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Felipe A. Asenjo

Publications and source records attributed to Felipe A. Asenjo.

At least 55 records · Page 3Linked to original sources
arXiv2021

Heat bullets

New localized structured solutions for the three-dimensional linear diffusion (heat) equation are presented. These new solutions are written in terms of Airy functions and either Gaussian or Bessel functions. They accelerate along their propagation direction, while in the plane orthogonal to it, they retain their either Gaussian or Bessel structure. These diffusion (heat) densities retain a localized structure in space as they propagate, and may be considered the heat analogue of Airy light bullets.

nlin.PS↗
arXiv2021

Accelerating solutions to the diffusion equation

We report accelerating diffusive solutions to the diffusion equation with a constant diffusion tensor. The maximum values of the diffusion density evolve in an accelerating fashion described by Airy functions. We show the diffusive accelerating behavior for one--dimensional systems, as well as for a general three--dimensional case. We also construct a modulated modified form of the diffusion solution that retains the accelerating features.

cond-mat.stat-mech↗
arXiv2021

Light--like propagation of self--interacting Klein--Gordon fields in cosmology

It is showed that complex scalar fields with a self-interaction potential may propagate along null geodesics on flat Friedmann--Lemaître--Robertson--Walker universes with different time-dependent scale factors. This occurs provided they self interact adequately, for different forms of potentials, and even for the massive case.

gr-qc↗
arXiv2021

A new approach to solving the Schrödinger equation

A new approach to find exact solutions to one--dimensional quantum mechanical systems is devised. The scheme is based on the introduction of a potential function for the wavefunction, and the equation it satisfies. We recover known solutions as well as to get new ones for both free and interacting particles with wavefunctions having vanishing and non--vanishing Bohm potentials. For most of the potentials, no solutions to the Schrödinger equation produce a vanishing Bohm potential. A (large but) restricted family of potentials allows the existence of particular solutions for which the Bohm potential vanishes. This family of potentials is determined, and several examples are presented. It is shown that some quantum, such as accelerated Airy wavefunctions, are due to the presence of non--vanishing Bohm potentials. New examples of this kind are found and discussed.

quant-ph↗
arXiv2021

Nondiffracting gravitational waves

It is proved that accelerating nondiffracting gravitational Airy wave--packets are solutions of linearized gravity. It is also showed that Airy functions are exact solutions to Einstein equations for non--accelerating nondiffracting gravitational wave--packets.

gr-qc↗
arXiv2021

Classical and Quantum Dispersion Relations

It is showed that, in general, classical and quantum dispersion relations are different due to the presence of the Bohm potential. There are exact particular solutions of the quantum (wave) theory which obey the classical dispersion relation, but they differ in the general case. The dispersion relations may also coincide when additional assumptions are made, such as WKB or eikonal approximations, for instance. This general result also holds for non--quantum wave equations derived from classical counterparts, such as in ray and wave optics, for instance. Explicit examples are given for covariant scalar, vectorial and tensorial fields in flat and curved spacetimes.

quant-ph↗
arXiv2021

Quantum particles that behave as free classical particles

The existence of non-vanishing Bohm potentials, in the Madelung-Bohm version of the Schrödinger equation, allows for the construction of particular solutions for states of quantum particles interacting with non-trivial external potentials that propagate as free classical particles. Such solutions are constructed with phases which satisfy the classical Hamilton-Jacobi for free particles and whose probability densities propagate with constant velocity, as free classical particles do.

quant-ph↗
arXiv2021

Casimir force induced by electromagnetic wave polarization in Kerr, Gödel and Bianchi--I spacetimes

Electromagnetic waves propagation on either rotating or anisotropic spacetime backgrounds (such as Kerr and Gödel metrics, or Bianchi-I metric) produce a reduction of the magnitude of Casimir forces between plates. These curved spacetimes behave as chiral or birefringent materials producing dispersion of electromagnetic waves, in such a way that right- and left-circularly polarized light waves propagate with different phase velocities. Results are explicitly calculated for discussed cases. The difference on the wavevectors of the two polarized electromagnetic waves produces an abatement of a Casimir force which depends on the interaction between the polarization of electromagnetic waves and the properties of the spacetime.

