3,872 research outputs found
Decaying dark energy in light of the latest cosmological dataset
Decaying Dark Energy models modify the background evolution of the most
common observables, such as the Hubble function, the luminosity distance and
the Cosmic Microwave Background temperature-redshift scaling relation. We use
the most recent observationally-determined datasets, including Supernovae Type
Ia and Gamma Ray Bursts data, along with and Cosmic Microwave Background
temperature versus data and the reduced Cosmic Microwave Background
parameters, to improve the previous constraints on these models. We perform a
Monte Carlo Markov Chain analysis to constrain the parameter space, on the
basis of two distinct methods. In view of the first method, the Hubble constant
and the matter density are left to vary freely. In this case, our results are
compatible with previous analyses associated with decaying Dark Energy models,
as well as with the most recent description of the cosmological background. In
view of the second method, we set the Hubble constant and the matter density to
their best fit values obtained by the {\it Planck} satellite, reducing the
parameter space to two dimensions, and improving the existent constraints on
the model's parameters. Our results suggest that the accelerated expansion of
the Universe is well described by the cosmological constant, and we argue that
forthcoming observations will play a determinant role to constrain/rule out
decaying Dark Energy.Comment: 15 pages, 3 figure, 2 table. Accepted in the Special Issue
"Cosmological Inflation, Dark Matter and Dark Energy" on Symmetry Journa
On the universality of MOG weak field approximation at galaxy cluster scale
In its weak field limit, Scalar-tensor-vector gravity theory introduces a
Yukawa-correction to the gravitational potential. Such a correction depends on
the two parameters, which accounts for the modification of the
gravitational constant, and which represents the scale length on
which the scalar field propagates. These parameters were found to be universal
when the modified gravitational potential was used to fit the galaxy rotation
curves and the mass profiles of galaxy clusters, both without Dark Matter. We
test the universality of these parameters using the the temperature
anisotropies due to the thermal Sunyaev-Zeldovich effect. In our model the
intra-cluster gas is in hydrostatic equilibrium within the modified
gravitational potential well and it is described by a polytropic equation of
state. We predict the thermal Sunyaev-Zeldovich temperature anisotropies
produced by Coma cluster, and we compare them with those obtained using the
Planck 2013 Nominal maps. In our analysis, we find and the scale
length, respectively, to be consistent and to depart from their universal
values. Our analysis points out that the assumption of the universality of the
Yukawa-correction to the gravitational potential is ruled out at more than
at galaxy clusters scale, while demonstrating that such a theory of
gravity is capable to fit the cluster profile if the scale dependence of the
gravitational potential is restored.Comment: 8 pages, 3 figures, 2 Tables. Accepted for publication on Physical
Letter
Testing f(R)-theories using the first time derivative of the orbital period of the binary pulsars
In this paper we use one of the Post-Keplerian parameters to obtain
constraints on f(R)-theories of gravity. Using Minkowskian limit, we compute
the prediction of f(R)-theories on the first time derivative of the orbital
period of a sample of binary stars, and we use our theoretical results to
perform a comparison with the observed one. Selecting a sample of relativistic
binary systems we estimate the parameters of an analytic f(R)-gravity. We find
that the theory is not ruled out if we consider only the double neutron star
systems, and in this case we can cover the existing gap between the General
Relativity prediction and the observed data.Comment: 10 pages, 3 figures, 2 tables Accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Probing the physical and mathematical structure of gravity by PSR
There are several approaches to extend General Relativity in order to explain
the phenomena related to the Dark Matter and Dark Energy. These theories,
generally called Extended Theories of Gravity, can be tested using observations
coming from relativistic binary systems as PSR . Using a class of
analytical -theories, one can construct the first time derivative of
orbital period of the binary systems starting from a quadrupolar gravitational
emission. Our aim is to set boundaries on the parameters of the theory in order
to understand if they are ruled out, or not, by the observations on PSR
. Finally, we have computed an upper limit on the graviton mass
showing that agree with constraint coming from other observations.Comment: 6 pages, 1 figure, accepted in International Journal of Geometric
Methods in Modern Physic
Modified gravity revealed along geodesic tracks
The study of the dynamics of a two-body system in modified gravity
constitutes a more complex problem than in Newtonian gravity. Numerical methods
are typically needed to solve the equations of geodesics. Despite the
