Cosmological bounds on the “millicharges” of mirror particles

Abstract

Mirror world, a parallel hidden sector with microphysics identical to ordinary particle physics, can have several interesting phenomenological and astrophysical implications and mirror matter can be a natural candidate for dark matter in the universe. If the ordinary and the mirror photons have a kinetic mixing due to the Lagrangian term (ǫ/2)F µν F ′µν , then mirror particles effectively acquire the electric charges ∼ ǫ with respect to the ordinary photon, so that they become a sort of particles historically coined as "millicharged" though nowadays they must be called more appropriately as "nanocharged". In this paper we revise the cosmological bounds on the kinetic mixing parameter and in the case of exact mirror parity set an upper limit ǫ < 3×10 −10 . Much weaker limit can be obtained in the case of asymmetric mirror sector, with an electroweak symmetry breaking scale larger than the ordinary electroweak scale.

Experimental limits on neutron disappearance into another braneworld

“…Even with more recent and stringent constraints [13,39], we get g < 9 × 10 7 m −1 from ε < 3 × 10 −10 (see Berezhiani and Lepidi in Ref. [39]). As a result, ultracold neutron experiments appear as a relevant approach to constrain g (Some other possibilities are not considered for obvious reasons 5 [40,41]).…”

“…[16], we get g < 3 × 10 10 m −1 from the millicharge constraint ε < 4.1 × 10 −5 [38]. Even with more recent and stringent constraints [13,39], we get g < 9 × 10 7 m −1 from ε < 3 × 10 −10 (see Berezhiani and Lepidi in Ref. [39]).…”

Composite strongly interacting dark matter

“…This provides stringent constraints on mirror dark matter [81]- [82] since both the dark photons and dark electrons/neutrinos can contribute to the excess. In our case, m e is always greater than 100 MeV so that only the dark photons can contribute (and we do not consider dark neutrinos).…”

Dark matter and generation of galactic magnetic fields

“…This true photon may predominantly interact with ordinary particles with the coupling 1 Mirror world with microphysics exactly identical to the Standard Model also provides a viable dark matter (see a review [34,35] and references therein). However, in this case the positronium oscillation limit on the photon-mirror photon kinetic mixing is very strong, ε < 4 × 10 −7 [23] and there are cosmological limits two orders of magnitude more restrictive [36]. In the case of asymmetric mirror sector [30][31][32][33], with m e > m e , the positronium limits are irrelevant, and the cosmological limits are also more flexible [36].…”