Leonardo Patiño

Note on the equation of state of geometric dark-energy in f(R) gravity

We focus on the analysis of three inequivalent equations of state of geometric dark energy in

Topological quantization of gravitational fields

f(R)

Increase of the energy necessary to probe ultraviolet theories due to the presence of a strong magnetic field

cosmology that have been considered in the past and discuss their differences, advantages and drawbacks.

About matter and dark-energy domination eras in

We introduce the method of topological quantization for gravitational fields in a systematic manner. First we show that any vacuum solution of Einstein’s equations can be represented in a principal fiber bundle with a connection that takes values in the Lie algebra of the Lorentz group. This result is generalized to include the case of gauge matter fields in multiple principal fiber bundles. We present several examples of gravitational configurations that include a gravitomagnetic monopole in linearized gravity, the C-energy of cylindrically symmetric fields, the Reissner–Nordstrom and the Kerr–Newman black holes. As a result of the application of the topological quantization procedure, in all the analyzed examples we obtain conditions implying that the parameters entering the metric in each case satisfy certain discretization relationships.

R^n

A bstractWe use the gauge gravity correspondence to study the renormalization group flow of a double trace fermionic operator in a quark-gluon plasma subject to the influence of a strong magnetic field and compare it with the results for the case at zero temperature and no magnetic field, where the flow between two fixed points is observed. Our results show that the energy necessary to access the physics of the ultraviolet theory increases with the intensity of the magnetic field under which the processes happen. We provide arguments to support that this increase is scheme independent, and to exhibit further evidence we do a very simple calculation showing that the dimensional reduction expected in the gauge theory in this scenario is effective up to an energy scale that grows with the strength of such a background field. We also show that independently of the renormalization scheme, the coupling of the double trace operators in the ultraviolet fixed point increases with the intensity of the background field. These effects combined can change both, the processes that are expected to be involved in a collision experiment at a given energy and the azimuthal anisotropy of the measurements resulting of them.

gravity or lack thereof

We provide further numerical evidence which shows that R^n models in f(R) metric gravity whether produces a late time acceleration in the Universe or a matter domination era (usually a transient one) but not both. Our results confirm the findings of Amendola et al. (2007), but using a different approach that avoids the mapping to scalar-tensor theories of gravity, and therefore, dispense us from any discussion or debate about frames (Einstein vs Jordan) which are endemic in this subject. This class of models has been used extensively in the literature as an alternative to the dark energy, but should be considered ruled out for being inconsistent with observations. Finally, we discuss a caveat in the analysis by Faraoni (2011), which was used to further constrain these models by using a chameleon mechanism.

On the non-existence of totally localised intersections of D3/D5 branes in type IIB SUGRA

In the present paper we study the most general configuration of intersecting D3/D5 branes in type IIB supergravity satisfying Poincare invariance in the directions common to the branes and SO(3) symmetry in the totally perpendicular directions. The form of these configurations is greatly restricted by the Killing spinor equations and the equations of motion, which among other things, force the Ramond-Ramond scalar to be zero and do not permit the existence of totally localised intersections of this kind.

Topological quantization of the free massive bosonic field

We present a topological quantization of free massive bosonic fields as the first example of a classical field theory with a quantum counterpart to be studied under this formalism. First, we identify certain harmonic map as a geometric representation of this physical system. We take as a concrete example the case of free massive bosonic fields in two dimensions represented by the minimal embedding of a two dimensional surface into a pp-wave spacetime. We use this geometric representation to construct the fiber bundle corresponding to some specific field configurations and then find their topological spectra, defined in terms of the Euler invariant. We discuss the results for some particular configurations and their consequences for the energy of the system.

Cosmology in

Using an approach that treats the Ricci scalar itself as a degree of freedom, we analyze the cosmological evolution within an f(R) model that has been proposed recently (exponential gravity) and that can be viable for explaining the accelerated expansion and other features of the Universe. This approach differs from the usual scalar-tensor method and, among other things, it spares us from dealing with unnecessary discussions about frames. It also leads to a simple system of equations which is particularly suited for a numerical analysis.