Nicola Maggiore

Analytic dc thermoelectric conductivities in holography with massive gravitons

We provide an analytical derivation of the thermo-electric transport coefficients of the simplest momentum-dissipating model in gauge/gravity where the lack of momentum conservation is realized by means of explicit graviton mass in the bulk. We rely on the procedure recently described by Donos and Gauntlett in the context of Q-lattices and holographic models where momentum dissipation is realized through non-trivial scalars. The analytical approach confirms the results found previously by means of numerical computations.

Thermo-electric transport in gauge/gravity models with momentum dissipation

A bstractWe present a systematic definition and analysis of the thermo-electric linear response in gauge/gravity systems focusing especially on models with massive gravity in the bulk and therefore momentum dissipation in the dual field theory. A precise treatment of finite counter-terms proves to be essential to yield a consistent physical picture whose hydrodynamic and beyond-hydrodynamics behaviors noticeably match with field theoretical expectations. The model furnishes a possible gauge/gravity description of the crossover from the quantum-critical to the disorder-dominated Fermi-liquid behaviors, as expected in graphene.

Coexistence of two vector order parameters: A holographic model for ferromagnetic superconductivity

A bstractWe study a generalization of the standard holographic p-wave superconductor featuring two interacting vector order parameters. Basing our argument on the symmetry and linear response properties of the model, we propose it as a holographic effective theory describing a strongly coupled ferromagnetic superconductor. We show that the two order parameters undergo concomitant condensations as a manifestation of an intrinsically interlaced charge/spin dynamics. Such intertwined dynamics is confirmed by the study of the transport properties. We characterize thoroughly the equilibrium and the linear response (i.e. optical conductivity and spin susceptibility) of the model at hand by means of a probe approximation analysis. Some insight about the effects of backreaction in the normal phase can be gained by analogy with the s-wave unbalanced holographic superconductor.

PERTURBATION THEORY FOR ANTISYMMETRIC TENSOR FIELDS IN FOUR DIMENSIONS

Perturbation theory for a class of topological field theories containing antisymmetric tensor fields is considered. These models are characterized by a supersymmetric structure which allows us to establish their perturbative finiteness.

Infrared and ultraviolet finiteness of topological BF theory in two dimensions

The two-dimensional topological BF model is considered in the Landau gauge in the framework of perturbation theory. Due to the singular behaviour of the ghost propagator at long distances, a mass term to the ghost fields is introduced as an infrared regulator. Relying on the supersymmetric algebraic structure of the resulting massive theory, the authors study the infrared and ultraviolet renormalizability of the model, with the outcome that it is perturbatively finite.

Protected operators in supersymmetric theories

The anomalous dimension of single and multi-trace composite operators of scalar fields is shown to vanish at all orders of the perturbative series. The proof hold for theories with N=2 supersymmetry with any number of hypermultiplets in a generic representation of the gauge group. It then applies to the finite N=4 theory as well as to non conformal N=2 models.Abstract The anomalous dimension of single and multi-trace composite operators of scalar fields is shown to vanish at all orders of the perturbative series. The proof hold for theories with N =2 supersymmetry with any number of hypermultiplets in a generic representation of the gauge group. It then applies to the finite N =4 theory as well as to nonconformal N =2 models.

Perturbative beta function of N = 2 super Yang-Mills theories

An algebraic proof of the nonrenormalization theorem for the perturbative beta function of the coupling constant of N=2 Super Yang-Mills theory is provided. The proof relies on a fundamental relationship between the N=2 Yang-Mills action and the local gauge invariant polynomial Tr phi^2, phi(x) being the scalar field of the N=2 vector gauge multiplet. The nonrenormalization theorem for the beta function follows from the vanishing of the anomalous dimension of Tr phi^2.An algebraic proof of the nonrenormalization theorem for the perturbative beta function of the coupling constant of N=2 Super Yang-Mills theory is provided. The proof relies on a fundamental relationship between the N=2 Yang-Mills action and the local gauge invariant polynomial Tr phi^2, phi(x) being the scalar field of the N=2 vector gauge multiplet. The nonrenormalization theorem for the beta function follows from the vanishing of the anomalous dimension of Tr phi^2.

Three-dimensional dynamics of four-dimensional topological BF theory with boundary

We consider the four-dimensional (4D) abelian topological BF theory with a planar boundary, following Symanziks method. We find the most general boundary conditions compatible with the field equations broken by the boundary. The residual gauge invariance is described by means of two Ward identities which generate a current algebra. We interpret this algebra as canonical commutation relations of fields, which we use to construct a 3D Lagrangian. As a remarkable by-product, we find a (unique) boundary condition which can be read as a duality relation between 3D dynamical variables.We consider the four dimensional abelian topological BF theory with a planar boundary introduced following the Symanziks method. We find the most general boundary conditions compatible with the fields equations broken by the boundary. The residual gauge invariance is described by means of two Ward identities which generate an algebra of conserved currents. We interpret this algebra as canonical commutation relations of fields, which we use to construct a three dimensional Lagrangian. As a remarkable by-product, the (unique) boundary condition which we found, can be read as a duality relation between 3D dynamical variables.

Non-Abelian BF theory for 2 + 1 dimensional topological states of matter

We present a field theoretical analysis of the 2+1 dimensional BF model with boundary in the Abelian and the non-Abelian case based on Symanziks separability condition. Our aim is to characterize the low-energy properties of time reversal invariant topological insulators. In both cases, on the edges, we obtain Kaalgebras with opposite chiralities reflecting the time reversal invariance of the theory. While the Abelian case presents an apparent arbitrariness in the value of the central charge, the physics on the boundary of the non-Abelian theory is completely determined by time reversal and gauge symmetry. The discussion of the non-Abelian BF model shows that time reversal symmetry on the boundary implies the existence of counter- propagating chiral currents.

Renormalizability of nonrenormalizable field theories

UERJ, Universidade do Estado do Rio de Janeiro, Departamento de Fi ´sica Teorica, Rua Sa˜o Francisco Xavier, 524, 20550-013,Maracana˜, Rio de Janeiro, Brazil~Received 8 December 1998; published 3 May 1999!We give a simple proof of the equivalence theorem, stating that two field theories related by nonlinear fieldtransformations have the same S matrix. We are thus able to identify a subclass of nonrenormalizable fieldtheories which are actually physically equivalent to renormalizable ones. Our strategy is to show by means ofthe Becchi-Rouet-Stora formalism that the ‘‘nonrenormalizable’’ part of such fake nonrenormalizable theoriesis a kind of gauge fixing, being confined in the cohomologically trivial sector of the theory.@S0556-2821~99!50112-4#PACS number~s!: 11.10.Gh