Black holes in extended gravity theories in Palatini formalism

We consider several physical scenarios where black holes within classical gravity theories including $R^2$ and Ricci-squared corrections and formulated \`a la Palatini can be analytically studied.Comment: 4 pages, contribution to the "Spanish Relativity Meeting in Portugal 2012 (Progress in Mathematical Relativity, Gravitation and Cosmology)", Springer Proceedings in Mathematics (to appear

Nonsingular charged black holes \`{a} la Palatini

We argue that the quantum nature of matter and gravity should lead to a discretization of the allowed states of the matter confined in the interior of black holes. To support and illustrate this idea, we consider a quadratic extension of General Relativity formulated \`{a} la Palatini and show that nonrotating, electrically charged black holes develop a compact core at the Planck density which is nonsingular if the mass spectrum satisfies a certain discreteness condition. We also find that the area of the core is proportional to the number of charges times the Planck area.Comment: 10 single column page

The Cross-Section of Interbank Rates: A Nonparametric Empirical Investigation

This paper analyzes the distribution of lending and borrowing credit spreads in the European interbank market conditional on main features of banks such as their size, operating currency and nationality. This is done by means of nonparametric kernel estimation methods for the cross-sectional density of interbank funding rates over a large sample of European banks trading in the e-MID market. The analysis is repeated over consecutive non-overlapping periods in order to assess and compare the effect of the factors during crisis and non-crisis periods. We find evidence of important differences between the borrowing and lending segment of the interbank market that are augmented during crises periods. Our results strongly support the existence of a size effect in the borrowing market. Largest banks enjoy the highest lending rates and the lowest borrowing rates. The collapse of Lehman Brothers accentuates the differences in funding conditions. In both borrowing and lending segments, crises are corresponded by high volatilities in daily funding costs. Banks using the Euro currency and in countries not affected by sovereign debt crises are benefited by lower funding costs. Our nonparametric analysis of densities conditional on banks' nationality suggests that distress in the interbank market can serve as an early warning indicator of sovereign risk

Non-singular Universes a la Palatini

It has recently been shown that f(R) theories formulated in the Palatini variational formalism are able to avoid the big bang singularity yielding instead a bouncing solution. The mechanism responsible for this behavior is similar to that observed in the effective dynamics of loop quantum cosmology and an f(R) theory exactly reproducing that dynamics has been found. I will show here that considering more general actions, with quadratic contributions of the Ricci tensor, results in a much richer phenomenology that yields bouncing solutions even in anisotropic (Bianchi I) scenarios. Some implications of these results are discussed.Comment: 4 pages, no figures. Contribution to the Spanish Relativity Meeting (ERE2010), 6-10 Sept. Granada, Spai

Acceleration radiation, transition probabilities, and trans-Planckian physics

An important question in the derivation of the acceleration radiation, which also arises in Hawking's derivation of black hole radiance, is the need to invoke trans-Planckian physics for the quantum field that originates the created quanta. We point out that this issue can be further clarified by reconsidering the analysis in terms of particle detectors, transition probabilities, and local two-point functions. By writing down separate expressions for the spontaneous- and induced-transition probabilities of a uniformly accelerated detector, we show that the bulk of the effect comes from the natural (non trans-Planckian) scale of the problem, which largely diminishes the importance of the trans-Planckian sector. This is so, at least, when trans-Planckian physics is defined in a Lorentz invariant way. This analysis also suggests how to define and estimate the role of trans-Planckian physics in the Hawking effect itself.Comment: 19 page

Designing and Testing HealthTracker for Activity Recognition and Energy Expenditure Estimation within the DAPHNE Platform

This paper describes the design and evaluation of a mobile software library, HealthTracker, which aims to produce activity and energy expenditure estimations in real-time from accelerometer and gyroscope data provided by wearable sensors. Using feature extraction together with a classifier trained using machine learning, the system will automatically and periodically send all the produced estimations to a cloud-based platform that will allow later evaluation by both the user and a physician or caretaker. The system is presented within the DAPHNE platform, an ICT ecosystem designed to provide a means for remote health and lifestyle monitoring and guidance between physicians and their patients