51 research outputs found
Constraints on Z' from W^+W^- production at the NLC with polarized beams
We discuss the potential of NLC500 and NLC1000 to probe Z-Z' mixing and mass
by the reaction e^+e^- -> W^+W^- with longitudinally polarized electrons. We
perform a model-independent analysis of the deviations from the Standard Model,
and apply it to a specific class of extended weak gauge models. Results
indicate that the corresponding bounds at the NLC500 complement the present
ones obtained from LEP1, and rapidly become quite stringent at the higher
energy of the NLC1000. Also, we emphasize the importance of initial beam
polarization in improving the sensitivity to mixing.Comment: 15 pages Latex, 8 figures available on request from
[email protected]
bosons in supersymmetric models confront electroweak data
We study constraints on additional bosons predicted in the
supersymmetric (SUSY) models by using the updated results of electroweak
experiments -- -pole experiments, measurements and low-energy neutral
current (LENC) experiments. We find that the effects of - mixing are
parametrized by (i) a tree-level contribution to the -parameter, (ii) the
effective - mass mixing angle \xibar. In addition, the effect of the
direct exchange of the heavier mass eigenstate in the LENC processes is
parametrized by (iii) a contact term \contact. We give the theoretical
predictions for the observables in the electroweak experiments together with
the standard model radiative corrections. Constraints on and
\xibar from the -pole and experiments and those on \contact from
the LENC experiments are separately shown. Impacts of the kinetic mixing
between the and gauge bosons on the
-analysis are studied. We show the 95% CL lower mass limit of as
a function of the effective - mixing parameter , a combination of
the mass and kinetic mixings. Theoretical prediction on and is
found for the and models by assuming the minimal
particle content of the SUSY models. In a certain region of the parameter
space, the boson mass in the detectable range of LHC is still allowed.Comment: LaTeX, 36pages, 4 figures. One referece added. Final version to
appear in Nucl. Phys.
Much Ado About Leptoquarks: A Comprehensive Analysis
We examine the phenomenological implications of a 200 GeV leptoquark in light
of the recent excess of events at HERA. Given the relative predictions of
events rates in e^+p versus e^-p, we demonstrate that classes of leptoquarks
may be excluded, including those contained in E_6 GUT models. It is shown that
future studies with polarized beams at HERA could reveal the chirality of the
leptoquark fermionic coupling and that given sufficient luminosity in each
e^\pm_{L,R} channel the leptoquark quantum numbers could be determined. The
implications of 200-220 GeV leptoquarks at the Tevatron are examined. While
present Tevatron data most likely excludes vector leptoquarks and leptogluons
in this mass region, it does allow for scalar leptoquarks. We find that while
leptoquarks have little influence on Drell-Yan production, further studies at
the Main Injector are possible in the single production channel. We investigate
precision electroweak measurements as well as the process e^+e^-\to q\bar q at
LEP II and find they provide no further restrictions on these leptoquark
models. We then ascertain that cross section and polarization asymmetry
measurements at the NLC provide the only direct mechanism to determine the
leptoquark's electroweak quantum numbers. The single production of leptoquarks
in \gamma e collisions by both the backscattered laser and Weisacker-Williams
techniques at the NLC is also discussed. Finally, we demonstrate that we can
obtain successful coupling constant unification in models with leptoquarks,
both with or without supersymmetry. The supersymmetric case requires the GUT
group to be larger than SU(5) such as flipped SU(5)\times U(1)_X.Comment: Corrected single production cross section at Tevatron, updated atomic
parity violation constraints, 55 page
A slitless spectroscopic survey for quasars near quasars
We present the results of the Quasars near Quasars (QNQ) survey, a CCD-based
slitless spectroscopic survey for faint V<22 quasars at 1.7<z<3.6 on 18
26.2'x33.5' fields centred on bright quasars at 2.76<z<4.69. In total 169
quasar candidates with emission lines were selected from the extracted
flux-calibrated spectra on the basis of well-defined automatic selection
criteria followed by visual inspection and verification. With follow-up
spectroscopy of 81 candidates that were likely to reside at z>1.7 we were able
to confirm 80 new quasars at 0.580<z<3.586 on 16 of our fields. 64 of the newly
discovered quasars are located at z>1.7. The overall high success rate implies
that most of the remaining 88 candidates are quasars as well, although the
majority of them likely resides at z<1.7 on the basis of the observed line
shapes and strengths. Due to the insufficient depth of the input source
catalogues needed for extraction of the slitless spectra our survey is not well
defined in terms of limiting magnitude for faint 2.5<z<3.6 quasars whose Lyman
alpha emission is detectable well beyond V=22, albeit at a continuum S/N<1.
