70 research outputs found
Casimir operators of the exceptional group G2
We calculate the degree 2 and 6 Casimirs operators in explicit form, with the
generators of G2 written in terms of the subalgebra A2Comment: 10 p., MAD/TH/93-05, (LaTex
The Charm Content of W+1 Jet Events as a Probe of the Strange Quark Distribution Function
We investigate the prospects for measuring the strange quark distribution
function of the proton in associated plus charm quark production at the
Tevatron. The quark signal produced by strange quark -- gluon fusion,
and , is approximately 5\%
of the inclusive jet cross section for jets with a transverse momentum
~GeV. We study the sensitivity of the plus charm quark cross
section to the parametrization of the strange quark distribution function, and
evaluate the various background processes. Strategies to identify charm quarks
in CDF and D\O \ are discussed. For a charm tagging efficiency of about 10\%
and an integrated luminosity of 30~pb or more, it should be possible to
constrain the strange quark distribution function from production at the
Tevatron.Comment: submitted to Phys. Lett. B, Latex, 12 pages + 4 postscript figures
encoded with uufile, FSU-HEP-930812, MAD/TH/93-6, MAD/PH/788. A postscript
file with text and embedded figures is available via anonymous ftp at
hepsg1.physics.fsu.edu, file is /pub/keller/fsu-hep-930812.p
Ruling Out a Strongly-Interacting Standard Higgs Model
Previous work has suggested that perturbation theory is unreliable for Higgs-
and Goldstone-boson scattering, at energies above the Higgs mass, for
relatively small values of the Higgs quartic coupling . By
performing a summation of nonlogarithmic terms, we show that perturbation
theory is in fact reliable up to relatively large coupling. This eliminates the
possibility of a strongly-interacting standard Higgs model at energies above
the Higgs mass, complementing earlier studies which excluded strong
interactions at energies near the Higgs mass. The summation can be formulated
in terms of an appropriate scale in the running coupling,
, so it can easily be incorporated in
renormalization-group improved tree-level amplitudes as well as higher-order
calculations.Comment: 29 pages, 6 figures. The complete paper including figures is also
available via WWW at
http://www.physik.tu-muenchen.de/tumphy/d/T30d/PAPERS/TUM-HEP-236-96.ps.g
Matching conditions and Higgs mass upper bounds revisited
Matching conditions relate couplings to particle masses. We discuss the
importance of one-loop matching conditions in Higgs and top-quark sector as
well as the choice of the matching scale. We argue for matching scales
and . Using these
results, the two-loop Higgs mass upper bounds are reanalyzed. Previous results
for few TeV are found to be too stringent. For
GeV we find GeV, the first error
indicating the theoretical uncertainty, the second error reflecting the
experimental uncertainty due to GeV.Comment: 20 pages, 6 figures; uses epsf and rotate macro
Testing nonperturbative techniques in the scalar sector of the standard model
We discuss the current picture of the standard model's scalar sector at
strong coupling. We compare the pattern observed in the scalar sector in
perturbation theory up to two-loop with the nonperturbative solution obtained
by a next-to-leading order 1/N expansion. In particular, we analyze two
resonant Higgs scattering processes, ff -> H -> f'f' and ff -> H -> ZZ, WW. We
describe the ingredients of the nonperturbative calculation, such as the
tachyonic regularization, the higher order 1/N intermediate renormalization,
and the numerical methods for evaluating the graphs.
We discuss briefly the perspectives and usefulness of extending these
nonperturbative methods to other theories
Heavy-Higgs Lifetime at Two Loops
The Standard-Model Higgs boson with mass decays almost
exclusively to pairs of and bosons. We calculate the dominant two-loop
corrections of to the partial widths of these decays. In
the on-mass-shell renormalization scheme, the correction factor is found to be
, where the second term is the
one-loop correction. We give full analytic results for all divergent two-loop
Feynman diagrams. A subset of finite two-loop vertex diagrams is computed to
high precision using numerical techniques. We find agreement with a previous
numerical analysis. The above correction factor is also in line with a recent
lattice calculation.Comment: 26 pages, 6 postscript figures. The complete paper including figures
is also available via WWW at
http://www.physik.tu-muenchen.de/tumphy/d/T30d/PAPERS/TUM-HEP-247-96.ps.g
Vacuum Stability, Perturbativity, and Scalar Singlet Dark Matter
We analyze the one-loop vacuum stability and perturbativity bounds on a
singlet extension of the Standard Model (SM) scalar sector containing a scalar
dark matter candidate. We show that the presence of the singlet-doublet quartic
interaction relaxes the vacuum stability lower bound on the SM Higgs mass as a
function of the cutoff and lowers the corresponding upper bound based on
perturbativity considerations. We also find that vacuum stability requirements
may place a lower bound on the singlet dark matter mass for given singlet
quartic self coupling, leading to restrictions on the parameter space
consistent with the observed relic density. We argue that discovery of a light
singlet scalar dark matter particle could provide indirect information on the
singlet quartic self-coupling.Comment: 25 pages, 10 figures; v2 - fixed minor typos; v3 - added to text
discussions of other references, changed coloring of figures for easier black
and white viewin
The Higgs resonance in vector boson scattering
A heavy Higgs resonance is described in a representation-independent way
which is valid for the whole energy range of 2 -> 2 scattering processes,
including the asymptotic behavior at low and high energies. The low-energy
theorems which follow from to the custodial SU_2 symmetry of the Higgs sector
restrict the possible parameterizations of the lineshape that are consistent in
perturbation theory. Matching conditions are specified which are necessary and
sufficient to relate the parameters arising in different expansions. The
construction is performed explicitly up to next-to-leading order.Comment: 25 pages, revtex, uses epsf, amssym
Differences Between the Pole and On-Shell Masses and Widths of the Higgs Boson
The differences between the on-shell mass and width of the Higgs boson and
their pole counterparts are evaluated in leading order. For a heavy Higgs
boson, they are found to be sensitive functions of the gauge parameter and
become numerically large over a class of gauges that includes the unitary
gauge. For a light Higgs boson, the differences remain small in all gauges. The
pinch-technique mass and width are found to be close to their pole counterparts
over a large range of Higgs boson masses.Comment: 9 pages (Latex), 3 figures (Postscript
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