Waves and instabilities in an anisotropic universe

¹ Department of Physics, Aristoteleion University of Thessaloniki, 54006 Thessaloniki, Greece
² Department of Physics, University of Cincinati, Cincinaty, OH 45219, USA

Corresponding author: D. Papadopoulos, papadop@astro.auth.gr

Received: 10 July 2001
Accepted: 18 October 2001

Abstract

The excitation of low frequency plasma waves in an expanding anisotropic cosmological model that contains a magnetic field frozen into the matter and pointing in the longitudinal direction is discussed. Using the exact equations governing finite-amplitude wave propagation in hydromagnetic media within the framework of the general theory of relativity, we show that a spectrum of magnetized sound waves will be excited and form large-scale “damped oscillations” in the expanding universe. The characteristic frequency of the excited waves is slightly shifted away from the sound frequency and the shift depends on the strength of the primordial magnetic field. This magnetic field dependent shift may have an effect on the acoustic peaks of the CMB.