Magnetized cosmological perturbations - art. no. 083519

A large-scale cosmic magnetic field affects not only the growth of density perturbations, but also rotational instabilities and anisotropic deformatio n in the density distribution. We give a fully relativistic treatment of al l these effects, incorporating the magneto-curvature coupling that arises i n a relativistic approach. We show that this coupling produces a small enha ncement of the growing mode on superhorizon scales. The magnetic field gene rates new nonadiabatic constant and decaying modes, as well as nonadiabatic corrections to the standard growing and decaying modes. Magnetized isocurv ature perturbations are purely decaying on superhorizon scales. On subhoriz on scales before recombination, magnetized density perturbations propagate as magnetosonic waves, leading to a small decrease in the spacing of acoust ic peaks. Fluctuations in the field direction induce scale-dependent vortic ity, and generate precession in the rotational vector. On small scales, mag netized density vortices propagate as Alfven waves during the radiation era . After recombination, they decay slower than nonmagnetized vortices. Magne tic fluctuations are also an active source of anisotropic distortion in the density distribution. We derive the evolution equations for this distortio n, and find a particular growing solution.