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The mirror world |
The idea of a new sector of particles, called mirror particles (or mirror world), was originally discussed by Lee and Yang in 1956 in their famous paper about parity violation in weak interaction.
They suggested
that the transformation in the particle space corresponding to the space inversion
x &rarr -x should not be the usual transformation P, but PR, where R corresponds the transformation of a particle (proton) into a reflected state in the mirror particle space.
After observation of parity non conservation Landau assumed that R=C, i.e. he suggested to identify antiparticles with the mirror matter, but then CP must be conserved which we know is not the case. The idea was further developed by A. Salam , and was clearly formulated in 1966 as a concept of the Mirror Universe by
Kobzarev, Okun and Pomeranchuk. In this paper it was shown that ordinary and mirror matter can communicate predominantly through gravity and proposed that the mirror matter objects can be present in our universe. Today's mirror matter models exist in two basic versions. The symmetric version proposed early was further developed and put into a modern context by Foot, Lew and Volkas . The asymmetric version was proposed by Berezhiani and
Mohapatra.
In the symmetric mirror model the idea is that for each ordinary particle, such as the photon, electron, proton and neutron, there is a corresponding mirror particle, of exactly the same mass as the ordinary particle. The PR operator interchanges the ordinary particles with the mirror particles so that the properties of the mirror particles completely mirror those of the ordinary particles. For example the mirror proton and mirror electron are stable and interact with the mirror photon in the same way in which the ordinary proton and electron interacts with the ordinary photons. The mirror particles are not produced in laboratory experiments just because they couple very weakly to the ordinary particles. In the modern language of gauge theories, the mirror particles are all singlets under the standard
G ≡ SU(3) x SU(2)L x U(1)Y
gauge interactions. Instead the mirror particles interact with a set ofmirror gauge particles, so that the gauge symmetry of the theory is doubled, i.e. GxG (the ordinary particles are, of course, singlets under the mirror gauge symmetry). Parity is conserved because the mirror particles experience V +A (i.e. right-handed) mirror weak interactions while the ordinary particles experience the usual V − A (i.e. left-handed) weak interactions.
Photon-mirror photon kinetic mixing is described by the interaction Lagrangian density
where Fmn (F'mn )is the field strength tensor for electromagnetism (mirror electromagnetism).
The effect of ordinary photon - mirror photon kinetic mixing is to give the mirror charged particles a small electric charge. That is, they couple to ordinary photons with charge 2ee .
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Last update: P. Crivelli - November 13, 2004