16,588 research outputs found
Testing Realistic Quark Mass Matrices in the Custodial Randall-Sundrum Model with Flavor Changing Top Decays
We study quark mass matrices in the Randall-Sundrum (RS) model with bulk
symmetry . The Yukawa couplings are
assumed to be within an order of magnitude of each other, and perturbative. We
find that quark mass matrices of the symmetrical form proposed by Koide
\textit{et. al.} [Y. Koide, H. Nishiura, K. Matsuda, T. Kikuchi and T.
Fukuyama, Phys. Rev. D {\bf 66}, 093006 (2002)] can be accommodated in the RS
framework with the assumption of hierarchyless Yukawa couplings, but not the
hermitian Fritzsch-type mass matrices. General asymmetrical mass matrices are
also found which fit well simultaneously with the quark masses and the
Cabibbo-Kobayashi-Maskawa matrix. Both left-handed (LH) and right-handed (RH)
quark rotation matrices are obtained that allow analysis of flavour changing
decay of both LH and RH top quarks. At a warped down scale of 1.65 TeV, the
total branching ratio of t \ra Z + jets can be as high as for symmetrical mass matrices and for
asymmetrical ones. This level of signal is within reach of the LHC.Comment: 30 pages, 6 figures. Reference added, typos corrected, discussions in
Sec. IV B expanded. Version conforms to the published versio
Phenomenology from a U(1) gauged hidden sector
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the matter content are uncharged
under the SM gauge groups. We consider a simple case where the hidden sector is
gauged under a U(1) with one Higgs singlet. The only couplings between SM and
the hidden sector are through mixings between the neutral gauge bosons of the
two respective sectors, and between the Higgs bosons. We find signals testable
at the LHC that can reveal the existence and shed light on the nature of such a
hidden sector.Comment: 5 pages, 2 figures. Talk given at the Lake Louise Winter Institute
2007, Feb. 19-24, Alberta, Canad
A Very Narrow Shadow Extra Z-boson at Colliders
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the ``shadow Higgs'' are uncharged
under the SM gauge groups. We consider a simple U(1) model with one Higgs
singlet. One mechanism which sheds light on the shadow sector is the mixing
between the neutral gauge boson of the SM and the additional U(1) gauge group.
The mixing happens through the usual mass-mixing and also kinetic-mixing, and
is the only way the ``shadow '' couples to the SM. We study in detail
modifications to the electroweak precision tests (EWPTs) that the presence of
such a shadow sector would bring, which in turn provide constraints on the
kinetic-mixing parameter, , left free in our model. The shadow
production rate at the LHC and ILC depends on . We find that
observable event rate at both facilities is possible for a reasonable range of
allowed by EWPTs.Comment: 10 pages, 7 figures. Note and refs. adde
High-energy asymptotic behavior of the Bourrely-Soffer-Wu model for elastic scattering
Some time ago, an accurate phenomenological approach, the BSW model, was
developed for proton-proton and antiproton-proton elastic scattering cross
sections at center-of-mass energies above 10 GeV. This model has been used to
give successful theoretical predictions for these processes, at successive
collider energies. The BSW model involves a combination of integrals that,
while computable numerically at fairly high energies, require some mathematical
analysis to reveal the high-energy asymptotic behavior. In this paper we
present a high-energy asymptotic representation of the scattering amplitude at
moderate momentum transfer, for the leading order in an expansion parameter
closely related to the logarithm of the center-of-mass energy. The fact that
the expansion parameter goes as the logarithm of the energy means that the
asymptotic behavior is accurate only for energies greatly beyond any
foreseeable experiment. However, we compare the asymptotic representation
against the numerically calculated model for energies in a less extreme region
of energy. The asymptotic representation is given by a simple formula which, in
particular, exhibits the oscillations of the differential cross section with
momentum transfer. We also compare the BSW asymptotic behavior with the
Singh-Roy unitarity upper bound for the diffraction peak.Comment: 27 pages, 11 figures,revised version to appear in Physical Review
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