Energy Conditions in $f(P)$ Gravity

TL;DR

This paper investigates energy conditions in $f(P)$ gravity, a new extension of Einsteinian gravity involving a curvature invariant, to constrain models and ensure consistency with cosmic acceleration and observational data.

Contribution

It introduces bounds on specific $f(P)$ models using energy conditions, demonstrating their viability for explaining accelerated cosmic expansion.

Findings

Both models satisfy energy conditions within certain parameter ranges.

Models can produce negative pressure and EoS near -1, consistent with accelerated expansion.

$f(P)$ gravity remains a promising alternative to Einstein's gravity.

Abstract

$f(P)$ gravity is a novel extension of ECG in which the Ricci scalar in the action is replaced by a function of the curvature invariant $P$ which represents the contractions of the Riemann tensor at the cubic order \cite{p}. The present work is concentrated on bounding some $f(P)$ gravity models using the concept of energy conditions where the functional forms of $f(P)$ are represented as \textbf{a)} $f(P) = \alpha \sqrt{P}$, and \textbf{b)} $f(P) = \alpha \exp (P)$, where $\alpha$ is the sole model parameter. Energy conditions are interesting linear relationships between pressure and density and have been extensively employed to derive interesting results in Einstein's gravity, and are also an excellent tool to impose constraints on any cosmological model. To place the bounds, we ensured that the energy density must remain positive, the pressure must remain negative, and the EoS parameter must attain a value close to $-1$ to make sure that the bounds respect the accelerated expansion of the Universe and are also in harmony with the latest observational data. We report that for both the models, suitable parameter spaces exist which satisfy the aforementioned conditions and therefore posit the $f(P)$ theory of gravity to be a promising modified theory of gravitation.