Type N Spacetimes as Solutions of Extended New Massive Gravity

TL;DR

This paper investigates algebraic type N spacetimes within extended new massive gravity models, demonstrating that solutions of BI-NMG mirror those of NMG and exploring the existence of critical point solutions with finite curvature corrections.

Contribution

It shows that type N solutions of BI-NMG follow from NMG solutions and extends the analysis to models with finite order curvature corrections, including critical point solutions.

Findings

Type N solutions of BI-NMG are derived from NMG solutions.

Finite curvature correction models admit type N solutions.

Critical point solutions with logarithmic behavior are found in finite curvature models.

Abstract

We study algebraic type N spacetimes in the extended new massive gravity (NMG), considering both the Born-Infeld model (BI-NMG) and the model of NMG with any finite order curvature corrections. We show that for these spacetimes, the field equations of BI-NMG take the form of the massive (tensorial) Klein-Gordon type equation, just as it happens for ordinary NMG. This fact enables us to obtain the type N solution to BI-NMG, utilizing the general type N solution of NMG, earlier found in our work. We also obtain type N solutions to NMG with all finite order curvature corrections and show that, in contrast to BI-NMG, this model admits the critical point solutions, which are counterparts of "logarithmic" AdS pp-waves solutions of NMG.