91 research outputs found
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.Comment: 7 pages, accepted in Class. Quantum Gra
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.Comment: Accepted for publication in Physical Review Letter
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
Birefringent light propagation on anisotropic cosmological backgrounds
Exact electromagnetic wave solutions to Maxwell equations on anisotropic
Bianchi I cosmological spacetime backgrounds are studied. The waves evolving on
Bianchi I spacetimes exhibit birefringence (associated to linear polarization)
and dispersion.
The particular case of a vacuum--dominated anisotropic Universe, which
reproduces a Friedmann-Robertson-Walker Universe (for late times) while for
earlier times it matches a Kasner Universe, is studied. The electromagnetic
waves do not, in general, follow null geodesics. This produces a modification
of the cosmological redshift, which is now dependent on light polarization and
dispersion and its non-null geodesic behavior. New results presented here may
help to tackle some issues related to the "horizon" problem.Comment: Accepted in Physical Review
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