gr-qc↗
arXiv2021

Dual wavefunctions in two-dimensional quantum mechanics

It is shown that the Schrodinger equation for a large family of pairs of two-dimensional quantum potentials possess wavefuctions for which the amplitude and the phase are interchangeable, producing two different solutions which are dual to each other. This is a property of solutions with vanishing Bohm potential. These solutions can be extended to three-dimensional systems. We explicitly calculate dual solutions for physical systems, such as the repulsive harmonic oscillator and the two-dimensional hydrogen atom. These dual wavefunctions are also solutions of an analogue optical system in the eikonal limit. In this case, the potential is related to the refractive index, allowing the study of this two-dimensional dual wavefunction solutions with an optical (analogue) system.

quant-ph↗
arXiv2021

Unification of massless field equations solutions for any spin

A unification of Klein--Gordon, Dirac, Maxwell, Rarita--Schwinger and Einstein equations exact solutions (for the massless fields cases) is presented. The method is based on writing all of the relevant dynamical fields in terms of products and derivatives of pre--potential functions, which satisfy d'Alambert equation. The coupled equations satisfied by the pre--potentials are non-linear. Remarkably, there are particular solutions of (gradient) orthogonal pre--potentials that satisfy the usual wave equation which may be used to construct {\it{exact non--trivial solutions to Klein--Gordon, Dirac, Maxwell, Rarita--Schwinger and (linearized and full) Einstein equations}}, thus giving rise to a unification of the solutions of all massless field equations for any spin. Some solutions written in terms of orthogonal pre--potentials are presented. Relations of this method to previously developed ones, as well as to other subjects in physics are pointed out.

quant-ph↗
arXiv2021

Bohm potential is real and its effects are measurable

We analyze Bohm's potential effects both in the realms of Quantum Mechanics and Optics, as well as in the study of other physical phenomena described in terms of classical and quantum wave equations. We approach this subject by using theoretical arguments as well as experimental evidence. We find that the effects produced by Bohm's potential are both theoretically responsible for the early success of Quantum Mechanics correctly describing atomic and nuclear phenomena and, more recently, by confirming surprising accelerating behavior of free waves and particles experimentally, for instance.

quant-ph↗
arXiv2021

Bohm potential for the time dependent harmonic oscillator

In the Madelung-Bohm approach to quantum mechanics, we consider a (time dependent) phase that depends quadratically on position and show that it leads to a Bohm potential that corresponds to a time dependent harmonic oscillator, provided the time dependent term in the phase obeys an Ermakov equation.

quant-ph↗
arXiv2020

Magnetic Reconnection as a Mechanism for Energy Extraction from Rotating Black Holes

Spinning black holes store rotational energy that can be extracted. When a black hole is immersed in an externally supplied magnetic field, reconnection of magnetic field lines within the ergosphere can generate negative energy (relative to infinity) particles that fall into the black hole event horizon while other particles escape stealing energy from the black hole. We show analytically that energy extraction via magnetic reconnection is possible when the black hole spin is high (dimensionless spin $a\sim1$) and the plasma is strongly magnetized (plasma magnetization $σ_0>1/3$). The parameter space region where energy extraction is allowed depends on the plasma magnetization and the orientation of the reconnecting magnetic field lines. For $σ_0 \gg 1$, the asymptotic negative energy at infinity per enthalpy of the decelerated plasma that is swallowed by a maximally rotating black hole is found to be $ε^\infty_- \simeq - \sqrt{σ_0/3}$. The accelerated plasma that escapes to infinity and takes away black hole energy asymptotes the energy at infinity per enthalpy $ε^\infty_+ \simeq \sqrt{3σ_0}$. We show that the maximum power extracted from the black hole by the escaping plasma is $P_{\rm extr}^{\rm max} \sim 0.1 M^2\sqrt{σ_0}\,w_0$ (here, $M$ is the black hole mass and $w_0$ is the plasma enthalpy density) for the collisionless plasma regime and one order of magnitude lower for the collisional regime. Energy extraction causes a significant spindown of the black hole when $a \sim 1$. The maximum efficiency of the plasma energization process via magnetic reconnection in the ergosphere is found to be $η_{\rm max} \simeq 3/2$. Since fast magnetic reconnection in the ergosphere should occur intermittently in the scenario proposed here, the associated emission within a few gravitational radii from the black hole is expected to display a bursty nature.

