1,108 research outputs found
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
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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 CĂłrdoba y Granada
El de judĂos y conversos ha sido un tema especialmente recurrente para la historiografĂa española, aunque los especialistas se han centrado mayoritariamente en la relaciĂłn de Ă©stos con la InquisiciĂłn, obviando, en gran medida, el análisis de su integraciĂłn en la sociedad cristiano vieja y de su capacidad de ascenso. AquĂ mostramos uno de los muchos ejemplos de familias de origen converso que mediante el poder del dinero y el engaño genealĂłgico, 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 evaluaciĂłn optomĂ©trica, la primera responsabilidad del especialista, es procurar al deportista amĂ©trope (miope, hipermĂ©trope, astĂgmata...) una Ăłptima calidad de visiĂłn, ya sea con gafas o, preferiblemente, con lentes de contacto, por las numerosas ventajas que Ă©stas presentan para el deportista. En los Ăşltimos años, especialmente, la industria de las lentes de contacto viene experimentando una evoluciĂłn imparable, con grandes innovaciones a nivel de materiales, diseños y frecuencias de reemplazo que se traducen en mayor calidad de visiĂłn, confort y seguridad para el usuario. Las lentes de contacto desechables (usar y tirar), suelen ser de primera elecciĂłn para los deportistas. En esta lĂnea se encuentra la lente de contacto Nike Max Sight, de reciente comercializaciĂłn en nuestro paĂs, y que sin duda, como ya está sucediendo en los EUA, puede comportar una pequeña revoluciĂłn 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
DesprĂ©s d’una avaluaciĂł optomètrica completa, la primera responsabilitat de l’especialista, Ă©s procurar una qualitat de visiĂł òptima a l’esportista ametrop (miop, hipermetrop, astigmĂ tic...), ja sigui amb ulleres o, preferiblement, amb lents de contacte, pels nombrosos avantatges que aquestes presenten per a l’esportista. En els Ăşltims anys, especialment, la indĂşstria de les lents de contacte ha experimentat una evoluciĂł imparable, amb grans innovacions en el camp dels materials, els dissenys i les freqüències de reemplaçament, que es tradueixen en mĂ©s qualitat de visiĂł, confort i seguretat per a l’usuari. Les lents de contacte d’un sol Ăşs (usar i llençar), solen ser la primera elecciĂł per als esportistes. En aquesta lĂnia es troba la lent de contacte Nike Max Sight, comercialitzada recentment al nostre paĂs i que, ben segur, com ja estĂ passant als USA, pot comportar una petita revoluciĂł en el context esporti
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