2,804 research outputs found
Dynamical Aspects of Generalized Palatini Theories of Gravity
We study the field equations of modified theories of gravity in which the
lagrangian is a general function of the Ricci scalar and Ricci-squared terms in
Palatini formalism. We show that the independent connection can be expressed as
the Levi-Civita connection of an auxiliary metric which, in particular cases of
interest, is related with the physical metric by means of a disformal
transformation. This relation between physical and auxiliary metric boils down
to a conformal transformation in the case of f(R) theories. We also show with
explicit models that the inclusion of Ricci squared terms in the action can
impose upper bounds on the accessible values of pressure and density, which
might have important consequences for the early time cosmology and black hole
formation scenarios. Our results indicate that the phenomenology of
f(R_{ab}R^{ab}) theories is much richer than that of f(R) and f(R_{ab}R^{ab})
theories and that they also share some similarities with Bekenstein's
relativistic theory of MOND.Comment: 8 pages, no figure
Bethe-Salpeter equation for doubly heavy baryons in the covariant instantaneous approximation
In the heavy quark limit, a doubly heavy baryon is regarded as composed of a
heavy diquark and a light quark. We establish the Bethe-Salpeter (BS) equations
for the heavy diquarks and the doubly heavy baryons, respectively, to leading
order in a expansion. The BS equations are solved numerically under
the covariant instantaneous approximation with the kernels containing scalar
confinement and one-gluon-exchange terms. The masses for the heavy diquarks and
the doubly heavy baryons are obtained and the non-leptonic decay widths for the
doubly heavy baryons emitting a pseudo-scalar meson are calculated within the
model.Comment: Corrections to the text, two references added, version accepted for
publication in Physical Review
Leptonic universality breaking in Upsilon decays as a probe of new physics
In this work we examine the possible existence of new physics beyond the
standard model which could modify the branching fractions of the leptonic
(mainly tauonic) decays of bottomonium vector resonances below the
threshold. The decay width is factorized as the product of two pieces: a) the
probability of an intermediate pseudoscalar color-singlet state
(coupling to the dominant Fock state of the Upsilon via a magnetic dipole
transition) and a soft (undetected) photon; b) the annihilation width of the
pair into two leptons, mediated by a non-standard CP-odd Higgs boson
of mass about 10 GeV, introducing a quadratic dependence on the lepton mass in
the partial width. The process would be unwittingly ascribed to the
leptonic channel thereby (slightly) breaking lepton universality. A possible
mixing of the pseudoscalar Higgs and bottomonium resonances is also considered.
Finally, several experimental signatures to check out the validity of the
conjecture are discussed.Comment: LaTeX, 22 pages, 2 EPS figure
Standard fuzzy uniform structures based on continuous t-norms
This paper deals with fuzzy uniform structures previously introduced by the authors [Fuzzy uniform structures and continuous t-norms, Fuzzy Sets Syst. 161 (2009) 1011-1021]. Our approach involves a covariant functor psi from the category of fuzzy uniform spaces and fuzzy uniformly continuous mappings (in our sense) to the category of uniform spaces and uniformly continuous mappings. We show that psi is well-behaved with respect to some significant fuzzy uniform concepts. and its behavior provides a method to introduce notions of tine fuzzy uniform structure and Stone-tech fuzzy compactification in this context. Our method also applies to obtain fuzzy versions of some classical results on topological algebra and hyperspaces. The case of quasi-uniform structures is also analyzed. (C) 2011 Elsevier B.V. All rights reserved.This research is supported by the Plan Nacional I+D+i, under Grants MTM2009-12872-C02-01 and MTM2009-12872-C02-02.Gutiérrez, J.; Romaguera Bonilla, S.; Sanchis, M. (2012). Standard fuzzy uniform structures based on continuous t-norms. Fuzzy Sets and Systems. 195:75-89. doi:10.1016/j.fss.2011.10.008S758919
Osteoma osteoide de paleta humeral con síndrome paraarticular
Los autores presentan un caso de osteoma osteoide de paleta humeral.
Destacan el problema diagnóstico que plantean los osteomas osteoides
yuxta-articulares y la importancia que tiene la tomografía axial computarizada
(TAC) para el diagnóstico y localización de la lesión, siendo esto
último fundamental para planificar el tratamiento quirúrgico.The authors show an intraarticular osteoid osteoma of the
elbow. They emphasize the diagnostic problem that it pos e and the
importance of CT Scann to diagnosis and localization of the lesion,
being this important to the surgical procedure
A heavy quark effective field lagrangian keeping particle and antiparticle mixed sectors
We derive a tree-level heavy quark effective Lagrangian keeping
particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair
annihilation and creation. However, when removing the unwanted degrees of
freedom from the effective Lagrangian one has to be careful in using the
classical equations of motion obeyed by the effective fields in order to get a
convergent expansion on the reciprocal of the heavy quark mass. Then the
application of the effective theory to such hard processes should be sensible
for special kinematic regimes as for example heavy quark pair production near
threshold.Comment: LaTeX, 14 pages, 1 EPS figure
On balancedness and D-Completeness of the space of Semi-lipschitz functions
Let (X, d) be a quasi-metric space and (Y, q) be a quasi-normed
linear space. We show that the normed cone of semi-Lipschitz functions from
(X, d) to (Y, q) that vanish at a point x0 E X, is balanced. Moreover, it is complete
in the sense of D. Doitchinov whenever (Y, q) is a biBanach spac
Silicon slow-light-based photonic mixer for microwave-frequencyconversion applications
This paper was published in OPTICS LETTERS and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.37.001721. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law[EN] We describe and demonstrate experimentally a method for photonic mixing of microwave signals by using a silicon electro-optical Mach¿Zehnder modulator enhanced via slow-light propagation. Slow light with a group index of ~11, achieved in a one-dimensional periodic structure, is exploited to improve the upconversion performance of an input frequency signal from 1 to 10.25 GHz. A minimum transmission point is used to successfully demonstrate the upconversion with very low conversion losses of ~7¿¿dB and excellent quality of the received I/Q modulated QPSK signal with an optimum EVM of ~8%.Financial support from FP7-224312 HELIOS project and Generalitat Valenciana under PROMETEO-2010-087 R&D Excellency Program (NANOMET) are acknowledged. F. Y.Gardes, D. J. Thomson, and G. T. Reed are supported by funding received from the UK EPSRC funding body under the grant “UK Silicon Photonics.” The author A. M. Gutiérrez thanks D. Marpaung for his useful
help.Gutiérrez Campo, AM.; Brimont, ACJ.; Herrera Llorente, J.; Aamer, M.; Martí Sendra, J.; Thomson, DJ.; Gardes, FY.... (2012). Silicon slow-light-based photonic mixer for microwave-frequencyconversion applications. Optics Letters. 37(10):1721-1723. https://doi.org/10.1364/OL.37.001721S17211723371
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