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 qe−p<10−26e 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 qe−p<5 × 10−20e (n = −2) to qe−p<2 × 10−26e (). 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, qγ<10−35e; for neutrinos, qν<4 × 10−35e; and for heavy (light) dark matter particles qdm<4 × 10−24e (qdm<4 × 10−30e).