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 × 10 −20 e ( n = −2) to q e−p <2 × 10 −26 e ( ). 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 γ <10 −35 e ; for neutrinos, q ν <4 × 10 −35 e ; and for heavy (light) dark matter particles q dm <4 × 10 −24 e ( q dm <4 × 10 −30 e ).