781 research outputs found
New Axial Interactions at a TeV
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
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.
The size of flavor changing effects induced by the symmetry breaking sector
It has recently been shown that strong interactions underlying electroweak
symmetry breaking will induce four-fermion amplitudes proportional to m_t^2,
which in turn will influence a variety of flavor changing processes. We argue
that the size of these effects are likely to be far below the current
experimental bounds.Comment: 5 pages, LaTeX, 1 figur
Soft asymptotics with mass gap
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
A theory input is needed for the estimation of the largest background for the
search at the LHC. This is the shape of the
spectrum from continuum 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
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 "-jets", and as well show how -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
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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