S-Branes, Negative Tension Branes and Cosmology

A general class of solutions of string background equations is studied and its physical interpretations are presented. These solutions correspond to generalizations of the standard black p-brane solutions to surfaces with curvature k=-1,0. The relation with the recently introduced S-branes is provided. The mass, charge, entropy and Hawking temperature are computed, illustrating the interpretation in terms of negative tension branes. Their cosmological interpretation is discussed as well as their potential instability under small perturbations.Comment: 10 pages. Talks given at: SUSY'02, ``the 10th International Conference on Supersymmetry and Unification of Fundamental Interactions'', DESY, Hamburg, Germany, 17-23 June 2002, and ``The 1st International Conference on String Phenomenology'', Oxford, July 6 - 11, 2002. References adde

Noncommutative associative superproduct for general supersymplectic forms

We define a noncommutative and nonanticommutative associative product for general supersymplectic forms, allowing the explicit treatment of non(anti)commutative field theories from general nonconstant string backgrounds like a graviphoton field. We propose a generalization of deformation quantization a la Fedosov to superspace, which considers noncommutativity in the tangent bundle instead of base space, by defining the Weyl super product of elements of Weyl super algebra bundles. Super Poincare symmetry is not broken and chirality seems not to be compromised in our formulation. We show that, for a particular case, the projection of the Weyl super product to the base space gives rise the Moyal product for non(anti)commutative theories.Comment: 22 pages, revtex4. References added. Comments added. Includes additional theorem proof

Modulated Reheating and Large Non-Gaussianity in String Cosmology

A generic feature of the known string inflationary models is that the same physics that makes the inflaton lighter than the Hubble scale during inflation often also makes other scalars this light. These scalars can acquire isocurvature fluctuations during inflation, and given that their VEVs determine the mass spectrum and the coupling constants of the effective low-energy field theory, these fluctuations give rise to couplings and masses that are modulated from one Hubble patch to another. These seem just what is required to obtain primordial adiabatic fluctuations through conversion into density perturbations through the `modulation mechanism', wherein reheating takes place with different efficiency in different regions of our Universe. Fluctuations generated in this way can generically produce non-gaussianity larger than obtained in single-field slow-roll inflation; potentially observable in the near future. We provide here the first explicit example of the modulation mechanism at work in string cosmology, within the framework of LARGE Volume Type-IIB string flux compactifications. The inflationary dynamics involves two light Kaehler moduli: a fibre divisor plays the role of the inflaton whose decay rate to visible sector degrees of freedom is modulated by the primordial fluctuations of a blow-up mode (which is made light by the use of poly-instanton corrections). We find the challenges of embedding the mechanism into a concrete UV completion constrains the properties of the non-gaussianity that is found, since for generic values of the underlying parameters, the model predicts a local bi-spectrum with fNL of order `a few'. However, a moderate tuning of the parameters gives also rise to explicit examples with fNL O(20) potentially observable by the Planck satellite.Comment: 42 pages, 2 figure

Inventando el pasado. La familia judeoconversa Herrera de Córdoba y Granada

El de judíos y conversos ha sido un tema especialmente recurrente para la historiografía española, aunque los especialistas se han centrado mayoritariamente en la relación de éstos con la Inquisición, obviando, en gran medida, el análisis de su integración en la sociedad cristiano vieja y de su capacidad de ascenso. Aquí mostramos uno de los muchos ejemplos de familias de origen converso que mediante el poder del dinero y el engaño genealógico, entre otras estrategias, lograron alcanzar las filas de la nobleza castellana.Jews and conversos has been a common issue for the Spanish historians although they only focus in the relationship between them and the Inquisition. As a result of that, we have not analysis of his integration in the Christian Society and his upward mobility. This article presents one of the many examples we have of one family with jewish ancestors whose members could become part of the nobility, in spite of his legacy, using his economical power and the genealogical hiding

Lentes de contacto en el deporte

Tras una completa evaluación optométrica, la primera responsabilidad del especialista, es procurar al deportista amétrope (miope, hipermétrope, astígmata...) una óptima calidad de visión, ya sea con gafas o, preferiblemente, con lentes de contacto, por las numerosas ventajas que éstas presentan para el deportista. En los últimos años, especialmente, la industria de las lentes de contacto viene experimentando una evolución imparable, con grandes innovaciones a nivel de materiales, diseños y frecuencias de reemplazo que se traducen en mayor calidad de visión, confort y seguridad para el usuario. Las lentes de contacto desechables (usar y tirar), suelen ser de primera elección para los deportistas. En esta línea se encuentra la lente de contacto Nike Max Sight, de reciente comercialización en nuestro país, y que sin duda, como ya está sucediendo en los EUA, puede comportar una pequeña revolución en el contexto deportivo

Towards the entropy of gravity time-dependent models via the Cardy-Verlinde formula

For models with several time-dependent components generalized entropies can be defined. This is shown for the Bianchi type IX model. We first derive the Cardy-Verlinde formula under the assumption that the first law of thermodynamics is valid. This leads to an explicit expression of the total entropy associated with this type of universes. Assuming the validity of the Cardy entropy formula, we obtain expressions for the corresponding Bekenstein, Bekenstein-Hawking and Hubble entropies. We discuss the validity of the Cardy-Verlinde formula and possible extensions of the outlined procedure to other time-dependent models.Comment: 13 page

Geometrothermodynamics

We present the fundamentals of geometrothermodynamics, an approach to study the properties of thermodynamic systems in terms of differential geometric concepts. It is based, on the one hand, upon the well-known contact structure of the thermodynamic phase space and, on the other hand, on the metric structure of the space of thermodynamic equilibrium states. In order to make these two structures compatible we introduce a Legendre invariant set of metrics in the phase space, and demand that their pullback generates metrics on the space of equilibrium states. We show that Weinhold's metric, which was introduced {\it ad hoc}, is not contained within this invariant set. We propose alternative metrics which allow us to redefine the concept of thermodynamic length in an invariant manner and to study phase transitions in terms of curvature singularities.Comment: Revised version, to be published in Jour. Math. Phy

Lents de contacte en l’esport

Després d’una avaluació optomètrica completa, la primera responsabilitat de l’especialista, és procurar una qualitat de visió òptima a l’esportista ametrop (miop, hipermetrop, astigmàtic...), ja sigui amb ulleres o, preferiblement, amb lents de contacte, pels nombrosos avantatges que aquestes presenten per a l’esportista. En els últims anys, especialment, la indústria de les lents de contacte ha experimentat una evolució imparable, amb grans innovacions en el camp dels materials, els dissenys i les freqüències de reemplaçament, que es tradueixen en més qualitat de visió, confort i seguretat per a l’usuari. Les lents de contacte d’un sol ús (usar i llençar), solen ser la primera elecció per als esportistes. En aquesta línia es troba la lent de contacte Nike Max Sight, comercialitzada recentment al nostre país i que, ben segur, com ja està passant als USA, pot comportar una petita revolució en el context esporti