis of effective field theories resulting from
non-supersymmetric perturbations to supersymmetric flux compactifications of
the type-IIB superstring with an eye towards those resulting from the
backreaction of a small number of anti-D3-branes. Independently of the
background, we show that the low-energy Lagrangian describing the fluctuations
of a stack of probe D3-branes exhibits soft supersymmetry breaking, despite
perturbations to marginal operators that were not fully considered in some
previous treatments. We take this as an indication that the breaking of
supersymmetry by anti-D3-branes or other sources may be spontaneous rather than
explicit. In support of this, we consider the action of an anti-D3-brane
probing an otherwise supersymmetric configuration and identify a candidate for
the corresponding goldstino.Comment: 36+5 pages. References added, minor typos correcte
One-loop corrections to the curvature perturbation from inflation
An estimate of the one-loop correction to the power spectrum of the
primordial curvature perturbation is given, assuming it is generated during a
phase of single-field, slow-roll inflation. The loop correction splits into two
parts, which can be calculated separately: a purely quantum-mechanical
contribution which is generated from the interference among quantized field
modes around the time when they cross the horizon, and a classical contribution
which comes from integrating the effect of field modes which have already
passed far beyond the horizon. The loop correction contains logarithms which
may invalidate the use of naive perturbation theory for cosmic microwave
background (CMB) predictions when the scale associated with the CMB is
exponentially different from the scale at which the fundamental theory which
governs inflation is formulated.Comment: 28 pages, uses feynmp.sty and ioplatex journal style. v2: supersedes
version published in JCAP. Some corrections and refinements to the discussion
and conclusions. v3: Corrects misidentification of quantum correction with an
IR effect. Improvements to the discussio
de Sitter invariance of the dS graviton vacuum
The two-point function of linearized gravitons on de Sitter space is infrared
divergent in the standard transverse traceless synchronous gauge defined by
cosmological coordinates (also called conformal or Poincare coordinates).
We show that this divergence can be removed by adding a linearized
diffeomorphism to each mode function; i.e., by an explicit change of gauge. It
follows that the graviton vacuum state is well-defined and de Sitter invariant
in agreement with various earlier arguments.Comment: 14 pages, 1 figur
IR divergences and kinetic equation in de Sitter space. (Poincare patch; Principal series)
We explicitly show that the one loop IR correction to the two--point function
in de Sitter space scalar QFT does not reduce just to the mass renormalization.
The proper interpretation of the loop corrections is via particle creation
revealing itself through the generation of the quantum averages and dominates over
the anomalous expectation values . For
these harmonics the Dyson--Schwinger equation reduces in the IR limit to the
kinetic equation. We solve the latter equation, which allows us to sum up all
loop leading IR contributions to the Whiteman function. We perform the
calculation for the principle series real scalar fields both in expanding and
contracting Poincare patches.Comment: 33 pages, 6 fig; Language was correcte
- …