Viable Inflationary Evolution from Loop Quantum Cosmology Scalar-Tensor Theory

In this work we construct a bottom-up reconstruction technique for Loop Quantum Cosmology scalar-tensor theories, from the observational indices. Particularly, the reconstruction technique is based on fixing the functional form of the scalar-to-tensor ratio as a function of the $e$-foldings number. The aim of the technique is to realize viable inflationary scenarios, and the only assumption that must hold true in order for the reconstruction technique to work is that the dynamical evolution of the scalar field obeys the slow-roll conditions. We shall use two functional forms for the scalar-to-tensor ratio, one of which corresponds to a popular inflationary class of models, the $\alpha$-attractors. For the latter, we shall calculate the leading order behavior of the spectral index and we shall demonstrate that the resulting inflationary theory is viable and compatible with the latest Planck and BICEP2/Keck-Array data. In addition, we shall find the classical limit of the theory, and as we demonstrate, the Loop Quantum Cosmology corrected theory and the classical theory are identical at leading order in the perturbative expansion quantified by the parameter $\rho_c$, which is the critical density of the quantum theory. Finally, by using the formalism of slow-roll scalar-tensor Loop Quantum Cosmology, we shall investigate how several inflationary potentials can be realized by the quantum theory, and we shall calculate directly the slow-roll indices and the corresponding observational indices. In addition, the $f(R)$ gravity frame picture is presented.Comment: PRD Accepte

Brane cosmology from observational surveys and its comparison with standard FRW cosmology

Several dark energy models on the brane are investigated. They are compared with corresponding theories in the frame of 4d Friedmann-Robertson-Walker cosmology. To constrain the parameters of the models considered, recent observational data, including SNIa apparent magnitude measurements, baryon acoustic oscillation results, Hubble parameter evolution data and matter density perturbations are used. Explicit formulas of the so-called {\it state-finder} parameters in teleparallel theories are obtained that could be useful to test these models and to establish a link between Loop Quantum Cosmology and Brane Cosmology. It is concluded that a joint analysis as the one developed here allows to estimate, in a very convenient way, possible deviation of the real universe cosmology from the standard Friedmann-Robertson-Walker one.Comment: 19 pages, 6 figures. arXiv admin note: text overlap with arXiv:1206.219

On the fate of the phantom dark energy universe in semiclassical gravity II: Scalar phantom fields

Quantum corrections coming from massless fields conformally coupled with gravity are studied, in order to see if they can lead to avoidance of the annoying Big Rip singularity which shows up in a flat Friedmann-Robertson-Walker universe filled with dark energy and modeled by a scalar phantom field. The dynamics of the model are discussed for all values of the two parameters, named $\alpha>0$ and $\beta<0$, corresponding to the regularization process. The new results are compared with the ones obtained in \cite{hae11} previously, where dark energy was modeled by means of a phantom fluid with equation of state $P=\omega\rho$, with $\omega<-1$

Possible polarisation and spin dependent aspects of quantum gravity

We argue that quantum gravity theories that carry a Lie algebraic modification of the Poincare' and Heisenberg algebras inevitably provide inhomogeneities that may serve as seeds for cosmological structure formation. Furthermore, in this class of theories one must expect a strong polarisation and spin dependence of various quantum-gravity effects.Comment: Awarded an "honourable mention" in the 2007 Gravity Research Foundation Essay Competitio

Gravitational particle production in massive chaotic inflation and the moduli problem

Particle production from vacuum fluctuations during inflation is briefly revisited. The moduli problem occurring with light particles produced at the end of inflation is addressed, namely the fact that some results are in disagreement with nucleosynthesis constrains. A universal solution to this problem is found which leads to reasonable reheating temperatures in all cases. It invokes the assumption that, immediately after inflation, the moduli evolve like non-relativistic matter. The assumption is justified in the context of massive chaotic inflation were, at the end of inflation, the universe evolves as if it was matter-dominated.Comment: 4 pages, no figures; to be published in Phys Rev Let

Does swimming styles specialization influence the hamstring muscle extensibility?

El objetivo de este estudio es comprobar si el estilo de natación en el que están especializados los nadadores, influye sobre la extensibilidad isquiosural de los deportistas que han participado en esta investigación. El test empleado para este trabajo es el test “sit and reach”. Se ha medido la extensibilidad isquiosural de todos los nadadores (N=36) de ambos sexos, que entrenan en un centro de tecnificación acuático español. La edad de los participantes del estudio oscila entre los 13 y los 17 años. Esta población de nadadores ha sido dividida en cuatro grupos diferentes, dependiendo del estilo de natación en el que están especializados (crol, espalda, braza y mariposa). Para conocer la influencia del estilo natación sobre los resultados obtenidos en el test “sit and reach”, se ha aplicado un test inicial y nueve meses más tarde un test final, lo que ha permitido conocer también la evolución de las mediciones Como conclusión, la extensibilidad isquiosural y su evolución, no está condicionada por el estilo de natación en el que están especializados los nadadores que han participado en este estudioThe aim of this research is to verify the swimming style in which swimmers are specialized, have has influences hamstring extensibility athletes who have had participated in this research. The employed test for this work was the “sits and reach" test. It was measured hamstring extensibility of all swimmers (N = 36) of both sexes, who train in Spanish aquatic center modernization. The age of the study participants is between 13 and 17 years. This population of swimmers has been divided into four different groups, depending on the style of swimming in which they are specialized (crawl, backstroke, breaststroke and butterfly). To determine the influence of swimming style on the results obtained in the test "sit and reach", it having had applied an initial test before, and a final test nine months later, which have had permitted also know the measurements evolution. In conclusion, the hamstring muscle extensibility and its evolution have had being not conditioned by swimming style of the swimmer

