Mirror matter
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In physics, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to regular matter suggested by Tsung Dao Lee and Chen Ning Yang [1] in 1956, when it was discovered that nature violates P-symmetry.
Modern physics deals with three basic types of spatial symmetry: reflection, rotation and translation. The known elementary particles respect rotation and translation symmetry but do not respect mirror reflection symmetry (also called P-symmetry).
It turns out that mirror reflection symmetry can still exist, but only if every particle has a mirror partner [1,2,3]. Mirror particles interact amongst themselves in the same way as ordinary particles, except where ordinary particles have left-handed interactions, mirror particles have right-handed interactions. In this way, it turns out that mirror reflection symmetry can exist as an exact symmetry of nature, provided that mirror matter exists.
Mirror particles have been suggested as candidates for the inferred dark matter in the universe [4,5,6,7,8]. Mirror matter, if it exists, would have to be very weakly interacting with ordinary matter. This is because the forces between mirror particles are mediated by mirror bosons. Mirror particles and ordinary particles can only interact with each other via gravity, via so-called kinetic mixing of mirror bosons with ordinary bosons or via the exchange of as of yet unknown particles. These interactions can only be very weak.
Mirror matter is a far less popular dark matter candidate than WIMPs or Weakly Interacting Massive Particles, which in supersymmetric theories is identified as the neutralino.
Observational effects of mirror matter
If mirror matter is present in the universe with sufficient abundance then its gravitional effects can be detected. Because mirror matter is analogous to ordinary matter, it is then to be expected that a fraction of the mirror matter exists in the form of mirror galaxies, mirror stars, mirror planets etc. These objects can be detected using gravitational lensing. One would also expect that some fraction of stars have mirror objects as their companion. In such cases one should be able to detect periodic Doppler shifts in the spectrum of the star [7]. There are some hints that such effects may already have been observed [9,10].
What if mirror matter does exist but has (almost) zero abundance? Like magnetic monopoles, mirror matter could have been diluted to unobservably low densities during the inflation epoch. Sheldon Glashow has shown that if at some high energy scale particles exist which interact strongly with both ordinary and mirror particles, radiative corrections will lead to a mixing between photons and mirror photons [11]. This mixing has the effect of giving mirror electric charges a very weak ordinary electric charge. Another effect of photon-mirror photon mixing is that it induces oscillations between positronium and mirror positronium. Positronium could then turn into mirror positronium and then decay into mirror photons. An experiment to measure this effect is currently being planned [12].
If mirror matter does exist in large abundances in the universe and if it interacts with ordinary matter via photon-mirror photon mixing, then this could be detected in dark matter direct detection experiments such as DAMA/NaI [13,14]. There would also be consequences for planetary science [15].
References
[1] T. D. Lee and C. N. Yang, Question of Parity Conservation in Weak Interactions, Phys. Rev. 104, 254–258 (1956) article (http://link.aps.org/abstract/PR/v104/p254).
[2] I. Kobzarev, L. Okun and I. Pomeranchuk, On the possibility of observing mirror particles, Sov. J. Nucl. Phys. 3, 837 (1966).
[3] M. Pavsic, External Inversion, Internal Inversion, and Reflection Invariance, Int. J. Theor. Phys. 9, 229-244 (1974) preprint (http://arxiv.org/abs/hep-ph/0105344).
[4] S. I. Blinnikov and M. Yu. Khlopov, On possible effects of 'mirror' particles, Sov. J. Nucl. Phys. 36, 472 (1982).
[5] S. I. Blinnikov and M. Yu. Khlopov, Possible astronomical effects of mirror particles, Sov. Astron. 27, 371-375 (1983).
[6] E. W. Kolb, M. Seckel and M. S. Turner, The shadow world of superstring theories, Nature 314, 415-419 (1985).
[7] M. Yu. Khlopov, G. M. Beskin, N. E. Bochkarev, L. A. Pushtilnik and S. A. Pushtilnik, observational physics of mirror world, Astron. Zh. Akad. Nauk CCCP 68, 42-57 (1991) preprint (http://library.fnal.gov/archive/test-preprint/fermilab-pub-89-193-a.shtml).
[8] H. M. Hodges, Mirror baryons as the dark matter, Phys. Rev. D 47, 456-459 (1993) article (http://link.aps.org/abstract/PRD/v47/p456).
[9] R. Foot, Have mirror stars been observed?, Phys. Lett. B 452, 83-86 (1999) preprint (http://arxiv.org/abs/astro-ph/9902065,).
[10] R. Foot, Have mirror planets been observed?, Phys. Lett. B 471, 191-194 (1999) preprint (http://arxiv.org/abs/astro-ph/9908276)
[11] S. L. Glashow, Positronium versus the mirror universe, Phys. Lett. B 167, 35-36 (1986) article (http://dx.doi.org/10.1016/0370-2693(86)90540-X).
[12] A. Badertscher et al., An apparatus to search for mirror dark matter via the invisible decay of orthopositronium in vacuum, Int. J. Mod. Phys. A 19, 3833-3848 (2004) preprint (http://arxiv.org/abs/hep-ex/0311031).
[13] R. Foot, Implications of the DAMA and CRESST experiments for mirror matter-type dark matter, Phys. Rev. D 69, 036001 (2004) preprint (http://arxiv.org/abs/hep-ph/0308254).
[14] R. Foot, Reconciling the positive DAMA annual modulation signal with the negative results of the CDMS II experiment, Mod. Phys. Lett. A 19, 1841-1846 (2004) preprint (http://arxiv.org/abs/astro-ph/0405362).
[15] R. Foot and S. Mitra, Mirror matter in the solar system: New evidence for mirror matter from Eros, Astropart. Phys. 19, 739-753 (2003) preprint (http://arxiv.org/abs/astro-ph/0211067).
External links
- Mirror matter webpage (http://www.ph.unimelb.edu.au/~foot/)
- A collection of scientific articles on various aspects of mirror matter theory (http://people.zeelandnet.nl/smitra/mirror.htm)