63 research outputs found
Cosmological reconstruction of realistic modified F(R) gravities
The cosmological reconstruction scheme for modified gravity is
developed in terms of e-folding (or, redshift). It is demonstrated how any FRW
cosmology may emerge from specific theory. The specific examples of
well-known cosmological evolution are reconstructed, including CDM
cosmology, deceleration with transition to phantom superacceleration era which
may develop singularity or be transient. The application of this scheme to
viable gravities unifying inflation with dark energy era is proposed.
The additional reconstruction of such models leads to non-leading gravitational
correction mainly relevant at the early/late universe and helping to pass the
cosmological bounds (if necessary). It is also shown how cosmological
reconstruction scheme may be generalized in the presence of scalar field.Comment: LaTex 11 page
Trembling cavities in the canonical approach
We present a canonical formalism facilitating investigations of the dynamical
Casimir effect by means of a response theory approach. We consider a massless
scalar field confined inside of an arbitaray domain , which undergoes
small displacements for a certain period of time. Under rather general
conditions a formula for the number of created particles per mode is derived.
The pertubative approach reveals the occurance of two generic processes
contributing to the particle production: the squeezing of the vacuum by
changing the shape and an acceleration effect due to motion af the boundaries.
The method is applied to the configuration of moving mirror(s). Some properties
as well as the relation to local Green function methods are discussed.
PACS-numbers: 12.20; 42.50; 03.70.+k; 42.65.Vh Keywords: Dynamical Casimir
effect; Moving mirrors; Cavity quantum field theory; Vibrating boundary
Influence of Generalized and Extended Uncertainty Principle on Thermodynamics of FRW universe
The influence of the generalized uncertainty principle (GUP) and extended
uncertainty principle (EUP) on the thermodynamics of the
Friedmann-Robertson-Walker (FRW) universe has been investigated. It is shown
that the entropy of the apparent horizon of the FRW universe gets a correction
if one considers the effect of the GUP or EUP. Moreover, starting with the
modified entropy and applying the first law of thermodynamics, , to the
apparent horizon of the FRW universe, we obtain the modified Friedmann
equations. The influence of the GUP or EUP on the thermodynamics of the FRW
universe provides a deep insight into the understanding of the quantum gravity
or large length scale corrections to the dynamics of the FRW universe.Comment: 7 papges, no figure, comments are welcome! v2:Typos corrected, some
references added; v3:typoes corrected, more references added, final version
to appear in Phys. Lett.
Corrections to Hawking-like Radiation for a Friedmann-Robertson-Walker Universe
Recently, a Hamilton-Jacobi method beyond semiclassical approximation in
black hole physics was developed by \emph{Banerjee} and
\emph{Majhi}\cite{beyond0}. In this paper, we generalize their analysis of
black holes to the case of Friedmann-Robertson-Walker (FRW) universe. It is
shown that all the higher order quantum corrections in the single particle
action are proportional to the usual semiclassical contribution. The
corrections to the Hawking-like temperature and entropy of apparent horizon for
FRW universe are also obtained. In the corrected entropy, the area law involves
logarithmic area correction together with the standard inverse power of area
term.Comment: 10 pages, no figures, comments are welcome; v2: references added and
some typoes corrected, to appear in Euro.Phys.J.C; v3:a defect corrected. We
thank Dr.Elias Vagenas for pointing out a defect of our pape
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Thermodynamics of String Field Theory Motivated Nonlocal Models
We investigate the thermodynamic properties of the nonlocal tachyon motivated
by their nonlocal structure in string field theory. We use previously developed
perturbative methods for nonlocal fields to calculate the partition function
and the equation of state in the high temperature limit. We find that in these
models the tachyons undergo a second order phase transition. We compare our
results with those of ordinary scalar field theory. We also calculate the one
loop finite temperature effective potential.Comment: 31 pages, 9 figure
Light-Front View of The Axial Anomaly
Motivated by an apparent puzzle of the light-front vacua incompatible with
the axial anomaly, we have considered the two-dimensional massless Schwinger
model for an arbitrary interpolating angle of the quantization surface. By
examining spectral deformation of the Dirac sea under an external electric
field semiclassically, we have found that the axial anomaly is quantization
angle independent. This indicates an intricate nontrivial vacuum structure
present even in the light-front limit.Comment: 12 pages, REVTEX, one figure postscript file encode
Impact of chronic stress protocols in learning and memory in rodents: systematic review and meta-analysis
The idea that maladaptive stress impairs cognitive function has been a cornerstone of decades in basic and clinical research. However, disparate findings have reinforced the need to aggregate results from multiple sources in order to confirm the validity of such statement. In this work, a systematic review and meta-analyses were performed to aggregate results from rodent studies investigating the impact of chronic stress on learning and memory. Results obtained from the included studies revealed a significant effect of stress on global cognitive performance. In addition, stressed rodents presented worse consolidation of learned memories, although no significantly differences between groups at the acquisition phase were found. Despite the methodological heterogeneity across studies, these effects were independent of the type of stress, animals' strains or age. However, our findings suggest that stress yields a more detrimental effect on spatial navigation tests' performance. Surprisingly, the vast majority of the selected studies in this field did not report appropriate statistics and were excluded from the quantitative analysis. We have therefore purposed a set of guidelines termed PROBE (Preferred Reporting Orientations for Behavioral Experiments) to promote an adequate reporting of behavioral experiments.This work was funded by the European Commission (FP7) "SwitchBox" (Contract HEALTH-F2-2010-259772) project and co-financed by the Portuguese North Regional Operational Program (ON.2 - O Novo Norte) under the National Strategic Reference Framework (QREN), through the European Regional Development Fund (FEDER), and by Fundacao Calouste Gulbenkian (Portugal) (Contract grant number: P-139977; project "Better mental health during ageing based on temporal prediction of individual brain ageing trajectories (TEMPO)"). PSM is supported by an FCT fellowship grant, from the PhD-iHES program, with the reference PDE/BDE/113601/2015.info:eu-repo/semantics/publishedVersio
Relevance of Stress and Female Sex Hormones for Emotion and Cognition
There are clear sex differences in incidence and onset of stress-related and other psychiatric disorders in humans. Yet, rodent models for psychiatric disorders are predominantly based on male animals. The strongest argument for not using female rodents is their estrous cycle and the fluctuating sex hormones per phase which multiplies the number of animals to be tested. Here, we will discuss studies focused on sex differences in emotionality and cognitive abilities in experimental conditions with and without stress. First, female sex hormones such as estrogens and progesterone affect emotions and cognition, contributing to sex differences in behavior. Second, females respond differently to stress than males which might be related to the phase of the estrous cycle. For example, female rats and mice express less anxiety than males in a novel environment. Proestrus females are less anxious than females in the other estrous phases. Third, males perform in spatial tasks superior to females. However, while stress impairs spatial memory in males, females improve their spatial abilities, depending on the task and kind of stressor. We conclude that the differences in emotion, cognition and responses to stress between males and females over the different phases of the estrous cycle should be used in animal models for stress-related psychiatric disorders
Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1.
In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field
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