Late-time constraints on modified Gauss-Bonnet cosmology. (arXiv:2208.02677v1 [gr-qc])

<a href="http://arxiv.org/find/gr-qc/1/au:+Bajardi_F/0/1/0/all/0/1">Francesco Bajardi</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+DAgostino_R/0/1/0/all/0/1">Rocco D'Agostino</a>

In this paper, we consider a gravitational action containing a combination of

the Ricci scalar, $R$, and the topological Gauss–Bonnet term, $G$.

Specifically, we study the cosmological features of a particular class of

modified gravity theories selected by symmetry considerations, namely the

$f(R,G)= R^n G^{1-n}$ model. In the context of a spatially flat, homogeneous

and isotropic background, we show that the currently observed acceleration of

the Universe can be addressed through geometry, hence avoiding emph{de facto}

the shortcomings of the cosmological constant. We thus present a strategy to

numerically solve the Friedmann equations in presence of pressureless matter

and obtain the redshift behavior of the Hubble expansion rate. Then, to check

the viability of the model, we place constraints on the free parameters of the

theory by means of a Bayesian Monte Carlo method applied to late-time cosmic

observations. Our results show that the $f(R,G)$ model is capable of mimicking

the low-redshift behavior of the standard $Lambda$CDM model, though

substantial differences emerge when going toward high redshifts, leading to the

absence of a standard matter-dominated epoch. Finally, we investigate the

energy conditions and show that, under suitable choices for the values of the

cosmographic parameters, they are all violated when considering the mean value

of $n$ obtained from our analysis, as occurs in the case of a dark fluid.

In this paper, we consider a gravitational action containing a combination of

the Ricci scalar, $R$, and the topological Gauss–Bonnet term, $G$.

Specifically, we study the cosmological features of a particular class of

modified gravity theories selected by symmetry considerations, namely the

$f(R,G)= R^n G^{1-n}$ model. In the context of a spatially flat, homogeneous

and isotropic background, we show that the currently observed acceleration of

the Universe can be addressed through geometry, hence avoiding emph{de facto}

the shortcomings of the cosmological constant. We thus present a strategy to

numerically solve the Friedmann equations in presence of pressureless matter

and obtain the redshift behavior of the Hubble expansion rate. Then, to check

the viability of the model, we place constraints on the free parameters of the

theory by means of a Bayesian Monte Carlo method applied to late-time cosmic

observations. Our results show that the $f(R,G)$ model is capable of mimicking

the low-redshift behavior of the standard $Lambda$CDM model, though

substantial differences emerge when going toward high redshifts, leading to the

absence of a standard matter-dominated epoch. Finally, we investigate the

energy conditions and show that, under suitable choices for the values of the

cosmographic parameters, they are all violated when considering the mean value

of $n$ obtained from our analysis, as occurs in the case of a dark fluid.

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