Constraints on the electrical charge asymmetry of the universe

We use the isotropy of the cosmic microwave background to place stringent constraints on a possible electrical charge asymmetry of the universe. We find the excess charge per baryon to be q(e-p) < 10(-26) e in the case of a uniform distribution of charge, where e is the charge of the electron. If the charge asymmetry is inhomogeneous, the constraints will depend on the spectral index, n, of the induced magnetic field and range from q(e-p) < 5 x 10(-20)e ( n = - 2) to q(e-p) < 2 x 10(-26)e ( n >= 2). If one could further assume that the charge asymmetries of individual particle species are not anti-correlated so as to cancel, this would imply, for photons, q(gamma) < 10(-35)e; for neutrinos, q(nu) < 4 x 10(-35)e; and for heavy ( light) dark matter particles q(dm) < 4 x 10(-24)e (q(dm) < 4 x 10(-30)e).