arXiv subjects

Theodoros Katsoulas

Publications and source records attributed to Theodoros Katsoulas.

5 recordsLinked to original sources

arXiv2026

Inflationary assessment of $F(\mathcal{R},\tilde{\mathcal{R}})$ Einstein-Cartan models

In the framework of $F(\mathcal{R},\tilde{\mathcal{R}})$ Einstein-Cartan gravity with an action depending both of the Ricci scalar and the so-called Holst-invariant curvature we consider models that include cubic terms of the latter in the action and study their inflationary behavior. These terms can have a considerable effect either positive or negative in relation to the agreement with present observational data, depending on parameters. In parameter regions where the quadratic models fail to produce results consistent with observational data, the presence of these additional cubic terms can lead to compatible predictions.

gr-qc↗

arXiv2025

Toward a gravitational network: Bridging metric-affine gravity and no-scale supergravity

We consider a class of models in the framework of metric-affine gravity and establish their correspondence to the bosonic sector of a class of no-scale supergravity models. The excellent inflationary behavior of the gravitational models considered is carried over to the corresponding supergravity ones, thus, enriching the landscape of inflation-compatible models.

hep-th↗

arXiv2025

Keeping the relation between the Starobinsky model and no-scale supergravity ACTive

We introduce a modification of the Starobinsky model in the form of an additional cubic Ricci scalar curvature term $\sim αR^3$, scaled by a dimensionless parameter $α$, with the resulting inflaton potential being the standard Starobinsky potential modified to first parametric order by an additive term. The resulting potential is identical to the potential obtained by a modification of the superpotential employed in the construction of the Starobinsky model in the framework of no-scale supergravity, thus, extending the correspondence between a class of no-scale supergravity models and modifications of the Starobinsky model. We analyze the inflationary predictions of the model and find that for $-4.2 \times 10^{-5} \lesssim α\lesssim -1.9 \times 10^{-5}$, the modified Starobinsky model is in full agreement with the recent observational data from the Atacama Cosmology Telescope, for a range of $e$-folds, $N_\star = 50-60$.

gr-qc↗

arXiv2025

General Einstein-Cartan quadratic gravity with derivative couplings

Within the framework of Einstein-Cartan gravity we consider an action, containing up to quadratic terms of the Ricci scalar and the Holst invariant, coupled non-minimally to a scalar field, including couplings of its derivatives to curvature. We derive the equivalent metric theory, featuring an extra dynamical pseudoscalar degree of freedom associated with the presence of the Holst term in the action. We study the evolution of the resulting two-field system in a FRW background and show that it evolves rapidly into an effective single-field inflationary model. We find that the model is consistent with the latest observational data for a wide range of its parameters, determining the necessary upper limits on derivative coupling parameters.

gr-qc↗

arXiv2024

Inflation and reheating in quadratic metric-affine gravity with derivative couplings

Within the framework of metric-affine theories of gravity, where both the metric and connection are treated as independent variables, we consider actions quadratic in the Ricci scalar curvature coupled non-minimally to a scalar field through derivative couplings. Our analysis delves into the inflationary predictions, revealing their consistency with the latest observational constraints across a wide range of parameters. This compatibility permits adjustments such as an increase in the spectral index and a reduction in the tensor-to-scalar ratio. While we do not propose a specific reheating mechanism, our analysis demonstrates that within the quadratic model of inflation, the maximum reheating temperature can reach $\sim 3\times10^{15}\, {\rm GeV}$.

gr-qc↗