4,704 research outputs found
Determining the Sign of the Z-Penguin Amplitude
We point out that the precision measurements of the pseudo observables R_b^0,
A_b, and A_FB^0,b performed at LEP and SLC suggest that in models with
minimal-flavor-violation the sign of the Z-penguin amplitude is identical to
the one present in the standard model. We determine the allowed range for the
non-standard contribution to the Inami-Lim function C and show by analyzing
possible scenarios with positive and negative interference of standard model
and new physics contributions, that the derived bound holds in each given case.
Finally, we derive lower and upper limits for the branching ratios of K^+ ->
pi^+ nu nubar, K_L -> pi^0 nu nubar, K_L -> mu^+ mu^-, B -> X_d,s nu nubar, and
B_d,s -> mu^+ mu^- within constrained minimal-flavor-violation making use of
the wealth of available data collected at the Z-pole.Comment: 20 pages, 5 pdf figures, 5 tables, uses pdflatex; further typos
corrected, matches PRD versio
Construction and Test of MDT Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the AT-
LAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurized drift tubes on either side of a space frame carrying an optical
monitoring system to correct for deformations. The full-scale prototype of a
large MDT chamber has been constructed with methods suitable for large-scale
production. X-ray measurements at CERN showed a positioning accuracy of the
sense wires in the chamber of better than the required 20 ?microns (rms). The
performance of the chamber was studied in a muon beam at CERN. Chamber
production for ATLAS now has started
Constraining the Two-Higgs-Doublet-Model parameter space
We confront the Two-Higgs-Doublet Model with a variety of experimental
constraints as well as theoretical consistency conditions. The most
constraining data are the \bar B\to X_s\gamma decay rate (at low values of
M_{H^\pm}), and \Delta\rho (at both low and high M_{H^\pm}). We also take into
account the B\bar B oscillation rate and R_b, or the width \Gamma(Z\to b\bar b)
(both of which restrict the model at low values of \tan\beta), and the
B^-\to\tau\nu_\tau decay rate, which restricts the model at high \tan\beta and
low M_{H^\pm}. Furthermore, the LEP2 non-discovery of a light, neutral Higgs
boson is considered, as well as the muon anomalous magnetic moment. Since
perturbative unitarity excludes high values of \tan\beta, the model turns out
to be very constrained. We outline the remaining allowed regions in the
\tan\beta-M_{H^\pm} plane for different values of the masses of the two
lightest neutral Higgs bosons, and describe some of their properties.Comment: 17 pages, 17 figure
Trilinear Higgs couplings in the two Higgs doublet model with CP violation
We carry out a detailed analysis of the general two Higgs doublet model with
CP violation. We describe two different parametrizations of this model, and
then study the Higgs boson masses and the trilinear Higgs couplings for these
two parametrizations. Within a rather general model, we find that the trilinear
Higgs couplings have a significant dependence on the details of the model, even
when the lightest Higgs boson mass is taken to be a fixed parameter. We include
radiative corrections in the one-loop effective potential approximation in our
analysis of the Higgs boson masses and the Higgs trilinear couplings. The
one-loop corrections to the trilinear couplings of the two Higgs doublet model
also depend significantly on the details of the model, and can be rather large.
We study quantitatively the trilinear Higgs couplings, and show that these
couplings are typically several times larger than the corresponding Standard
Model trilinear Higgs coupling in some regions of the parameter space. We also
briefly discuss the decoupling limit of the two Higgs doublet model.Comment: 23 pages, 15 figures. v2: References added, version to appear in PR
Further constraints on the evolution of Ks-selected galaxies in the GOODS/CDFS field
We have selected and analysed the properties of a sample of 2905 Ks<21.5
galaxies in ~ 131 sq.arcmin of the Great Observatories Origins Deep Survey
(GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the
evolution of Ks-selected galaxies with respect to the results already obtained
in previous studies. We made use of the public deep multiwavelength imaging
from the optical B through the infrared (IR) 4.5 micron bands, in conjunction
with available spectroscopic and COMBO17 data in the CDFS, to construct an
optimised redshift catalogue for our galaxy sample. We computed the Ks-band LF
and determined that its characteristic magnitude has a substantial brightening
and a decreasing total density from z=0 to =2.5. We also analysed the
colours and number density evolution of galaxies with different stellar masses.
