Speaker
Description
Using the M-theory uplift inclusive of O(R^4)-corrections as worked out in V.Yadav, A.Misra [ATMP 26(2022)10, 3801-3894], of thermal QCD-like theories in the deconfined phase at intermediate-coupling, the bulk-viscosity-to-shear-viscosity ratio (ζ/η) is calculated (via Green-Kubo/Eling-Oz methods), showing that the O(R^4 ) corrections enable an interpolation between strong- and weak-coupling results consistent with lattice QCD in the (QCD-inspired) intermediate-N MQGP limit, which was shown to possess Contact 3-Structures (A. Misra, G. Yadav, IJGMMP (2025) 2550284). Further, from the EoS, we show that the dual is paramagnetic, and by analyzing the flavor D6-brane gauge-field fluctuations in the absence/presence of strong magnetic fields, we compute the photoproduction spectral function, and interestingly find good agreement with 5D gauged supergravity results [D. Avilla et al, PRD 107(2023) 6, 066010]. We conjecture that (i) the lack of N-path connectedness in the space of (Almost) Contact Structures derivable from G2-structue on compact 7-folds that are M-theory fibrations over a non-Kaehler six-fold that is itself a thermal-circle fibration over deformed Sasaki-Einstein T1,1, as shown in in the aforementioned IJGMMP paper corresponds to branch-point singularities in the complexified gauge coupling, figuring in the complexified bulk-to-shear-viscosity ratio that receives O(R^4) corrections, and (ii) Contact Structure in the UV approaches Almost Contact Structure. The talk will be based on Fortsch.Phys. 73 (2025) 12, e70044, and Phys.Rev.D 110 (2024) 12, 126010.