610 research outputs found

    New Axial Interactions at a TeV

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    We consider a heavy fourth family with masses lying in the symmetry breaking channel of a new strong gauge interaction. This interaction generates a heavy quark axial-type operator, whose effects can be enhanced through multiple insertions. In terms of the strength of this operator we can express new negative contributions to the S and T parameters and the shifts of the Z couplings to the third family. In particular we find that the new contribution to T is strongly constrained by the experimental constraints on the Z coupling to the tau.Comment: 14 pages, 1 figure, PRD versio

    Metacolor

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    A new mechanism is presented for the generation of quark and lepton masses, based on a heavy fourth family and a new sector of massless fermions. The massless fermions have only discrete chiral symmetries and they are confined by the metacolor force. The resulting electroweak corrections may be smaller than in technicolor theories.Comment: 11 pages, LaTeX, UTPT-93-09. (The title has changed from "Massless Technicolor" and more discussion of dynamics has been added.

    Soft asymptotics with mass gap

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    From the operator product expansion the gluon condensate controls a certain power law correction to the ultraviolet behavior of the gauge theory. This is reflected by the asymptotic behavior of the effective gluon mass function as determined by its Schwinger-Dyson equation. We show that the current state of the art determination of the gluon mass function by Binosi, Ibanez and Papavassiliou points to a vanishing gluon condensate. If this is correct then the vacuum energy also vanishes in massless QCD. This result can be interpreted as a statement about a softness in the ultraviolet behavior and the consistency of this behavior with a mass gap.Comment: 10 pages, 4 figures, improved discussion, version to appear in Physics Letters

    NLO tools and the background to H→WWH\rightarrow WW

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    A theory input is needed for the estimation of the largest background for the H→WWH\rightarrow WW search at the LHC. This is the shape of the mℓℓm_{\ell\ell} spectrum from continuum WWWW production. We find this to depend on how NLO matrix elements are merged with parton showers, and we compare the results from a number of different implementations. The results suggest that both the size of the background estimate and its uncertainty may have been underestimated. This conclusion is reinforced by a "Note Added", which comments on the LHC results released on November 14 2012.Comment: 11 pages, 2 figures, published versio

    Approaching a strong fourth family

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    A heavy fourth family is an example of new physics which is well defined and familiar in some respects, but which nevertheless has radical implications. In particular it eliminates a light Higgs description of electroweak symmetry breaking. We discuss an early signal for heavy quarks at the LHC in the form of an excess of "WW-jets", and as well show how WW-jets may be useful in the reconstruction of the heavy quark masses. We argue that fourth family quarks can be distinguished from vector-like quarks of a similar mass at roughly the same time that a same sign lepton signal becomes visible. Given the large mass of the fourth neutrino we describe how a picture for neutrino mass emerges in the absence of right-handed neutrinos, and how it suggests the existence of a remnant flavor gauge symmetry. Based on talk given at "Second Workshop on Beyond 3 Generation Standard Model -- New Fermions at the Crossroads of Tevatron and LHC", January 2010, Taipei Taiwan.Comment: 14 pages, 10 figures, references added and slight change

    Comparison of 1/mQ^2 Corrections in Mesons and Baryons

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    We extend our relativistic quark model to the study of the decay Lambda_b -> Lambda_c ell nu and verify that the model satisfies the heavy-quark symmetry constraints at order 1/mQ^2. We isolate a strong dependence on a parameter which measures the relative distortion in the light-quark wave functions of the Lambda_b and Lambda_c. This parameter and the 1/mQ^2 corrections turn out to be small. The dependence on a corresponding parameter in the meson case leads to large 1/mQ^2 corrections.Comment: 9 pages, LaTeX, 3 self-contained LaTeX figures in separate fil
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