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Felipe A. Asenjo

Publications and source records attributed to Felipe A. Asenjo.

90 records · Page 5Linked to original sources
arXiv2016

Class of exact solutions for a cosmological model of unified gravitational and quintessence fields

A new approach to tackle Einstein equations for an isotropic and homogeneous Friedmann--Robertson--Walker Universe in the presence of a quintessence scalar field is devised. It provides a way to get a simple exact solution to these equations. This solution determines the quintessence potential uniquely and it differs from solutions which have been used to study inflation previously. It relays on a unification of geometry and dark matter implemented through the definition of a functional relation between the scale factor of the Universe and the quintessence field. For a positive curvature Universe, this solution produces perpetual accelerated expansion rate of the Universe, while the Hubble parameter increases abruptly, attains a maximum value and decreases thereafter. The behavior of this cosmological solution is discussed and its main features are displayed. The formalism is extended to include matter and radiation.

gr-qc↗
arXiv2015

Generalized Magnetofluid Connections in Pair Plasmas

We extend the magnetic connection theorem of ideal magnetohydrodynamics to nonideal relativistic pair plasmas. Adopting a generalized Ohm's law, we prove the existence of generalized magnetofluid connections that are preserved by the plasma dynamics. We show that these connections are related to a general antisymmetric tensor that unifies the electromagnetic and fluid fields. The generalized magnetofluid connections set important constraints on the plasma dynamics by forbidding transitions between configurations with different magnetofluid connectivity. An approximated solution is explicitly shown where the corrections due to current inertial effects are found.

physics.plasm-ph↗
arXiv2015

Supersymmetric Majorana Quantum Cosmologies

The Einstein equations for an isotropic and homogeneous Friedmann--Robertson--Walker Universe in the presence of a quintessence scalar field are shown to be described in a unified way, formally identical to the dynamics of a relativistic particle moving on a two--dimensional spacetime. The correct Lagrangian for the system is presented and used to construct a spinor quantum cosmology theory using Breit's prescription. The theory is supersymmetric when written in Majorana representation. The spinor components interact through a potential that unifies spacetime curvature and quintessence. An exact supersymmetric solution for $k=0$ case is exhibited. This quantum cosmology model may be interpreted as a theory of interacting universes.

gr-qc↗
arXiv2015

Generalized Magnetofluid Connections in Relativistic Magnetohydrodynamics

The concept of magnetic connections is extended to non-ideal relativistic magnetohydrodynamical plasmas. Adopting a general set of equations for relativistic magnetohydrodynamics including thermal-inertial, thermal electromotive, Hall and current-inertia effects, we derive a new covariant connection equation showing the existence of generalized magnetofluid connections that are preserved during the dissipationless plasma dynamics. These connections are intimately linked to a general antisymmetric tensor that unifies the electromagnetic and fluid fields, allowing the extension of the magnetic connection notion to a much broader concept.

physics.plasm-ph↗
arXiv2014

Thermal-inertial effects on magnetic reconnection in relativistic pair plasmas

The magnetic reconnection process is studied in relativistic pair plasmas when the thermal and inertial properties of the magnetohydrodynamical fluid are included. We find that in both Sweet-Parker and Petschek relativistic scenarios there is an increase of the reconnection rate owing to the thermal-inertial effects, both satisfying causality. To characterize the new effects we define a thermal-inertial number which is independent of the relativistic Lundquist number, implying that reconnection can be achieved even for vanishing resistivity as a result of only thermal-inertial effects. The current model has fundamental importance for relativistic collisionless reconnection, as it constitutes the simplest way to get reconnection rates faster than those accessible with the sole resistivity.

physics.plasm-ph↗
arXiv2014

Spinning massive test particles in cosmological and general static spherically symmetric spacetimes

