Unattainability of the trans-Planckian regime in nonlocal quantum gravity

Based on the ultraviolet asymptotic freedom of nonlocal quantum gravity, we show that the trans-Planckian energy regime is unattainable in laboratory experiments. As physical implications, it turns out that the violation of causality, typical of nonlocal field theories, can never be detected in particle accelerators, while the asymptotic freedom of the theory provides an elegant solution to the so called trans-Planckian cosmological problem.

Condiciones iniciales, comienzo y origen. Limitaciones de algunos planteamientos monistas en cosmología

Resumen: En su último libro Hawking y Mlodinow afirman que la teoría M unifica las teorías físicas, contiene las leyes más fundamentales y responde las grandes preguntas de la humanidad. Es decir, el despliegue del universo se reduciría a un conjunto de leyes único. Este trabajo pretende: 1) Señalar algunos supuestos epistemológicos asumidos sin sufi­ciente fundamentación. 2) Proponer las nociones de condiciones iniciales, comienzo y origen, como un marco adecuado para distinguir las diferentes dimensiones del problema cosmológico. 3) Desde esta distinción enfatizar la importancia del trabajo interdisciplinar para estudiar los temas de frontera entre la ciencia y la filosofía. Palabras clave: modelos cosmológico, Steven Hawking, condiciones iniciales, evolución cósmica, origen del universo. Abstract. In their last book Hawking and Mlodinow argue that M-Theory unifies physi­cal theories, contains the most fundamental laws and answers the great questions of humanity. Namely, the unfolding of the universe would be reduced to a single set of laws. This paper seeks: 1) to identify some epistemological assumptions made with insufficient justification; 2) to propose the notion of initial conditions, beginning and origin as an ap­propriate framework to distinguish different dimensions of the cosmological problem; 3) from this distinction to emphasize the importance of interdisciplinary work to study bor­der issues between science and philosophy. Keywords: cosmological models, Steven Hawking, initial conditions, cosmic evolution, origin of the universe. Recibido: 16/02/2013 Aprobado: 18/04/2013

The General Theory of Relativity (Continued)

This chapter shows that in the limit of weak fields and low velocities, the equation of the geodesic line reduces to Newton's equation of motion. It proceeds to derive the gravitational field equation. Next, the chapter uses the gravitational field equation to derive the three effects that served as the first tests of the theory: the bending of light by the gravitational field of the sun, the shift to the red of spectral lines emitted by atoms in a gravitational field (gravitational redshift), and the motion of the perihelion of planet Mercury. After a short remark about expressing Maxwell's equations of the electromagnetic field, the chapter turns to the “so-called cosmological problem.” Its main theme is the defense of Mach's principle, which states that all inertial phenomena, namely the fictitious forces arising in accelerated reference frames, are caused by all the masses in the universe.

A CRITICAL ANALYSIS OF THE COSMOLOGICAL IMPLEMENTATION OF LOOP QUANTUM GRAVITY

This papers offers a critical discussion on the procedure by which Loop Quantum Cosmology (LQC) is constructed from the full Loop Quantum Gravity (LQG) theory. Revising recent issues in preserving SU(2) symmetry when quantizing the isotropic Universe, we trace a new perspective in approaching the cosmological problem within quantum geometry. The cosmological sector of LQG is reviewed and a critical point of view on LQC is presented. It is outlined how a polymer-like scale for quantum cosmology can be predicted from a proper fundamental graph underlying the homogeneous and isotropic continuous picture. However, such a minimum scale does not coincide with the choice made in LQC. Finally, the perspectives towards a consistent cosmological LQG model based on such a graph structure are discussed.

Magnetic Fields in Galaxies

The origin and evolution of magnetic fields in the Universe is a cosmological problem. Although exotic mechanisms for magneotgenesis cannot be ruled out, galactic magnetic fields could have been seeded by magnetic fields from stars and accretion disks, and must be continuously regenerated due to the ongoing replacement of the interstellar medium. Unlike stellar dynamos, galactic dynamos operate in a multicomponent gas at low collisionality and high magnetic Prandtl number. Their background turbulence is highly compressible, the plasma β ~ 1, and there has been time for only a few large exponentiation times at large scale over cosmic time. Points of similarity include the importance of magnetic buoyancy, the large range of turbulent scales and tiny microscopic scales, and the coupling between the magnetic field and certain properties of the flow. Understanding the origin and maintenance of the large scale galactic magnetic field is the most challenging aspect of the problem.

Tidal Dwarf Galaxies and Missing Baryons

Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons,” known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, “dark matter” is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and “missing baryons” or “dark baryons” is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”.

INTRODUCING NEUTRINO MASS INTO UNIVERSAL EXTRA DIMENSION MODELS AND SOLVING COSMOLOGICAL PROBLEM

Universal extra dimension (UED) models with right-handed neutrinos are studied. The introduction of the neutrinos makes us possible not only to describe Dirac neutrino masses but also to solve the cosmological problem called the KK graviton problem. This problem is essentially caused by the late time decay of a KK photon into a KK graviton and a photon, and it distorts the spectrum of the cosmic microwave background or the diffuse photon. We point out that, once we introduce right-handed neutrinos to UED models, the KK photon decays dominantly into neutrinos and does not emit a photon. We also discuss sub-dominant modes with a photon in the decay quantitatively, and show that their branching ratios are so small that the spectra are not distorted.