669 research outputs found
Inflaton Decay in an Alpha Vacuum
We study the alpha vacua of de Sitter space by considering the decay rate of
the inflaton field coupled to a scalar field placed in an alpha vacuum. We find
an {\em alpha dependent} Bose enhancement relative to the Bunch-Davies vacuum
and, surprisingly, no non-renormalizable divergences. We also consider a
modified alpha dependent time ordering prescription for the Feynman propagator
and show that it leads to an alpha independent result. This result suggests
that it may be possible to calculate in any alpha vacuum if we employ the
appropriate causality preserving prescription.Comment: 16 pages, 1 figure, Revtex 4 preprin
De Sitter Breaking through Infrared Divergences
Just because the propagator of some field obeys a de Sitter invariant
equation does not mean it possesses a de Sitter invariant solution. The classic
example is the propagator of a massless, minimally coupled scalar. We show that
the same thing happens for massive scalars with , and for massive
transverse vectors with , where is the dimension
of spacetime and is the Hubble parameter. Although all masses in these
ranges give infrared divergent mode sums, using dimensional regularization (or
any other analytic continuation technique) to define the mode sums leads to the
incorrect conclusion that de Sitter invariant solutions exist except at
discrete values of the masses.Comment: 27 pages, no figures, uses LaTeX 2epsilo
Heralded gate search with genetic algorithms for quantum computation
In this paper we present genetic algorithms based search technique for the
linear optics schemes, performing two-qubit quantum gates. We successfully
applied this technique for finding heralded two-qubit gates and obtained the
new schemes with performance parameters equal to the best currently known. The
new simple metrics is introduced which enables comparison of schemes with
different heralding mechanisms. The scheme performance degradation is discussed
for the cases when detectors in the heralding part of the scheme are not
photon-number-resolving. We propose a procedure for overcoming this drawback
which allows us to restore the reliable heralding signal even with
not-photon-number-resolving detectors
Transforming to Lorentz Gauge on de Sitter
We demonstrate that certain gauge fixing functionals cannot be added to the
action on backgrounds such as de Sitter in which a linearization instability is
present. We also construct the field dependent gauge transformation which
carries the electromagnetic vector potential from a convenient, non-de Sitter
invariant gauge to the de Sitter invariant, Lorentz gauge. The transformed
propagator agrees with the de Sitter invariant result previously found by
solving the propagator equation in Lorentz gauge. This shows that the gauge
transformation technique will eliminate unphysical breaking of de Sitter
invariance introduced by a gauge condition. It is suggested that the same
technique can be used to finally resolve the issue of whether or not free
gravitons are de Sitter invariant.Comment: 45 page
Localized Particle States and Dynamics Gravitational Effects
Scalar particles--i.e., scalar-field excitations--in de Sitter space exhibit
behavior unlike either classical particles in expanding space or quantum
particles in flat spacetime. Their energies oscillate forever, and their
interactions are spread out in energy. Here it is shown that these features
characterize not only normal-mode excitations spread out over all space, but
localized particles or wave packets as well. Both one-particle and coherent
states of a massive, minimally coupled scalar field in de Sitter space,
associated with classical wave packets, are constructed explicitly. Their
energy expectation values and corresponding Unruh-DeWitt detector response
functions are calculated. Numerical evaluation of these quantities for a simple
set of classical wave packets clearly displays these novel features. Hence,
given the observed accelerating expansion of the Universe, it is possible that
observation of an ultralow-mass scalar particle could yield direct confirmation
of distinct predictions of quantum field theory in curved spacetime.Comment: 12 pages, 5 figure
Investigation of flat spectrum radio sources by the interplanetary scintillation method at 111 MHz
Interplanetary scintillation observations of 48 of the 55 Augusto et al.
(1998) flat spectrum radio sources were carried out at 111 MHz using the
interplanetary scintillation method on the Large Phased Array (LPA) in Russia.
Due to the large size of the LPA beam (1\degr \times 0.5\degr) a careful
inspection of all possible confusion sources was made using extant large radio
surveys: 37 of the 48 sources are not confused. We were able to estimate the
scintillating flux densities of 13 sources, getting upper limits for the
remaining 35. Gathering more or improving extant VLBI data on these sources
might significantly improve our results. This proof-of-concept project tells us
that compact () flat spectrum radio sources show strong enough
scintillations at 111 MHz to establish/constrain their spectra (low-frequency
end).Comment: 14 pages, 3 figure
Conformally invariant wave-equations and massless fields in de Sitter spacetime
Conformally invariant wave equations in de Sitter space, for scalar and
vector fields, are introduced in the present paper. Solutions of their wave
equations and the related two-point functions, in the ambient space notation,
have been calculated. The ``Hilbert'' space structure and the field operator,
in terms of coordinate independent de Sitter plane waves, have been defined.
The construction of the paper is based on the analyticity in the complexified
pseudo-Riemanian manifold, presented first by Bros et al.. Minkowskian limits
of these functions are analyzed. The relation between the ambient space
notation and the intrinsic coordinates is then studied in the final stage.Comment: 21 pages, LaTeX, some details adde
Two loop stress-energy tensor for inflationary scalar electrodynamics
We calculate the expectation value of the coincident product of two field
strength tensors at two loop order in scalar electrodynamics on de Sitter
background. The result agrees with the stochastic formulation which we have
developed in a companion paper [2] for the nonperturbative resummation of
leading logarithms of the scale factor. When combined with a previous
computation of scalar bilinears [1], our current result also gives the two loop
stress-energy tensor for inflationary scalar electrodynamics. This shows a
secular decrease in the vacuum energy which derives from the vacuum
polarization induced by the inflationary production of charged scalars.Comment: 62 pages, 1 eps figur
The Coincidence Limit of the Graviton Propagator in de Donder Gauge on de Sitter Background
We explicitly work out the de Sitter breaking contributions to the recent
solution for the de Donder gauge graviton propagator on de Sitter. We also
provide explicit power series expansions for the two structure functions, which
are suitable for implementing dimensional regularization. And we evaluate the
coincidence limit of the propagator.Comment: 41 pages, uses LaTeX 2e, version 2 has some typoes correcte
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