23 research outputs found
Growth index of matter perturbations in the light of Dark Energy Survey
We study how the cosmological constraints from growth data are improved by
including the measurements of bias from Dark Energy Survey (DES). In
particular, we utilize the biasing properties of the DES Luminous Red Galaxies
(LRGs) and the growth data provided by the various galaxy surveys in order to
constrain the growth index () of the linear matter perturbations.
Considering a constant growth index we can put tight constraints, up to accuracy, on . Specifically, using the priors of the Dark Energy
Survey and implementing a joint likelihood procedure between theoretical
expectations and data we find that the best fit value is in between
and . On the other hand utilizing the
Planck priors we obtain and . This
shows a small but non-zero deviation from General Relativity (), nevertheless the confidence level is in the range . Moreover, we find that the estimated mass of the dark-matter halo
in which LRGs survive lies in the interval and , for the different bias
models. Finally, allowing to evolve with redshift [Taylor expansion:
] we find that the
parameter solution space accommodates the GR
prediction at levels.Comment: 8 pages, 3 figures, discussion added, to appear in European Physical
Journal C (EPJC
First evidence that non-metricity f (Q) gravity could challenge Lambda CDM
We propose a novel model in the framework of f(Q) gravity, which is a
gravitational modification class arising from the incorporation of
non-metricity. The model has General Relativity as a particular limit,
it has the same number of free parameters to those of Lambda CDM,
however at a cosmological framework it gives rise to a scenario that
does not have Lambda CDM as a limit. Nevertheless, confrontation with
observations at both background and perturbation levels, namely with
Supernovae type Ia (SNIa), Baryonic Acoustic Oscillations (BAO), cosmic
chronometers (CC), and Redshift Space Distortion (RSD) data, reveals
that the scenario, according to AIC, BIC and DIC information criteria,
is in some datasets slightly preferred comparing to Lambda CDM
cosmology, although in all cases the two models are statistically
indiscriminate. Finally, the model does not exhibit early dark energy
features, and thus it immediately passes BBN constraints, while the
variation of the effective Newton's constant lies well inside the
observational bounds. (C) 2021 The Authors. Published by Elsevier B.V
Observational constraints on Myrzakulov gravity
We use data from Supernovae Pantheon sample, from baryonic acoustic
oscillations, and from cosmic chronometers measurements of the Hubble
parameter, alongside arguments from big bang nucleosynthesis, in order
to extract constraints on Myrzakulov F(R,N) gravity. This is a
connection-based theory belonging to the Riemann-Cartan subclass, that
uses a specific but nonspecial connection, which then leads to extra
degrees of freedom. Our analysis shows that both considered models lead
to approximately 1 sigma compatibility in all cases. For the involved
dimensionless parameter, we find that it is constrained to an interval
around zero; however, the corresponding contours are slightly shifted
toward positive values. Furthermore, we use the obtained parameter
chains to reconstruct the corresponding Hubble function, as well as the
dark energy equation-of-state parameter, as a function of redshift. As
we show, model 1 is very close to Lambda-Cold Dark Matter (Lambda CDM)
scenario, while model 2 resembles it at low redshifts; however, at
earlier times, deviations are allowed. Finally, applying the Akaike
Information Criterion, Bayesian Information Criterion, and combined
Deviance Information Criterion criteria, we deduce that both models
present a very efficient fitting behavior and are statistically
equivalent with Lambda CDM cosmology, despite the fact that model 2 does
not contain the latter as a limit
Observational constraints on Barrow holographic dark energy
We use observational data from Supernovae (SNIa) Pantheon sample, as well as from direct measurements of the Hubble parameter from the cosmic chronometers (CC) sample, in order to extract constraints on the scenario of Barrow holographic dark energy. The latter is a holographic dark energy model based on the recently proposed Barrow entropy, which arises from the modification of the black-hole surface due to quantum-gravitational effects. We first consider the case where the new deformation exponent is the sole model parameter, and we show that although the standard value , which corresponds to zero deformation, lies within the region, a deviation is favored. In the case where we let both and the second model parameter to be free we find that a deviation from standard holographic dark energy is preferred. Additionally, applying the Akaike, Bayesian and Deviance Information Criteria, we conclude that the one-parameter model is statistically compatible with paradigm, and preferred comparing to the two-parameter one. Finally, concerning the present value of the Hubble parameter we find that it is close to the Planck value