MAGNETOHYDRODYNAMICS IN A HOMOGENEOUS COSMOLOGICAL BACKGROUND

Magnetohydrodynamic waves through a plasma with a general equation of state P proportional to rho(gamma) in the presence of a homogeneous am bient background magnetic field are studied in a general Friedmann-Rob ertson-Walker background universe with the metric components being an arbitrary power function of time (similar to t(n)). We find that for a suitable choice of gamma and n our results reduce to those found by H olcomb and Tajima [Phys. Rev. D 40, 3809 (1989)] and later by Holcomb [Astrophys. J. 362, 381 (1990)]. Our general approach to this problem makes it possible to realize the existence of an extra term in the equ ation for the velocity of the fluid, which until now had remained unno ticed. This extra term has no Newtonian analogue. Unlike the usual res ults in magnetohydrodynamics, transverse waves traveling perpendicular to the background magnetic held are found to exist.