Training focused on deep cervical muscles to prevent neck pain

El objetivo del estudio fue crear un programa de entrenamiento de la musculatura cervical profunda, para orientar a los profesionales de la actividad física y del deporte en el trabajo con ella. Hay muy pocas pautas relacionadas con el trabajo de ésta, al mismo tiempo que la literatura científica nos muestra su estrecha relación con el dolor cervical. Por ello, se utilizan las investigaciones previas para crear un programa de entrenamiento centrado en la musculatura cervical profunda. Así como sus correspondientes métodos de evaluación, entre los que se incluye un nuevo test de extensión cervical con el que se pretende conseguir una valoración de la fuerza y la resistencia más adecuada. Finalmente se presenta un estudio de caso de una mujer sin dolor cervical, pero con factores de riesgo asociados, que sigue el programa como forma de prevención, mostrando un claro progreso tras la finalización de esteThe objective of the study was to create a training program for deep cervical muscles and help physical activity and sports professionals when exercising them. There are very few guidelines related to exercising these muscles, but at the same time, scientific literature demonstrates its close connection with neck pain. Therefore, previous research is used in order to develop a training program focused on deep cervical muscles, as well as its corresponding evaluation methods, including a new cervical extensor test aimed at achieving a more accurate estimation of strength and resistance. Finally, a case study is presented; a woman not suffering from neck pain but having associated risk factors, who follows the program as a means of preventing it, showing clear progress after its completio

Does loop quantum cosmology replace the big rip singularity by a non-singular bounce?

It is stated that holonomy corrections in loop quantum cosmology introduce a modification in Friedmann's equation which prevent the big rip singularity. Recently in \cite{h12} it has been proved that this modified Friedmann equation is obtained in an inconsistent way, what means that the results deduced from it, in particular the big rip singularity avoidance, are not justified. The problem is that holonomy corrections modify the gravitational part of the Hamiltonian of the system leading, after Legendre's transformation, to a non covariant Lagrangian which is in contradiction with one of the main principles of General Relativity. A more consistent way to deal with the big rip singularity avoidance is to disregard modification in the gravitational part of the Hamiltonian, and only consider inverse volume effects \cite{bo02a}. In this case we will see that, not like the big bang singularity, the big rip singularity survives in loop quantum cosmology. Another way to deal with the big rip avoidance is to take into account geometric quantum effects given by the the Wheeler-De Witt equation. In that case, even though the wave packets spread, the expectation values satisfy the same equations as their classical analogues. Then, following the viewpoint adopted in loop quantum cosmology, one can conclude that the big rip singularity survives when one takes into account these quantum effects. However, the spreading of the wave packets prevents the recover of the semiclassical time, and thus, one might conclude that the classical evolution of the universe come to and end before the big rip is reached. This is not conclusive because. as we will see, it always exists other external times that allows us to define the classical and quantum evolution of the universe up to the big rip singularity.Comment: Accepted for publication in JCA

Physical activity and smoking habit in adolescent students

El objetivo de este estudio fue detectar en qué medida afecta la actividad física y el hábito tabáquico en estudiantes de Enseñanza Secundaria. Se estudiaron 168 adolescentes no fumadores y fumadores recién iniciados. Se midieron peso, talla, presión arterial, frecuencia cardíaca, actividad física, fuerza, flexibilidad y resistencia y una prueba espirométrica. Tanto en chicas y chicos fumadores, se evidenciaron peores resultados en la mayoría de los parámetros espirométricos (FEV1, FEF25-75%, FVC) y un envejecimiento prematuro del pulmón, más acentuado en chicas. La actividad físico-deportiva moderada se asocia a adolescentes que menos fuman y tienen más facilidad para abandonar el hábito tabáquicoThe aim of the study was to detect how physical education and smoking habits affect secondary school students, 168 non smokers and newly initiated were studied. Weight, height, heart rate, blood pressure, physical activity, strength, flexibility and endurance, and spirometric tests were analyzed. In both, female and male smokers, obtained worse results in the mayority of spirometric parameters (FEV1, FEF25-75%, FVC) and premature lung ageing, more pointed in females. Moderate physical-sporting activity is associated to adolescents who smoke less and quit smoking more easil