1,209 research outputs found
Ab initio linear scaling response theory: Electric polarizability by perturbed projection
A linear scaling method for calculation of the static {\em ab inito} response
within self-consistent field theory is developed and applied to calculation of
the static electric polarizability. The method is based on density matrix
perturbation theory [Niklasson and Challacombe, cond-mat/0311591], obtaining
response functions directly via a perturbative approach to spectral projection.
The accuracy and efficiency of the linear scaling method is demonstrated for a
series of three-dimensional water clusters at the RHF/6-31G** level of theory.
Locality of the response under a global electric field perturbation is
numerically demonstrated by approximate exponential decay of derivative density
matrix elements.Comment: 4.25 pages in PRL format, 2 figure
Polarimetric variations of binary stars. V. Pre-main-sequence spectroscopic binaries located in Ophiuchus and Scorpius
We present polarimetric observations of 7 pre-main-sequence (PMS)
spectroscopic binaries located in the rho Oph and Upper Sco star forming
regions (SFRs). The average observed polarizations at 7660A are between 0.5%
and 3.5%. After estimates of the interstellar polarization are removed, all
binaries have an intrinsic polarization above 0.4%. Two binaries,
NTTS162814-2427 and NTTS162819-2423S, present high levels of intrinsic
polarization between 1.5% and 2.1%. All 7 PMS binaries have a statistically
variable or possibly variable polarization. Combining these results with our
previous sample of binaries located in the Tau, Aur and Ori SFRs, 68% of the
binaries have an intrinsic polarization above 0.5%, and 90% of the binaries are
polarimetrically variable or possibly variable. NTTS160814-1857,
NTTS162814-2427, and NTTS162819-2423S are clearly polarimetrically variable.
The first two also exhibit phase-locked variations over ~10 and ~40 orbits
respectively. NTTS160905-1859 shows periodic variations that are not
phased-locked and only present for short intervals of time. The amplitudes of
the variations reach a few tenths of a percent. The high-eccentricity system
NTTS162814-2427 shows single-periodic variations, in agreement with our
previous numerical simulations. Non-periodic events introduce stochastic noise
that partially masks the periodic variations and prevents the Brown, McLean, &
Emslie (1978) formalism from finding a reasonable estimate of the inclination.Comment: 63 pages, including 21 figures and 18 tables, accepted by A
The Effect of Multiple Scattering on the Polarization from Binary Star Envelopes. I. Self- and Externally Illuminated Disks
We present the results of a Monte Carlo radiative transfer code that
calculates the polarization produced by multiple Thomson scattering and
variable absorptive opacity in a circumstellar disk around one component of a
close detached binary system. We consider in detail the polarization variations
over the binary cycle that result from the disk's illumination by the external
star and by its own volume emission. We identify key features of these
polarization phase curves and investigate their behavior as functions of
optical depth, albedo, and inclination for geometrically thin and thick disks.
The polarization due to disk self-illumination is sensitive to the internal
optical characteristics of the disk, while the polarization arising from
external illumination is mainly sensitive to the disk's geometrical thickness.
With appropriate flux weighting, these results, combined with those for an
internally illuminated disk, allow simulation of the polarization signature
from an arbitrary binary-disk system.Comment: 34 pages, 17 figures. Submitted to ApJ, revised in response to
referee comments. Color figures available from
http://www.ruf.rice.edu/~jhoffman/monte/colorfigs.htm
Polarimetric variations of binary stars. IV. Pre-main-sequence spectroscopic binaries located in Taurus, Auriga, and Orion
We present polarimetric observations of 14 pre-main-sequence (PMS) binaries
located in the Taurus, Auriga, and Orion star forming regions. The majority of
the average observed polarizations are below 0.5%, and none are above 0.9%.
After removal of estimates of the interstellar polarization, about half the
binaries have an intrinsic polarization above 0.5%, even though most of them do
not present other evidences for the presence of circumstellar dust. Various
tests reveal that 77% of the PMS binaries have or possibly have a variable
polarization. LkCa3, Par1540, and Par2494 present detectable periodic and
phase-locked variations. The periodic polarimetric variations are noisier and
of a lesser amplitude (~0.1%) than for other types of binaries, such as hot
stars. This could be due to stochastic events that produce deviations in the
average polarization, a non-favorable geometry (circumbinary envelope), or the
nature of the scatterers (dust grains are less efficient polarizers than
electrons). Par1540 is a Weak-line TTauri Star, but nonetheless has enough dust
in its environment to produce detectable levels of polarization and variations.
