# Mirror matter

In physics, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter.

## Overview

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 or parity). Of the four fundamental interactionselectromagnetism, the strong interaction, the weak interaction, and gravity—only the weak interaction breaks parity.

Parity violation in weak interactions was first postulated by Tsung Dao Lee and Chen Ning Yang[1] in 1956 as a solution to the τ-θ puzzle. They suggested a number of experiments to test if the weak interaction is invariant under parity. These experiments were performed half a year later and they confirmed that the weak interactions of the known particles violate parity.[2][3][4]

However, parity symmetry can be restored as a fundamental symmetry of nature if the particle content is enlarged so that every particle has a mirror partner. The theory in its modern form was described in 1991,[5] although the basic idea dates back further.[1][6][7] 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 a "mirror" particle exists for every ordinary particle. Parity can also be spontaneously broken depending on the Higgs potential.[8][9] While in the case of unbroken parity symmetry the masses of particles are the same as their mirror partners, in case of broken parity symmetry the mirror partners are lighter or heavier.

Mirror matter, if it exists, would need to interact weakly[clarification needed] with ordinary matter. This is because the forces between mirror particles are mediated by mirror bosons. With the exception of the graviton, none of the known bosons can be identical to their mirror partners. The only way mirror matter can interact with ordinary matter via forces other than gravity is via kinetic mixing of mirror bosons with ordinary bosons or via the exchange of Holdom particles.[10] These interactions can only be very weak. Mirror particles have therefore been suggested as candidates for the inferred dark matter in the universe.[11][12][13][14][15]

In another context[which?], mirror matter has been proposed to give rise to an effective Higgs mechanism responsible for the electroweak symmetry breaking. In such a scenario, mirror fermions have masses on the order of 1 TeV since they interact with an additional interaction, while some of the mirror bosons are identical to the ordinary gauge bosons. In order to emphasize the distinction of this model from the ones above[which?], these mirror particles are usually called katoptrons.[16][17]

## Observational effects

### Abundance

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.[18] This mixing has the effect of giving mirror electric charges a very small 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.

The mixing between photons and mirror photons could be present in tree level Feynman diagrams or arise as a consequence of quantum corrections due to the presence of particles that carry both ordinary and mirror charges. In the latter case, the quantum corrections have to vanish at the one and two loop level Feynman diagrams, otherwise the predicted value of the kinetic mixing parameter would be larger than experimentally allowed.[18]

An experiment to measure this effect is currently being planned.[19]

### Dark matter

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 and its successor DAMA/LIBRA. In fact, it is one of the few dark matter candidates which can explain the positive DAMA/NaI dark matter signal whilst still being consistent with the null results of other dark matter experiments.[20][21]

### Electromagnetic effects

Mirror matter may also be detected in electromagnetic field penetration experiments[22] and there would also be consequences for planetary science[23][24] and astrophysics.[25]

### GZK puzzle

Mirror matter could also be responsible for the GZK puzzle. Topological defects in the mirror sector could produce mirror neutrinos which can oscillate to ordinary neutrinos.[26] Another possible way to evade the GZK bound is via neutron–mirror neutron oscillations.[27][28][29][30]

### Gravitational effects

If mirror matter is present in the universe with sufficient abundance then its gravitational 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 microlensing.[31] 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.[14] There are some hints that such effects may already have been observed.[32][33]

