Dark Energy in vector-tensor theories of gravity

We consider a general class of vector-tensor theories of gravity and show that solutions with accelerated expansion and a future type III singularity are a common feature in these models. We also show that there are only six vector-tensor theories with the same small scales behavior as General Relativity and, in addition, only two of them can be made completely free from instabilities. Finally, two particular models as candidates for dark energy are proposed: on one hand, a cosmic vector that allows to alleviate the usual naturalness and coincidence problems and, on the other hand, the electromagnetic field is shown to give rise to an effective cosmological constant on large scales whose value can be explained in terms of inflation at the electroweak scale.Comment: 4 pages, 1 table. Contribution to the proceedings of Spanish Relativity Meeting 2009, Bilbao, Spain, 7-11 September 200

Cosmic magnetic fields and dark energy in extended electromagnetism

We discuss an extended version of electromagnetism in which the usual gauge fixing term is promoted into a physical contribution that introduces a new scalar state in the theory. This new state can be generated from vacuum quantum fluctuations during an inflationary era and, on super-Hubble scales, gives rise to an effective cosmological constant. The value of such a cosmological constant coincides with the one inferred from observations as long as inflation took place at the electroweak scale. On the other hand, the new state also generates an effective electric charge density on sub-Hubble scales that produces both vorticity and magnetic fields with coherent lengths as large as the present Hubble horizon.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish Relativity Meeting 2010, Granada, Spain, 6-10 September 201

Infrared lessons for ultraviolet gravity: the case of massive gravity and Born-Infeld

We generalize the ultraviolet sector of gravitation via a Born-Infeld action using lessons from massive gravity. The theory contains all of the elementary symmetric polynomials and is treated in the Palatini formalism. We show how the connection can be solved algebraically to be the Levi-Civita connection of an effective metric. The non-linearity of the algebraic equations yields several branches, one of which always reduces to General Relativity at low curvatures. We explore in detail a {\it minimal} version of the theory, for which we study solutions in the presence of a perfect fluid with special attention to the cosmological evolution. In vacuum we recover Ricci-flat solutions, but also an additional physical solution corresponding to an Einstein space. The existence of two physical branches remains for non-vacuum solutions and, in addition, the branch that connects to the Einstein space in vacuum is not very sensitive to the specific value of the energy density. For the branch that connects to the General Relativity limit we generically find three behaviours for the Hubble function depending on the equation of state of the fluid, namely: either there is a maximum value for the energy density that connects continuously with vacuum, or the energy density can be arbitrarily large but the Hubble function saturates and remains constant at high energy densities, or the energy density is unbounded and the Hubble function grows faster than in General Relativity. The second case is particularly interesting because it could offer an interesting inflationary epoch even in the presence of a dust component. Finally, we discuss the possibility of avoiding certain types of singularities within the minimal model.Comment: 31 pages, 3 figures (Journal version, references added

Effects of biasing on the galaxy power spectrum at large scales

n this paper we study the effect of biasing on the power spectrum at large scales. We show that even though non-linear biasing does introduce a white noise contribution on large scales, the $P(k)\propto k^n$ behavior of the matter power spectrum on large scales may still be visible and above the white noise for about one decade. We show, that the Kaiser biasing scheme which leads to linear bias of the correlation function on {\em large} scales, also generates a linear bias of the {\rm power spectrum} on rather small scales. This is a consequence of the divergence on small scales of the pure Harrison-Zeldovich spectrum. However, biasing becomes k-dependent when we damp the underlying power spectrum on small scales. We also discuss the effect of biasing on the baryon acoustic oscillations.Comment: 9 pages, 4 figures. One figure and comments clarifying the linear biasing on small scales and references added. V3 version accepted in PR

Born-Infeld Gravity: Constraints from Light-by-Light Scattering and an Effective Field Theory Perspective

By using a novel technique that establishes a correspondence between general relativity and metric-affine theories based on the Ricci tensor, we are able to set stringent constraints on the free parameter of Born-Infeld gravity from the ones recently obtained for Born-Infeld electrodynamics by using light-by-light scattering data from ATLAS. We also discuss how these gravity theories plus matter fit within an effective field theory framework.Comment: 7 page

The Frustration of Novelty and Basic Psychological Needs as Predictors of Maladaptive Outcomes in Physical Education

