Isotropy theorem for cosmological Yang-Mills theories

We consider homogeneous non-abelian vector fields with general potential terms in an expanding universe. We find a mechanical analogy with a system of N interacting particles (with N the dimension of the gauge group) moving in three dimensions under the action of a central potential. In the case of bounded and rapid evolution compared to the rate of expansion, we show by making use of a generalization of the virial theorem that for arbitrary potential and polarization pattern, the average energy-momentum tensor is always diagonal and isotropic despite the intrinsic anisotropic evolution of the vector field. We consider also the case in which a gauge-fixing term is introduced in the action and show that the average equation of state does not depend on such a term. Finally, we extend the results to arbitrary background geometries and show that the average energy-momentum tensor of a rapidly evolving Yang-Mills fields is always isotropic and has the perfect fluid form for any locally inertial observer.Comment: 8 pages, 3 figure

Isotropy theorem for arbitrary-spin cosmological fields

We show that the energy-momentum tensor of homogeneous fields of arbitrary spin in an expanding universe is always isotropic in average provided the fields remain bounded and evolve rapidly compared to the rate of expansion. An analytic expression for the average equation of state is obtained for Lagrangians with generic power-law kinetic and potential terms. As an example we consider the behavior of a spin-two field in the standard Fierz-Pauli theory of massive gravity. The results can be extended to general space-time geometries for locally inertial observers.Comment: 4 pages, 0 figures. Published on JCA

Cosmological perturbations in coherent oscillating scalar field models

The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials $V(\phi)=\lambda \vert\phi\vert^{n}/n$. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained $c_{\text{eff}}^2 = \omega=(n-2)/(n+2)$ with $\omega$ the effective equation of state. We also obtain the first order correction in $k^2/\omega_{\text{eff}}^2$, when the wavenumber $k$ of the perturbations is much smaller than the background oscillation frequency, $\omega_{\text{eff}}$. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for $\delta\phi$; and for sub-Hubble modes, exploiting Floquet's theorem.Comment: 13 pages, 6 figures. Published on JHE

Yellowstone National Park: History, features and management of the National Park

Jareño Martí, CF. (2012). Yellowstone National Park: History, features and management of the National Park. Universitat Politècnica de València. http://hdl.handle.net/10251/14629Archivo delegad

Capacidade de absorção da inflação e seu efeito sobre o preço das ações: uma revisão da literatura

This article addresses the inflation absorption capability of companies classified by sectors, as well as its impact in the price of shares. It starts by justifying the importance of the subject of study and then it presents a review of the international literature on the subject. The pioneer works on the subject are highlighted and a classification of the studies that have been analyzed is provided. Then, it analyzes the Spanish case in order to complete the main conclusions of the study. According to the authors, the inflation absorption capability, allows us to know the capability that companies from a determined sector have to translate the inflationary changes that happen in the economy into prices. The companies with a high capability of absorption will tend to present higher quotations, and will be less sensitive to inflationary changes.Este artículo aborda la capacidad de absorción de la inflación que tienen las empresas clasificadas por sectores, así como su impacto en el precio de las acciones. Se comienza justificando la importancia del tema objeto de estudio, para luego presentar una revisión de la literatura internacional. Se destacan los trabajos pioneros en la materia y se aporta una clasificación de los estudios examinados. Luego, se analiza el caso español, para finalizar con las principales conclusiones del estudio. Según los autores, la capacidad de absorción de la inflación permite conocer la habilidad que tienen las empresas de un determinado sector para trasladar a precios los cambios inflacionistas que acontecen en la economía. Las empresas con alta capacidad de absorción de la inflación tenderán a presentar cotizaciones más elevadas y, además, serán menos sensibles a cambios inflacionistas.Este artigo aborda a capacidade de absorção da inflação que têm as empresas classificadas por setores, assim como seu impacto no preço das ações. Começa-se justificando a importância do tema objeto de estudo, para logo apresentar uma revisão da literatura internacional. Destacam-se os trabalhos pioneiros na matéria e fornece uma classificação dos estudos analisados. Logo, analisa-se o caso espanhol, para finalizar com as principais conclusões do estudo. Segundo os autores, a capacidade de absorção da inflação permite conhecer a habilidade que têm as empresas de um determinado setor para transladar a preços as mudanças inflacionárias que acontecem na economia. As empresas com alta capacidade de absorção da inflação tenderão a apresentar cotizações mais elevadas e, além disso, serão menos sensíveis a mudanças inflacionárias

US Stock Market And Macroeconomic Factors

This paper analyzes the relationship between the US stock market and some relevant US macroeconomic factors, such as gross domestic product, the consumer price index, the industrial production index, the unemployment rate and long-term interest rates. All the relevant factors show statistically significant relationships with the stock market except for the consumer price index, and the signs are consistent with the findings of previous literature