complexity of the problem, the study of a two-body system in gravity
leads to a new exciting perspective hinting the right strategy to adopt in
order to probe modified gravity. Our results point out some differences between
the {\em semiclassical} (Newtonian) approach, and the {\em relativistic}
(geodesic) one thus suggesting that the latter represents the best strategy for
future tests of modified theories of gravity. { Finally, we have also
highlighted the capability of forthcoming observations to serve as smoking gun
of modified gravity revealing a departure from GR or further reducing the
parameter space of gravity}. \keywords{ gravity \and binary system
\and geodesics \and precessionComment: 7 Pages, 2 figures. Accepted for publication on The European Physics
Journal
Analysis of the Yukawa gravitational potential in gravity I: semiclassical periastron advance
The {\it concordance} cosmological model has been successfully tested
throughout the last decades. Despite its successes, the fundamental nature of
dark matter and dark energy is still unknown. Modifications of the
gravitational action have been proposed as an alternative to these dark
components. The straightforward modification of gravity is to generalize the
action to a function, , of the scalar curvature. Thus one is able to
describe the emergence and the evolution of the Large Scale Structure without
any additional (unknown) dark component. In the weak field limit of the
-gravity, a modified Newtonian gravitational potential arises. This
gravitational potential accounts for an extra force, generally called fifth
force, that produces a precession of the orbital motion even in the classic
mechanical approach. We have shown that the orbits in the modified potential
can be written as Keplerian orbits under some conditions on the strength and
scale length of this extra force. Nevertheless, we have also shown that this
extra term gives rise to the precession of the orbit. Thus, comparing our
prediction with the measurements of the precession of some planetary motions,
we have found that the strength of the fifth force must be in the range
whit the characteristic scale length to fixed to the
fiducial values of AU.Comment: 9 pages, 5 figures, accepted for publication in Phys. Rev.
Constraining gravity by the Large Scale Structure
Over the past decades, General Relativity and the concordance CDM
model have been successfully tested using several different astrophysical and
cosmological probes based on large datasets ({\it precision cosmology}).
Despite their successes, some shortcomings emerge due to the fact that General
Relativity should be revised at infrared and ultraviolet limits and to the fact
that the fundamental nature of Dark Matter and Dark Energy is still a puzzle to
be solved. In this perspective, gravity have been extensively
investigated being the most straightforward way to modify General Relativity
and to overcame some of the above shortcomings. In this paper, we review
various aspects of gravity at extragalactic and cosmological levels. In
particular, we consider cluster of galaxies, cosmological perturbations, and
N-Body simulations, focusing on those models that satisfy both cosmological and
local gravity constraints. The perspective is that some classes of
models can be consistently constrained by Large Scale Structure.Comment: 37 pages, 3 Tables, 6 Figures. Invited Review belonging "Special
Issue Modified Gravity Cosmology: From Inflation to Dark Energy". The
manuscript matches the accepted version. References update
Constraining ultralight bosons in dwarf spheroidal galaxies with a radially varying anisotropy
Axions, and axion-like particles, have come back into fashion in the last
decades as a possible solution to the galactic-scale crisis suffered by the
cold dark matter model. In the framework of the wave Dark Matter model, we have
carried out a Jeans Analysis on eight dwarf spheroidal galaxies that are
orbiting around the Milky Way, and we have constrained the boson mass.
Differently to a previous analysis, we adopted an anisotropy parameter that
varies with the distance from the centre of the galaxy to assess whether this
assumption would help to resolve, or at least alleviate, the well-known tension
with the value of the boson mass favoured by the cosmological analysis. Our
results indicate that, differently to what happens in ultra-faint dwarf
galaxies, such a tension cannot be lifted introducing a variable anisotropy
parameter, leaving as a possible solution the existence of additional axion or
axion-like particles with higher masses as naturally predicted in the Axiverse.Comment: 13 pages, 5, figures, 3 tables. Accepted on PR
Testing f(R)-Theories by Binary Pulsars
Using the Post-Keplerian parameters to obtain, in the Minkowskian limit we obtain constraints on f(R)-theories of gravity from the first time derivative of the orbital period of a sample of binary stars. In the approximation in which the theory is Taylor expandable, we can estimate the parameters of an an analytic f(R)-theory, and fullling the gap between the General Relativity prediction and the one cames from observation, we show that the theory is not ruled out
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