1,170 research outputs found
Cosmological backreaction of a quantized massless scalar field
We consider the backreaction problem of a quantized minimally coupled
massless scalar field in cosmology. The adiabatically regularized stress-energy
tensor in a general Friedmann-Robertson-Walker background is approximately
evaluated by using the fact that subhorizon modes evolve adiabatically and
superhorizon modes are frozen. The vacuum energy density is verified to obey a
new first order differential equation depending on a dimensionless parameter of
order unity, which calibrates subhorizon/superhorizon division. We check the
validity of the approximation by calculating the corresponding vacuum energy
densities in fixed backgrounds, which are shown to agree with the known results
in de Sitter space and space-times undergoing power law expansions. We then
apply our findings to slow-roll inflationary models. Although backreaction
effects are found to be negligible during the near exponential expansion, the
vacuum energy density generated during this period might be important at later
stages since it decreases slower than radiation or dust.Comment: 20 pages, 2 figures, v2: comments and a reference added, to appear in
JCA
The inflationary prediction for primordial non-gaussianity
We extend the \delta N formalism so that it gives all of the stochastic
properties of the primordial curvature perturbation \zeta if the initial field
perturbations are gaussian. The calculation requires only the knowledge of some
family of unperturbed universes. A formula is given for the normalisation \fnl
of the bispectrum of \zeta, which is the main signal of non-gaussianity.
Examples of the use of the formula are given, and its relation to cosmological
perturbation theory is explained.Comment: Revtex Latex file. 4 pages, no figures. v4: minor changes, typos
corrected, references added and updated. Version published in Physical Review
Letter
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
Imaging analysis of LDEF craters
Two small craters in Al from the Long Duration Exposure Facility (LDEF) experiment tray A11E00F (no. 74, 119 micron diameter and no. 31, 158 micron diameter) were analyzed using Auger electron spectroscopy (AES), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), low voltage scanning electron microscopy (LVSEM), and SEM energy dispersive spectroscopy (EDS). High resolution images and sensitive elemental and molecular analysis were obtained with this combined approach. The result of these analyses are presented
Hadamard States and Adiabatic Vacua
Reversing a slight detrimental effect of the mailer related to TeXabilityComment: 10pages, LaTeX (RevTeX-preprint style
Vacuum polarization near cosmic string in RS2 brane world
Gravitational field of cosmic strings in theories with extra spatial
dimensions must differ significantly from that in the Einstein's theory. This
means that all gravity induced properties of cosmic strings need to be revised
too. Here we consider the effect of vacuum polarization outside a straight
infinitely thin cosmic string embedded in a RS2 brane world. Perturbation
technique combined with the method of dimensional regularization is used to
calculate for a massless scalar field.Comment: 8 pages, RevTeX
Universal Dynamic Conductivity and Quantized Visible Opacity of Suspended Graphene
We show that the optical transparency of suspended graphene is defined by the
fine structure constant, alpha, the parameter that describes coupling between
light and relativistic electrons and is traditionally associated with quantum
electrodynamics rather than condensed matter physics. Despite being only one
atom thick, graphene is found to absorb a significant (pi times alpha=2.3%)
fraction of incident white light, which is a consequence of graphene's unique
electronic structure. This value translates into universal dynamic conductivity
G =e^2/4h_bar within a few percent accuracy
Energy Density in Expanding Universes as Seen by Unruh's Detector
We consider the response of an Unruh detector to scalar fields in an
expanding space-time. When combining transition elements of the scalar field
Hamiltonian with the interaction operator of detector and field, one finds at
second order in time-dependent perturbation theory a transition amplitude,
which actually dominates in the ultraviolet over the first order contribution.
In particular, the detector response faithfully reproduces the particle number
implied by the stress-energy of a minimally coupled scalar field, which is
inversely proportional to the energy of a scalar mode. This finding disagrees
with the contention that in de Sitter space, the response of the detector drops
exponentially with particle energy and therefore indicates a thermal spectrum.Comment: 15 pages, 1 figur
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
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