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Sanchez-Conde M.A.,Kavli Institute for Particle Astrophysics and Cosmology | Prada F.,Campus of International Excellence UAMCSIC | Prada F.,Autonomous University of Madrid | Prada F.,Institute Astrofisica Of Andalucia Iaa Csic
Monthly Notices of the Royal Astronomical Society | Year: 2014

In the standard cold dark matter (CDM) theory for understanding the formation of structure in theUniverse, there exists a tight connection between the properties of darkmatter (DM) haloes, and their formation epochs. Such relation can be expressed in terms of a single key parameter, namely the halo concentration. In this work, we examine the median concentration-mass relation, c(M), at present time, over more than 20 orders of magnitude in halo mass, i.e. from tiny Earth-mass microhaloes up to galaxy clusters. The c(M) model proposed by Prada et al. (2012), which links the halo concentration with the rms amplitude of matter linear fluctuations, describes remarkably well all the available N-body simulation data down to ~10-6 h -1M( microhaloes. A clear fattening of the halo concentration-mass relation towards smaller masses is observed, that excludes the commonly adopted power-law c(M) models, and stands as a natural prediction for the CDM paradigm. We provide a parametrization for the c(M) relation that works accurately for all halo masses. This feature in the c(M) relation at low masses has decisive consequences e.g. for γ -ray DM searches, as it implies more modest boosts of the DM annihilation flux due to substructure, i.e. ~35 for galaxy clusters and ~15 for galaxies like our own, as compared to those huge values adopted in the literature that rely on such power-law c(M) extrapolations. We provide a parametrization of the boosts that can be safely used for dwarfs to galaxy cluster-size haloes. © 2014 The Authors. Source

Carballo-Rubio R.,Institute Astrofisica Of Andalucia Iaa Csic
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

To guarantee the stability of the cosmological constant sector against radiative corrections coming from quantum matter fields, one of the most natural ingredients to invoke is the symmetry under scale transformations of the gravitational field. Previous attempts to follow this path have nevertheless failed in providing a consistent picture. Here, we point out that this failure is intimately tied up to an assumption that is typically embedded in modern studies of the gravitational interaction: invariance under the full group of diffeomorphisms. We base the discussion on the gravitational theory known as Weyl transverse gravity. While leading to the same classical solutions as general relativity, and so to the same classical phenomenology, we show that in the presence of quantum matter (i) the degeneracy between these theories is broken (general relativity exhibits the well-known cosmological constant problem, while in Weyl transverse gravity, the cosmological constant sector is protected due to gravitational scale invariance), and (ii) this is possible as the result of abandoning the assumption of full diffeomorphism invariance, which permits circumventing classic results on scale-invariance anomalies and guarantees that gravitational scale invariance survives quantum corrections. Both results signal new directions in the quest of finding an ultraviolet completion of gravity. © 2015 American Physical Society. Source

Castro-Tirado A.J.,Institute Astrofisica Of Andalucia Iaa Csic
Advances in Astronomy | Year: 2010

This paper presents a historical introduction to the field of Robotic Astronomy, from the point of view of a scientist working in this field for more than a decade. The author discusses the basic definitions, the differing telescope control operating systems, observatory managers, as well as a few current scientific applications. Copyright © 2010 Alberto Javier Castro-Tirado. Source

Barcelo C.,Institute Astrofisica Of Andalucia Iaa Csic | Carballo-Rubio R.,Institute Astrofisica Of Andalucia Iaa Csic | Garay L.J.,Complutense University of Madrid | Garay L.J.,CSIC - Institute for the Structure of Matter | Jannes G.,Charles III University of Madrid
Classical and Quantum Gravity | Year: 2015

It is logically possible that regularly evaporating black holes (REBHs) exist in nature. In fact, the prevalent theoretical view is that these are indeed the real objects behind the curtain in astrophysical scenarios. There are several proposals for regularizing the classical singularity of black holes so that their formation and evaporation do not lead to information-loss problems. One characteristic is shared by most of these proposals: these REBHs present long-lived trapping horizons, with absolutely enormous evaporation lifetimes in whatever measure. Guided by the discomfort with these enormous and thus inaccessible lifetimes, we elaborate here on an alternative regularization of the classical singularity, previously proposed by the authors in an emergent gravity framework, which leads to a completely different scenario. In our scheme the collapse of a stellar object would result in a genuine time-symmetric bounce, which in geometrical terms amounts to the connection of a black-hole geometry with a white-hole geometry in a regular manner. The two most differential characteristics of this proposal are: (i) the complete bouncing geometry is a solution of standard classical general relativity everywhere except in a transient region that necessarily extends beyond the gravitational radius associated with the total mass of the collapsing object; and (ii) the duration of the bounce as seen by external observers is very brief (fractions of milliseconds for neutron-star-like collapses). This scenario motivates the search for new forms of stellar equilibrium different from black holes. In a brief epilogue we compare our proposal with a similar geometrical setting recently proposed by Haggard and Rovelli. © 2015 IOP Publishing Ltd. Source

Rodriguez-Lopez C.,Institute Astrofisica Of Andalucia Iaa Csic | Macdonald J.,University of Delaware | Moya A.,CSIC - National Institute of Aerospace Technology
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

We present the results of the first theoretical non-radial, non-adiabatic pulsational study of M dwarf stellar models with masses in the range 0.1-0.5M⊙. We find the fundamental radial mode to be unstable due to an ε mechanism, caused by deuterium (D) burning for the young 0.1 and 0.2M⊙ models, by non-equilibrium He3 burning for the 0.2 and 0.25M⊙ models of 104Myr and by a flux-blocking mechanism for the partially convective 0.4 and 0.5M⊙ models once they reach the age of 500Myr. The periods of the overstable modes excited by the D burning are in the range 4.2-5.2h for the 0.1M⊙ models and is of the order of 8.4h for the 0.2M⊙ models. The periods of the modes excited by He3 burning and flux blocking are in the range 23-40min. The more massive and oldest models are more promising for the observational detection of pulsations as their ratio of instability e-folding time to age is more favourable. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

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