251 research outputs found
Gauge invariant cosmological perturbations for the nonminimally coupled inflaton field
We construct the gauge invariant free action for cosmological perturbations
for the nonminimally coupled inflaton field in the Jordan frame. For this the
phase space formalism is used, which keeps track of all the dynamical and
constraint fields. We perform explicit conformal transformations to demonstrate
the physical equivalence between the Jordan and Einstein frames at the level of
quadratic perturbations. We show how to generalize the formalism to the case of
a more complicated scalar sector with an internal symmetry, such as Higgs
inflation. This work represents a first step in developing gauge invariant
perturbation theory for nonminimally coupled inflationary models.Comment: 21 pages, references added, typos corrected, extended section IV on
Higgs inflatio
Quantum effects can render w<-1 on cosmological scales
We report on a revision of our previous computation of the renormalized
expectation value of the stress-energy tensor of a massless, minimally coupled
scalar with a quartic self-interaction on a locally de Sitter background. This
model is important because it demonstrates that quantum effects can lead to
violations of the weak energy condition on cosmological scales - on average,
not just in fluctuations - although the effect in this particular model is far
too small to be observed. The revision consists of modifying the propagator so
that dimensional regularization can be used when the dimension of the
renormalized theory is not four. Although the finite part of the stress-energy
tensor does not change (in D=4) from our previous result, the counterterms do.
We also speculate that a certain, finite and separately conserved part of the
stress tensor can be subsumed into a natural correction of the initial state
from free Bunch-Davies vacuum.Comment: 9 pages, references adde
A Simple Operator Check of the Effective Fermion Mode Function during Inflation
We present a relatively simple operator formalism which reproduces the
leading infrared logarithm of the one loop quantum gravitational correction to
the fermion mode function on a locally de Sitter background. This rule may
serve as the basis for an eventual stochastic formulation of quantum gravity
during inflation. Such a formalism would not only effect a vast simplification
in obtaining the leading powers of at fixed loop orders, it would also
permit us to sum the series of leading logarithms. A potentially important
point is that our rule does not seem to be consistent with any simple infrared
truncation of the fields. Our analysis also highlights the importance of spin
as a gravitational interaction that persists even when kinetic energy has
redshifted to zero.Comment: 39 pages, no figuire.(1) New version has clarified the ultimate
motivation by adding sentences to the abstract and to the penultimate
paragraph of the introduction. (2) By combining a number of references and
equations we have managed to reduce the length by 2 page
Nonperturbative infrared effects for light scalar fields in de Sitter space
We study the phi^4 scalar field theory in de Sitter space using the 2PI
effective action formalism. This formalism enables us to investigate the
nonperturbative quantum effects. We use the mean field and gap equations and
calculate the physical mass and effective potential. We find that
nonperturbative infrared effects on de Sitter space produce a curvature-induced
mass and work to restore the broken Z_2 symmetry.Comment: 14 pages, 3 figures, section 2 revised, discussion in section 4
changed, results not change
Path Integral for Inflationary Perturbations
The quantum theory of cosmological perturbations in single field inflation is
formulated in terms of a path integral. Starting from a canonical formulation,
we show how the free propagators can be obtained from the well known
gauge-invariant quadratic action for scalar and tensor perturbations, and
determine the interactions to arbitrary order. This approach does not require
the explicit solution of the energy and momentum constraints, a novel feature
which simplifies the determination of the interaction vertices. The constraints
and the necessary imposition of gauge conditions is reflected in the appearance
of various commuting and anti-commuting auxiliary fields in the action. These
auxiliary fields are not propagating physical degrees of freedom but need to be
included in internal lines and loops in a diagrammatic expansion. To illustrate
the formalism we discuss the tree-level 3-point and 4-point functions of the
inflaton perturbations, reproducing the results already obtained by the methods
used in the current literature. Loop calculations are left for future work.Comment: (v1) 28 pages, no figures; (v2) 29 pages, minor changes, matches
published versio
Two Loop Scalar Bilinears for Inflationary SQED
We evaluate the one and two loop contributions to the expectation values of
two coincident and gauge invariant scalar bilinears in the theory of massless,
minimally coupled scalar quantum electrodynamics on a locally de Sitter
background. One of these bilinears is the product of two covariantly
differentiated scalars, the other is the product of two undifferentiated
scalars. The computations are done using dimensional regularization and the
Schwinger-Keldysh formalism. Our results are in perfect agreement with the
stochastic predictions at this order.Comment: 43 pages, LaTeX 2epsilon, 5 figures (using axodraw.sty) Version 2 has
updated references and important corrections to Tables 3-5 and to eqns
(139-141), (145-146), (153-155), (158) and (160
A graviton propagator for inflation
We construct the scalar and graviton propagator in quasi de Sitter space up
to first order in the slow roll parameter . After
a rescaling, the propagators are similar to those in de Sitter space with an
correction to the effective mass. The limit
corresponds to the E(3) vacuum that breaks de Sitter symmetry, but does not
break spatial isotropy and homogeneity. The new propagators allow for a
self-consistent, dynamical study of quantum back-reaction effects during
inflation.Comment: 23 page
Unruh response functions for scalar fields in de Sitter space
We calculate the response functions of a freely falling Unruh detector in de
Sitter space coupled to scalar fields of different coupling to the curvature,
including the minimally coupled massless case. Although the responses differ
strongly in the infrared as a consequence of the amplification of superhorizon
modes, the energy levels of the detector are thermally populated.Comment: 16 pages, 1 figure, accepted for publication by Classical and Quantum
Gravit
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
Use of Vibrational Spectroscopic Techniques for the Characterization of Structured Particles for Chemical Robots
This work is aimed at utilization of vibrational spectroscopic techniques for characterization of several
types of structural particles suitable for the construction of chemical robots. Several case studies are presented
and discussed: (i) PNIPAM-coated silica particles, (ii) surface-functionalized magnetic nanoparticles
modified by citric and oleic acid, (iii) nanocomposit SERS-active substrates consisting of self-assembled
monolayers of linear α,ω-aliphatic diammines with different lengths on Ag metal surface and a flat Ag electrode
followed by testing of sensing activity of AD/NPs systems in the detection of the pesticide aldrin.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3515
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