3,510 research outputs found
Constraining dark energy
In this paper we propose a mechanism that protects theories violating a
holographic bound suggested in arXiv:1203.5476 from developing accelerated
expansion. The mechanism builts on work on transplanckian physics, and a
non-trivial choice of vacuum states. If correct, it lends further support for
detectable signatures in the CMBR signalling new physics.Comment: 8 pages. arXiv admin note: text overlap with arXiv:astro-ph/0606474.
Minor misprints correcte
A remark on alpha vacua for quantum field theories on de Sitter space
It is shown that the so-called -vacua which have been proposed as
candidates for states of free quantum fields on de Sitter space have infinitely
strong fluctuations for typical observables as averaged renormalized energy
momentum tensor
On the gravitational collapse in anti-de Sitter space-time
We study the semiclassical evolution of a self-gravitating thick shell in
Anti-de Sitter space-time. We treat the matter on the shell as made of
quantized bosons and evaluate the back-reaction of the loss of gravitational
energy which is radiated away as a non-adiabatic effect. A peculiar feature of
anti-de Sitter is that such an emission also occurs for large shell radius,
contrary to the asymptotically flat case.Comment: Changed to Elsevier style, 9 pages, 1 figure. Minor typos corrected.
Accepted for publication in Phys. Lett.
Stability of flux vacua in the presence of charged black holes
In this letter we consider a charged black hole in a flux compactification of
type IIB string theory. Both the black hole and the fluxes will induce
potentials for the complex structure moduli. We choose the compact dimensions
to be described locally by a deformed conifold, creating a large hierarchy. We
demonstrate that the presence of a black hole typically will not change the
minimum of the moduli potential in a substantial way. However, we also point
out a couple of possible loop-holes, which in some cases could lead to
interesting physical consequences such as changes in the hierarchy.Comment: 14 pages. Published versio
On Thermalization in de Sitter Space
We discuss thermalization in de Sitter space and argue, from two different
points of view, that the typical time needed for thermalization is of order
, where is the radius of the de Sitter space in question.
This time scale gives plenty of room for non-thermal deviations to survive
during long periods of inflation. We also speculate in more general terms on
the meaning of the time scale for finite quantum systems inside isolated boxes,
and comment on the relation to the Poincar\'{e} recurrence time.Comment: 14 pages, 2 figures, latex, references added. Improved discussion in
section 3 adde
Transplanckian energy production and slow roll inflation
In this paper we investigate how the energy density due to a non-standard
choice of initial vacuum affects the expansion of the universe during
inflation. To do this we introduce source terms in the Friedmann equations
making sure that we respect the relation between gravity and thermodynamics. We
find that the energy production automatically implies a slow rolling
cosmological constant. Hence we also conclude that there is no well defined
value for the cosmological constant in the presence of sources. We speculate
that a non-standard vacuum can provide slow roll inflation on its own.Comment: 16 pages, 2 figures, version 2: minor corrections to section 4 and
references adde
Creation of Fundamental Strings by Crossing D-branes
We study the force balance between orthogonally positioned -brane and
-brane. The force due to graviton and dilaton exchange is repulsive in
this case. We identify the attractive force that balances this repulsion as due
to one-half of a fundamental string stretched between the branes. As the
-brane passes through the -brane, the connecting string changes
direction, which may be interpreted as creation of one fundamental string. We
show this directly from the structure of the Chern-Simons terms in the D-brane
effective actions. We also discuss the effect of string creation on the 0-brane
quantum mechanics in the type I' theory. The creation of a fundamental string
is related by U-duality to the creation of a 3-brane discussed by Hanany and
Witten. Both processes have a common origin in M-theory: as two M5-branes with
one common direction cross, a M2-brane stretched between them is created.Comment: 6 pages, Late
Probing F-theory With Multiple Branes
We study multiple 3-branes on an F theory orientifold. The world-volume
theory of the 3-branes is d=4, N=2 Sp(2k) gauge theory with an antisymmetric
tensor and four flavors of matter in the fundamental. The solution of this
gauge theory is found for vanishing bare mass of the antisymmetric tensor
matter, and massive fundamental matter. The integrable system underlying this
theory is constructed.Comment: 9 pages, harvma
Non-Relativistic Superstrings: A New Soluble Sector of AdS_5xS^5
We find a new sector of string theory in AdS_5xS^5 describing
non-relativistic superstrings in that geometry. The worldsheet theory of
non-relativistic strings in AdS_5xS^5 is derived and shown to reduce to a
supersymmetric free field theory in AdS_2. Non-relativistic string theory
provides a new calculable setting in which to study holography.Comment: 29 pages, LATEX forma
Trans-Planckian footprints in inflationary cosmology
We consider a minimum uncertainty vacuum choice at a fixed energy scale
Lambda as an effective description of trans-Planckian physics, and discuss its
implications for the linear perturbations of a massless scalar field in
power-law inflationary models. We find possible effects with a magnitude of
order H/\Lambda in the power spectrum, in analogy with previous results for
de-Sitter space-time.Comment: 4 pages, 1 figure, final version to appear in Physics Letters
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