Within our sample, and in contrast to what is observed for less massive
systems, the vast majority (~ 85-90%) of the most massive (M>2.5x10^11 Msun)
local galaxies appear to be in place before redshift z ~1. Around 65-70% of the
total assemble between redshifts z=1 and z=3 and most of them display extremely
red colours, suggesting that plausible star formation in these very massive
systems should mainly proceed in obscured, short-timescale bursts. The
remaining fraction (up to ~ 20%) could be in place at even higher redshifts
z=3-4, pushing the first epoch of formation of massive galaxies beyond the
limits of current near-IR surveys.Comment: Accepted for publication in MNRAS. 16 pages, 15 figure
Modeling sources of variation for growth and predatory demand of Lake Erie walleye (Stizostedion vitreum), 1986-1995
Abstract in English and FrenchGiven the variable nature of the Lake Erie ecosystem, we investigated biotic and abiotic sources of variation for walleye (Stizostedion vitreum) growth, consumption, and population-wide predatory demand. We
determined how temperature, population structure, and age-specific consumption influenced walleye growth and
consumption during 1986-1995. For each year, we used individual-based bioenergetics modeling to compare growth
and consumption by walleye in Lake Erie's western or central basin with those of walleye moving seasonally
between basins. Population structure strongly affected walleye growth and consumption but had little influence on
interbasin growth rate comparisons. Based on water temperature alone, growth and consumption by western basin
walleye were generally lower than for central basin or migratory populations and were more limited by summer
water temperatures. In simulations combining effects of population structure, temperature, and age-specific
consumption, migratory walleye grew most rapidly, taking advantage of temperature-related growth peaks in both
basins. Estimates of walleye predatory demand declined with population size from 1988 through 1995. With natural
feedbacks, predatory demand interacts with prey production, limiting walleye reproductive potential when prey
availability is low. However, immediate impact on predatory inertia is limited, complicating our ability to predict
how predatory demand and prey availability interact in Lake Erie.Support for
this project was provided by a University Fellowship from the Graduate School of the Ohio State University (to
M.W.K.) and by Federal Aid in Sportfish Restoration F-69-P, administered jointly by the U.S. Fish and Wildlife
Service and the Ohio Division of Wildlife, and by the Department of Zoology, Ohio State University
Construction and Test of the Precision Drift Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the
ATLAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurised drift tubes on either side of a space frame carrying an optical
deformation monitoring system. The chambers have to provide a track position
resolution of 40 microns with a single-tube resolution of at least 80 microns
and a sense wire positioning accu- racy of 20 ?microns (rms). The feasibility
was demonstrated with the full-scale prototype of one of the largest MDT
chambers with 432 drift tubes of 3.8 m length. For the ATLAS muon spectrometer,
88 chambers of this type have to be built. The first chamber has been completed
with a wire positioning accuracy of 14 microns (rms)
Explicit CP violation in the Dine-Seiberg-Thomas model
The possibility of explicit CP violation is studied in a supersymmetric model
proposed by Dine, Seiberg, and Thomas, with two effective dimension-five
operators. The explicit CP violation may be triggered by complex phases in the
coefficients for the dimension-five operators in the Higgs potential, and by a
complex phase in the scalar top quark masses. Although the scenario of explicit
CP violation is found to be inconsistent with the experimental data at LEP2 at
the tree level, it may be possible at the one-loop level. For a reasonable
parameter space, the masses of the neutral Higgs bosons and their couplings to
a pair of bosons are consistent with the LEP2 data, at the one-loop level.Comment: 5 pages, 2 figure
Properties of 125 GeV Higgs boson in non-decoupling MSSM scenarios
Tantalizing hints of the Higgs boson of mass around 125 GeV have been
reported at the LHC. We explore the MSSM parameter space in which the 125 GeV
state is identified as the heavier of the CP even Higgs bosons, and study two
scenarios where the two photon production rate can be significantly larger than
the standard model (SM). In one scenario, is
enhanced by a light stau contribution, while the () rate
stays around the SM rate. In the other scenario, is
suppressed and not only the but also the
() rates should be enhanced. The rate can be
significantly larger or smaller than the SM rate in both scenarios. Other
common features of the scenarios include top quark decays into charged Higgs
boson, single and pair production of all Higgs bosons in collisions at
GeV.Comment: 20 pages, 5 figures, accepted version for publication in JHE
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