arXiv subjects

Felipe A. Asenjo

Publications and source records attributed to Felipe A. Asenjo.

At least 37 records · Page 2Linked to original sources

arXiv2024

Accelerating Airy tensor modes of cosmological gravitational waves

From a classical analysis, it is shown that the nondiffractive accelerating gravitational Airy wave packets are solutions of Einstein equations for their linearized tensor modes in a Friedmann-Lemaître-Robertson-Walker cosmological background filled with a perfect fluid, with equations of state $w=1/3$ and $w=-1/3$. These solutions have finite energy, presenting accelerating behavior due to the structured spatial form of the wavepacket. This is manifested by curved trajectories along the wave path. Also, using spectral functions, it is possible, with these packets, to construct more general, arbitrary wave packets. All these new solutions bring insights on new forms for gravitational wave propagation.

gr-qc↗

arXiv2024

Expanding CGL: The CGL double-adiabatic approximation in the Expanding Solar Wind

Different in situ satellite observations within 0.3 to 1 AU from the Sun reveal deviations in the thermodynamics of solar wind expansion. Specifically, these deviations challenge the applicability of the double adiabatic or CGL theory, indicating potential influences such as perpendicular heating and/or parallel cooling of ions. The study aims to investigate the plasma expansion phenomena using the Expanding Box Model (EBM) coupled with an ideal MHD description of the plasma. The primary objective is to understand the observed deviations from the CGL predictions, and how the expansion can affect the conservation of the adiabatic invariants, particularly focusing on the impact of transverse expansion on the CGL equations. To address the plasma expansion, we employed the Expanding Box Model (EBM) coupled with the ideal-MHD formalism used for CGL theory. This model provides a unique system of reference co-moving with the solar wind, allowing for the incorporation of transverse expansion into the double adiabatic equations. Solving the equations for different magnetic field profiles, we compute the evolution of anisotropy and plasma beta, which deviates from CGL predictions and empirical observations. This deviation is attributed to the plasma cooling effect induced by the Expanding Box Model (EBM). Results suggest that heating mechanisms play a crucial role in counteracting plasma cooling during expansion.

physics.plasm-ph↗

arXiv2024

Energy extracted from Hartle-Thorne strange stars

It is discussed how Penrose process can be used in a strange star, described by the Hartle-Thorne metric, to extract its rotational energy. This metric has an ergosphere region that depends only on its angular momentum. It is shown that massive particles with negative energy can exist in this ergosphere, exploring the conditions on the radial distance and on angular momentum for this to occur. It is also calculated the total amount of rotational energy that can be extracted from the strange star, and how these conditions cannot be fulfilled by a star with regular matter.

gr-qc↗

arXiv2024

Extended BMT equations and the anomalous magnetic moment

We propose a generalized form of the Thomas-Bargmann-Michel-Telegdi equations. These are first-order in both electric and magnetic fields and retain the conventional conserved quantities and constraints. Within this novel phenomenological framework, we delve into an archetypal measurement scenario. Specifically, we scrutinize the contributions to the standard definition of the anomalous magnetic moment observable, highlighting each new correction term.

hep-ph↗

arXiv2023

Electromagnetic plasma waves in dark energy cosmology

We explore electromagnetic wave modes that can exist in a cosmological plasma dominated by dark energy due to a cosmological constant. It is found that, in the cold and hot plasma cases, electromagnetic plasma wave modes can be found exactly. The effect of this cosmology appears as a time-dependent potential in the wave equation for the electromagnetic modes, that effectively modify the frequency response of the plasma. This potential depends on the metric of the spacetime and on the thermodynamical properties of the plasma. For both cases, cold and hot, the solutions are found in terms of Airy and Bessel functions, respectively. When those solutions are required to have vanishing initial conditions, a discretization on the wavelengths of the electromagnetic plasma waves is imposed. Thus, only some specific wave modes can exist in this dark energy cosmology. Relaxing those conditions, we obtain other solutions that approximate to plane waves only in the very hot plasma limit.

astro-ph.CO↗

arXiv2023

Abnormal light propagation and the underdetermination of theory by evidence in astrophysics

