Work

Index saddle for the D1-D5-P black string and its decoupling limit

Year: 2026

Type: paratext

Abstract: A bstract Boruch, Emparan, Iliesiu, and Murthy recently discussed index saddles for 5D black strings, showing that the black string saddle admits a decoupling limit to a complex, finite-temperature BTZ × S 2 saddle that computes the index of the dual CFT. In this paper, we pursue an analogous construction for the D1-D5-P black string. We construct a four-charge index saddle in the four-dimensional STU model as the BPS limit of the non-extremal four-charge black hole, and show that it exhibits the new form of attraction. We then uplift it successively to five and six dimensions, via the 4D-5D connection and a chain of string dualities, to obtain the gravitational index saddle for the D1-D5-P black string. We take a systematic decoupling limit of this index saddle and obtain the BTZ × S 3 saddle that computes the index of the D1-D5 CFT.

Source: Journal of High Energy Physics

DOI: 10.1007/jhep10(2026)123

Authors: Kanhu Kishore Nanda, P. Shanmugapriya, Amitabh Virmani

Institutions: Chennai Mathematical Institute, Tata Institute of Fundamental Research, International Centre for Theoretical Sciences

Language: English

Topic: Black Holes and Theoretical Physics

Subfield: Nuclear and High Energy Physics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: diamond