Focusing of geodesic congruences in an accelerated expanding Universe

We study the accelerated expansion of the Universe through its consequences on a congruence of geodesics. We make use of the Raychaudhuri equation which describes the evolution of the expansion rate for a congruence of timelike or null geodesics. In particular, we focus on the space-time geometry contribution to this equation. By straightforward calculation from the metric of a Robertson-Walker cosmological model, it follows that in an accelerated expanding Universe the space-time contribution to the Raychaudhuri equation is positive for the fundamental congruence, favoring a non-focusing of the congruence of geodesics. However, the accelerated expansion of the present Universe does not imply a tendency of the fundamental congruence to diverge. It is shown that this is in fact the case for certain congruences of timelike geodesics without vorticity. Therefore, the focusing of geodesics remains feasible in an accelerated expanding Universe. Furthermore, a negative contribution to the Raychaudhuri equation from space-time geometry which is usually interpreted as the manifestation of the attractive character of gravity is restored in an accelerated expanding Robertson-Walker space-time at high speeds.Comment: 11 pages, 2 figures. Final version changed to match published version in JCAP. References updated. Conclusions unchange

Brane oscillations and the cosmic coincidence problem

We show that, under general assumptions, in six-dimensional brane-world models with compactified large extra dimensions, the energy density of brane oscillations scales as that of cold dark matter and its present value is compatible with observations. Such value is obtained from the only dimensional scale in the theory, namely, the fundamental scale of gravity in six dimensions $M_6\sim 1$ TeV, without any fine-tuning or the introduction of additional mass scales apart from the large size of the extra dimensions. It has been suggested that the same kind of models could provide also the correct magnitude of the cosmological constant. This observation can be relevant for the resolution of the cosmic coincidence problem in the brane-world scenario.Comment: 5 pages, RevTeX. Comments on the renormalization of the branon mass included. Final version to appear in Phys.Rev.D (R

On the non-attractive character of gravity in f(R) theories

Raychaudhuri equation is found provided that particular energy conditions are assumed and regardless the considered solution of the Einstein's equations. This fact is usually interpreted as a manifestation of the attractive character of gravity. Nevertheless, a positive contribution to Raychaudhuri equation from space-time geometry should occur since this is the case in an accelerated expanding Robertson-Walker model for congruences followed by fundamental observers. Modified gravity theories provide the possibility of a positive contribution although the standard energy conditions are assumed. We address this important issue in the context of f(R) theories, deriving explicit upper bounds for the contribution of space-time geometry to the Raychaudhuri equation. Then, we examine the parameter constraints for some paradigmatic f(R) models in order to ensure a positive contribution to this equation. Furthermore, we consider the implications of these upper bounds in the equivalent formulation of f(R) theories as a Brans-Dicke model

Core Structure of Global Vortices in Brane World Models

We study analytically and numerically the core structure of global vortices forming on topologically deformed brane-worlds with a single toroidally compact extra dimension. It is shown that for an extra dimension size larger than the scale of symmetry breaking the magnitude of the complex scalar field at the vortex center can dynamically remain non-zero. Singlevaluedness and regularity are not violated. Instead, the winding escapes to the extra dimension at the vortex center. As the extra dimension size decreases the field magnitude at the core dynamically decreases also and in the limit of zero extra dimension size we reobtain the familiar global vortex solution. Extensions to other types of defects and gauged symmetries are also discussed.Comment: 6 two column pages, 3 figure

Diagnostic efficacy of sentinel node biopsy in oral squamous cell carcinoma : cohort study and meta-analysis

