arXiv subjects

Jorge Alfaro

Publications and source records attributed to Jorge Alfaro.

At least 37 records · Page 2Linked to original sources

arXiv2017

$\tildeδ$ Gravity and Schwarzschild Solution

$\tildeδ$ Gravity is a gravitational field model, where the geometry is governed by two symmetric tensors, $g_{μν}$ and $\tilde{g}_{μν}$, and new matter fields ($\tildeδ$ Matter fields) are added to the original matter fields. These new components appear motivated by a new symmetry, called $\tildeδ$ symmetry. In previous works, the model is used to explain the expansion of the Universe without Dark Energy and use $\tildeδ$ Matter as a source of Dark Matter. In this paper, we will developed an initial study of Schwarzschild geometry in $\tildeδ$ Gravity to complement the Dark Matter analysis and introduce other phenomena. We will get a modified deflection of light produced by the sun, the perihelion precession and black hole solution.

gr-qc↗

arXiv2017

Non-Relativistic $\tildeδ$ Gravity: A Description of Dark Matter

$\tildeδ$ Gravity is a gravitational field model, where the geometry is governed by two symmetric tensors, $g_{μν}$ and $\tilde{g}_{μν}$, and new matter fields ($\tildeδ$ Matter fields) are added to the original matter fields. These new components appear motivated by a new symmetry, called $\tildeδ$ symmetry. In previous works, the model is used to explain the expansion of the Universe without Dark Energy. This result and the additional contribution to the mass by $\tildeδ$ Matter are motivations to study the Dark Matter effect with $\tildeδ$ Gravity. In this work, we will derive the Non-Relativistic limit to obtain a correction to the rotation velocity in a galaxy, then we will analyze the most common galaxy density profiles to describe Dark Matter.

gr-qc↗

arXiv2017

On the propagation of gravitational waves in a $Λ$CDM universe

We study here how the presence of non-zero matter density and a cosmological constant could affect the observation of gravitational waves in Pulsar Timing Arrays. Conventionally, the effect of matter and cosmological constant is included by considering the redshift in frequency due to the expansion. However, there is an additional effect due to the change of coordinate systems from the natural ones in the region where waves are produced to the ones used to measure the pulsar timing residuals. This change is unavoidable as the strong gravitational field in a black hole merger distorts clocks and rules. Harmonic waves produced in such a merger become anharmonic when detected by a cosmological observer. The effect is small but appears to be observable for the type of gravitational waves to which PTA are sensitive and for the favoured values of the cosmological parameters.

hep-th↗

arXiv2017

$\tildeδ$ Gravity, $\tildeδ$ matter and the accelerated expansion of the Universe

A gravitational field model based on two symmetric tensors, $g_{μν}$ and $\tilde{g}_{μν}$, is presented. In this model, new matter fields are added to the original matter fields, motivated by an additional symmetry ($\tildeδ$ symmetry). We call them $\tildeδ$ matter fields. We find that massive particles do not follow geodesics, while trajectories of massless particles are null geodesics of an effective metric. Then we study the Cosmological case, where we get an accelerated expansion of the Universe without dark energy.

gr-qc↗

arXiv2017

Bose-Einstein graviton condensate in a Schwarzschild black hole

We analyze in detail a previous proposal by Dvali and Gómez that black holes could be treated as consisting of a Bose-Einstein condensate of gravitons. In order to do so we extend the Einstein-Hilbert action with a chemical potential-like term, thus placing ourselves in a grand-canonical ensemble. The form and characteristics of this chemical potential-like piece are discussed in some detail. We argue that the resulting equations of motion derived from the action could be interpreted as the Gross-Pitaevskii equation describing a graviton Bose-Einstein condensate trapped by the black hole gravitational field. After this, we proceed to expand the ensuring equations of motion up to second order around the classical Schwarzschild metric so that some non-linear terms in the metric fluctuation are kept. Next we search for solutions and, modulo some very plausible assumptions, we find out that the condensate vanishes outside the horizon but is non-zero in its interior. Inspired by a linearized approximation around the horizon we are able to find an exact solution for the mean-field wave function describing the graviton Bose-Einstein condensate in the black hole interior. After this, we can rederive some of the relations involving the number of gravitons $N$ and the black hole characteristics along the lines suggested by Dvali and Gómez.

gr-qc↗

arXiv2016

Mandelstam-Leibbrandt prescription

The light cone gauge is used frequently in string theory as well as gauge theories and gravitation. Loop integrals however have to be infrared regulated to remove spurious poles. The most popular and consistent of these infrared regulators is the Mandelstam-Leibbrandt(ML) prescription. The calculations with ML are rather cumbersome, though. In this work we show that the ML can be replaced by a symmetry of the regulator. This symmetry simplify the calculations, reducing them to conventional dimensional regularization integrals.

