A T-fold black hole in doubled type IIB

Abstract

We construct an asymptotically flat T-fold representative of a four-dimensional dyonic black-hole charge orbit in doubled type-IIB theory. Starting from the F1-P-NS5-KKM toroidal seed, an integral parabolic T-duality monodromy is imposed on an active doubled three-torus. The non-geometric data enter only through this global patching: the Reissner-Nordstrom-type term is sourced by conserved four-dimensional electric and magnetic field strengths in the doubled Kaluza-Klein/winding local system, not by an internal algebraic Q -flux alone. Exact duality preserves the local equations, the BPS index and the O(6,6) -invariant of the NS-NS/ N=4 charge sublattice governing the entropy. The minimal Einstein-Maxwell dilaton slice contains a running scalar branch and an equal-charge Reissner-Nordstrom limit; the extremal near-horizon region is locally AdS2 & times;S2 , with the compact factor globally T-duality patched.