Publication date: May 2014
Abstract:
Astrophysical plasmas in the surrounding of compact objects and subject
to intense gravitational and electromagnetic fields are believed to give
rise to relativistic regimes. Theoretical and observational evidences
suggest that magnetized plasmas of this type are collisionless and can
persist for long times (e.g., with respect to a distant observer,
coordinate, time), while exhibiting geometrical structures characterized
by the absence of well-defined spatial symmetries. In this paper, the
problem is posed whether such configurations can correspond to some kind
of kinetic equilibrium. The issue is addressed from a theoretical
perspective in the framework of a covariant Vlasov statistical
description, which relies on the method of invariants. For this purpose,
a systematic covariant variational formulation of gyrokinetic theory is
developed, which holds without requiring any symmetry condition on the
background fields. As a result, an asymptotic representation of the
relativistic particle magnetic moment is obtained from its formal exact
solution, in terms of a suitably defined invariant series expansion
parameter (perturbative representation). On such a basis, it is shown
that spatially non-symmetric kinetic equilibria can actually be
determined, an example being provided by Gaussian-like distributions. As
an application, the physical mechanisms related to the occurrence of a
non-vanishing equilibrium fluid 4-flow are investigated.
Authors:
Cremaschini, Claudio; Tessarotto, Massimo; Stuchlík, Zdeněk;