An Einstein-like theory of gravity with a non-newtonian weak-field limit

We propose a model describing Einstein gravity coupled to a scalar field with an exponential potential. We show that the weak-field limit of the model has static solutions given by a gravitational potential behaving for large distances as \ln r . The Newtonian term GM/r appears only as subleading. Our model can be used to give a phenomenological explanation of the rotation curves of the galaxies without postulating the presence of dark matter. This can be achieved only by giving up at galactic scales Einstein equivalence principle.Comment: Final version, accepted for publication on General Relativity and Gravitatio

Acoustic analogs of two-dimensional black holes

We present a general method for constructing acoustic analogs of the black hole solutions of two-dimensional (2D) dilaton gravity. Because by dimensional reduction every spherically symmetric, four-dimensional (4D) black hole admits a 2D description, the method can be also used to construct analogue models of 4D black holes. We also show that after fixing the gauge degrees of freedom the 2D gravitational dynamics is equivalent to an one-dimensional fluid dynamics. This enables us to find a natural definition of mass $M$, temperature $T$ and entropy $S$ of the acoustic black hole. In particular the first principle of thermodynamics $dM=TdS$ becomes a consequence of the fluid dynamics equations. We also discuss the general solutions of the fluid dynamics and two particular cases, the 2D Anti-de sitter black hole and the 4D Schwarzschild black hole.Comment: some references adde

Social theory and the analysis of transactions

Este artículo analiza una seria objeción a las teorías sociales que apoyan los mecanismos apagados y las fuerzas escondidas que, a su vez, influyen en los actores sociales: ellas destacan la necesidad teórica de confirmar sus presuposiciones tanto si ellas son demostradas como si son desmentidas por los fenómenos en los que ellas mismas se centran. En primer lugar, el autor examina cómo Latour ha puesto en evidencia decididamente este problema. Se trata, pues, de uno de los objetivos polémicos principales de Latour, la teoría social de Bourdieu, para demostrar que, en realidad, Bourdieu compartió las preocupaciones de Latour. Este artículo lleva a cabo este objetivo deteniéndose en la relación entre la noción de rule-following de Wittgenstein y la de habitus de Bourdieu. En la base de este análisis, el autor profundiza el concepto de transactions, que atañe a las interpretaciones discursivas de los actores y al contexto semiótico en los que se insertan. Este análisis finaliza con las consecuencias teóricopolíticas de este tipo de metodología.This article discusses a serious objection to social theories that claim opaque mechanisms and hidden forces operate over social actors’ head: they bespeak the theorists’ need to confirm their presuppositions whether they are proven or disproven by the phenomena they focus on. The author first explores the way in which Latour has convincingly unearthed this problem. He then analyzes one of Latour’s primary polemical targets, Bourdieu’s social theory, to show that in reality Bourdieu shared Latour’s concerns. The article does so by exploring the nexus between Wittgenstein’s notion of rule-following and notion of Bourdieu’s habitus. Based on this analysis, the author elaborates on the concept of “transactions”, which draws attention to both the actors’ discursive performances and the semiotic context where they take place. The article concludes by illustrating the theoretical-political consequences of this methodological commitment

Higgs Bosons in Extra Dimensions

In this paper, motivated by the recent discovery of a Higgs-like boson at the LHC with a mass m_H\simeq 126 GeV, we review different models where the hierarchy problem is solved by means of a warped extra dimension. In the Randall-Sundrum model electroweak observables provide very strong bounds on the mass of KK modes which motivates extensions to overcome this problem. Two extensions are briefly discussed. One particular extension is based on the deformation of the metric such that it strongly departs from the AdS_5 structure in the IR region while it goes asymptotically to AdS_5 in the UV brane. This model has the IR brane close to a naked metric singularity (which is outside the physical interval) characteristic of soft-walls constructions. The proximity of the singularity provides a strong wave-function renormalization for the Higgs field which suppresses the T and S parameters. The second class of considered extensions are based on the introduction of an extra gauge group in the bulk such that the custodial SU(2)_R symmetry is gauged and protects the T parameter. By further enlarging the bulk gauge symmetry one can find models where the Higgs is identified with the fifth component of gauge fields and for which the Higgs potential, along with the Higgs mass, can be dynamically determined by the Coleman-Weinberg mechanism.Comment: 29 pages, 13 figures. Invited review for IJMP

Half-quadratic transportation problems

We present a primal--dual memory efficient algorithm for solving a relaxed version of the general transportation problem. Our approach approximates the original cost function with a differentiable one that is solved as a sequence of weighted quadratic transportation problems. The new formulation allows us to solve differentiable, non-- convex transportation problems