Speaker
Description
Cosmic inflation is one of the most successful frameworks for addressing the fundamental problems of the standard Big Bang model, including the horizon, flatness, and magnetic monopole problems. Among various inflationary scenarios, solitonic potentials, due to their topological features and dynamical stability, have attracted considerable attention in cosmological studies. This study investigates the Double-Sine-Gordon (DSG) potential,
\begin{equation}
V(\phi) = \alpha \cos(N\phi) + \beta \cos(2N\phi),
\end{equation}
where $\phi$ denotes the inflaton field, while $\alpha$, $\beta$, and $N$ are free parameters controlling the amplitude, relative contribution of each harmonic term, and the frequency of the oscillatory structure, respectively. The model is studied within two different gravitational frameworks: General Relativity (GR) and Rastall gravity, the latter being a representative of geometry-matter non-minimal coupling theories.
In both frameworks, the inflationary models based on the DSG potential are consistent with the Planck Collaboration 2018 data combined with BK18 and BAO observations, and satisfy the theoretical requirements imposed by the Trans-Planckian Censorship Conjecture (TCC). However, differences emerge between the two approaches. The analysis of the inflationary dynamics reveals differences in the parameter space and the range of viable number of e-folds between the two gravitational frameworks, while remaining consistent with observational constraints.
The reheating phase in both models is well described, yielding a positive reheating number of e-folds $(N_{\text{reh}})$ and a final reheating temperature $(T_{\text{reh}})$ ranging from $10^{-2}\,\text{GeV}$ to $10^{16}\,\text{GeV}$. Additionally, the analysis constrains the free parameters of the DSG potential, including $N$, $\alpha$, and $\beta$, as well as the Rastall parameter, identifying viable regions of parameter space consistent with both observational and theoretical bounds.
This comparison highlights that while the DSG potential provides a viable inflationary model within GR, its implementation in Rastall gravity exhibits enhanced theoretical consistency and broader compatibility with observational constraints, making it a promising candidate for modeling the early Universe.