arXiv subjects

M. S. Eldaher

Publications and source records attributed to M. S. Eldaher.

3 recordsLinked to original sources

arXiv2023

Salvaging Power-Law Inflation through Warming

Power-Law inflation with scale factor $a \propto t^m$ is investigated in the context of warm inflation. The treatment is performed in the weak and strong dissipation limits. In addition, we discuss the three common cases for the thermal dissipation coefficient $Γ(T)$. We compare the theoretical results of the Power-Law model within warm inflation with the observational constraints from Planck $2018$ and BICEP/Keck 2018, as presented by the tensor-to-scalar ratio $r$ and spectral index $n_s$. The model results agree largely with the observations for most of the $Γ(T)$ cases. Furthermore, in order to address the problem of exiting the inflationary epoch, we suggest a perturbed modification to the power-law definition so that it becomes affine, and find that this small change indicates a way for having an exit scenario with a suitable e-foldings number. Finally, we examine this perturbation ansatz within the context of cold inflation with exponential potential, and we find that it can accommodate the observational data with sufficient e-foldings. Our study suggests that the power-law inflation and the exponential potential, in both warm and cold inflation contexts, can in principle be made consistent with the observations and with a possible graceful exit.

astro-ph.CO↗

arXiv2022

Natural Inflation with non minimal coupling to gravity in $R^2$ gravity under the Palatini formalism

Natural Inflation with non-minimal coupling (NMC) to gravity, embodied by a Lagrangian term $ξϕ^2 R $, is investigated in the context of an extended gravity of the form $R+ αR^2$. The treatment is performed in the Palatini formalism. We discuss various limits of the model ``$α\gg 1$'' and ``$α\ll 1$'' in light of two scenarios of inflation: a ``Slow roll'' and a ``Constant roll'' scenario. By analyzing the observational consequences of the model, our results show a significant improvement regarding compatibility between the theoretical results of this model and the observational constraints from Planck 2018 and BICEP/Keck 2018, as exemplified by the tensor-to-scalar ratio and spectral index. Furthermore, a broader range for the parameter space of natural inflation is now compatible with the confidence contours of Planck \& BICEP/Keck results. The joint effects of the contributions of both the NMC to gravity and the $αR^2$ make a significant improvement: $αR^2$ gravity influences scalar-tensor ratio values, whereas NMC to gravity has a more significant impact on the spectral index values. Contributions from both terms allow more previously excluded intervals to be included being compatible now with observational data. These conclusions about the roles of NMC to gravity and, particularly, the extended gravity remain mainly valid with a periodic NMC similar in form to the natural inflation potential.

astro-ph.CO↗

arXiv2021

Inflation by Variation of the Strong Coupling Constant: update for Planck 2018

We apply the "systematic" $1^{st}$ order cosmological perturbation theory method to re-derive the formulation of an inflationary model generated by variation of constants, then to study the case where it is non-minimally coupled to gravity within both the "Metric" and "Palatini" formulations. Accommodating Planck 2018 data with a length scale $\ell$ larger than Planck Length $L_{pl}$ requires amending the model. First, we assume $f(R)$ gravity where we show that an $R^2$-term within Palatini formulation is able to make the model viable. All along the discussions, we elucidate the origin of the difference between the "Metric" and "Palatini" formalisms, and also highlight the terms dropped when applying the shortcut "potential formulae method", unlike the "systematic' method", for the observable parameters. Second, another variant of the model, represented by a two-exponentials potential, fits also the data with $\ell> L_{pl}$.

astro-ph.CO↗