We investigate the propagation of certain non-plane wave solutions to Maxwell's equations in both flat and curved spacetimes. We find that such solutions (or rather parts of them) exhibit accelerative behaviour, and in particular do not propagate on straight lines. Having established these results, we then turn to their conceptual significance -- which, in brief, we take to be the following: (i) one should not assume that the part of electromagnetic waves from outer space that is subject to detection is localised onto null trajectories; therefore (ii) astrophysicists and cosmologists should at least be wary about making such assumptions in their inferences from obtained data, for to do so may lead to incorrect inferences regarding the nature of our universe.

physics.hist-ph↗

arXiv2023

Accelerating self-modulated nonlinear waves in weakly and strongly magnetized relativistic plasmas

It is known that a nonlinear Schrödinger equation describes the self-modulation of a large amplitude circularly polarized wave in relativistic electron-positron plasmas in the weakly and strongly magnetized limits. Here, we show that such equation can be written as a modified second Painlevé equation, producing accelerated propagating wave solutions for those nonlinear plasmas. This solution even allows the plasma wave to reverse its direction of propagation. The acceleration parameter depends on the plasma magnetization. This accelerating solution is different to the usual soliton solution propagating at constant speed.

physics.plasm-ph↗

arXiv2023

Existence of Korteweg-de Vries Solitons and Relevance of Relativistic Effects in a Dusty Electron-Ion Plasma

Nonlinear effects in the propagation of perturbations in a dusty electron-ion plasma is studied, considering fully relativistic wave motion. A multifluid model is considered for the particles, from which a KdV equation can be derived. In general, two different soliton solutions are found depending on the kind of dispersion of the KdV equation. We study when the dispersion coefficient of this equation is positive. In this case, two kind of behavior are possible, one associated with a slow wave mode, another with a fast wave mode. It is shown that, depending on the value of the system parameters, compressive and/or rarefactive solitons, or no soliton at all, can be found and that relativistic effects for ions are much more relevant than for electrons. It is also found that relativistic effects can strongly decrease the soliton amplitude for the slow mode, whereas for the fast mode they can lead to compressive-rarefactive soliton transitions and vice versa, depending on the dust charge density in both modes.

physics.plasm-ph↗

arXiv2023

Time-domain supersymmetry for massless scalar and electromagnetic fields in anisotropic cosmologies

It is shown that any cosmological anisotropic model produces supersymmetric theories for both massless scalar and electromagnetic fields. This supersymmetric theory is the time-domain analogue of a supersymmetric quantum mechanical theory. In this case, the variations of the anisotropic scale factors of the Universe are responsible for triggering the supersymmetry. For scalar fields, the superpartner fields evolve in two different cosmological scenarios (Universes). On the other hand, for propagating electromagnetic fields, supersymmetry is manifested through its polarization degrees of freedom in one Universe. In this case, polarization degrees of freedom of electromagnetic waves, which are orthogonal to its propagation direction, become superpartners from each other. This behavior can be measured, for example, through the rotation of the plane of polarization of cosmological light.

gr-qc↗

arXiv2023

Exact and paraxial Airy propagation of relativistic electron plasma wavepackets

The different forms of propagation of relativistic electron plasma wavepackets in terms of Airy functions are studied. It is shown that exact solutions can be constructed showing accelerated propagations along coordinates transverse to the thermal speed cone coordinate. Similarly, Airy propagation is a solution for relativistic electron plasma waves in the paraxial approximation. This regime is considered in time-domain, when paraxial approximation is considered for frequency, and in space-domain, when paraxial approximation is considered for wavelength. In both different cases, the wavepackets remains structured in the transverse plane. Using these solutions we are able to define generalized and arbitrary Airy wavepackets for electron plasma waves, depeding on arbitrary spectral functions. Examples of this construction are presented. These electron plasma Airy wavepackets are the most general solutions of this kind.

physics.plasm-ph↗

arXiv2023

Supersymmetric behavior of polarized electromagnetic waves in anisotropic media

A medium with specific anisotropic refractive indices can induce a supersymmetric behavior in the propagation of polarized electromagnetic waves, in an analogue fashion to a quantum mechanical system. The polarizations of the wave are the ones which behave as superpartners from each other. For this to happen, the anisotropy of the medium must be transverse to the direction of propagation of the wave, with different refractive indices along the direction of each polarization. These refractive indices must follow a very specific relation in order to trigger the supersymetric response of the electromagnetic wave, each of them with spatial dependence on the longitudinal (propagation) direction of the wave. In this form, in these materials, different polarized light can be used to test supersymmetry in an optical fashion.