A Lagrangian formalism is used to study the motion of a spinning massive particle in Friedmann--Robertson--Walker and Gödel spacetimes, as well as in a general Schwarzschild-like spacetime and in static spherically symmetric conformally flat spacetimes. Exact solutions for the motion of the particle and general exact expressions for the momenta and velocities are displayed for different cases. In particular, the solution for the motion in spherically symmetric metrics is presented in the equatorial plane. The exact solutions are found using constants of motion of the particle, namely its mass, its spin, its angular momentum, and a fourth constant, which is its energy when the metric is time independent, and a different constant otherwise. These constants are associated to Killing vectors. In the case of the motion on the Friedmann--Robertson--Walker metric, a new constant of motion is found. This is the fourth constant which generalizes previously known results obtained for spinless particles. In the case of general Schwarzschild-like spacetimes, our results allow for the exploration of the case of the Reissner-Nordstrom-(Anti)de Sitter metric. Finally, for the case of the conformally flat spacetimes, the solution is explicitly evaluated for different metric tensors associated to a universe filled with static perfect fluids and electromagnetic radiation. For some combination of the values of the constants of motion the particle trajectories may exhibit spacelike velocity vectors in portions of the trajectories.

gr-qc↗
arXiv2013

Hot Fluids and Nonlinear Quantum Mechanics

It is shown that a hot relativistic fluid could be viewed as a collection of self-interacting quantum objects. They obey a nonlinear equation which is a modification of the quantum equation obeyed by elementary constituents of the fluid. A uniform phenomenological prescription, to affect the quantum transition from a corresponding classical system, is invoked to derive the nonlinear Schrödinger, Klein-Gordon, and Pauli-Schrödinger equations. It is expected that the created nonlinear quantum mechanics would advance, in a fundamental way, both the conceptual understanding and computational abilities, particularly, in the field of extremely high energy-density physics.

physics.flu-dyn↗
arXiv2013

On a consistent macroscopic description for a spin quantum plasma with interparticle interactions

Quantum mechanical averaging of the particle concentration operator is an effective starting point for derivation of the many-particle quantum hydrodynamic equations. In many-particle quantum systems, we have to separate the ordered motion of the local center of mass (velocity field), the thermal, and the quantum motion. The quantum mechanical average process, invoked here, is completely determined, and is different from the usual averaging processes that introduces undefined probabilities for quantum states. It is shown that the Madelung decomposition for the $N$-particle spinor wave function allows the correct introduction of the velocity field, and gives explicit expressions for the quantum contributions to both the momentum, and the spin flux. The formalism also contains plasma effects produced by the Coulomb and spin-spin interparticle interactions. It is shown that both interactions appear in plasma dynamics as effective electric and magnetic fields. As result we find a fully coherent description for spin quantum plasma in the self-consistent field approximation for interparticle interactions. A simple consequence - the change brought about by interparticle correlations on the propagation of electrostatic waves in a spin quantum plasma - is discussed.

physics.plasm-ph↗
arXiv2012

Can gravitation accelerate neutrinos?

The Lagrangian equations of motion for massive spinning test particles (tops) moving on a gravitational background using General Relativity are presented. The paths followed by tops are nongeodesic. An exact solution for the motion of tops on a Schwarzschild background which allows for superluminal propagation of tops is studied. It is shown that the solution becomes relevant for particles with small masses, such as neutrinos. This general result is used to calculate the necessary condition to produce superluminal motion in part of the trajectory of a small mass particle in a weak gravitational field. The condition for superluminal motion establishes a relation between the mass, energy and total angular momentum of the particle.

physics.gen-ph↗
arXiv2012

Magnetic field generation in curved spacetimes

Using the generally covariant magnetofluid formalism for a hot plasma, a new curvature (of space time) driven mechanism for generating seed vorticity/magnetic field is presented. The "battery" owes its origin to the interaction between gravity (epitomized in the spatial variation of the metric tensor) and the inhomogeneous plasma thermodynamics. The general relativistic drive for the seed field is evaluated in a simplified model of a hot plasma accreting around a Schwarzschild black hole. Some astrophysical applications are suggested.

astro-ph.HE↗
arXiv2012

Generating vorticity and magnetic fields in plasmas in general relativity: spacetime curvature drive

