rpp2010-rev-searches-quark-lep-compositeness

rpp2010-rev-searches-quark-lep-compositeness - 1 SEARCHES...

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– 1– SEARCHES FOR QUARK AND LEPTON COMPOSITENESS Revised 2001 by K. Hagiwara (KEK), and K. Hikasa and M. Tanabashi (Tohoku University). If quarks and leptons are made of constituents, then at the scale of constituent binding energies, there should appear new interactions among quarks and leptons. At energies much below the compositeness scale (Λ), these interactions are suppressed by inverse powers of Λ. The dominant effect should come from the lowest dimensional interactions with four fermions (contact terms), whose most general chirally invariant form reads [1] L = g 2 2 η LL ψ L γ μ ψ L ψ L γ μ ψ L + η RR ψ R γ μ ψ R ψ R γ μ ψ R +2 η LR ψ L γ μ ψ L ψ R γ μ ψ R . (1) Chiral invariance provides a natural explanation why quark and lepton masses are much smaller than their inverse size Λ. We may determine the scale Λ unambiguously by using the above form of the effective interactions; the conventional method [1] is to fix its scale by setting g 2 / 4 π = g 2 (Λ) / 4 π = 1 for the new strong interaction coupling and by setting the largest magnitude of the coefficients η αβ to be unity. In the following, we denote Λ = Λ ± LL for ( η LL , η RR , η LR ) = ( ± 1 , 0 , 0) , Λ = Λ ± RR for ( η LL , η RR , η LR ) = (0 , ± 1 , 0) , Λ = Λ ± V V for ( η LL , η RR , η LR ) = ( ± 1 , ± 1 , ± 1) , Λ = Λ ± AA for ( η LL , η RR , η LR ) = ( ± 1 , ± 1 , 1) , (2) as typical examples. Such interactions can arise by constituent interchange (when the fermions have common constituents, e.g. , for ee ee ) and/or by exchange of the binding quanta (when- ever binding quanta couple to constituents of both particles). Another typical consequence of compositeness is the appear- ance of excited leptons and quarks ( and q ). Phenomeno- logically, an excited lepton is defined to be a heavy lepton
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