physics.optics↗

arXiv2023

London-like tensor modes of gravitational waves in cosmic string cosmology

From a classical analysis, we show that gravitational waves in a cosmological medium with equation of state $ω=-1/3$ can follow a London-like equation, implying that some gravitational wave solutions present a decay for certain wavelengths. This scenario, corresponding to a cosmic string cosmology, induces an attenuation temporal scale on the gravitational wave propagation. We discuss on how these solutions impose a limit on the wavelength of the waves that can propagate, which depends on the type of spatial curvature and the energy density content of this type of cosmology.

gr-qc↗

arXiv2023

Non-unitary transformation approach to $\mathcal{PT}$ dynamics

We show that several Hamiltonians that are $\mathcal{PT}$ symmetric may be taken to Hermitian Hamiltonians via a non-unitary transformation and vice versa. We also show that for some specific Hamiltonians such non-unitary transformations may be associated, via a fractional-Wick rotation, to complex time.

quant-ph↗

arXiv2022

Thermal-Inertial Effects on Relativistic Asymmetric Magnetic Reconnection

A general description for relativistic magnetic reconnection is given in terms of asymmetric inflow plasma conditions, such as plasma density, velocity magnetic field strength, and their respective thermal-inertial effects. In this work, we show that thermal-inertial effects increase reconnection rates, generalizing previous results. Furthermore, different reconnection rates can be defined depending on the initial asymmetric conditions for the inflow plasma into the reconnection region. We explore two possibilities for reconnection rates, which, depending on the asymmetric magnetization, display different strengths. We discuss the importance on defining appropriate reconnection rates for corresponding asymmetric plasma systems in the context of previous results.

physics.plasm-ph↗

arXiv2022

Parametric amplification of electromagnetic plasma waves in resonance with a dispersive background gravitational wave

It is shown that a sub-luminal electromagnetic plasma wave, propagating in phase with a background sub-luminal gravitational wave in a dispersive medium, can undergo parametric amplification. For this phenomena to occur, the dispersive characteristics of the two waves must properly match. The response frequencies of the two waves (medium dependent) must lie within a definite and restrictive range. The combined dynamics is represented by a Whitaker-Hill equation, the quintessential model for parametric instabilities. The exponential growth of the electromagnetic wave is displayed at the resonance; the plasma wave grows at the expense of the background gravitational wave. Different physical scenarios, where the phenomenon can be possible, are discussed.

physics.plasm-ph↗

arXiv2022

Supersymmetric relativistic quantum mechanics in time-domain

A supersymmetric relativistic quantum theory in the temporal domain is developed for bi-spinor fields satisfying the Dirac equation. The simplest time-domain supersymmetric theory can be postulated for fields with time-dependent mass, showing an equivalence with the bosonic supersymmetric theory in time-domain. Solutions are presented and they are used to produce probability oscillations between mass states. As an application of this idea, we study the two-neutrino oscillation problem, showing that flavour state oscillations may emerge from the supersymmetry originated by the time-dependence of the unique mass of the neutrino.

quant-ph↗

arXiv2021

Bohm approach to the Gouy phase shift

By adapting the Madelung-Bohm formalism to paraxial wave propagation we show, by using Ermakov-Lewis techniques, that the Gouy phase is related to the form of the phase chosen in order to produce a Gaussian function as a propagated field. For this, we introduce a quantum mechanical invariant, that it is explicitly time dependent despite the fact that the Hamiltonian is itself time-independent. We finally show that the effective Bohm {\it index of refraction} generates a GRIN medium that produces the focusing needed for the Gouy phase.

physics.optics↗

arXiv2021

Using smartphone photographs of the Moon to acquaint students with non-Euclidean geometry

Although they are sometimes considered problematic to grasp by students, the concepts behind non-Euclidean geometry can be taught using astronomical images. By using photographs of the Moon taken with a smartphone through a simple telescope, we were able to introduce these concepts to high-school students and college newcomers. By recognizing different Moon geological structures within the photograph, we teach students how to calculate distances of mountain ranges or areas of craters on the Moon's surface, introducing the notions of geodesics and spherical triangles. Furthermore, students can empirically see that the correct estimations for the actual values cannot be obtained using flat geometry. Instead, by using three--dimensional curved geometry, precise estimates of lengths and areas of geological elements in the Moon can be computed with less than 4\% error. These procedures help students understand, concretely, non-Euclidean geometry concepts.

physics.ed-ph↗