In the presence of the primordial magnetic field , initial vector ( vorticity ) perturbations produce cosmological Alfvén waves and leave imprints on cosmic microwave background ( CMB ) temperature and polarization anisotropy .

We have investigated imprints of cosmological Alfvén waves in CMB anisotropy .
For data constraints , we have used the power spectrum of the recent CMB observations , and correlations estimated from WMAP Internal Linear Combination ( ILC ) maps .
Our analysis shows 3 \sigma evidence of cosmological Alfvén waves .
Using the 3 \sigma limit from our analysis and the Alfvén velocity limit from the total energy density constraint , we impose a lower bound on the amplitude of primordial vector perturbation : 4 \times 10 ^ { -12 } at k _ { 0 } = 0.002 / \mathrm { Mpc } .