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September 10, 2025

Slow-roll inflation in the f(φ,T) gravity theory

AAshmitaBirla Institute of Technology and Science, Pilani - Goa Campus PSPayel SarkarNational Institute of Science Education and Research PDPrasanta Kumar DasBirla Institute of Technology and Science, Pilani - Goa Campus

Key Points

Both inflaton potentials can predict the scalar spectral index consistent with Planck 2018 data, implying their viability.
In Cases I and III, both gravitational parameters are capable of predicting values within a certain range of the Planck data, indicating robust models.
The analysis shows a high scalar-to-tensor ratio in Case II, yet it still manages to predict the scalar spectral index within desired parameters.
Modified gravity theories demonstrate sensitivity to inflaton dynamics, underscoring their importance in understanding cosmic inflation.

Abstract

In this paper, we study inflation in a modified gravity framework by introducing a direct coupling term between a scalar field Formula: see text (inflaton) and the trace of the energy–momentum tensor Formula: see text as Formula: see text to the Einstein–Hilbert action. We consider two inflaton potentials (i) Formula: see text, (ii) Formula: see text and investigate the sensitivity of the modified gravity parameters Formula: see text and Formula: see text on the inflaton dynamics in the parameter space Formula: see text of the inflaton potentials. We derive the potential slow-roll parameters, scalar spectral index Formula: see text, and tensor-to-scalar ratio Formula: see text in the above Formula: see text gravity theory and analyze the following three choices of modified gravity parameters Formula: see text (i) Case I: Formula: see text i.e. we neglect the higher order Formula: see text term in the analysis, (ii) Case II: Formula: see text, Formula: see text and do the analysis with only Formula: see text term, (iii) Case III: Formula: see text and Formula: see text i.e. keeping both Formula: see text and Formula: see text terms. For a range of potential parameters, we obtain constraints on Formula: see text and Formula: see text in each of the above three cases using the PLANCK 2018 data. In both Cases I and III, we found that both the potentials were capable of predicting the value of Formula: see text within a range of Formula: see text of the Planck 2018 data, while simultaneously satisfying the constraint Formula: see text. In Case II, we observe that the scalar-to-tensor ratio is rather high however it can still predict the scalar spectral index within the range of Planck 2018 data.

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