While not useful for characterising the evolving space density of quasars, our
sample provides many new closely spaced quasar sightlines around intensely
studied quasars for further investigations on the three-dimensional
distribution of the intergalactic medium.Comment: 18 pages, 16 figures, accepted by A&A, includes Table 2 from online
material, full paper with appendices containing additional figures and tables
available at http://www.aip.de/People/gworseck/qnqpaper/qnqpaper_final.pd
Search for new physics indirect effects in at linear colliders with polarized beams
We discuss the potential of a linear collider to explore
manifestations of extended (or alternative) electroweak models of current
interest, through measurements of the reaction with both
initial and final states polarization. Specifically, we consider the
possibility to put stringent constraints on lepton mixing (or extended lepton
couplings) and mixing, showing in particular the usefulness of
polarization in order to disentangle these effects.Comment: 12 pages, latex, seven figures (available from [email protected]
The ugrizYJHK luminosity distributions and densities from the combined MGC, SDSS and UKIDSS LAS datasets
We combine data from the MGC, SDSS and UKIDSS LAS surveys to produce
ugrizYJHK luminosity functions and densities from within a common, low redshift
volume (z<0.1, ~71,000 h_1^-3 Mpc^3 for L* systems) with 100 per cent
spectroscopic completeness. In the optical the fitted Schechter functions are
comparable in shape to those previously reported values but with higher
normalisations (typically 0, 30, 20, 15, 5 per cent higher phi*-values in u, g,
r, i, z respectively over those reported by the SDSS team). We attribute these
to differences in the redshift ranges probed, incompleteness, and adopted
normalisation methods. In the NIR we find significantly different Schechter
function parameters (mainly in the M* values) to those previously reported and
attribute this to the improvement in the quality of the imaging data over
previous studies. This is the first homogeneous measurement of the
extragalactic luminosity density which fully samples both the optical and
near-IR regimes. Unlike previous compilations that have noted a discontinuity
between the optical and near-IR regimes our homogeneous dataset shows a smooth
cosmic spectral energy distribution (CSED). After correcting for dust
attenuation we compare our CSED to the expected values based on recent
constraints on the cosmic star-formation history and the initial mass function.Comment: 17 pages, 13 figures, Accepted in MNRAS: 2010 January 18; in original
form 2009 August 1
A Comprehensive Study of Leptoquark Bounds
We make a comprehensive study of indirect bounds on scalar leptoquarks that
couple chirally and diagonally to the first generation by examining available
data from low energy experiments as well as from high energy e+ e- and p pbar
accelerators. The strongest bounds turn out to arise from low energy data: For
leptoquarks that couple to right--handed quarks, the most stringent bound comes
from atomic parity violation. For leptoquarks that couple to left--handed
quarks, there are two mass regions: At low masses the bounds arise from atomic
parity violation or from universality in leptonic pi decays. At masses above a
few hundred GeV's, the dominant bounds come from the FCNC processes that are
unavoidable in these leptoquarks: The FCNC bound of the up sector, that arises
from D-Dbar mixing, combines with the FCNC bounds from the down sector, that
arise from rare K decays and K-Kbar mixing, to a bound on the flavour
CONSERVING coupling to the first generation.
The bounds restrict leptoquarks that couple with electromagnetic strength to
lie above 600 GeV or 630 GeV for leptoquarks that couple to RH quarks, and
above 1040 GeV, 440 GeV, and 750 GeV for the SU(2)_W scalar, doublet and
triplet leptoquarks that couple to LH quarks. These bounds are considerably
stronger than the first results from the direct searches at HERA. Our bounds
also already exclude large regions in the parameter space that could be
examined by various methods proposed for indirect leptoquark searches.Comment: 23 Pages (LaTeX), including 3 uufiled postscript figures.
WIS--93/90/Sept--PH. To appear in PRD. Changes: updated numbers ---> stronger
bound
Information and Discrimination from b Quark Production on Z Resonance
We introduce and define operatively in a model independent way a new ``heavy"
b-vertexparameter, , that can be derived from the measurement of a
special polarization asymmetry for production of b-quarks on Z resonance. We
show that the combination of the measurement of with that of a second
and previously defined ``heavy" b-vertex parameter can
discriminate a number of models of New Physics that remain associated to
different ``trajectories" in the plane of the variations of the two parameters.
This is shown in particular for some popular SUSY and technicolor-type models.
In general, this discrimination is possible if a measurement of
\underline{both} parameters is performed.Comment: 22 pages, 6 figures available by air mail upon request, (e-mail
[email protected] PM/94-04, UTS-DFT-94-02 .( revised version
with corrected references
Global Study of Electron-Quark Contact Interactions
We perform a global fit of data relevant to contact interactions,
including deep inelastic scattering at high from ZEUS and H1, atomic
physics parity violation in Cesium from JILA, polarized on nuclei
scattering experiments at SLAC, Mainz and Bates, Drell-Yan production at the
Tevatron, the total hadronic cross section at LEP, and
neutrino-nucleon scattering from CCFR. With only the new HERA data, the
presence of contact interactions improves the fit compared to the Standard
Model. When other data sets are included, the size of the contact contributions
is reduced and the overall fit represents no real improvement over the Standard
Model.Comment: 26 pages (now single-spaced), Revtex, 2 eps figures, uses epsf.sty.
Some clarifications, minor corrections, 2 new references, also 3 new tables
which present 95% CL bounds on the contact interaction scales Lambd
Low-Energy Parity-Violation and New Physics
The new physics sensitivity of a variety of low-energy parity-violating (PV)
observables is analyzed. A comparison is made between atomic PV for a single
isotope, atomic PV using isotope ratios, and PV electron-hadron and
electron-electron scattering. The complementarity among these observables, as
well as with high-energy processes, is emphasized. Theoretical uncertainties
entering the interpretation of low-energy measurements are discussed.Comment: 37 pages, 2 figures. Omissions to Tables I and V corrected along with
some minor typographical errors. To appear in Phys. Rev.
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