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 parameter
s 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 Newtons constant lies well inside the observational bounds.
We use data from Supernovae (SNIa) Pantheon sample, from Baryonic Acoustic Oscillations (BAO), and from cosmic chronometers measurements of the Hubble parameter (CC), alongside arguments from Big Bang Nucleosynthesis (BBN), in order to extract constr
aints on Myrzakulov $F(R,T)$ gravity. This is a connection-based theory belonging to the Riemann-Cartan subclass, that uses a specific but non-special connection, which then leads to extra degrees of freedom. Our analysis shows that both considered models lead to $sim 1 sigma$ 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 towards positive values. Furthermore, we use the obtained parameter chains so 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 $Lambda$CDM scenario, while Model 2 resembles it at low redshifts, however at earlier times deviations are allowed. Finally, applying the AIC, BIC and the combined DIC 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.
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 $Delta$ is the sole model parameter, and we show that although the standard value $Delta=0$, which corresponds to zero deformation, lies within the 1$sigma$ region, a deviation is favored. In the case where we let both $Delta$ 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 $Lambda$CDM 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.
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 ($gamma$) of the linear matter perturbations. Considering a constant growth index we can put tight constraints, up to $sim 10%$ accuracy, on $gamma$. 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 $gamma=0.64pm 0.075$ and $0.65pm 0.063$. On the other hand utilizing the Planck priors we obtain $gamma=0.680pm 0.089$ and $0.690pm 0.071$. This shows a small but non-zero deviation from General Relativity ($gamma_{rm GR}approx 6/11$), nevertheless the confidence level is in the range $sim 1.3-2sigma$. Moreover, we find that the estimated mass of the dark-matter halo in which LRGs survive lies in the interval $sim 6.2 times 10^{12} h^{-1} M_{odot}$ and $1.2 times 10^{13} h^{-1} M_{odot}$, for the different bias models. Finally, allowing $gamma$ to evolve with redshift [Taylor expansion: $gamma(z)=gamma_{0}+gamma_{1}z/(1+z)$] we find that the $(gamma_{0},gamma_{1})$ parameter solution space accommodates the GR prediction at $sim 1.7-2.9sigma$ levels.
