569 research outputs found
Lamb Shift of Unruh Detector Levels
We argue that the energy levels of an Unruh detector experience an effect
similar to the Lamb shift in Quantum Electrodynamics. As a consequence, the
spectrum of energy levels in a curved background is different from that in flat
space. As examples, we consider a detector in an expanding Universe and in
Rindler space, and for the latter case we suggest a new expression for the
local virtual energy density seen by an accelerated observer. In the
ultraviolet domain, that is when the space between the energy levels is larger
than the Hubble rate or the acceleration of the detector, the Lamb shift
quantitatively dominates over the thermal response rate.Comment: 20 page
Stochastic dark energy from inflationary quantum fluctuations
We study the quantum backreaction from inflationary fluctuations of a very
light, non-minimally coupled spectator scalar and show that it is a viable
candiate for dark energy. The problem is solved by suitably adapting the
formalism of stochastic inflation. This allows us to self-consistently account
for the backreaction on the background expansion rate of the Universe where its
effects are large. This framework is equivalent to that of semiclassical
gravity in which matter vacuum fluctuations are included at the one loop level,
but purely quantum gravitational fluctuations are neglected. Our results show
that dark energy in our model can be characterized by a distinct effective
equation of state parameter (as a function of redshift) which allows for
testing of the model at the level of the background.Comment: 32 pages, 5 figures; published version, significant change
Inflation in an effective gravitational model & asymptotic safety
We consider an inflationary model motivated by quantum effects of
gravitational and matter fields near the Planck scale. Our Lagrangian is a
re-summed version of the effective Lagrangian recently obtained by Demmel,
Saueressig and Zanusso~\cite{Demmel:2015oqa} in the context of gravity as an
asymptotically safe theory. It represents a refined Starobinsky model, , where is the
Ricci scalar, and are constants and is an energy scale. By
implementing the COBE normalisation and the Planck constraint on the scalar
spectrum, we show that increasing leads to an increased value of both the
scalar spectral index and the tensor-to-scalar ratio . Requiring
to be consistent with the Planck collaboration upper limit, we find that
can be as large as , the value possibly measurable by Stage IV
CMB ground experiments and certainly from future dedicated space missions. The
predicted running of the scalar spectral index is still
of the order (as in the Starobinsky model), about one order
of magnitude smaller than the current observational bound.Comment: 29 pages, 6 figure
The Scalar Field Kernel in Cosmological Spaces
We construct the quantum mechanical evolution operator in the Functional
Schrodinger picture - the kernel - for a scalar field in spatially homogeneous
FLRW spacetimes when the field is a) free and b) coupled to a spacetime
dependent source term. The essential element in the construction is the causal
propagator, linked to the commutator of two Heisenberg picture scalar fields.
We show that the kernels can be expressed solely in terms of the causal
propagator and derivatives of the causal propagator. Furthermore, we show that
our kernel reveals the standard light cone structure in FLRW spacetimes. We
finally apply the result to Minkowski spacetime, to de Sitter spacetime and
calculate the forward time evolution of the vacuum in a general FLRW spacetime.Comment: 13 pages, 1 figur
Baryogenesis from the amplification of vacuum fluctuations during inflation
We propose that the baryon asymmetry of the Universe may originate from the
amplification of quantum fluctuations of a light complex scalar field during
inflation. CP-violation is sourced by complex mass terms, which are smaller
than the Hubble rate, as well as non-standard kinetic terms. We find that, when
assuming 60 e-folds of inflation, an asymmetry in accordance with observation
can result for models where the energy scale of inflation is of the order of
10^16 GeV. Lower scales may be achieved when assuming substantially larger
amounts of e-folds.Comment: 18 page
Field trials of an improved cost-effective device for detecting peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae) in rural Argentina
An improved device for detecting peridomestic Triatoma infestans consisting of one-liter recycled Tetra Brik milk boxes with a central structure was tested using a matched-pair study design in two rural areas in Argentina. In Olta (La Rioja), the boxes were installed beneath the thatched roofs and on the vertical wooden posts of each peridomestic structure. After a 5-month exposure, at least one of the recovered boxes detected 88% of the 24 T. infestans-positive sites, and 86% of the 7 negative sites by timed manual collections at baseline. In Amamá (Santiago del Estero), the boxes were paired with the best performing prototype tested before (shelter unit). After 3 months, some evidence of infestation was detected in 89% (boxes) and 79% (shelters) of 18-19 sites positive by timed collections, whereas 19% and 16% of 32 negative sites were positive, respectively. Neither device differed significantly in the qualitative or quantitative collection of every sign of infestation. The installation site did not modify significantly the boxes' sampling efficiency in both study areas. As the total cost of each box was half as expensive as each shelter unit, the boxes are thus the most cost-effective and easy-to-use tool for detecting peridomestic T. infestans currently available.Fil: Vazquez Prokopec, Gonzalo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; ArgentinaFil: Ceballos, Leonardo A.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; ArgentinaFil: Salomón, Oscar Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Dirección Nacional de Institutos de Investigación. Administración Nacional de Laboratorios e Institutos de Salud. Centro Nacional de Diagnóstico e Investigaciones Endemo-epidémicas; ArgentinaFil: Gurtler, Ricardo Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentin
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
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
Instabilities in the nonsymmetric theory of gravitation
We consider the linearized nonsymmetric theory of gravitation (NGT) within
the background of an expanding universe and near a Schwarzschild metric. We
show that the theory always develops instabilities unless the linearized
nonsymmetric lagrangian reduces to a particular simple form. This theory
contains a gauge invariant kinetic term, a mass term for the antisymmetric
metric-field and a coupling with the Ricci curvature scalar. This form cannot
be obtained within NGT. Next we discuss NGT beyond linearized level and
conjecture that the instabilities are not a relic of the linearization, but are
a general feature of the full theory. Finally we show that one cannot add
ad-hoc constraints to remove the instabilities as is possible with the
instabilities found in NGT by Clayton.Comment: 29 page
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