438 research outputs found
Observational signatures of Jordan-Brans-Dicke theories of gravity
We analyze the Jordan-Brans-Dicke model (JBD) of gravity, where deviations
from General Relativity (GR) are described by a scalar field non-minimally
coupled to gravity. The theory is characterized by a constant coupling
parameter, ; GR is recovered in the limit . In such theories, gravity modifications manifest at early times,
so that one cannot rely on the usual approach of looking for inconsistencies in
the expansion history and perturbations growth in order to discriminate between
JBD and GR. However, we show that a similar technique can be successfully
applied to early and late times observables instead. Cosmological parameters
inferred extrapolating early-time observations to the present will match those
recovered from direct late-time observations only if the correct gravity theory
is used. We use the primary CMB, as will be seen by the Planck satellite, as
the early-time observable; and forthcoming and planned Supernov{\ae}, Baryonic
Acoustic Oscillations and Weak Lensing experiments as late-time observables. We
find that detection of values of as large as 500 and 1000 is
within reach of the upcoming (2010) and next-generation (2020) experiments,
respectively.Comment: minor revision, references added, matching version published in JCA
A new diagrammatic representation for correlation functions in the in-in formalism
In this paper we provide an alternative method to compute correlation
functions in the in-in formalism, with a modified set of Feynman rules to
compute loop corrections. The diagrammatic expansion is based on an iterative
solution of the equation of motion for the quantum operators with only retarded
propagators, which makes each diagram intrinsically local (whereas in the
standard case locality is the result of several cancellations) and endowed with
a straightforward physical interpretation. While the final result is strictly
equivalent, as a bonus the formulation presented here also contains less graphs
than other diagrammatic approaches to in-in correlation functions. Our method
is particularly suitable for applications to cosmology.Comment: 14 pages, matches the published version. includes a modified version
of axodraw.sty that works with the Revtex4 clas
Role of microRNAs in the main molecular pathways of hepatocellular carcinoma
Hepatocellular carcinoma (HCC) is the most common primary liver malignant neoplasia. HCC is characterized by a poor prognosis. The need to find new molecular markers for its diagnosis and prognosis has led to a progressive increase in the number of scientific studies on this topic. MicroRNAs (miRNAs) are small noncoding RNA that play a role in almost all main cellular pathways. miRNAs are involved in the regulation of expression of the major tumor-related genes in carcinogenesis, acting as oncogenes or tumor suppressor genes. The aim of this review was to identify papers published in 2017 investigating the role of miRNAs in HCC tumorigenesis. miRNAs were classified according to their role in the main molecular pathways involved in HCC tumorigenesis: (1) mTOR; (2) Wnt; (3) JAK/STAT; (4) apoptosis; and (5) MAPK. The role of miRNAs in prognosis/response prediction was taken into consideration. Bearing in mind that the analysis of miRNAs in serum and other body fluids would be crucial for clinical management, the role of circulating miRNAs in HCC patients was also investigated. The most represented miRNA-regulated pathway in HCC is mTOR, but apoptosis, Wnt, JAK/STAT or MAPK pathways are also influenced by miRNA expression levels. These miRNAs could thus be used in clinical practice as diagnostic, prognostic or therapeutic targets for HCC treatment
Cosmological Model-independent Gamma-ray Bursts Calibration and its Cosmological Constraint to Dark Energy
As so far, the redshift of Gamma-ray bursts (GRBs) can extend to
which makes it as a complementary probe of dark energy to supernova Ia (SN Ia).
However, the calibration of GRBs is still a big challenge when they are used to
constrain cosmological models. Though, the absolute magnitude of GRBs is still
unknown, the slopes of GRBs correlations can be used as a useful constraint to
dark energy in a completely cosmological model independent way. In this paper,
we follow Wang's model-independent distance measurement method and calculate
their values by using 109 GRBs events via the so-called Amati relation. Then,
we use the obtained model-independent distances to constrain CDM model
as an example.Comment: 16 pages, 5 figure
CMB polarization from secondary vector and tensor modes
We consider a novel contribution to the polarization of the Cosmic Microwave
Background induced by vector and tensor modes generated by the non-linear
evolution of primordial scalar perturbations. Our calculation is based on
relativistic second-order perturbation theory and allows to estimate the
effects of these secondary modes on the polarization angular power-spectra. We
show that a non-vanishing B-mode polarization unavoidably arises from pure
scalar initial perturbations, thus limiting our ability to detect the signature
of primordial gravitational waves generated during inflation. This secondary
effect dominates over that of primordial tensors for an inflationary
tensor-to-scalar ratio . The magnitude of the effect is smaller than
the contamination produced by the conversion of polarization of type E into
type B, by weak gravitational lensing. However the lensing signal can be
cleaned, making the secondary modes discussed here the actual background
limiting the detection of small amplitude primordial gravitational waves.Comment: 14 pages, 3 figures, minor changes matching the version to be
published in Phys. Rev.
