Penrose limits and TsT for fibered $I$-branes

TL;DR

This work analyzes a generalized single-trace T Tbar deformation of the fibered I-brane background via TsT transformations, comparing the effects of performing TsT before versus after the Penrose limit. By deriving the deformed supergravity fields and performing a Penrose limit, the authors map the string spectrum to a BMN-like sector in the dual gauge theory and extract a spin-chain description, finding solvability preserved in the TsT-then-Penrose-limit case. The Penrose-limit-after-TsT cases are more intricate, with several coordinate choices yielding asymptotically free IR sectors or parallelizable pp-waves, indicating a rich structure of nonlocal or irrelevant deformations in the gauge theory. The results reinforce the view that TsT deformations provide a controlled, holographically dual route to generalized T Tbar-like deformations in lower-dimensional holographic pairs, while highlighting non-commutativity of limits and promising avenues for exploring non-supersymmetric deformations. Overall, the paper advances understanding of how TsT-induced deformations of fibered brane backgrounds translate into solvable spin-chain dynamics and potentially novel IR physics in the dual theories.

Abstract

In this paper we analyze a generalized "single-trace $T\bar T$" deformation, defined by a TsT transformation, of the fibered $I$-brane solution from \cite{Nunez2023}. We use the Penrose limit to understand it, and we consider both the TsT followed by the Penrose limit, as well as the Penrose limit followed by TsT. We describe the spin chains obtained in field theory. In the first case we find that, indeed, the TsT transformation preserves solvability in a simple way, as in the standard $T\bar T$ case. In the second case, we have several options, but none is simple enough to be conclusive, however, one case gives us an asymptotically free and IR nontrivial field theory sector, and another a new parallelizable pp wave.