Konstadinos Siampos

Stability of strings dual to flux tubes between static quarks in N=4 SYM

Abstract Computing heavy quark–antiquark potentials within the AdS/CFT correspondence often leads to behaviors that differ from what one expects on general physical grounds and field-theory considerations. To isolate the configurations of physical interest, it is of utmost importance to examine the stability of the string solutions dual to the flux tubes between the quark and antiquark. Here, we formulate and prove several general statements concerning the perturbative stability of such string solutions, relevant for static quark–antiquark pairs in a general class of backgrounds, and we apply the results to N = 4 SYM at finite temperature and at generic points of the Coulomb branch. In all cases, the problematic regions are found to be unstable and hence physically irrelevant.

M2-M5 blackfold funnels

A bstractWe analyze the basic M2-M5 intersection in the supergravity regime using the blackfold approach. This approach allows us to recover the 1/4-BPS self-dual string soliton solution of Howe, Lambert and West as a three-funnel solution of an effective fivebrane worldvolume theory in a new regime, the regime of a large number of M2 and M5 branes. In addition, it allows us to discuss finite temperature effects for non-extremal self-dual string soliton solutions and wormhole solutions interpolating between stacks of M5 and anti-M5 branes. The purpose of this paper is to exhibit these solutions and their basic properties.

The all-loop non-Abelian Thirring model and its RG flow

Abstract We analyze the renormalization group flow in a recently constructed class of integrable σ-models which interpolate between WZW current algebra models and the non-Abelian T-duals of PCM for a simple group G. They are characterized by the integer level k of the current algebra, a deformation parameter λ and they exhibit a remarkable invariance involving the inversion of λ. We compute the β-function for λ to leading order in 1 k . Based on agreement with previous results for the exact β-function of the non-Abelian bosonized Thirring model and matching global symmetries, we state that our integrable models are the resummed version (capturing all counterterms in perturbation theory) of the non-Abelian bosonized Thirring model for a simple group G. Finally, we present an analogous treatment in a simple example of a closely related class of models interpolating between gauged WZW coset CFTs and the non-Abelian T-duals of PCM for the coset G / H .

Canonical pure spinor (fermionic) T-duality

We establish that the recently discovered fermionic T-duality can be viewed as a canonical transformation in phase space. This requires a careful treatment of constrained Hamiltonian systems. Additionally, we show how the canonical transformation approach for bosonic T-duality can be extended to include Ramond–Ramond backgrounds in the pure spinor formalism.

Stability of string configurations dual to quarkonium states in AdS/CFT

Abstract We extend our earlier work, regarding the perturbative stability of string configurations used for computing the interaction potential of heavy quarks within the gauge/gravity correspondence, to cover a more general class of gravity duals. We provide results, mostly based on analytic methods and corroborated by numerical calculations, which apply to strings in a general class of backgrounds that encompass boosted, spinning and marginally-deformed D3-brane backgrounds. For the case of spinning branes we demonstrate in a few examples that perturbative stability of strings may require strong conditions complementing those following by thermodynamic stability of the dual field theories. For marginally-deformed backgrounds, we find that even in the conformal case stability requires an upper value for the imaginary part σ of the deformation parameter, whereas in regions of the Coulomb branch where there exists linear confinement we find that there exist stable string configurations for certain ranges of values of the parameter σ . We finally discuss the case of open strings with fixed endpoints propagating in Rindler space, which turns out to have an exact classical-mechanical analog.

Gauged WZW-type theories and the all-loop anisotropic non-Abelian Thirring model

We study what we call the all-loop anisotropic bosonized Thirring σ-model. This interpolates between the WZW model and the non-Abelian T-dual of the principal chiral model for a simple group. It has an invariance involving the inversion of the matrix parameterizing the coupling constants. We compute the general renormalization group flow equations which assume a remarkably simple form and derive its properties. For symmetric couplings, they consistently truncate to previous results in the literature. One of the examples we provide gives rise to a first order system of differential equations interpolating between the Lagrange and the Darboux–Halphen integrable systems.

Entropy of the self-dual string soliton

A bstractWe compute the entropy and the corresponding central charge of the selfdual string soliton in the supergravity regime using the blackfold description of the fully localized M2-M5 intersection.

Renormalization of Lorentz non-invariant actions and manifest T-duality

Abstract We study general two-dimensional σ -models which do not possess manifest Lorentz invariance. We show how demanding that Lorentz invariance is recovered as an emergent on-shell symmetry constrains these σ -models. The resulting actions have an underlying group-theoretic structure and resemble Poisson–Lie T-duality invariant actions. We consider the one-loop renormalization of these models and show that the quantum Lorentz anomaly is absent. We calculate the running of the couplings in general and show, with certain non-trivial examples, that this agrees with that of the T-dual models obtained classically from the duality invariant action. Hence, in these cases solving constraints before and after quantization are commuting operations.

Quantum equivalence in Poisson-Lie T-duality

We prove that, general σ-models related by Poisson-Lie T-duality are quantum equivalent under one-loop renormalization group flow. We reveal general properties of the flows, we study the associated generalized coset models and provide explicit examples.

Holographic perfect fluidity, Cotton energy-momentum duality and transport properties

A bstractWe investigate background metrics for 2 + 1-dimensional holographic theories where the equilibrium solution behaves as a perfect fluid, and admits thus a thermodynamic description. We introduce stationary perfect-Cotton geometries, where the Cotton-York tensor takes the form of the energy-momentum tensor of a perfect fluid, i.e. they are of Petrov type Dt. Fluids in equilibrium in such boundary geometries have non-trivial vorticity. The corresponding bulk can be exactly reconstructed to obtain 3 + 1-dimensional stationary black-hole solutions with no naked singularities for appropriate values of the black-hole mass. It follows that an infinite number of transport coefficients vanish for holographic fluids. Our results imply an intimate relationship between black-hole uniqueness and holographic perfect equilibrium. They also point towards a Cotton/energy-momentum tensor duality constraining the fluid vorticity, as an intriguing boundary manifestation of the bulk mass/nut duality.