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##
Time reversal

Cosmological development of the Universe requires existence of hitherto
unknown mechanisms of CP or T violation. New T-violating phenomena may
be generated e.g. by a -term
in QCD interactions, or by the exchange of leptoquarks, Higgs or right
handed weak bosons with complex couplings. T-violating correlation experiments
determine spin polarisations and/or momenta of the particles involved in
the decay process. The systems studied include the muon, neutron, ^{8}Li
and ^{19}Ne nuclei, K^{+} and K^{0} mesons,
and -hyperons;
and recently even polarised Z^{0}. The achieved accuracies reach
10^{-3} in the T-violating amplitudes with respect to the regular
weak interaction strength. Here, progress is achieved by a combination
of new experimental techniques and development of the premium quality polarised
beams and targets. T-violation in muon decay will be further investigated
at PSI. New experiments with slow neutrons are in development at National
Institute of Standards and Technology (NIST)-USA, and at the spallation
neutron source under commissioning at PSI. These studies determine the
complex amplitudes of the vector, axial vector, scalar or tensor weak interaction
terms, which are related to the coupling constants and masses of the exchanged
new gauge bosons. We quote the limits of 3 TeV/c^{2}
from beta decay for the mass/amplitude ratios in lepto-quark exchange.
T-violating electric dipole moments (EDM) arise at the Lagrangian level
from the QCD's
term. In other theories, nonzero EDM's are induced e.g. via higher order
processes (quantum loop corrections). Classical EDM tests are performed
with polarised free neutrons. Present experiments restrict the neutron
EDM to values less than 1.1 x 10^{-25} e.cm. Results on atomic
EDM close to the above limit have also been obtained using complex systems
: Hg and Tl atoms, or TIF molecules. New, challenging ideas are pursued
to improve the sensitivity by three orders of magnitude. The complexities
of the new experiments call for large international collaborations. Studies
have already begun in the USA and Japan in the context of new spallation
sources. The new EDM experiments will either establish a finite effect,
or reject some popular theories such as Weinberg's multi-Higgs or left-right
symmetric models.

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tests **Up:** Fundamental
symmetries **Previous:** Parity
violation

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