1,934 research outputs found
Compact Ultra Dense Matter Impactors
We study interactions of meteorlike compact ultradense objects (CUDO), having
nuclear or greater density, with Earth and other rocky bodies in the Solar
System as a possible source of information about novel forms of matter. We
study the energy loss in CUDO puncture of the body and discuss differences
between regular matter and CUDO impacts.Comment: 5 pages, 1 figure; v4 identical to published PR
Entanglement creation between two causally-disconnected objects
We study the full entanglement dynamics of two uniformly accelerated
Unruh-DeWitt detectors with no direct interaction in between but each coupled
to a common quantum field and moving back-to-back in the field vacuum. For two
detectors initially prepared in a separable state our exact results show that
quantum entanglement between the detectors can be created by the quantum field
under some specific circumstances, though each detector never enters the
other's light cone in this setup. In the weak coupling limit, this entanglement
creation can occur only if the initial moment is placed early enough and the
proper acceleration of the detectors is not too large or too small compared to
the natural frequency of the detectors. Once entanglement is created it lasts
only a finite duration, and always disappears at late times. Prior result by
Reznik derived using the time-dependent perturbation theory with extended
integration domain is shown to be a limiting case of our exact solutions at
some specific moment. In the strong coupling and high acceleration regime,
vacuum fluctuations experienced by each detector locally always dominate over
the cross correlations between the detectors, so entanglement between the
detectors will never be generated.Comment: 16 pages, 8 figures; added Ref.[7] and related discussion
Instability of (1+1) de sitter space in the presence of interacting fields
Instabilities of two dimensional (1+1) de Sitter space induced by interacting
fields are studied. As for the case of flat Minkowski space, several
interacting fermion models can be translated into free boson ones and vice
versa. It is found that interacting fermion theories do not lead to any
instabilities, while the interacting bosonic sine-Gordon model does lead to a
breakdown of de Sitter symmetry and to the vanishing of the vacuum expectation
value of the S matrix.Comment: 7 page
Detection of acceleration radiation in a Bose-Einstein condensate
We propose and study methods for detecting the Unruh effect in a
Bose-Einstein condensate. The Bogoliubov vacuum of a Bose-Einstein condensate
is used here to simulate a scalar field-theory, and accelerated atom dots or
optical lattices as means for detecting phonon radiation due to acceleration
effects. We study Unruh's effect for linear acceleration and circular
acceleration. In particular, we study the dispersive effects of the Bogoliubov
spectrum on the ideal case of exact thermalization. Our results suggest that
Unruh's acceleration radiation can be tested using current accessible
experimental methods.Comment: 5 pages, 3 figure
Quantum evolution across singularities
Attempts to consider evolution across space-time singularities often lead to
quantum systems with time-dependent Hamiltonians developing an isolated
singularity as a function of time. Examples include matrix theory in certain
singular time-dependent backgounds and free quantum fields on the
two-dimensional compactified Milne universe. Due to the presence of the
singularities in the time dependence, the conventional quantum-mechanical
evolution is not well-defined for such systems. We propose a natural way,
mathematically analogous to renormalization in conventional quantum field
theory, to construct unitary quantum evolution across the singularity. We carry
out this procedure explicitly for free fields on the compactified Milne
universe and compare our results with the matching conditions considered in
earlier work (which were based on the covering Minkowski space).Comment: revised with an emphasis on local counterterm subtraction rather than
analyticity; version to be submitted for publicatio
Soliton Solutions to the Einstein Equations in Five Dimensions
We present a new class of solutions in odd dimensions to Einstein's equations
containing either a positive or negative cosmological constant. These solutions
resemble the even-dimensional Eguchi-Hanson--(anti)-de Sitter ((A)dS) metrics,
with the added feature of having Lorentzian signatures. They provide an
affirmative answer to the open question as to whether or not there exist
solutions with negative cosmological constant that asymptotically approach
AdS, but have less energy than AdS. We present