astro-ph.HE↗
arXiv2020

Propagation of light in linear and quadratic GRIN media: The Bohm potential

It is shown that field propagation in linear and quadratic gradient-index (GRIN) media obeys the same rules of free propagation in the sense that a field propagating in free space has a (mathematical) form that may be {\it exported} to those particular GRIN media. The Bohm potential is introduced in order to explain the reason of such behavior: it changes the dynamics by modifying the original potential. The concrete cases of two different initials conditions for each potential are analyzed.

physics.optics↗
arXiv2020

Generalized Magnetofluid Connections in Curved Spacetime

The ideal magnetohydrodynamic theorem on the conservation of the magnetic connections between plasma elements is extended to non-ideal relativistic plasmas in curved spacetime. The existence of generalized magnetofluid connections that are preserved by the plasma dynamics is formalized by means of a covariant connection equation that includes different non-ideal effects. These generalized connections are constituted by 2-dimensional hypersurfaces, which are linked to an antisymmetric tensor field that unifies the electromagnetic and fluid fields. They can be interpreted in terms of generalized magnetofluid vorticity field lines by considering a 3+1 foliation of spacetime and a time resetting projection that compensates for the loss of simultaneity in different reference frames between spatially separated events. The worldsheets of the generalized magnetofluid vorticity field lines play a fundamental role in the plasma dynamics by prohibiting evolutions that do not preserve the magnetofluid connectivity.

physics.plasm-ph↗
arXiv2020

Phenomenological dynamics of COVID-19 pandemic: meta-analysis for adjustment parameters

We present a phenomenological procedure of dealing with the COVID--19 data provided by government health agencies of eleven different countries. Instead of using the (exact or approximate) solutions to the SIR (or other) model(s) to fit the data by adjusting the time--independent parameters included in those models, we introduce dynamical parameters whose time--dependence may be phenomenologically obtained by adequately extrapolating a chosen subset of the daily provided data. This phenomenological approach works extremely well to properly adjust the number of infected (and removed) individuals in time, for the countries we consider. Besides, it can handle the sub--epidemic events that some countries may experience. In this way, we obtain the evolution of the pandemic without using any a priori model based on differential equations.

physics.soc-ph↗
arXiv2020

Exact equilibrium state for pair plasmas near the horizon of a Schwarzschild black hole

A pair plasma in hidrostatic equilibrium near the horizon of a Schwarzschild black hole is an exact state. In this work, we show that an exact non--hidrostatic equilibrium state can be sustained for a pair plasma, in which its constituents are moving near the horizon of the black hole. This equilibrium state solution is not due to a vortical formalism, but by the balance of forces in the plasma. This new equilibrium state has a pressure for the hydrostatic equilibrium, although the plasma moves. The equilibrium is achieved by the generation of a magnetic field that emerges by the interplay between the plasma dynamics and the gravitational field, having no flat spacetime analogue. No electric fields are needed to sustain the equilibria. The magnetic field shows an exponential decaying behavior, governed by a function that depends on the properties of the pair plasma and the black, and that plays the role of a characteristc length of the dynamics of the magnetic field.

physics.plasm-ph↗