hep-th↗

arXiv2015

Electroweak standard model with very special relativity

The Very Special Relativity Electroweak Standard Model (VSR EW SM) is a theory with $SU(2)_L \times U(1)_R$ symmetry, with the same number of leptons and gauge fields as in the usual Weinberg-Salam (WS) model. No new particles are introduced. The model is renormalizable and unitarity is preserved. However, photons obtain mass and the massive bosons obtain different masses for different polarizations. Besides, neutrino masses are generated. A VSR invariant term will produce neutrino oscillations and new processes are allowed. In particular, we compute the rate of the decays $μ\rightarrow e + γ$. All these processes, which are forbidden in the Electroweak Standard Model, put stringent bounds on the parameters of our model and measure the violation of Lorentz invariance. We investigate the canonical quantization of this non-local model. Second quantization is carried out obtaining a well defined particle concept. Additionally, we do a counting of the degrees of freedom associated to the gauge bosons involved in this work, after Spontaneous Symmetry Breaking has been realized. Violations of Lorentz invariance have been predicted by several theories of Quantum Gravity \cite{amu}. It is a remarkable possibility that the low energy effects of Lorentz violation induced by Quantum Gravity could be contained in the non-local terms of the VSR EW SM.

hep-ph↗

arXiv2014

Bosonic (p - 1)-forms in Einstein-Cartan theory of gravity

We introduce bosonic (p - 1)-form fields that couple to the spin connection of the Einstein-Cartan theory of gravity thus becoming a non-trivial source of space-time torsion. We analyze all the general features of both the matter and the gravitational sectors of the theory. Finally we briefly consider the implications of the existence of such fields in different physical settings.

hep-th↗

arXiv2014

Very Special Relativity and Lorentz Violating Theories

Very special relativity (VSR) keeps the main features of special relativity but breaks rotational invariance. It can not be regarded as a fundamental symmetry of nature because many observed phenomena depend on the existence of Lorentz boosts. However, within the scope of Lorentz violating theories it can have a role since it is breaking Lorentz symmetry in a very mild way. In this context, when VSR terms are incorporated in a Lorentz invariant theory several possibilities are allowed. In order to generate such terms systematically we start with a formulation for a spinning particle in VSR. It is then coupled minimally to the electromagnetic field and a gyromagnetic factor is added to give rise to a magnetic moment. In order to analyze the effects of VSR in Thomas precession a spin vector is then proposed in terms of the spinning particle variables. It is then found the VSR contributions to the equation which determines the spin precession angular velocity.

hep-th↗

arXiv2013

Non Abelian Fields in Very Special Relativity

We study non-Abelian fields in the context of very special relativity (VSR). For this we define the covariant derivative and the gauge field gauge transformations, both of them involving a fixed null vector $n_μ$, related to the VSR breaking of the Lorentz group to the Hom(2) or Sim(2) subgroups. As in the Abelian case the gauge field becomes massive. Moreover we show that the VSR gauge transformations form a closed algebra. We then write actions coupling the gauge field to various matter fields (bosonic and fermionic). We mention how we can use the spontaneous symmetry breaking mechanism to give a flavor dependent VSR mass to the gauge bosons. Finally, we quantize the model using the BRST formalism to fix the gauge. The model is renormalizable and unitary and for non abelian groups, asymptotically free.

hep-th↗

arXiv2012

Cosmology in Delta-Gravity

We present a model of the gravitational field based on two symmetric tensors. Gravity is affected by the new field, but outside matter the predictions of the model coincide exactly with general relativity, so all classical tests are satisfied. We find that massive particles do not follow a geodesic while massless particles trajectories are null geodesics of an effective metric. We study the Cosmological case, where we get an accelerated expansion of the universe without dark energy. We also introduce the possibility to explain dark matter with $\tildeδ$ gravity.

gr-qc↗

arXiv2012

Spontaneous generation of geometry in four dimensions

We present the extension to 4 dimensions of an euclidean 2-dimensional model that exhibits spontaneous generation of a metric. In this model gravitons emerge as Goldstone bosons of a global SO(D) X GL(D) symmetry broken down to SO(D). The microscopic theory can be formulated without having to appeal to any particular space-time metric and only assumes the pre-existence of a manifold endowed with an affine connection. We emphasize that not even a flat metric needs to be assumed; in this sense the microscopic theory is quasi-topological. The vierbein appears as a condensate of the fundamental fermions. In spite of having non-standard characteristics, the microscopic theory appears to be renormalizable. The effective long-distance theory is obtained perturbatively around a vacuum that, if the background affine connection is set to zero, is (euclidean) de Sitter space-time. If perturbatively small connections are introduced on this background, fluctuations of the metric (i.e. gravitons) appear; they are described by an effective theory at long distances whose more relevant operators correspond to the Einstein-Hilbert action with a cosmological constant. This effective action is derived in the large N limit, N being the number of fermion species in the fundamental theory. The counterterms required by the microscopic theory are directly related to the cosmological constant and Newton constant and their couplings could eventually be adjusted to the physical values of Mp and Λ.

