104 research outputs found
The Possibility of a Non-Lagrangian Theory of Gravity
General Relativity resembles a very elegant crystal glass: If we touch its
principles, that is, its Lagrangian, there is a risk of breaking everything.
Or, if we will, it is like a short blanket: Curing some problems creates new
problems. This paper is devoted to bring to light the reasons why we pursue the
possibility of a non-Lagrangian theory of gravity under the hypothesis of an
extension of the original general relativity with an ansatz inspired in the
fundamental principles of classical and quantum physics.Comment: 6 pages, 1 figure. Version accepted in Universe MDP
Nonparametric reconstruction of the Om diagnostic to test LCDM
Cosmic acceleration is usually related with the unknown dark energy, which
equation of state, w(z), is constrained and numerically confronted with
independent astrophysical data. In order to make a diagnostic of w(z), the
introduction of a null test of dark energy can be done using a diagnostic
function of redshift, Om. In this work we present a nonparametric
reconstruction of this diagnostic using the so-called Loess-Simex factory to
test the concordance model with the advantage that this approach offers an
alternative way to relax the use of priors and find a possible 'w' that
reliably describe the data with no previous knowledge of a cosmological model.
Our results demonstrate that the method applied to the dynamical Om diagnostic
finds a preference for a dark energy model with equation of state w =-2/3,
which correspond to a static domain wall network.Comment: 10 pages, 5 figures, 2 table
DBI Galileon inflation in the light of Planck 2015
In this work we consider a DBI Galileon (DBIG) inflationary model and
constrain its parameter space with the Planck 2015 and BICEP2/Keck array and
Planck (BKP) joint analysis data by means of a potential independent analysis.
We focus our attention on inflationary solutions characterized by a constant or
varying sound speed as well as warp factor. We impose bounds on stringy aspects
of the model, such as the warp factor and the induced gravity
parameter . We study the parameter space of the model
and find that the tensor-to-scalar ratio can be as low as
and inflation happens to be at GUT scale. In addition,
we obtain the tilt of the tensor power spectrum and test the standard
inflationary consistency relation against the latest
bounds from the combined results of BKP+Laser Interferometer
Gravitational-Waves Observatory (LIGO), and find that DBIG inflation predicts a
red spectral index for the tensor power spectrum.Comment: Version accepted in JCAP. 25 pages, 10 figures, new refs adde
Exploring bulk viscous unified scenarios with gravitational waves standard sirens
We consider the unified bulk viscous scenarios and constrain them using the Cosmic Microwave Background observations from Planck 2018 and the Pantheon sample from Type Ia supernovae. Then we generate the luminosity distance measurements from O(103)
mock Gravitational Wave Standard Sirens (GWSS) events for the proposed Einstein Telescope. We then combine these mock luminosity distance measurements from the GWSS with the current cosmological probes in order to forecast how the mock GWSS data could be effective in constraining these bulk viscous scenarios. Our results show that a non-zero time dependent bulk viscosity in the universe sector is strongly preferred by the current cosmological probes and will possibly be confirmed at many standard deviations by the future GWSS measurements. We further mention that the addition of GWSS data can significantly reduce the uncertainties of the key cosmological parameters obtained from the usual cosmological probes employed in this work
Unified description of the dynamics of quintessential scalar fields
Using the dynamical system approach, we describe the general dynamics of
cosmological scalar fields in terms of critical points and heteroclinic lines.
It is found that critical points describe the initial and final states of the
scalar field dynamics, but that heteroclinic lines which give a more complete
description of the evolution in between the critical points. In particular, the
heteroclinic line that departs from the (saddle) critical point of perfect
fluid-domination is the representative path in phase space of quintessence
fields that may be viable dark energy candidates. We also discuss the attractor
properties of the heteroclinic lines, and their importance for the description
of thawing and freezing fields.Comment: Minor changes to the text and two new figures, main conclusions
unchanged. 12 pages, 11 figures, uses RevTe
Non-minimally Coupled Cosmological Models with the Higgs-like Potentials and Negative Cosmological Constant
We study dynamics of non-minimally coupled scalar field cosmological models
with Higgs-like potentials and a negative cosmological constant. In these
models the inflationary stage of the Universe evolution changes into a
quasi-cyclic stage of the Universe evolution with oscillation behaviour of the
Hubble parameter from positive to negative values. Depending on the initial
conditions the Hubble parameter can perform either one or several cycles before
to become negative forever.Comment: 22 pages, 6 figures, v4:Section 2 expanded, references added,
accepted for publication in Class. Quant. Gra
Tension between SN and BAO: current status and future forecasts
Using real and synthetic Type Ia SNe (SNeIa) and baryon acoustic oscillations
(BAO) data representing current observations forecasts, this paper investigates
the tension between those probes in the dark energy equation of state (EoS)
reconstruction considering the well known CPL model and Wang's low correlation
reformulation. In particular, here we present simulations of BAO data from both
the the radial and transverse directions. We also explore the influence of
priors on Omega_m and Omega_b on the tension issue, by considering 1-sigma
deviations in either one or both of them. Our results indicate that for some
priors there is no tension between a single dataset (either SNeIa or BAO) and
their combination (SNeIa+BAO). Our criterion to discern the existence of
tension (sigma-distance) is also useful to establish which is the dataset with
most constraining power; in this respect SNeIa and BAO data switch roles when
current and future data are considered, as forecasts predict and spectacular
quality improvement on BAO data. We also find that the results on the tension
are blind to the way the CPL model is addressed: there is a perfect match
between the original formulation and that by the low correlation optimized, but
the errors on the parameters are much narrower in all cases of our exhaustive
exploration, thus serving the purpose of stressing the convenience of this
reparametrization.Comment: 21 pages, under review in JCA
Possible dark energy imprints in gravitational wave spectrum of mixed neutron-dark-energy stars
In the present paper we study the oscillation spectrum of neutron stars
containing both ordinary matter and dark energy in different proportions.
Within the model we consider, the equilibrium configurations are numerically
constructed and the results show that the properties of the mixed
neuron-dark-energy star can differ significantly when the amount of dark energy
in the stars is varied. The oscillations of the mixed neuron-dark-energy stars
are studied in the Cowling approximation. As a result we find that the
frequencies of the fundamental mode and the higher overtones are strongly
affected by the dark energy content. This can be used in the future to detect
the presence of dark energy in the neutron stars and to constrain the
dark-energy models.Comment: 17 pages, 8 figures, LaTe
- …