In the context of strongly coupled thermal QCD-like theories, the bulk viscosity($ζ$)-to-shear viscosity($η$) ratio using the type IIA-theory dual of thermal QCD-like theories was shown to vary like $\frac{1}{3} - c_s^2$ (arXiv:1807.04713) ($c_s$ being the speed of sound), and the same ($\fracζη$) at weak coupling using kinetic theory and finite temperature field theory, was shown and is known to vary like $\left(\frac{1}{3} - c_s^2\right)^2$ (arXiv:1807.04713). The novelties of the results of this paper are that we not only show for the first time from ${\cal M}$ theory that at intermediate coupling, with the inclusion of the ${\cal O}(R^4)$ corrections, the result obtained for $\fracζη$ interpolates between the strong and weak coupling results in a way consistent with lattice computations of $SU(3)$ Gluodynamics (arXiv:0710.3717 [hep-lat]) within statistical errors (and within the temperature range permissible by our ${\cal M}$-theory uplift), but also observe that this behavior is related to the existence of Contact 3-Structures that exist only at intermediate coupling effected by the intermediate-$N$ "MQGP" limit of (arXiv:2211.13186[hep-th]). We also obtain an explicit dependence of $\fracζη$ on (fractional powers of) the temperature-dependent/running gauge coupling (and its temperature derivative), and verify that the weak-coupling result dominates at large temperatures. We further conjecture that the aforementioned fractional-power-dependence of $\fracζη$ on the gauge coupling is related to the lack of ``$N$-connectedness'' in the parameter space of Contact 3-Structures (as shown in arXiv:2211.13186[hep-th]).
In this paper we extend the study initiated in arXiv:2302.04709v2 [hep-th] to the computation of one-loop elastic amplitudes. We consider 1+1 dimensional massive bosonic Lagrangians with polynomial-like potentials and absence of inelastic processes at the tree level; starting from these assumptions we show how to write sums of one-loop diagrams as products and integrals of tree-level amplitudes. We derive in this way a universal formula for the one-loop two-to-two S-matrices in terms of tree S-matrices. We test our results on different integrable theories, such as sinh-Gordon, Bullough Dodd and the full class of simply-laced affine Toda theories, finding perfect agreement with the bootstrapped S-matrices known in the literature. We show how Landau singularities in amplitudes are naturally captured by our universal formula while they are lost in results based on unitarity-cut methods implemented in the past arXiv:1304.1798v3 [hep-th], arXiv:1405.7947v2 [hep-th].
Using the UV-complete top-down type IIB holographic dual of large-$N$ thermal QCD as constructed in arXiv:hep-th/0902.1540, in arXiv:1507.02692[hep-th], the type IIB background of arXiv:hep-th/0902.1540 was shown to be thermodynamically stable. We also showed that the temperature dependence of DC electrical conductivity mimics a one-dimensional Luttinger liquid, and the requirement of the Einstein relation to be satisfied requires a specific dependence of the Ouyang embedding parameter on the horizon radius. In arXiv:1606.04949[hep-th], we obtained the speed of sound, the shear mode diffusion constant and the shear viscosity $η$ (and $\fracη{s}$) upto (N)ext to (L)eading (O)rder in $N$ by looking at the scalar, vector and tensor modes of metric perturbations and solve Einstein's equation involving appropriate gauge-invariant combination of perturbations as constructed in arXiv:hep-th/0506184. Another interesting result for the temperature dependence of the thermal (and electrical) conductivity and the consequent deviation from the Wiedemann-Franz law, upon comparison with arXiv:0903.3054[cond-mat], was obtained at leading order in $N$. The results for the above qualitatively mimic a 1+1-dimensional Luttinger liquid with impurities. Also we obtained the QCD deconfinement temperature compatible with lattice results. On the holographic phenomenology side, in arXiv:1703.01306 [hep-th], we computed the masses of the $0^{++}, 0^{-+},0^{--}, 1^{++}, 2^{++}$ `glueball' states in the same aforementioned backgrounds. All these calculations were done both for a thermal background with an IR cut-off $r_0$ and a black hole background with horizon radius $r_h$. We used WKB quantization conditions on one hand and imposed Neumann/Dirichlet boundary conditions at $r_0$/$r_h$ on the solutions to the equations of motion on the other.
A bstractWe consider electrically charged static nonextremal black holes in d-dimensional Einstein-Maxwell-(A)dS gravity, whose horizon is a generic Einstein space in d − 2 dimensions. It is shown that for this system the Hamilton-Jacobi equation is exactly solvable and admits two branches of solutions. One of them exhibits a non-simply connected domain of integration constants and does not reduce to the well-known solution for the d = 4 BPS case. The principal functions generate two first order flows that are analytically different, but support the same general solution. One of the two sets of flow equations corresponds to those found by Lü, Pope and Vázquez-Poritz in hep-th/0307001 and (for d = 4 and Λ = 0) by Miller, Schalm and Weinberg in hep-th/0612308. This clarifies also the reason for the very existence of first order equations for nonextremal black holes, namely, they are just the expressions for the conjugate momenta in terms of derivatives of the principal function in a Hamilton-Jacobi formalism. In the last part of our paper we analyze how much of these integrability properties generalizes to matter-coupled N = 2, d = 4 gauged supergravity.
We perform the Hamiltonian analysis of the bimetric theory of gravity introduced in [arXiv:1109.3515 [hep-th]]. We carefully analyze the requirement of the preservation of all constraints and we find that there is no additional constraint that could eliminate the ghost mode.
A bstractWe study the thermodynamical torus partition function of superstring on the near-extremal black NS5-brane background. The exact partition function has been computed with the helps of our previous works: [arXiv:1012.5721 [hep-th]], [arXiv:1109.3365[hep-th]], and naturally decomposed into two parts. The first part is contributed from strings freely propagating in the asymptotic region, which are identified as the superstring gas at the Hawking temperature on the linear-dilaton background. The second part includes the contribution localized around the ‘tip of cigar’, which characterizes the non-extremality. Remarkably, the latter part includes massless excitations with non-vanishing thermal winding, which signifies that the Hagedorn-like behavior effectively appears, even though the Hawking temperature is much lower than the Hagedorn temperature. We also explore the high-temperature backgrounds defined by the orbifolding along the Euclidean time direction. In those cases, the thermal winding modes localized around the tip are found to be tachyonic, reflecting the singularities of Euclidean backgrounds caused by orbifolding.