Sensitivity of Hawking radiation to superluminal dispersion relations

We analyze the Hawking radiation process due to collapsing configurations in the presence of superluminal modifications of the dispersion relation. With such superluminal dispersion relations, the horizon effectively becomes a frequency-dependent concept. In particular, at every moment of the collapse, there is a critical frequency above which no horizon is experienced. We show that, as a consequence, the late-time radiation suffers strong modifications, both quantitative and qualitative, compared to the standard Hawking picture. Concretely, we show that the radiation spectrum becomes dependent on the measuring time, on the surface gravities associated with different frequencies, and on the critical frequency. Even if the critical frequency is well above the Planck scale, important modifications still show up.Comment: 14 pages, 7 figures. Extensive paragraph added in conclusions to clarify obtained result

Towards the Journal of Applied Cognitive Neuroscience

In his book The Structure of Science Evolution, Thomas Khum defines a paradigmas “a set of beliefs, values and accepted techniques that define the exercise of a scientific discipline”. A new paradigm is a change of vision, a reconstruction of our knowledge in the light of discoveries; in the words of Socratics, “all cognition is a recognition”.In his book The Structure of Science Evolution, Thomas Khum defines a paradigmas “a set of beliefs, values and accepted techniques that define the exercise of a scientific discipline”. A new paradigm is a change of vision, a reconstruction of our knowledge in the light of discoveries; in the words of Socratics, “all cognition is a recognition”

Emission of correlated photon pairs from superluminal perturbations in dispersive media

We develop a perturbative theory that describes a superluminal refractive perturbation propagating in a dispersive medium and the subsequent excitation of the quantum vacuum zero-point fluctuations. We find a process similar to the anomalous Doppler effect: photons are emitted in correlated pairs and mainly within a Cerenkov-like cone, one on the forward and the other in backward directions. The number of photon pairs emitted from the perturbation increases strongly with the degree of superluminality and under realizable experimental conditions, it can reach up to ~0.01 photons per pulse. Moreover, it is in principle possible to engineer the host medium so as to modify the effective group refractive index. In the presence of "fast light" media, e.g. a with group index smaller than unity, a further ~10x enhancement may be achieved and the photon emission spectrum is characterized by two sharp peaks that, in future experiments would clearly identify the correlated emission of photon pairs.Comment: 9 pages, 7 figure

Participatory processes and institutional debate activities as key complementary aspects for embedding sustainability in higher education

Introducing sustainable development into educational programs of universities tend to be approached under two complementary strategies: “top-down” and “bottom-up”. Top-down strategies promote the adaptation of the institutional framework to the new challenges that sustainable development generates into technical expertise areas. Bottom-up strategies focus on institutional activities oriented to convincing or supporting lecturers in integrating sustainable development in their different courses and projects. However, these actions are not enough for the actual challenge if sustainable development is seen as a transformative social learning process in which the role of academia regarding sustainable development “is not on integration but rather one of innovation and systemic change within our institutions that will allow for more transformative learning to take place”. Thus, there are other strategies “in-between” that complement these to approaches, because they help to accelerate the institutional culture shift and therefore facilitate the concrete changes needed. The aim of this paper is to describe the UPC experience on the development of two complementary aspects developed under its UPC Sustainable 2015 institutional strategy: participatory processes and institutional debate activities.Peer Reviewe

Gravitational dynamics in Bose Einstein condensates

Analogue models for gravity intend to provide a framework where matter and gravity, as well as their intertwined dynamics, emerge from degrees of freedom that have a priori nothing to do with what we call gravity or matter. Bose Einstein condensates (BEC) are a natural example of analogue model since one can identify matter propagating on a (pseudo-Riemannian) metric with collective excitations above the condensate of atoms. However, until now, a description of the "analogue gravitational dynamics" for such model was missing. We show here that in a BEC system with massive quasi-particles, the gravitational dynamics can be encoded in a modified (semi-classical) Poisson equation. In particular, gravity is of extreme short range (characterized by the healing length) and the cosmological constant appears from the non-condensed fraction of atoms in the quasi-particle vacuum. While some of these features make the analogue gravitational dynamics of our BEC system quite different from standard Newtonian gravity, we nonetheless show that it can be used to draw some interesting lessons about "emergent gravity" scenarios.Comment: Replaced with published version. 15 pages, no figures, revtex4. Reference adde

Time-resolved density correlations as probe of squeezing in toroidal Bose-Einstein condensates

I study the evolution of mean field and linear quantum fluctuations in a toroidal Bose-Einstein condensate, whose interaction strength is quenched from a finite (repulsive) value to zero. The azimuthal equal-time density-density correlation function is calculated and shows temporal oscillations with twice the (final) excitation frequencies after the transition. These oscillations are a direct consequence of positive and negative frequency mixing during non-adiabatic evolution. I will argue that a time-resolved measurement of the equal-time density correlator might be used to calculate the moduli of the Bogoliubov coefficients and thus the amount of squeezing imposed on a mode, i.e., the number of atoms excited out of the condensate.Comment: 18 pages, IOP styl

Diseño, fundamentación y validación de un programa virtual colaborativo en educación ambiental

Los programas colaborativos constituyen una adecuada herramienta para hacer Educación Ambiental. A lo largo del texto fundamentamos el modelo didáctico MACELEA que ha servido para la creación y puesta en marcha del programa colaborativo virtual de innovación curricular Ecourban. Describimos los aspectos más relevantes para su diseño e implementación, y damos cuenta de los criterios de validez y componentes de innovación virtual que lo sustentan: contextual, pedagógico-didáctica, epistemológica, multimedia, cognitiva y comunicacional.Collaborative programmes are an appropriate tool for Environmental Education. In this work we show the foundations of the didactic model, that we have named MACELEA and which has served for the implementation of a virtual collaborative program to promote the curricular innovation: Ecourban. Here we describe the most relevant dimensions of its design and development, so as the validity criteria and components of virtual innovation: contextual, pedagogical-didactic, epistemological, multimedia, cognitive and communicative

Anti-de Sitter wormhole kink

The metric describing a given finite sector of a four-dimensional asymptotically anti-de Sitter wormhole can be transformed into the metric of the time constant sections of a Tangherlini black hole in a five-dimensional anti-de Sitter spacetime when one allows light cones to tip over on the hypersurfaces according to the conservation laws of an one-kink. The resulting kinked metric can be maximally extended, giving then rise to an instantonic structure on the euclidean continuation of both the Tangherlini time and the radial coordinate. In the semiclassical regime, this kink is related to the existence of closed timelike curves.Comment: 10 pages, to appear in IJMP

The trans-Planckian problem as a guiding principle

We use the avoidance of the trans-Planckian problem of Hawking radiation as a guiding principle in searching for a compelling scenario for the evaporation of black holes or black-hole-like objects. We argue that there exist only three possible scenarios, depending on whether the classical notion of long-lived horizon is preserved by high-energy physics and on whether the dark and compact astrophysical objects that we observe have long-lived horizons in the first place. Along the way, we find that (i) a theory with high-energy superluminal signalling and a long-lived trapping horizon would be extremely unstable in astrophysical terms and that (ii) stellar pulsations of objects hovering right outside but extremely close to their gravitational radius can result in a mechanism for Hawking-like emission.Comment: 20 pages, 4 figures. v2: minor clarifications. Published versio