Background The need for novelty has been recently proposed as a candidate need within basic psychological needs theory (BPNT). In physical education (PE), research has shown that meeting students’ need for novelty is often positively associated with enhanced (and negatively associated with impaired) pupils’ well-being. Frustrating students’ novelty has also been negatively related to achieving multiple positive outcomes in PE. However, no research has explored whether frustration of novelty is positively associated with maladaptive consequences for pupils in this educational context, which is a necessary criterion to be included within BPNT. Purpose In this correlational study, we aimed to determine whether frustration of novelty was associated with up to 10 maladaptive outcomes in a similar way as the frustration of the three basic psychological needs (autonomy, competence, and relatedness). The maladaptive outcomes analyzed were amotivation, boredom, negative affect, entity beliefs, fear of failure, worry, concentration disruption, somatic and social physique anxiety, and oppositional defiance. Research design Cross-sectional study. Methods A total of 533 students (Mage = 14.47, SD = 1.34; 56.66% female) from eight secondary schools completed online questionnaires assessing their basic psychological needs frustration, novelty frustration and diverse maladaptive outcomes in PE. Pearson's correlations and hierarchical regression analyses controlling by sex, age, and race, were calculated to test the associations among these variables. Findings The correlation coefficients for novelty frustration were like those found for the three basic psychological needs concerning maladaptive outcomes in PE students. Particularly, hierarchical regression analyses showed that frustrating novelty in PE predicted amotivation (β = .11, p = .039), boredom (β = .23, p < .001), entity beliefs (β = .12, p = .039), and concentration disruption (β = .12, p = .049). Conclusions Results showed that novelty frustration was positively related to experiencing some negative consequences in PE, which is an important criterion within BPNT. Future training programs aimed at promoting optimal (and preventing detrimental) motivational styles in PE teachers could use these results to optimize students’ PE experiences

Changes in bariatric patients’ physical activity levels and health-related quality of life following a postoperative motivational physical activity intervention

Purpose: Self-determination theory (SDT) has been widely used as a useful motivational framework for improving long-term adherence to physical activity (PA) and health-related quality of life (HRQoL). The aim of this study was to examine the effects of a 6-month motivational PA intervention (MPAI) on bariatric patients’ PA levels and HRQoL from pre-surgery to the end of the MPAI (7 months post-surgery). Additionally, a re-test was performed 13 months post-surgery. Methods: 40 participants undergoing sleeve gastrectomy were assigned to a 6-month MPAI or to a control group. The MPAI was based on techniques and messages from SDT. At baseline and post-intervention measures, both groups wore accelerometers for one week and completed the SF-36 questionnaire. Results: 32 participants (78.1% female) completed all measures and were included in the final analyses. PA levels did not significantly differ between groups as a consequence of the intervention. Clinically significant differences (d ≥ 0.5) favoring the MPAI group were found for SF-36 domains of bodily pain (at pre-surgery, increasing at 7- and 13-months post-surgery), general health and vitality (7 months post-surgery), and physical functioning and the physical component score (both 7- and 13-months post-surgery). Social functioning also showed clinically significant differences favoring the MPAI group at pre-surgery, increasing at 7 months post-surgery. These differences disappeared at 13 months post-surgery. Conclusions: SDT-based PA interventions could enhance several dimensions of bariatric patients’ HRQoL after surgery. Further research is needed to understand what motivational processes are key aspects to promote PA participation in these patients

A self-determined exploration of adolescents’ and parents’ experiences derived from a multidimensional school-based physical activity intervention

Purpose: Adolescents’ and parents’ experiences within a multidimensional schoolbased physical activity intervention grounded on self-determination theory were explored. Method: Qualitative data from 29 adolescents (aged 15-17 years) and three parents on behalf of the total students' families were collected via participant observation (research diary), semistructured interviews, and focus groups. Results: Adolescents perceived that the application of motivational strategies, based on selfdetermination theory, satisfied their basic psychological needs for autonomy, competence and relatedness, favored self-determined motivation, and gave rise to adaptive consequences (improved physical activity knowledge, creation of affective bonds, and increased leisure-time physical activity). These results were supported by the information reported by the students' parents. Discussion/Conclusions: The findings support the implementation of self-determination theory-based multidimensional interventions to promote adolescents’ physical activity participation. This study also presents several motivational strategies which could be useful for the design and implementation of future school-based physical activity intervention

Geothermometrical modelling applied to the CO2-rich thermal waters of the Lanjarón hydrothermal system (Granada, Spain)

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