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

Electronic, vibrational and magnetic properties of a novel C_{48}N_{12} aza-fullerene

We study the structural, electronic, vibrational and magnetic properties of a novel ${\rm C}_{48}{\rm N}_{12}$ aza-fullerene using density functional theory and restricted Hartree-Fock theory. Optimized geometries and total energy of this fullerene have been calculated. We find that for ${\rm C}_{48}{\rm N}_{12}$ the total ground state energy is about -67617 eV, the HOMO-LUMO gap is about 1.9 eV, five strong IR spectral lines are located at the vibrational frequencies, 461.5 ${\rm cm}^{-1}$, 568.4 ${\rm cm}^{-1}$, 579.3 ${\rm cm}^{-1}$, 1236.1 ${\rm cm}^{-1}$, 1338.9 ${\rm cm}^{-1}$, the Raman scattering activities and depolarization ratios are zero, and 10 NMR spectral signals are predicted. Calculations of diamagnetic shielding factor, static dipole polarizabilities and hyperpolarizabilities of ${\rm C}_{48}{\rm N}_{12}$ are performed and discussed.Comment: published in Chem.Phys.Let

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

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

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

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

Measurement of the Strong Coupling Constant from Inclusive Jet Production at the Tevatron pˉp\bar pp Collider

We report a measurement of the strong coupling constant, $\alpha_s(M_Z)$, extracted from inclusive jet production in $p\bar{p}$ collisions at $\sqrt{s}=$1800 GeV. The QCD prediction for the evolution of $\alpha_s$ with jet transverse energy $E_T$ is tested over the range 40<$E_T$<450 GeV using $E_T$ for the renormalization scale. The data show good agreement with QCD in the region below 250 GeV. In the text we discuss the data-theory comparison in the region from 250 to 450 GeV. The value of $\alpha_s$ at the mass of the $Z^0$ boson averaged over the range 40<$E_T$<250 GeV is found to be $\alpha_s(M_{Z})= 0.1178 \pm 0.0001{(\rm stat)}^{+0.0081}_{-0.0095}{\rm (exp. syst)}$. The associated theoretical uncertainties are mainly due to the choice of renormalization scale (^{+6%}_{-4%}) and input parton distribution functions (5%).Comment: 7 pages, 3 figures, using RevTeX. Submitted to Physical Review Letter

Search for Chargino-Neutralino Associated Production at the Fermilab Tevatron Collider

We have searched in $p \bar{p}$ collisions at $\sqrt{s}$ = 1.8 TeV for events with three charged leptons and missing transverse energy. In the Minimal Supersymmetric Standard Model, we expect trilepton events from chargino-neutralino (\chione \chitwo) pair production, with subsequent decay into leptons. We observe no candidate $e^+e^-e^\pm$, $e^+e^-\mu^\pm$, $e^\pm\mu^+\mu^-$ or $\mu^+\mu^-\mu^\pm$ events in 106 pb$^{-1}$ integrated luminosity. We present limits on the sum of the branching ratios times cross section for the four channels: \sigma_{\chione\chitwo}\cdot BR(\chione\chitwo\to 3\ell+X) 81.5 \mgev\sp and M_\chitwo > 82.2 \mgev\sp for $\tan\beta=2$, $\mu =-600$~\mgev\sp and M_\squark= M_\gluino.Comment: 9 pages and 3 figure

A Study of B0 -> J/psi K(*)0 pi+ pi- Decays with the Collider Detector at Fermilab

We report a study of the decays B0 -> J/psi K(*)0 pi+ pi-, which involve the creation of a u u-bar or d d-bar quark pair in addition to a b-bar -> c-bar(c s-bar) decay. The data sample consists of 110 1/pb of p p-bar collisions at sqrt{s} = 1.8 TeV collected by the CDF detector at the Fermilab Tevatron collider during 1992-1995. We measure the branching ratios to be BR(B0 -> J/psi K*0 pi+ pi-) = (8.0 +- 2.2 +- 1.5) * 10^{-4} and BR(B0 -> J/psi K0 pi+ pi-) = (1.1 +- 0.4 +- 0.2) * 10^{-3}. Contributions to these decays are seen from psi(2S) K(*)0, J/psi K0 rho0, J/psi K*+ pi-, and J/psi K1(1270)

Search for the Supersymmetric Partner of the Top-Quark in ppˉp \bar{p} Collisions at s=1.8TeV\sqrt{s} = 1.8 {\rm TeV}

We report on a search for the supersymmetric partner of the top quark (stop) produced in $t \bar{t}$ events using $110 {\rm pb}^{-1}$ of $p \bar{p}$ collisions at $\sqrt{s} = 1.8 {\rm TeV}$ 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 $t \bar{t}$ 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}$^{2}$.Comment: 11 pages, 4 figure