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In physics, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter. 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 interactions—electromagnetism, 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〔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 )〕 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.〔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).〕〔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).〕〔J. J. Friedman and V. L. Telegdi, ''Nuclear emulsion evidence for parity nonconservation in the decay chain '', Phys. Rev. 105, 1681 (1957).〕 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 written down in 1991,〔R. Foot, H. Lew and R. R. Volkas, ''A model with fundamental improper space-time symmetries'', Physics Letters B272, 67 (1991)〕 although the basic idea dates back further.〔〔I. Kobzarev, L. Okun and I. Pomeranchuk, ''On the possibility of observing mirror particles'', Sov. J. Nucl. Phys. 3, 837 (1966).〕〔M. Pavsic, ''External Inversion, Internal Inversion, and Reflection Invariance'', Int. J. Theor. Phys. 9, 229-244 (1974) (preprint ).〕 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.〔Z. Berezhiani and R. N. Mohapatra, ''Reconciling Present Neutrino Puzzles: Sterile Neutrinos as Mirror Neutrinos'', Phys. Rev. D 52, 6607-6611 (1995) (preprint ).〕〔R. Foot, H. Lew and R. R. Volkas, ''Unbroken versus broken mirror world: a tale of two vacua'', JHEP 0007, 032 (2000) (preprint ).〕 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 have to be very weakly interacting 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 so-called ''kinetic mixing'' of mirror bosons with ordinary bosons or via the exchange of Holdom particles.〔http://www.bbc.co.uk/dna/h2g2/A1164052〕 These interactions can only be very weak. Mirror particles have therefore been suggested as candidates for the inferred dark matter in the universe.〔S. I. Blinnikov and M. Yu. Khlopov, ''On possible effects of 'mirror' particles'', Sov. J. Nucl. Phys. 36, 472 (1982).〕〔S. I. Blinnikov and M. Yu. Khlopov, ''Possible astronomical effects of mirror particles'', Sov. Astron. 27, 371-375 (1983).〕〔E. W. Kolb, M. Seckel and M. S. Turner, ''The shadow world of superstring theories'', Nature 314, 415-419 (1985). 〕〔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 ).〕〔H. M. Hodges, ''Mirror baryons as the dark matter'', Phys. Rev. D 47, 456-459 (1993) (article ).〕 In another context, 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, these mirror particles are usually called katoptrons.〔G. Triantaphyllou, ''Mass generation and the dynamical role of the Katoptron group'', Mod.Phys.Lett.A16:53-62,2001〕〔G. Triantaphyllou, G. Zoupanos, ''Strongly interacting fermions from a higher dimensional unified gauge theory'', Phys.Lett.B489:420-426,2000〕 ==Observational effects of mirror matter== 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.〔R. N. Mohapatra and V. L. Teplitz, ''Mirror matter MACHOs.'' Phys. Lett. B, 462, 302 - 309 (1999) (article ).〕 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.〔 There are some hints that such effects may already have been observed.〔R. Foot, ''Have mirror stars been observed?'', Phys. Lett. B 452, 83-86 (1999) (preprint ).〕〔R. Foot, ''Have mirror planets been observed?'', Phys. Lett. B 471, 191-194 (1999) (preprint ).〕 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.〔S. L. Glashow, ''Positronium versus the mirror universe'', Phys. Lett. B 167, 35-36 (1986) (article ).〕 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.〔 An experiment to measure this effect is currently being planned.〔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 ).〕 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.〔R. Foot, ''Implications of the DAMA and CRESST experiments for mirror matter-type dark matter'', Phys. Rev. D 69, 036001 (2004) (preprint ).〕〔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 ).〕 Mirror matter may also be detected in electromagnetic field penetration experiments〔S. Mitra, ''Detecting dark matter in electromagnetic field penetration experiments'', Phys. Rev. D 74, 043532 (2006) (preprint ).〕 and there would also be consequences for planetary science〔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 ).〕〔R. Foot and Z.K. Silagadze, ''Do mirror planets exist in our solar system?'' Acta Phys. Polon. B 32, 2271-2278 (2001) (preprint ).〕 and astrophysics.〔A. De Angelis and R. Pain, ''Improved limits on photon velocity oscillations'', Mod. Phys. Lett. A 17, 2491-2496 (2002) (preprint ).〕 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.〔V. Berezinsky and A. Vilenkin, ''Ultra high energy neutrinos from hidden-sector topological defects'', Phys. Rev. D 62, 083512 (2000) (preprint ).〕 Another possible way to evade the GZK bound is via neutron–mirror neutron oscillations.〔Z. Berezhiani and L. Bento, ''Neutron - Mirror Neutron Oscillations: How Fast Might They Be?'', Phys. Rev. Lett. 96, 081801 (2006) (preprint ).〕〔Z. Berezhiani and L. Bento, ''Fast Neutron - Mirror Neutron Oscillation and Ultra High Energy Cosmic Rays'', Phys. Lett. B 635, 253-259 (2006) (preprint ).〕〔R. N. Mohapatra, S. Nasri and S. Nussinov, ''Some Implications of Neutron Mirror Neutron Oscillation'', Phys. Lett. B 627, 124-130 (2005) (preprint ).〕〔Yu. N. Pokotilovski, ''On the experimental search for neutron -- mirror neutron oscillations'', Phys. Lett. B 639, 214-217 (2006) (preprint ).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mirror matter」の詳細全文を読む スポンサード リンク
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