hep-th↗

arXiv2011

Superluminal neutrinos and the Standard Model

Recently the OPERA collaboration {\cite{opera}} has reported the observation of superluminal neutrinos traveling a distance of 730 km from Grand Sasso Laboratory to CERN.These results contradict the basic tenet of the Theory of Special Relativity: No particle can travel faster than light in vacuum. Moreover they seem to be in conflict with the speed of (anti)neutrinos detected from the explosion of the SP1987A Super Nova{\cite{SP1987A}}.Here we show that the relative velocity between neutrino and photon has the following property: It depends weakly on the energy of the particle excepts in certain regions(thresholds) where discrete jumps appear.This explains both Opera and SP1987A Super Nova data.

hep-ph↗

arXiv2011

A Finite Quantum Gravity Field Theory Model

We discuss the quantization of Delta gravity, a two symmetric tensors model of gravity. This model, in Cosmology, shows accelerated expansion without a cosmological constant. We present the $\tildeδ$ transformation which defines the geometry of the model. Then we show that all delta type models live at one loop only. We apply this to General Relativity and we calculate the one loop divergent part of the Effective Action showing its null contribution in vacuum, implying a finite model. Then we proceed to study the existence of ghosts in the model. Finally, we study the form of the finite quantum corrections to the classical action of the model.

gr-qc↗

arXiv2010

The emergence of geometry: a two-dimensional toy model

We review the similarities between the effective chiral lagrangrian, relevant for low-energy strong interactions, and the Einstein-Hilbert action. We use these analogies to suggest a specific mechanism whereby gravitons would emerge as Goldstone bosons of a global SO(D) X GL(D) symmetry broken down to SO(D) by fermion condensation. We propose a two-dimensional toy model where a dynamical zwei-bein is generated from a topological theory without any pre-existing metric structure, the space being endowed only with an affine connection. A metric appears only after the symmetry breaking; thus the notion of distance is an induced effective one. In spite of several non-standard features this simple toy model appears to be renormalizable and at long distances is described by an effective lagrangian that corresponds to that of two-dimensional gravity (Liouville theory). The induced cosmological constant is related to the dynamical mass M acquired by the fermion fields in the breaking, which also acts as an infrared regulator. The low-energy expansion is valid for momenta k >M, i.e. for supra-horizon scales. We briefly discuss a possible implementation of a similar mechanism in four dimensions.

hep-th↗

arXiv2009

Gauge invariant non-linear electrodynamics motivated by a spontaneous breaking of the Lorentz symmetry

We introduce a new version of non-linear electrodynamics which is produced by a spontaneous symmetry breaking of Lorentz invariance induced by the non-zero expectation value of the electromagnetic field strength. The symmetry breaking potential is argued to effectively arise from the integration of massive gauge bosons and fermions in an underlying fundamental theory. All possible choices of the vacuum lead only to the remaining invariant subgroups T(2) and HOM(2). We explore the plane wave solutions of the linearized sector of the model for an arbitrary vacuum. They present two types of dispersion relations. One corresponds to the case of the usual Maxwell electrodynamics with the standard polarization properties of the fields. The other dispersion relation involves anisotropies determined by the structure of the vacuum. The model is stable in the small Lorentz invariance violation approximation. We have embedded our model in the photon sector of the Standard Model Extension in order to set bounds for our parameters. The one-way anisotropic speed of light is calculated for a general vacuum and its isotropic component is strongly bounded by ${\tilde δc}/c < 2 \times 10^{-32}$. The anisotropic violation contribution is estimated by introducing an alternative definition for the difference of the two-way speed of light in perpendicular directions $Δc$, which is also strongly bounded by ${Δc}/c < 10^{-32}$. Finally, we speculate on the relation of the vacuum energy of the model with the cosmological constant and propose a connection between the vacuum fields and the intergalactic magnetic fields.

hep-ph↗

arXiv2009

Lorentz Violation on The Primordial Baryogenesis

Recently many studies have considered the possibility of a Lorentz Invariance Violation (LIV), and explored its consequences in a wide range of experiments. If this is true, a LIV could explains some mysteries in Cosmology. In this paper specifically, we will analyze the effects on The Primordial Baryogenesis because it is one of the more important and mysterious phenomena of the Big-Bang, that happened at very high energies, so we have a real chance to obtain an important effect. We will see that this effect could exist, depending directly on the temperature, that is very high at this time in the history of the Universe. So, it is possible to use this result as a test for a LIV and explore the possibility that the boson that started the baryogenesis explains, in part, the dark matter. We will obtain estimates about the beginning time of the baryogenesis and the boson mass too, that come directly from the LIV.

hep-ph↗

arXiv2007

Velocity and Distribution of Primordial Neutrinos

The Cosmic Neutrinos Background (\textbf{CNB}) are Primordial Neutrinos decoupled when the Universe was very young. Its detection is complicated, especially if we take into account neutrino mass and a possible breaking of Lorentz Invariance at high energy, but has a fundamental relevance to study the Big-Bang. In this paper, we will see that a Lorentz Violation does not produce important modification, but the mass does. We will show how the neutrinos current velocity, with respect to comobile system to Universe expansion, is of the order of 1065 $[\frac{km}{s}]$, much less than light velocity. Besides, we will see that the neutrinos distribution is complex due to Planetary motion. This prediction differs totally from the usual massless case, where we would get a correction similar to the Dipolar Moment of the \textbf{CMB}.

astro-ph↗