Objectives: To evaluate the efficacy of sentinel node biopsy (SNB) in oral squamous cell carcinoma (OSCC). Design: A prospective study of a cohort of 25 consecutive patients with OSCC anatomopathological confirmation through biopsy, without oncological pre-treatment, in clinical stage T1-T4N0, of these 25 patients 14 were T1-T2N0. The absence of regional disease (N0) was determined by means of clinical exploration and cervical tomography (CT). To establish the overall sensitivity of the technique, a meta-analysis was carried out of 10 series published to February 2005 where SNB had been applied to head and neck cancer, adding our 14 T1-T2N0 cases, thus making a total of 260 patients. Results: Identification by SNB was accurate in 96% of the 25 cases, with a sensitivity of 66.7%. Analyzing only the T1-T2N0 cases (n=14), the accuracy was 100% with a sensitivity of 1 (CI 95%, 0.29-1.00). The overall sensitivity was 93%. The accuracy in identifying the sentinel node varied between 66% and 100%. The SN was identified in 251 of 260 cases, of those, 71 were true positive, 5 false negative and 175 true negative. The overall sensitivity was 93.4% (CI 95%, 85.3-97.8), with a specificity of 100% (CI 95%, 0.98-100). The weighted negative probability quotient was 0.176 (CI 0.103-0.301) and that of positive probability 24.75 (CI 95%, 10.8-56.71). The weighted diagnostic odds ratio was 183.71 (CI 95%, 59.36-568.56). If we accept that the prevalence of hidden regional disease is 30%, a negative sentinel node has 5% possibility of having hidden disease. Conclusions: Our data provide a certain degree of evidence that, due to its high sensitivity, the SNB procedure can be applied to the initial stages of OSCC

Dark Matter and Fundamental Physics with the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV-TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2-3 different sizes, distributed over a large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10 deg. In the following study, we investigate the prospects for CTA to study several science questions that influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations, we employ a Monte Carlo based approach to evaluate the prospects for detection. First, we discuss CTA prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, in the region close to the Galactic Centre, and in clusters of galaxies. The possible search for spatial signatures, facilitated by the larger field of view of CTA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma rays from very distant blazars. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz Invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.Comment: (31 pages, Accepted for publication in Astroparticle Physics

Search for new phenomena in monophoton final states in proton-proton collisions at root s=8 TeV

Peer reviewe

Phylogenetic, Microbiome, and Diet Characterisation of Wall Lizards in the Columbretes Archipelago (Spain): Clues for Their Conservation

[eng] The Columbretes archipelago consists of a group of small volcanic islets located in the western Mediterranean near the east of the Iberian Peninsula. Four of its islands are inhabited by the wall lizard Podarcis liolepis, whose populations have been considered vulnerable. The purpose of this study was to assess the level of genetic diversity across the archipelago and the possible evolutionary origin of the Columbretes lizard populations. Additionally, we investigated the evolutionary ecology of these populations using a DNA-based metabarcoding approach to characterise both their microbiota and trophic interactions. The genetic results reported very low genetic diversity and corroborated the conspecificity between insular populations and P. liolepis from the mainland (Peñagolosa region). The results of the metabarcoding analyses based on faecal samples were in accordance with an omnivorous ecology, suggesting that specific microbiota communities in the insular populations might be correlated with differences in host ecology and phylogeny. These results are a valuable contribution to the current understanding of the evolution of Columbretes' lizards and provide important information for conservation management

Multilocus and morphological analysis of south-eastern Iberian Wall lizards (Squamata, Podarcis)

[eng The phylogenetic relationships among the wall lizards of the Podarcis hispanicus complex that inhabit the south-east (SE) of the Iberian Peninsula and other lineages of the complex remain unclear. In this study, four mitochondrial and two nuclear markers were used to study genetic relationships within this complex. The phylogenetic analyses based on mtDNA gene trees constructed with ML and BI, and a species tree using *BEAST support three divergent clades in this region: the Valencia, Galera and Albacete/Murcia lineages. These three lineages were also corroborated in species delimitation analyses based on mtDNA using bPTP, mPTP, GMYC, ABGD and BAPS. Bayesian inference species delimitation method (BPP) based on both nuclear data and a combined data set (mtDNA + nuclear) showed high posterior probabilities for these three SE lineages (≥0.94) and another Bayesian analysis (STACEY) based on combined data set recovered the same three groups in this region. Divergence time dating of the species tree provided an estimated divergence of the Galera lineage from the other SE group (Podarcis vaucheri, (Albacete/Murcia, Valencia)) at 12.48 Ma. During this period, the Betic-Rifian arc was isolated, which could have caused the isolation of the Galera form distributed to the south of the Betic Corridor. Although lizards from the Albacete/Murcia and Galera lineage are morphologically similar, they clearly represent distinct genetic lineages. The noteworthy separation of the Galera lineage enables us to conclude that this lineage must be considered as a new full species