Thermal non-Gaussianity in holographic cosmology
Recently it has been shown that the thermal holographic fluctuations can give
rise to an almost scale invariant spectrum of metric perturbations since in
this scenario the energy is proportional to the area of the boundary rather
than the volume. Here we calculate the non-Gaussianity of the spectrum of
cosmological fluctuations in holographic phase, which can imprint on the
radiation dominated universe by an abrupt transition. We find that if the
matter is phantom-like, the non-Gaussianity can reach or even be larger than . Especially in the limit , the non-Gaussianity is very large and negative. Furthermore, since the
energy is proportional to the area, the thermal holographic non-Gaussianity
depends linearly on if we neglect the variation in during the
transition (fixed temperature).Comment: 13 pages, Minor corrections and one reference added;v3,minor
correction
Observational Constraints to Ricci Dark Energy Model by Using: SN, BAO, OHD, fgas Data Sets
In this paper, we perform a global constraint on the Ricci dark energy model
with both the flat case and the non-flat case, using the Markov Chain Monte
Carlo (MCMC) method and the combined observational data from the cluster X-ray
gas mass fraction, Supernovae of type Ia (397), baryon acoustic oscillations,
current Cosmic Microwave Background, and the observational Hubble function. In
the flat model, we obtain the best fit values of the parameters in regions: ,
, , . In the non-flat
model, the best fit parameters are found in
regions:,
, , ,
. Compared to the constraint results in
the model by using the same datasets, it is shown that
the current combined datasets prefer the model to the
Ricci dark energy model.Comment: 12 pages, 3 figure
Prospects in Constraining the Dark Energy Potential
We generalize to non-flat geometries the formalism of Simon et al. (2005) to
reconstruct the dark energy potential. This formalism makes use of quantities
similar to the Horizon-flow parameters in inflation, can, in principle, be made
non-parametric and is general enough to be applied outside the simple, single
scalar field quintessence. Since presently available and forthcoming data do
not allow a non-parametric and exact reconstruction of the potential, we
consider a general parametric description in term of Chebyshev polynomials. We
then consider present and future measurements of H(z), Baryon Acoustic
Oscillations surveys and Supernovae type 1A surveys, and investigate their
constraints on the dark energy potential. We find that, relaxing the flatness
assumption increases the errors on the reconstructed dark energy evolution but
does not open up significant degeneracies, provided that a modest prior on
geometry is imposed. Direct measurements of H(z), such as those provided by BAO
surveys, are crucially important to constrain the evolution of the dark energy
potential and the dark energy equation of state, especially for non-trivial
deviations from the standard LambdaCDM model.Comment: 22 pages, 7 figures. 2 references correcte
On Non-Gaussianity in the Curvaton Scenario
Since a positive future detection of non-linearity in the cosmic microwave
background anisotropy pattern might allow to descriminate among different
mechanisms giving rise to cosmological adiabatic perturbations, we study the
evolution of the second-order cosmological curvature perturbation on
super-horizon scales in the curvaton scenario. We provide the exact expression
for the non-Gaussianity in the primordial perturbations including gravitational
second-order corrections which are particularly relevant in the case in which
the curvaton dominates the energy density before it decays. As a byproduct, we
show that in the standard scenario where cosmological curvature perturbations
are induced by the inflaton field, the second-order curvature perturbation is
conserved even during the reheating stage after inflation.Comment: LaTeX file, 8 pages. Some typos corrected. In Sec. IIIA non-local
gradient terms explicitly accounted for in the final non-linear parameter and
references adde
Scale-dependent bias induced by local non-Gaussianity: A comparison to N-body simulations
We investigate the effect of primordial non-Gaussianity of the local f_NL
type on the auto- and cross-power spectrum of dark matter haloes using
simulations of the LCDM cosmology. We perform a series of large N-body
simulations of both positive and negative f_NL, spanning the range between 10
and 100. Theoretical models predict a scale-dependent bias correction \Delta
b(k,f_NL) that depends on the linear halo bias b(M). We measure the power
spectra for a range of halo mass and redshifts covering the relevant range of
existing galaxy and quasar populations. We show that auto and cross-correlation
analyses of bias are consistent with each other. We find that for low
wavenumbers with k<0.03 h/Mpc the theory and the simulations agree well with
each other for biased haloes with b(M)>1.5. We show that a scale-independent
bias correction improves the comparison between theory and simulations on
smaller scales, where the scale-dependent effect rapidly becomes negligible.
The current limits on f_NL from Slosar et al. (2008) come mostly from very
large scales k<0.01 h/Mpc and, therefore, remain valid. For the halo samples
with b(M)<1.5-2 we find that the scale- dependent bias from non-Gaussianity
actually exceeds the theoretical predictions. Our results are consistent with
the bias correction scaling linearly with f_NL.Comment: 13 pages, 10 figures. (v2): substantial changes. added a physically
motivated scale-independent bias correction which improves significantly the
agreement with the simulations (v3): matches published versio
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