Using the generally covariant magnetofluid formalism for a hot plasma, a new spacetime curvature driven mechanism for generating seed vorticity/magnetic field is presented. The ``battery'' owes its origin to the interaction between gravity and the inhomogeneous plasma thermodynamics. The general relativistic drive is evaluated for two simple cases: seed formation in a simplified model of a hot plasma accreting in stable orbits around a Schwarzschild black hole, and for particles in free fall near the horizon. Some astrophysical applications are suggested.

physics.plasm-ph↗
arXiv2011

Vortical Dynamics of spinning quantum plasmas - Helicity Conservation

It is shown that a vorticity, constructed from spin field of a quantum spinning plasma, combines with the classical generalized vorticity (representing the magnetic and the velocity fields) to yield a new grand generalized vorticity that obeys the standard vortex dynamics. Expressions for the quantum or spin vorticity, and for the resulting generalized helicity invariant are derived. Reduction of the rather complex spinning quantum system to a well known and highly investigated classical form opens familiar channels for the delineation of physics peculiar to dense plasmas spanning solid state to astrophysical objects. A simple example is worked out to show that the magnetics of a spinning plasma can be much richer than that of the corresponding classical system.

physics.plasm-ph↗
arXiv2011

Analogue black hole in magnetohydrodynamics

We consider an irrotational plasma fluid evolving under the effect of a background magnetic field. The magnetohydrodynamic formalism is used to describe the electromagnetic waves and the dynamics is described by a scalar field that follows a second order differential equation. This equation can also be recovered as the wave equation associated to a field in a curved space-time. Through this analogy we recreate a sonic horizon, equivalent to those found in perfect fluid theories. However, in this case, the magnetic field creates a pressure in the plasma which contributes to the magnetoacoustic speed that builds the horizon. This effect enhances the temperature produced by the Hawking radiation expected from this analogue black hole, and eventually, making its experimental detection worth to consider.

gr-qc↗
arXiv2010

Induced plasma magnetization due to magnetic monopoles

When magnetic monopoles are introduced in plasma equations, the propagation of electromagnetic waves is modified. In this work is shown that this modification leads to the emergence of a ponderomotive force which induces a magnetization of the plasma. As a result, a cyclotron frequency is induced in electrons. This frequency is proportional to the square of the magnetic charge.

physics.plasm-ph↗
arXiv2010

Exact solution for large amplitude circularly polarized electromagnetic waves in incompressible spin quantum Hall magnetohydrodynamics

It is shown that incompressible spin quantum Hall magnetohydrodynamics allows an exact solution for the propagation of a circularly polarized electromagnetic wave. The solution is obtained assuming a condition between the fluid velocity and the magnetic field which eliminates the nonlinear terms in Maxwell equations. As a result of the coupling with spin, the propagation mode depends on the amplitude of the magnetic field. From the full solution, the limits of small and large wavenumber are studied obtaining linear and a nonlinear spin-modified modes.

physics.plasm-ph↗
arXiv2010

The quantum effects of the spin and the Bohm potential in the oblique propagation of magnetosonic waves

We study the quantum corrections to the oblique propagation of the magnetosonic waves in a warm quantum magnetoplasma composed by mobile ions and electrons. We use a fluid formalism to include quantum corrections due to the Bohm potential and to magnetization energy of electrons due to its spin. The effects of both quantum corrections are shown in the dispersion relation for perpendicular, parallel and oblique propagation. We find that the quantum contributions to the low-frequency depends on the type of propagation we are studying.

physics.plasm-ph↗
arXiv2010

The effect of spin magnetization in the damping of electron plasma oscillations

The effect of spin of particles in the propagation of plasma waves is studied using a semi-classical kinetic theory for a magnetized plasma. We focus in the simple damping effects for the electrostatic wave modes besides Landau damping. Without taking into account more quantum effects than spin contribution to Vlasov's equation, we show that spin produces a new damping or instability which is proportional to the zeroth order magnetization of the system. This correction depends on the electromagnetic part of the wave which is coupled with the spin vector.

physics.plasm-ph↗