399 research outputs found
Regular Stringy Black Holes?
We study the first-order corrections to the singular 4-dimensional
massless stringy black holes studied in the nineties in the context of the
Heterotic Superstring. We show that the corrections not only induce a
non-vanishing mass and give rise to an event horizon, but also eliminate the
singularity giving rise to a regular spacetime whose global structure includes
further asymptotically flat regions in which the spacetime's mass is positive
or negative. We study the timelike and null geodesics and their effective
potential, showing that the spacetime is geodesically complete. We discuss the
validity of this solution, arguing that the very interesting and peculiar
properties of the solution are associated to the negative energy contributions
coming from the terms quadratic in the curvature. As a matter of fact, the
10-dimensional configuration is singular. We extract some general lessons on
attempts to eliminate black-hole singularities by introducing terms of higher
order in the curvature.Comment: 5 pages, 2 figure
Non-Abelian black holes in string theory
We study a family of 5-dimensional non-Abelian black holes that can be
obtained by adding an instanton field to the well-known D1D5W Abelian black
holes. Naively, the non-Abelian fields seem to contribute to the black-hole
entropy but not to the mass due to their rapid fall-off at spatial infinity. By
uplifting the 5-dimensional supergravity solution to 10-dimensional Heterotic
Supergravity first and then dualizing it into a Type-I Supergravity solution,
we show that the non-Abelian fields are associated to D5-branes dissolved into
the D9-branes (dual to the Heterotic "gauge 5-branes") and that their
associated RR charge does not, in fact, contribute to the entropy, which only
depends on the number16 pages of D-strings and D5 branes and the momentum along
the D-strings, as in the Abelian case. These "dissolved" or "gauge" D5-branes
do contribute to the mass in the expected form. The correct interpretation of
the 5-dimensional charges in terms of the string-theory objects solves the
non-Abelian hair puzzle, allowing for the microscopic accounting of the
entropy. We discuss the validity of the solution when alpha prime corrections
are taken into account.Comment: Latex 2e file, 21 pages. A full appendix on alpha prime corrections
and the corresponding discussions have been added. The conclusions have
suffered minor changes. Version accepted in JHE
The invisible reality: English teaching materials and the formation of gender and sexually oriented stereotypes (with a focus on primary education)
Gender stereotypes, understood as those structured sets of beliefs about personal attributes of women and men, have a great influence over self-perspective and the social interaction and organisation. However, their effects are sometimes invisible, and a great effort should be made to develop awareness of their influence in the population. Our main claim is that School has an essential role to teach gender and sexual equality through the curricula, using teaching materials that are free of these stereotypes. The main aim of this study is to examine the presence of gender and sexually oriented stereotypes in various English teaching materials within the context of the Spanish Primary School, focusing on its last stage. This research carries out a qualitative and quantitative analysis of three English textbooks together with the students' and teachers' perceptions of gender stereotypes. The analysis is done thanks to the review of key concepts, such as gender awareness and sexual identity, as well as the presentation of various examination tools that have allowed us to evaluate the sexist content in the textbooks selected and offer some guidelines to avoid them in the English classroom
An efficient and scalable platform for java source code analysis using overlaid graph representations
© 2013 IEEE. Although source code programs are commonly written as textual information, they enclose syntactic and semantic information that is usually represented as graphs. This information is used for many different purposes, such as static program analysis, advanced code search, coding guideline checking, software metrics computation, and extraction of semantic and syntactic information to create predictive models. Most of the existing systems that provide these kinds of services are designed ad hoc for the particular purpose they are aimed at. For this reason, we created ProgQuery, a platform to allow users to write their own Java program analyses in a declarative fashion, using graph representations. We modify the Java compiler to compute seven syntactic and semantic representations, and store them in a Neo4j graph database. Such representations are overlaid, meaning that syntactic and semantic nodes of the different graphs are interconnected to allow combining different kinds of information in the queries/analyses. We evaluate ProgQuery and compare it to the related systems. Our platform outperforms the other systems in analysis time, and scales better to program sizes and analysis complexity. Moreover, the queries coded show that ProgQuery is more expressive than the other approaches. The additional information stored by ProgQuery increases the database size and associated insertion time, but these increases are significantly lower than the query/analysis performance gains obtained.Spanish Department of Science, Innovation and Universities under Project RTI2018-099235-B-I00
Laws of Black Hole Mechanics from Holst Action
The formulation of Weak Isolated Horizons (WIH) based on the Isolated Horizon
formulation of black hole horizons is reconsidered. The first part of the paper
deals with the derivation of laws of mechanics of a WIH. While the zeroth law
follows from the WIH boundary conditions, first law depends on the action
chosen. We construct the covariant phase space for a spacetime having an WIH as
inner boundary for the Holst action. This requires the introduction of new
potential functions so that the symplectic structure is foliation independent.
We show that a precise cancellation among various terms leads to the usual
first law for WIH. Subsequently, we show from the same covariant phase space
that for spherical horizons, the topological theory on the inner boundary is a
U(1) Chern-Simons theory.Comment: References added, Minor Corrections 25 pages 1 fi
Primordial Fluctuations within Teleparallelism
We study the cosmological perturbations for the possible inflation scenario
in the teleparallel equivalence of general relativity specified with
parallelizable topological conditions. By acquiring the identical physical
observables to general relativity under the teleparallel formalism, we perform
a 3+1 decomposition of the vierbein field, which can be interpreted as the time
gauge fixing between coordinate and tangent frames. We also extend our
discussion to the higher-order action, gravity.Comment: 17 pages, no figure, revised version accepted by PR
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