  We assume that the cold dark matter consists of spin-1/2 and spin-0 particles
described by a bispinor field \psi and a scalar field \phi, sterile from all
Standard Model charges (in contrast, neutralinos, supersymmetric candidates for
cold dark matter, are not sterile from weak Standard Model charges). We
propose, however, that such a sterile world can contact with our Standard Model
world not only through gravity but also through a portal provided by photons
coupled to sterile particles by means of two very weak effective interactions
-(f/M^2)\phi F^{\mu\nu}\phi F_{\mu\nu} and -(f'/M^2) (\bar\psi \sigma^{\mu\nu}
\psi)\phi F_{\mu\nu}, where M is a very large mass scale and f and f' are
dimensionless coupling constants. Thus, in our picture, the electromagnetic
field F_{\mu\nu} - as the only Standard Model field - participates in both
worlds, providing a nongravitational link between them (other than the popular
supersymmetric weak interaction, active in the case of neutralinos). In
consequence, there appears a tiny quasi-magnetic correction to the conventional
electromagnetic current (described in Appendix A).