evidence that these solutions are the lowest-energy states within their
asymptotic class.Comment: 9 pages, Latex; Final version that appeared in Phys. Rev. Lett; title
changed by journal from original title "Eguchi-Hanson Solitons
Contact Term, its Holographic Description in QCD and Dark Energy
In this work we study the well known contact term, which is the key element
in resolving the so-called problem in QCD. We study this term using
the dual Holographic Description. We argue that in the dual picture the contact
term is saturated by the D2 branes which can be interpreted as the tunnelling
events in Minkowski space-time. We quote a number of direct lattice results
supporting this identification. We also argue that the contact term receives a
Casimir -like correction \sim (\Lqcd R)^{-1} rather than naively expected
\exp(-\Lqcd R) when the Minkowski space-time is replaced by
a large but finite manifold with a size . Such a behaviour is consistent
with other QFT-based computations when power like corrections are due to
nontrivial properties of topological sectors of the theory. In holographic
description such a behaviour is due to massless Ramond-Ramond (RR) field living
in the bulk of multidimensional space when power like corrections is a natural
outcome of massless RR field. In many respects the phenomenon is similar to the
Aharonov -Casher effect when the "modular electric field" can penetrate into a
superconductor where the electric field is exponentially screened. The role of
"modular operator" from Aharonov -Casher effect is played by large gauge
transformation operator in 4d QCD, resulting the transparency of the
system to topologically nontrivial pure gauge configurations. We discuss some
profound consequences of our findings. In particular, we speculate that a slow
variation of the contact term in expanding universe might be the main source of
the observed Dark Energy.Comment: Final version to appear in Phys. Rev. D. Comments added on
interpretation of the "topological Casimir effect" from 5d viewpoint where it
can be thought as conventional Casimir effec
Ultraviolet Divergences in Cosmological Correlations
A method is developed for dealing with ultraviolet divergences in
calculations of cosmological correlations, which does not depend on dimensional
regularization. An extended version of the WKB approximation is used to analyze
the divergences in these calculations, and these divergences are controlled by
the introduction of Pauli--Villars regulator fields. This approach is
illustrated in the theory of a scalar field with arbitrary self-interactions in
a fixed flat-space Robertson--Walker metric with arbitrary scale factor .
Explicit formulas are given for the counterterms needed to cancel all
dependence on the regulator properties, and an explicit prescription is given
for calculating finite regulator-independent correlation functions. The
possibility of infrared divergences in this theory is briefly considered.Comment: References added on various regularization methods. Improved
discussion of further issues. 26 pages, 1 figur
The string wave function across a Kasner singularity
A collision of orbifold planes in eleven dimensions has been proposed as an
explanation of the hot big bang. When the two planes are close to each other,
the winding membranes become the lightest modes of the theory, and can be
effectively described in terms of fundamental strings in a ten dimensional
background. Near the brane collision, the eleven-dimensional metric is an
Euclidean space times a 1+1-dimensional Milne universe. However, one may expect
small perturbations to lead into a more general Kasner background. In this
paper we extend the previous classical analysis of winding membranes to Kasner
backgrounds, and using the Hamiltonian equations, solve for the wave function
of loops with circular symmetry. The evolution across the singularity is
regular, and explained in terms of the excitement of higher oscillation modes.
We also show there is finite particle production and unitarity is preserved.Comment: 28 pages, 10 figure
Anisotropic higher derivative gravity and inflationary universe
Stability analysis of the Kantowski-Sachs type universe in pure higher
derivative gravity theory is studied in details. The non-redundant generalized
Friedmann equation of the system is derived by introducing a reduced one
dimensional generalized KS type action. This method greatly reduces the labor
in deriving field equations of any complicate models. Existence and stability
of inflationary solution in the presence of higher derivative terms are also
studied in details. Implications to the choice of physical theories are
discussed in details in this paper.Comment: 9 page
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