36 research outputs found
On the renormalization procedure for quantum fields with modified dispersion relation in curved spacetimes
We review our recent results on the renormalization procedure for a free
quantum scalar field with modified dispersion relations in curved spacetimes.
For dispersion relations containing up to powers of the spatial momentum,
the subtraction necessary to renormalize depends
on . We first describe our previous analysis for spatially flat
Friedman-Robertson-Walker and Bianchi type I metrics. Then we present a new
power counting analysis for general background metrics in the weak field
approximation.Comment: Talk given at the 7th Alexander Friedmann International Seminar on
Gravitation and Cosmology, Joao Pessoa, Brazil, July 200
Nonlinear effects of dark energy clustering beyond the acoustic scales
We extend the resummation method of Anselmi & Pietroni (2012) to compute the
total density power spectrum in models of quintessence characterized by a
vanishing speed of sound. For standard CDM cosmologies, this
resummation scheme allows predictions with an accuracy at the few percent level
beyond the range of scales where acoustic oscillations are present, therefore
comparable to other, common numerical tools. In addition, our theoretical
approach indicates an approximate but valuable and simple relation between the
power spectra for standard quintessence models and models where scalar field
perturbations appear at all scales. This, in turn, provides an educated guess
for the prediction of nonlinear growth in models with generic speed of sound,
particularly valuable since no numerical results are yet available.Comment: 28 pages, 12 figure
Extreme parameter sensitivity in quasidilaton massive gravity
We reanalyze the behavior of Friedmann-Lema\^itre-Robertson-Walker
cosmologies in the recently proposed quasidilaton massive-gravity model, and
discover that the background dynamics present hitherto unreported features that
require unexpected fine-tuning of the additional fundamental parameters of the
theory for an observationally consistent background cosmology. We also identify
new allowed regions in the parameters space and exclude some of the previously
considered ones. The evolution of the mass of gravitational waves reveals
non-trivial behavior, exhibiting a mass squared that may be negative in the
past, and that presently, while positive, is larger than the square of the
Hubble parameter. These properties of the gravity-wave mass have the potential
to lead to observational tests of the theory. While quasidilaton massive
gravity is known to have issues with stability at short distances, the current
analysis is a first step toward the investigation of the more stable extended
quasidilaton massive gravity theory, with some expectation that both the
fine-tuning of parameters and the interesting behavior of the gravity-wave mass
will persist.Comment: 10 pages, 7 figure
Massless Interacting Scalar Fields in de Sitter space
We present a method to compute the two-point functions for an scalar
field model in de Sitter spacetime, avoiding the well known infrared problems
for massless fields. The method is based on an exact treatment of the Euclidean
zero modes and a perturbative one of the nonzero modes, and involves a partial
resummation of the leading secular terms. This resummation, crucial to obtain a
decay of the correlation functions, is implemented along with a double
expansion in an effective coupling constant and in . The
results reduce to those known in the leading infrared approximation and
coincide with the ones obtained directly in Lorentzian de Sitter spacetime in
the large limit. The new method allows for a systematic calculation of
higher order corrections both in and in .Comment: 8 pages. Summarized version of JHEP 09 (2016) 117 [arXiv:1606.03481].
Published in the Proceedings of the 19th International Seminar on High Energy
Physics (QUARKS-2016
model in Euclidean de Sitter space: beyond the leading infrared approximation
We consider an scalar field model with quartic interaction in
-dimensional Euclidean de Sitter space. In order to avoid the problems of
the standard perturbative calculations for light and massless fields, we
generalize to the theory a systematic method introduced previously for a
single field, which treats the zero modes exactly and the nonzero modes
perturbatively. We compute the two-point functions taking into account not only
the leading infrared contribution, coming from the self-interaction of the zero
modes, but also corrections due to the interaction of the ultraviolet modes.
For the model defined in the corresponding Lorentzian de Sitter spacetime, we
obtain the two-point functions by analytical continuation. We point out that a
partial resummation of the leading secular terms (which necessarily involves
nonzero modes) is required to obtain a decay at large distances for massless
fields. We implement this resummation along with a systematic double expansion
in an effective coupling constant and in 1/N. We explicitly
perform the calculation up to the next-to-next-to-leading order in
and up to next-to-leading order in 1/N. The results reduce to
those known in the leading infrared approximation. We also show that they
coincide with the ones obtained directly in Lorentzian de Sitter spacetime in
the large N limit, provided the same renormalization scheme is used.Comment: 31 pages, 5 figures. Minor changes. Published versio
Hartree approximation in curved spacetimes revisited II: The semiclassical Einstein equations and de Sitter self-consistent solutions
We consider the semiclassical Einstein equations (SEE) in the presence of a
quantum scalar field with self-interaction . Working in the
Hartree truncation of the two-particle irreducible (2PI) effective action, we
compute the vacuum expectation value of the energy-momentum tensor of the
scalar field, which act as a source of the SEE. We obtain the renormalized SEE
by implementing a consistent renormalization procedure. We apply our results to
find self-consistent de Sitter solutions to the SEE in situations with or
without spontaneous breaking of the -symmetry.Comment: 32 pages, 4 figure
Quantum backreaction of -symmetric scalar fields and de Sitter spacetimes at the renormalization point: renormalization schemes and the screening of the cosmological constant
We consider a theory of self-interacting quantum scalar fields with
quartic -symmetric potential, with a coupling constant , in a
generic curved spacetime. We analyze the renormalization process of the
Semiclassical Einstein Equations at leading order in the expansion for
different renormailzation schemes, namely: the traditional one that sets the
geometry of the spacetime to be Minkowski at the renormalization point, and new
schemes (originally proposed in [1,2]) which set the geometry to be that of a
fixed de Sitter spacetime. In particular, we study the quantum backreaction for
fields in de Sitter spacetimes with masses much smaller than the expansion rate
. We find that the scheme that uses the classical de Sitter background
solution at the renormalization point, stands out as the most appropriate to
study the quantum effects on de Sitter spacetimes. Adopting such scheme we
obtain the backreaction is suppressed by with no logarithmic
enhancement factor of , giving only a small screening of the
classical cosmological constant due to the backreaction of such quantum fields.
We point out the use of the new schemes can also be more appropriate than the
traditional one to study quantum effects in other spacetimes relevant for
cosmology.Comment: 14 pages, 3 figures; v2 agrees with the published version; in v2 we
introduced new clarifications and we replaced the figures by new ones in
order to fix a mistake in v1 and to provide additional details of the result
Bayesian sensitivity of binary pulsars to ultra-light dark matter
Ultra-light dark matter perturbs the orbital motion of binary pulsars, in
particular by causing peculiar time variations of a binary's orbital
parameters, which then induce variations in the pulses' times-of-arrival.
Binary pulsars have therefore been shown to be promising detectors of
ultra-light dark matter. To date, the sensitivity of binary pulsars to
ultra-light dark matter has only been studied for dark matter masses in a
narrow resonance band around a multiple of the binary pulsar orbital frequency.
In this study we devise a two-step, bayesian method that enables us to compute
semi-analytically the sensitivity for all masses, also away from the resonance,
and to combine several observed binaries into one global sensitivity curve. We
then apply our method to the case of a universal, linearly-coupled, scalar
ultra-light dark matter. We find that with next-generation radio observatories
the sensitivity to the ultra-light dark matter coupling will surpass that of
solar-system constraints for a decade in mass around
, even beyond resonance.Comment: 40 pages,15 figure