## References

1. ^ a b T. D. Lee and C. N. Yang, Question of Parity Conservation in Weak Interactions, Phys. Rev. 104, 254–258 (1956) article, Erratum ibid 106, 1371 (1957) Erratum
2. ^ C. S. Wu, E. Ambler, R. W. Hayward, D. D. Hopes and R. R. Hudson, Experimental test of parity conservation in beta decay, Phys. Rev. 105, 1413 (1957).
3. ^ R. L. Garwin, L.M. Lederman and M. Weinrich, Observations of the failure of conservation of parity and charge conjugation in meson decays: The magnetic moment of the free muon, Phys. Rev. 105, 1415 (1957).
4. ^ J. J. Friedman and V. L. Telegdi, Nuclear emulsion evidence for parity nonconservation in the decay chain ${\displaystyle \pi ^{+}\rightarrow \mu ^{+}\rightarrow e^{+}}$, Phys. Rev. 105, 1681 (1957).
5. ^ R. Foot, H. Lew and R. R. Volkas, A model with fundamental improper space-time symmetries, Physics Letters B272, 67 (1991)
6. ^ I. Kobzarev, L. Okun and I. Pomeranchuk, On the possibility of observing mirror particles, Sov. J. Nucl. Phys. 3, 837 (1966).
7. ^ M. Pavsic, External Inversion, Internal Inversion, and Reflection Invariance, Int. J. Theor. Phys. 9, 229-244 (1974) preprint.
8. ^ Z. Berezhiani and R. N. Mohapatra, Reconciling Present Neutrino Puzzles: Sterile Neutrinos as Mirror Neutrinos, Phys. Rev. D 52, 6607-6611 (1995) preprint.
9. ^ R. Foot, H. Lew and R. R. Volkas, Unbroken versus broken mirror world: a tale of two vacua, JHEP 0007, 032 (2000) preprint.
10. ^ http://www.bbc.co.uk/dna/h2g2/A1164052
11. ^ Blinnikov S. I. (1982). "On possible effects of 'mirror' particles". Sov. J. Nucl. Phys. 36: 472.
12. ^ Blinnikov S. I. (1983). "Possible astronomical effects of mirror particles". Sov. Astron. 27: 371–375. Bibcode:1983SvA....27..371B.
13. ^ Kolb E. W., Seckel M., Turner M. S. (1985). "The shadow world of superstring theories". Nature. 314: 415–419. Bibcode:1985Natur.314..415K. doi:10.1038/314415a0.
14. ^ a b 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 SSSR 68, 42-57 (1991) preprint Archived 2007-12-13 at the Wayback Machine..
15. ^ Hodges H. M. (1993). "Mirror baryons as the dark matter". Phys. Rev. D. 47: 456–459. Bibcode:1993PhRvD..47..456H. doi:10.1103/PhysRevD.47.456.
16. ^ Triantaphyllou G (2001). "Mass generation and the dynamical role of the Katoptron group". Mod.Phys. Lett. A16: 53–62.
17. ^ Triantaphyllou G., Zoupanos G. (2000). "Strongly interacting fermions from a higher dimensional unified gauge theory". Phys. Lett. B489: 420–426.
18. ^ a b S. L. Glashow, Positronium versus the mirror universe, Phys. Lett. B 167, 35-36 (1986) article.
19. ^ 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.
20. ^ R. Foot, Implications of the DAMA and CRESST experiments for mirror matter-type dark matter, Phys. Rev. D 69, 036001 (2004) preprint.
21. ^ 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.
22. ^ S. Mitra, Detecting dark matter in electromagnetic field penetration experiments, Phys. Rev. D 74, 043532 (2006) preprint.
23. ^ 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.
24. ^ R. Foot and Z.K. Silagadze, Do mirror planets exist in our solar system? Acta Phys. Polon. B 32, 2271-2278 (2001) abstract.
25. ^ A. De Angelis and R. Pain, Improved limits on photon velocity oscillations, Mod. Phys. Lett. A 17, 2491-2496 (2002) preprint.
26. ^ V. Berezinsky and A. Vilenkin, Ultra high energy neutrinos from hidden-sector topological defects, Phys. Rev. D 62, 083512 (2000) preprint.
27. ^ Z. Berezhiani and L. Bento, Neutron - Mirror Neutron Oscillations: How Fast Might They Be?, Phys. Rev. Lett. 96, 081801 (2006) preprint.
28. ^ Z. Berezhiani and L. Bento, Fast Neutron - Mirror Neutron Oscillation and Ultra High Energy Cosmic Rays, Phys. Lett. B 635, 253-259 (2006) preprint.
29. ^ R. N. Mohapatra, S. Nasri and S. Nussinov, Some Implications of Neutron Mirror Neutron Oscillation, Phys. Lett. B 627, 124-130 (2005) preprint.
30. ^ Yu. N. Pokotilovski, On the experimental search for neutron -- mirror neutron oscillations, Phys. Lett. B 639, 214-217 (2006) preprint.
31. ^ R. N. Mohapatra and V. L. Teplitz, Mirror matter MACHOs. Phys. Lett. B, 462, 302 - 309 (1999) article.
32. ^ R. Foot, Have mirror stars been observed?, Phys. Lett. B 452, 83-86 (1999) preprint.
33. ^ R. Foot, Have mirror planets been observed?, Phys. Lett. B 471, 191-194 (1999) preprint.

Reference Blinnikov S.I.(1982) should be Blinnikov S.I., Khlopov M.Yu.(1982) Reference Blinnikov S.I.(1983) should be Blinnikov S.I., Khlopov M.Yu.(1983)