529 research outputs found
Reply to Comment on "Chiral suppression of scalar glueball decay"
Reply to the comment of Chao, He, and Ma
Chiral Suppression of Scalar Glueball Decay
Because glueballs are SU(3)_{Flavor} singlets, they are expected to couple
equally to u,d, and s quarks, so that equal coupling strengths to \pi^+\pi^-
and K^+K^- are predicted. However, we show that chiral symmetry implies the
scalar glueball amplitude for G_0 \to \qbq is proportional to the quark mass,
so that mixing with \sbs mesons is enhanced and decays to K^+K^- are favored
over \pi^+\pi^-. Together with evidence from lattice calculations and from
experiment, this supports the hypothesis that f_0(1710) is the ground state
scalar glueball.Comment: 9 pages; This revision reconciles posting (approximately) with
published version. Posting contains figures that are omitted in the
publicatio
Higgs boson mass constraints from precision data and direct searches
Two of the nine measurements of , the effective weak interaction mixing angle, are found to be in significant conflict with the direct search limits for the Standard Model (SM) Higgs boson. Using a scale factor method, analogous to one used by the Particle Data Group, we assess the possible effect of these discrepancies on the SM fit of the Higgs boson mass. The scale factor fits increase the value of by as much as two standard deviations. The central value of the Higgs boson mass increases as much as a factor of two, to GeV, and the 95% confidence level upper limit increases to as much as 750 GeV. The scale factor is based not simply on the discrepant measurements, as was the case in a previous analysis, but on an aggregate goodness-of-fit confidence level for the nine measurements and the limit. The method is generally applicable to fits in which one or more of a collection of measurements are in conflict with a physical boundary or limit. In the present context, the results suggest caution in drawing conclusions about the Higgs boson mass from the existing data
Strong scattering at the end of the 90's: theory and experimental prospects
The nature of electroweak symmetry breaking can only be established definitively by the direct discovery and detailed study of the symmetry breaking quanta at high energy colliders. At the LHC the ability to observe TeV scale strong WW scattering confers a no-lose capability to establish the mass scale and interaction strength of the symmetry breaking quanta, even if the symmetry breaking quanta resist discovery and whether strong WW scattering is observed or excluded. This lecture discusses the motivation to consider strong WW scattering in light of what we have learned from precision electroweak data during the decade. The theoretical basis for strong WW scattering is explained with an introductory review of the Higgs mechanism from a general perspective that encompasses light, perturbative Higgs bosons or nonperturbative, dynamical symmetry breaking by TeV scale strong interactions. The experimental signals and backgrounds are reviewed and the sensitivity of experiments at the LHC is assessed
Inelastic Channels in WW Scattering
If the electroweak symmetry-breaking sector becomes strongly interacting at
high energies, it can be probed through longitudinal scattering. We present
a model with many inelastic channels in the scattering process,
corresponding to the production of heavy fermion pairs. These heavy fermions
affect the elastic scattering of 's by propagating in loops, greatly
reducing the amplitudes in some charge channels. We conclude that the
symmetry-breaking sector cannot be fully explored by using, for example, the
mode alone, even when no resonance is present; all scattering modes must be measured.Comment: phyzzx, 13 pp. plus 4 figures, JHU-TIPAC-930005, MSUHEP-93/0
The Z ->anti-b b decay asymmetry: lose-lose for the Standard Model
Combining precision measurements and the Higgs boson search limit, the
electroweak data has evolved to a point where new physics is favored whether
the 3.2 sigma A_{FB}^b anomaly is genuine or not. Such new physics could
greatly alter the inferred value of the Higgs boson mass.Comment: This is the published version. The previous version (v4) contains
some additional background informatio
Bounding CKM Mixing with a Fourth Family
CKM mixing between third family quarks and a possible fourth family is
constrained by global fits to the precision electroweak data. The dominant
constraint is from nondecoupling oblique corrections rather than the Zbb vertex
correction used in previous analyses. The possibility of large mixing suggested
by some recent analyses of FCNC processes is excluded, but 3-4 mixing of the
same order as the Cabbibo mixing of the first two families is allowed.Comment: 16 pages, 3 figures: added references, minor revision
Combining real and virtual Higgs boson mass constraints
Within the framework of the standard model we observe that there is a
significant discrepancy between the most precise boson decay asymmetry
measurement and the limit from direct searches for Higgs boson production.
Using methods inspired by the Particle Data Group we explore the possible
effect on fits of the Higgs boson mass. In each case the central value and the
95% confidence level upper limit increase significantly relative to the
conventional fit. The results suggest caution in drawing conclusions about the
Higgs boson mass from the existing data.Comment: 11 pages, Latex. Citations are added and paper is otherwise
reconciled with version to be published in Physical Review Letter
The Fourth SM Family Neutrino at Future Linear Colliders
It is known that Flavor Democracy favors the existence of the fourth standard
model (SM) family. In order to give nonzero masses for the first three family
fermions Flavor Democracy has to be slightly broken. A parametrization for
democracy breaking, which gives the correct values for fundamental fermion
masses and, at the same time, predicts quark and lepton CKM matrices in a good
agreement with the experimental data, is proposed. The pair productions of the
fourth SM family Dirac and Majorana neutrinos at future
linear colliders with GeV, 1 TeV and 3 TeV are considered. The
cross section for the process
and the branching ratios for possible decay modes of the both neutrinos are
determined. The decays of the fourth family neutrinos into muon channels
provide cleanest signature at
colliders. Meanwhile, in our parametrization this channel is
dominant. bosons produced in decays of the fourth family neutrinos will be
seen in detector as either di-jets or isolated leptons. As an example we
consider the production of 200 GeV mass fourth family neutrinos at
GeV linear colliders by taking into account di-muon plus
four-jet events as signatures.Comment: 16 pages, 3 figures, 10 table
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