14 research outputs found
Hadronic Light-by-Light Scattering in the Muonium Hyperfine Splitting
We consider an impact of hadronic light-by-light scattering on the muonium
hyperfine structure. A shift of the hyperfine interval is calculated with the light-by-light scattering approximated
by exchange of pseudoscalar and pseudovector mesons. Constraints from the
operator product expansion in QCD are used to fix parameters of the model
similar to the one used earlier for the hadronic light-by-light scattering in
calculations of the muon anomalous magnetic moment. The pseudovector exchange
is dominant in the resulting shift, . Although the effect is tiny it is useful in understanding
the level of hadronic uncertainties.Comment: 16 pages, 7 figures, a reference adde
Hadronic Contributions to the Muon Anomaly in the Constituent Chiral Quark Model
The hadronic contributions to the anomalous magnetic moment of the muon which
are relevant for the confrontation between theory and experiment at the present
level of accuracy, are evaluated within the same framework: the constituent
chiral quark model. This includes the contributions from the dominant hadronic
vacuum polarization as well as from the next--to--leading order hadronic vacuum
polarization, the contributions from the hadronic light-by-light scattering,
and the contributions from the electroweak hadronic vertex.
They are all evaluated as a function of only one free parameter: the
constituent quark mass. We also comment on the comparison between our results
and other phenomenological evaluations.Comment: Several misprints corrected and a clarifying sentence added. Three
figures superposed and two references added. Version to appear in JHE
Neutralino Dark Matter in Mirage Mediation
We study the phenomenology of neutralino dark matter (DM) in mirage mediation
scenario of supersymmetry breaking which results from the moduli stabilization
in some string/brane models. Depending upon the model parameters, especially
the anomaly to modulus mediation ratio determined by the moduli stabilization
mechanism, the nature of the lightest supersymmetric particle (LSP) changes
from Bino-like neutralino to Higgsino-like one via Bino-Higgsino mixing region.
For the Bino-like LSP, the standard thermal production mechanism can give a
right amount of relic DM density through the stop/stau-neutralino
coannihilation or the pseudo-scalar Higgs resonance process. We also examine
the prospect of direct and indirect DM detection in various parameter regions
of mirage mediation. Neutralino DM in galactic halo might be detected by near
future direct detection experiments in the case of Bino-Higgsino mixed LSP. The
gamma ray flux from Galactic Center might be detectable also if the DM density
profile takes a cuspy shape.Comment: One reference adde
What two models may teach us about duality violations in QCD
Though the operator product expansion is applicable in the calculation of
current correlation functions in the Euclidean region, when approaching the
Minkowskian domain, violations of quark-hadron duality are expected to occur,
due to the presence of bound-state or resonance poles. In QCD finite-energy sum
rules, contour integrals in the complex energy plane down to the Minkowskian
axis have to be performed, and thus the question arises what the impact of
duality violations may be. The structure and possible relevance of duality
violations is investigated on the basis of two models: the Coulomb system and a
model for light-quark correlators which has already been studied previously. As
might yet be naively expected, duality violations are in some sense "maximal"
for zero-width bound states and they become weaker for broader resonances whose
poles lie further away from the physical axis. Furthermore, to a certain
extent, they can be suppressed by choosing appropriate weight functions in the
finite-energy sum rules. A simplified Ansatz for including effects of duality
violations in phenomenological QCD sum rule analyses is discussed as well.Comment: 17 pages, 6 figures; version to appear in JHE
Search for fourth generation quarks and leptons at the Fermilab Tevatron and CERN Large Hadron Collider
If next generations of heavy quarks and leptons exist within the standard
model (SM), they can manifest themselves in Higgs boson production at the
Tevatron and the LHC, before being actually observed. This generation leads to
an increase of the Higgs boson production cross section via gluon fusion at
hadron colliders by a factor 6-9. So, the study of this process at the Tevatron
and LHC can finally fix the number of generations in the SM. Using the
Higgs boson decay channel, the studies at the upgraded Tevatron will answer the
question about the next generation for mass values 135 GeV \lsim M_H\lsim 190
GeV. Studying the channel we show its large potential for the
study of the Higgs boson at the LHC even in the standard case of three
generations. At the Tevatron, studies in this channel could explore the mass
range 110-140 GeV.Comment: 13 pages, 4 figures, LaTeX/RevTeX, final version accepted for
publicatio
Colliders and Cosmology
Dark matter in variations of constrained minimal supersymmetric standard
models will be discussed. Particular attention will be given to the comparison
between accelerator and direct detection constraints.Comment: Submitted for the SUSY07 proceedings, 15 pages, LaTex, 26 eps figure
Desperately Seeking Supersymmetry [SUSY]
In this article we try to clarify why supersymmetry [SUSY] and supersymmetric
grand unified theories [SUSY GUTs] are the new standard model of particle
physics, i.e. the standard by which all other theories and experiments are
measured.Comment: 69 pages, 15 figures, new references adde
QCD Corrections to Higgs Boson Production: Non- Leading Terms in the Heavy Quark Limit
We compute analytic results for the QCD corrections to Higgs boson production
via gluon fusion in hadronic collisions in the limit in which the top quark is
much heavier than the Higgs boson. The first non-leading corrections of
\O(\alpha_s^3 \mh^2/m_t^2) are given and numerical results presented for both
LHC and SSC energies. We confirm earlier numerical results showing that the
dominant corrections have the same mass dependence as the Born cross section.Comment: 27 pages plus 8 figures in uuencoded tar-compressed format, BNL-DK