Transport properties of spacetime-filling branes

A model consisting of (d+1)-dimensional gravity coupled to spacetime filling charged branes is used to study the effects of backreaction. The charged black holes arising from this simple model reflect the non-linearity of the gauge field and are thermodynamically stable. By analysing fluctuations of the system we corroborate that at low values of the temperature (or large chemical potential) backreaction effects from the branes are dominant. We also provide a generalisation of the Iqbal and Liu strategy to calculate the DC conductivity, in which a mass term for the gauge field fluctuation is included. This mass term gives the value of the residue of the pole at zero frequency in the imaginary part of the AC conductivity, as well as the running of the DC conductivity with the bulk radius.Comment: 27 pages + appendix, 11 figures. v2: analysis of fluctuations improve

On actions for (entangling) surfaces and DCFTs

The dynamics of surfaces and interfaces describe many physical systems, including fluid membranes, entanglement entropy and the coupling of defects to quantum field theories. Based on the formulation of submanifold calculus developed by Carter, we introduce a new variational principle for (entangling) surfaces. This principle captures all diffeomorphism constraints on surface/interface actions and their associated spacetime stress tensor. The different couplings to the geometric tensors appearing in the surface action are interpreted in terms of response coefficients within elasticity theory. An example of a surface action with edges at the two-derivative level is studied, including both the parity-even and parity-odd sectors. Its conformally invariant counterpart restricts the type of conformal anomalies that can appear in two-dimensional submanifolds with boundaries. Analogously to hydrodynamics, it is shown that classification methods can be used to constrain the stress tensor of (entangling) surfaces at a given order in derivatives. This analysis reveals a purely geometric parity-odd contribution to the Young modulus of a thin elastic membrane. Extending this novel variational principle to BCFTs and DCFTs in curved spacetimes allows to obtain the Ward identities for diffeomorphism and Weyl transformations. In this context, we provide a formal derivation of the contact terms in the stress tensor and of the displacement operator for a broad class of actions.Comment: v2: 71pp, 1fig, comments and references added, typos fixed, to be published in JHE

BPS black holes from massive IIA on S6^6

We present BPS black hole solutions in a four-dimensional $\mathcal{N}=2$ supergravity with an abelian dyonic gauging of the universal hypermultiplet moduli space. This supergravity arises as the SU(3)-invariant subsector in the reduction of massive IIA supergravity on a six-sphere. The solutions are supported by non-constant scalar, vector and tensor fields and interpolate between a unique $\textrm{AdS}_{2} \,\times\, \textrm{H}^2$ geometry in the near-horizon region and the domain-wall DW$_{4}$ (four-dimensional) description of the D2-brane at the boundary. Some special solutions with charged AdS$_{4}$ or non-relativistic scaling behaviours in the ultraviolet are also presented.Comment: 20 pages, 4 figures and 1 appendix. v2: New appendix, comments and references added, published versio

Desde Luis Iglesias y Jesualdo a Sujomlinski : Construyendo lazos entre las pedagogías latinoamericanas y la pedagogía socialista

En el primer cuatrimestre de 2010 durante la cursada de la cátedra de Educación I se les propuso a los estudiantes el poder cursar en forma optativa un trabajo de campo que propuso la búsqueda, la indagación y la sistematización de las experiencias pedagógicas de Jesualdo y Luis F. Iglesias, haciendo hincapié en los aportes que ellos han realizado al campo pedagógico latinoamericano. Desde ese espacio, se analizaron las experiencias pedagógicas a partir de los paradigmas abordados en Educación I y las discusiones sobre el campo pedagógico que la cátedra busca problematizar. Las influencias que han tenido Luis Iglesias y Jesualdo para pensar sus prácticas pedagógicas fueron muy variadas pero coinciden en haber realizado lecturas profundas sobre el movimiento de la escuela nueva y sobre el pensamiento pedagógico de las izquierdas. Desde dichas indagaciones bibliográficas se pudieron establecer lazos entre las prácticas pedagógicas de ambos maestros con cuestionamientos que realizaba la pedagogía socialista. Aunque dichas indagaciones no estuvieron propuestas de antemano, se pudo pensar en trazar recorridos posibles para la búsqueda de puentes que enlacen los problemas pedagógicos de ambos maestros latinoamericanos con la problemática que ha vivenciado el maestro socialista Vasili Sujomlinski. Sujomlinski fue director de una escuela rural alejada de las grandes ciudades, en la aldea ucraniana de Pavlish. Sujomlinski, al igual que Iglesias y Jesualdo, fue maestro autor de obra, ya que ha publicado varios libros sobre su experiencia docente y fue merecedor de t161tulos honoríficos. Junto con los estudiantes, hemos enriquecido no sólo nuestra formación académica, estableciendo relaciones que liguen las indagaciones realizadas con mi trabajo de tesis de la Maestría en Pedagogías Críticas y Problemáticas Socioeducativas que busca intentar problematizar las categorías de expresión creadora y la libre expresión que plantearon Jesualdo e Iglesias en sus trabajos pedagógicos. Creemos importante que los estudiantes de la carrera de Ciencias de la Educación de la UBA, conozcan las propuestas y las acciones pedagógicas de Luis Iglesias y Jesualdo junto con la experiencia docente de Sujomlinski; porque han pensado políticamente el rol pedagógico haciendo cuestionamientos al sistema escolar, al lugar del conocimiento y al papel de los estudiantes y educadores. Poder valorar dichas experiencias permitirá continuar indagando y reflexionando sobre la pedagogía enriqueciendo las miradas sobre nuestro objeto de estudio

The open string membrane paradigm with external electromagnetic fields

We study the effective geometry felt by the fluctuations of open strings living on the worldvolume of probe D-branes in the presence of background electromagnetic fields. This is captured by an effective action consisting of a Maxwell term and a topological term, with the role of the metric played by the open string metric. Studying generalized Eddington-Finkelstein coordinates for stationary but non-static manifolds, we consider an open string membrane paradigm to obtain a generic formula for the DC transport coefficients, including the effect of external electromagnetic fields present on the worldvolume of the probe branes. We show that the previously studied singular shell, present when a critical electric field strength is turned on, behaves as a horizon for the open string degrees of freedom. The results of this analysis can be used to define a membrane paradigm for a very general class of spacetimes with non-diagonal metrics.Comment: 31 pages, 3 figures, v2: Appendix added, minor correction

Horizon universality and anomalous conductivities

We show that the value of chiral conductivities associated with anomalous transport is universal in a general class of strongly coupled quantum field theories. Our result applies to theories with no dynamical gluon fields and admitting a gravitational holographic dual in the large N limit. On the gravity side the result follows from near horizon universality of the fluctuation equations, similar to the holographic calculation of the shear viscosity.Comment: 13 page