New canonical analysis for consistent extension of $\lambda R$ gravity

TL;DR

This paper performs a canonical analysis of extended $ ext{lambda} R$ gravity models, especially at $ ext{lambda}=rac{1}{3}$, and explores their constraint structure and degrees of freedom, comparing them to linearized General Relativity.

Contribution

It provides a detailed canonical analysis of $ ext{lambda} R$ gravity extended with BPS and Cotton-square terms, highlighting the special case at $ ext{lambda}=rac{1}{3}$ and its relation to GR.

Findings

At $ ext{lambda}=rac{1}{3}$, an extra second-class constraint appears.

The $ ext{lambda} R$-Cotton-square model has the same degrees of freedom as linearized GR.

The analysis constructs Dirac brackets for the extended models.

Abstract

The canonical analysis of the $\lambda R$ model extended with the term due to Blas, Pujolas, and Sibiryakov $[BPS]$ is performed. The analysis is developed for any value of $\lambda$, but particular attention is paid to the point $\lambda=\frac{1}{3}$ because of the closeness with linearized General Relativity [GR]. Then, we add the higher-order conformal term, the so-called Cotton-square term, to study the constraint structure of what constitutes an example of kinetic-conformal Horava's gravity. At the conformal point, an extra second-class constraint appears; this does not arise at other values of $\lambda$. Then, the Dirac brackets are constructed, and we will observe that the $\lambda R$-Cotton-square model shares the same number of degrees of freedom with linearized $GR$.