Physics from beyond the Standard Model, such as leptoquarks, can induce four fermion operators involving a quark, an anti-quark, a lepton and an anti-lepton. We update the (flavour-dependent) constraints on the coefficients of such interactions, arising from collider searches for contact interactions, meson decays and other rare processes. We then make naive estimates for the magnitude of the coefficients, as could arise in texture models or from inverse hierarchies in the kinetic term coefficients. These "expectations" suggest that rare Kaon decays could be a good place to look for such operators. * E-mail address: s.davidson@ipnl.in2p3.fr 2 We extract bounds from D + s decays, although there is a few σ discrepancy among these decays and lattice results, which has been discussed in leptoquark models [47].3 So the ǫ V −A ǫ S+P interefence term, which is included to make the decay rate self-consistent, will not be used to set bounds.4
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