668 research outputs found
Puntualizaciones sobre «La transición». Apropósito de un encuentro reciente
The object of this article is in fact a review of a spanish contribution to the topic on the ways from Antiquity to mediaeval times, in short, on the « transition». Ten studies are here presented, resumed and, if it is necessary, criticized with own references to its pages, where such affirmations are realized. There is also a up-date point of view on the late Antiquity and beyond
Para un nuevo debate sobre la crisis del s. III (en Hispania), al hilo de un estudio reciente
Sin resume
Notas complementarias sobre el preámbulo del edicto del 301: ¿Lectura económica o histórica?
Sin resume
A generalized non-Gaussian consistency relation for single field inflation
We show that a perturbed inflationary spacetime, driven by a canonical single
scalar field, is invariant under a special class of coordinate transformations
together with a field reparametrization of the curvature perturbation in
co-moving gauge. This transformation may be used to derive the squeezed limit
of the 3-point correlation function of the co-moving curvature perturbations
valid in the case that these do not freeze after horizon crossing. This leads
to a generalized version of Maldacena's non-Gaussian consistency relation in
the sense that the bispectrum squeezed limit is completely determined by
spacetime diffeomorphisms. Just as in the case of the standard consistency
relation, this result may be understood as the consequence of how
long-wavelength modes modulate those of shorter wavelengths. This relation
allows one to derive the well known violation to the consistency relation
encountered in ultra slow-roll, where curvature perturbations grow
exponentially after horizon crossing.Comment: 16 pages, v3: matches published version (JCAP
Vanishing of local non-Gaussianity in canonical single field inflation
We study the production of observable primordial local non-Gaussianity in two
opposite regimes of canonical single field inflation: attractor (standard
single field slow-roll inflation) and non attractor (ultra slow-roll
inflation). In the attractor regime, the standard derivation of the
bispectrum's squeezed limit using co-moving coordinates gives the well known
Maldacena's consistency relation . On the other hand,
in the non-attractor regime, the squeezed limit offers a substantial violation
of this relation given by . In this work we argue that,
independently of whether inflation is attractor or non-attractor, the size of
the observable primordial local non-Gaussianity is predicted to be
(a result that was already understood to hold in the case of
attractor models). To show this, we follow the use of the so-called Conformal
Fermi Coordinates (CFC), recently introduced in the literature. These
coordinates parametrize the local environment of inertial observers in a
perturbed FRW spacetime, allowing one to identify and compute gauge invariant
quantities, such as -point correlation functions. Concretely, we find that
during inflation, after all the modes have exited the horizon, the squeezed
limit of the 3-point correlation function of curvature perturbations vanishes
in the CFC frame, regardless of the inflationary regime. We argue that such a
cancellation should persist after inflation ends.Comment: 27 pages, v2:matches published version(JCAP
Accesibilidad web : un problema pendiente
El presente artículo plantea la necesidad de un cambio en el diseño accesible de los sitios web, teniendo en cuenta que no todos navegamos de igual manera ni tenemos las mismas habilidades o capacidades. También incide en la nueva legislación europea y española al respecto que obliga a instituciones y administraciones públicas a cumplir unos niveles mínimos de accesibilidad a partir de este mismo año 2006 y las consecuencias que estas leyes tienen en el sector de empresas relacionadas con el diseño y la producción de sitios web
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