New insights into properties of large-N holographic thermal QCD at finite gauge coupling at (the non-conformal/next-to) leading order in N

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In this paper we study bulk viscosity in a thermal QCD model with large number of colors at two extreme limits: the very weak and the very strong 't Hooft couplings. The weak coupling scenario is based on kinetic theory, and one may go to the very strong coupling dynamics via an intermediate coupling regime. Although the former has a clear description in terms of kinetic theory, the intermediate coupling regime, which uses lattice results, suffers from usual technical challenges that render an explicit determination of bulk viscosity somewhat difficult. On the other hand, the very strong 't Hooft coupling dynamics may be studied using string theories at both weak and strong string couplings using gravity duals in type IIB as well as M-theory respectively. In type IIB we provide the precise fluctuation modes of the metric in the gravity dual responsible for bulk viscosity, compute the speed of sound in the medium and analyze the ratio of the bulk to shear viscosities. In M-theory, where we uplift the type IIA mirror dual of the UV complete type IIB model, we study and compare both the bulk viscosity and the sound speed by analyzing the quasi-normal modes in the system at strong IIA string coupling. By deriving the spectral function, we show the consistency of our results both for the actual values of the parameters involved as well for the bound on the ratio of bulk to shear viscosities. 65 5.1 The mirror type IIA model and its M-theory uplift 66 5.2 Quasi-normal modes, attenuation constant and the sound speed 70 5.3 The case with a vanishing bare resolution parameter 76 5.4 Shear viscosity, entropy and the bulk viscosity bound 80 6. Type IIA spectral function and the viscosity bound at strong coupling with non-zero flavors 85 6.1 Background gauge fluxes and perturbations on the flavor branes 86 6.2 Equation of motion for gauge field fluctuations 88 6.3 On-shell action and the strong coupling spectral function 95 6.4 The strong string coupling limit and pure classical supergravity 103 -1 -7. Conclusions and discussions 107 A. A Gauge-Invariant Combination of Scalar Modes of Metric Perturbations 112 A.1 The equation of motion for the fluctuation mode H tt 113 A.2 The equation of motion for the combined mode H s 115 A.3 The equations of motion for the remaining fluctuation modes 116 B. A derivation of the on-shell action and the Green's function 118C. Effective number of three-brane charges with background threeforms and the horizon radius 1201 Violation of this bound is seen in the presence of higher derivative terms, discussed first in [23]. In the absence of these terms, the KSS [22] bound continues to hold at strong 't Hooft coupling.2 The non-conformal string theory studied in [30] is different from what we consider here. In [30] it's the N = 2 * supersymmetric gauge theory obtained by a mass deformation of N = 4 Super Yang Mills theory. See also [31] and [32] for an even earlier study on bulk viscosity from first principles.

Section: The Mirror Type Iia Model and Its M-theory Upliftmentioning

confidence: 99%

Section: Quasi-normal Modes Attenuation Constant and The Sound Speedmentioning

confidence: 99%

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Bulk viscosity at extreme limits: from kinetic theory to strings

Czajka

Dasgupta

Gale

et al. 2019

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“…In this section, we will provide a lightning review of the type IIB background of [2] -a UV complete holographic dual of large-N thermal QCD -discuss the 'MQGP' limit of [1] along with the motivation for considering this limit, issues as discussed in [1] pertaining to construction of delocalized S(trominger) Y(au) Z(aslow) mirror and approximate supersymmetry along with (an appendix-supplemented) discussion on the SYZ mirror in fact being independent of angular delocalization, construction explicit SU(3) and G 2 structures respectively of type IIB/IIA and M-theory uplift as constructed for the first time in [12], [13].…”

Section: Introductionmentioning

confidence: 99%

“…it was shown in [13,18] that the aforementioned T 3 is the T 2 -invariant sLag of [17] for a deformed/resolved conifold. Hence, the local T 3 of (3) is the sLag needed to effect the construction of the SYZ mirror.…”

Section: Introductionmentioning

confidence: 99%

M-theory exotic scalar glueball decays to mesons at finite coupling

Yadav

Misra

2018

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Using the pull-back of the perturbed type IIA metric corresponding to the perturbation of [1]'s M-theory uplift of [2]'s UV-complete top-down type IIB holographic dual of large-N thermal QCD, at finite coupling, we obtain the interaction Lagrangian corresponding to exotic scalar glueball(G E )ρ/π-meson interaction, linear in the exotic scalar glueball and up to quartic order in the π mesons. In the Lagrangian the coupling constants are determined as (radial integrals of) [1]'s M-theory uplift's metric components and six radial functions appearing in the M-theory metric perturbations. Assuming M G > 2M ρ , we then compute ρ → 2π, G E → 2π, 2ρ, ρ + 2π decay widths as well as the direct and indirect (mediated via ρ mesons) G E → 4π decays. For numerics, we choose f 0[1710] and compare with previous calculations. We emphasize that our results can be made to match PDG data (and improvements thereof) exactly by appropriate tuning of some constants of integration appearing in the solution of the M-theory metric perturbations and the ρ and π meson radial profile functions -a flexibility that our calculations permits. *

Pole skipping and chaos in anisotropic plasma: a holographic study

Sil

2021

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Recently, a direct signature of chaos in many body system has been realized from the energy density retarded Green’s function using the phenomenon of ‘pole skipping’. Moreover, special locations in the complex frequency and momentum plane are found, known as the pole skipping points such that the retarded Green’s function can not be defined uniquely there. In this paper, we compute the correction/shift to the pole skipping points due to a spatial anisotropy in a holographic system by performing near horizon analysis of EOMs involving different bulk field perturbations, namely the scalar, the axion and the metric field. For vector and scalar modes of metric perturbations we construct the gauge invariant variable in order to obtain the master equation. Two separate cases for every bulk field EOMs is considered with the fluctuation propagating parallel and perpendicular to the direction of anisotropy. We compute the dispersion relation for momentum diffusion along the transverse direction in the shear channel and show that it passes through the first three successive pole skipping points. The pole skipping phenomenon in the sound channel is found to occur in the upper half plane such that the parameters Lyapunov exponent λL and the butterfly velocity vB are explicitly obtained thus establishing the connection with many body chaos.