Consequences of Gravity-Induced Couplings in Theories with Many Particle Species

In theories with many copies of the Standard Model virtual black hole exchange may produce effective higher dimensional operators that can be treated below the cutoff scale as fundamental vertices of interspecies non-gravitational interaction. We consider the vertex that couples fermions of one species through magnetic moment to photons of other species, and study the quantum corrections it generates. In particular, we find kinetic mixing between photons of different species produced via fermion loops. Diagonalization of gauge kinetic terms then renders the fermions millicharged under other species' electromagnetism. We explore some phenomenological consequences of such effects by considering possible observable signatures in collider experiments and constraining the interaction strength. The derived bounds are in agreement with non-democratic nature of micro black hole coupling.