A fourth interesting case is W134, which displays rapid changes in polarization
that could be due to eclipses. We compare the observations with some of our
numerical simulations, and also show that an analysis of the periodic
polarimetric variations with the Brown, McLean, & Emslie (BME) formalism to
find the orbital inclination is for the moment premature: non-periodic events
introduce stochastic noise that partially masks the periodic low-amplitude
variations and prevents the BME formalism from finding a reasonable estimate of
the orbital inclination.Comment: 70 pages, 20 figures, to be published in the Astronomical Journa
Measurement of the p\bar{p}\sqrt{s}$ = 1.8 TeV
We update the measurement of the top production cross section using the CDF
detector at the Fermilab Tevatron. This measurement uses decays to
the final states +jets and +jets. We search for quarks from
decays via secondary-vertex identification or the identification of
semileptonic decays of the and cascade quarks. The background to the
production is determined primarily through a Monte Carlo simulation.
However, we calibrate the simulation and evaluate its uncertainty using several
independent data samples. For a top mass of 175 , we measure
pb and pb using
the secondary vertex and the lepton tagging algorithms, respectively. Finally,
we combine these results with those from other decay channels and
obtain pb.Comment: The manuscript consists of 130 pages, 35 figures and 42 tables in
RevTex. The manuscript is submitted to Physical Review D. Fixed typo in
author lis
Search for the Supersymmetric Partner of the Top-Quark in Collisions at
We report on a search for the supersymmetric partner of the top quark (stop)
produced in events using of
collisions at recorded with the Collider Detector at
Fermilab. In the case of a light stop squark, the decay of the top quark into
stop plus the lightest supersymmetric particle (LSP) could have a significant
branching ratio. The observed events are consistent with Standard Model production and decay. Hence, we set limits on the branching ratio of
the top quark decaying into stop plus LSP, excluding branching ratios above 45%
for a LSP mass up to 40 {\rm GeV/c}.Comment: 11 pages, 4 figure
Measurement of J/Psi and Psi(2S) Polarization in ppbar Collisions at sqrt(s) = 1.8 TeV
We have measured the polarization of J/Psi and Psi(2S) mesons produced in
p\bar{p} collisions at \sqrt{s} = 1.8 TeV, using data collected at CDF during
1992-95.
The polarization of promptly produced J/Psi [Psi(2S)] mesons is isolated from
those produced in B-hadron decay, and measured over the kinematic range 4[5.5]
< P_T < 20 GeV/c and |y| < 0.6. For P_T \gessim 12 GeV/c we do not observe
significant polarization in the prompt component.Comment: Revised version, accepted for publication in Physical Review Letter
Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV
We present results of searches for diphoton resonances produced both
inclusively and also in association with a vector boson (W or Z) using 100
pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on
the product of cross section times branching ratio for both p\bar
p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive
production to the expectations from heavy sgoldstinos we derive limits on the
supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the
sgoldstino mass and the choice of other parameters. Also, using a NLO
prediction for the associated production of a Higgs boson with a W or Z boson,
we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we
set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which
couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82
GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure
Limits on Gravitino Production and New Processes with Large Missing Transverse Energy in p-pbar Collisions at sqrt(s)=1.8 TeV
Events collected by the Collider Detector at Fermilab (CDF) with an energetic
jet plus large missing transverse energy can be used to search for physics
beyond the Standard Model. We see no deviations from the expected background
and set upper limits on the production of new processes. We consider in
addition the production of light gravitinos within the framework of the Gauge
Mediated Supersymmetry Breaking models and set a limit at 95% confidence level
on the breaking scale sqrt(F) >= 217 GeV, which excludes gravitino masses
smaller than 1.1x10^-5 eV/c^2.Comment: 13 pages, 4 figures. Submitted to Physical Review Letter
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