5,610 research outputs found

    The Anomalous Magnetic Moments of the Electron and the Muon - Improved QED Predictions Using Pade Approximants

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    We use Pade Approximants to obtain improved predictions for the anomalous magnetic moments of the electron and the muon. These are needed because of the very precise experimental values presently obtained for the electron, and soon to be obtained at BNL for the muon. The Pade prediction for the QED contribution to the anomalous magnetic moment of the muon differs significantly from the naive perturbative prediction.Comment: 8 pages (LateX); SLAC-PUB-6670, CERN-TH-7451/94, TAUP-2201-94, OSU-RN-393/94. Typo correcte

    A Prediction for the 4-Loop \beta Function

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    We predict that the four-loop contribution \beta_3 to the QCD \beta function in the MS-bar prescription is given by \beta_3\simeq 23,600(900) - 6,400(200) N_f + 350(70) N_f^2 + 1.5 N_f^3, where N_f is the number of flavours and the coefficient of N_f^3 is an exact result from large-N_f expansion. In the phenomenologically-interesting case N_f=3, we estimate \beta_3 = (7.6 \pm 0.1) x 10^3. We discuss our estimates of the errors in these QCD predictions, basing them on the demonstrated accuracy of our method in test applications to the O(N) \Phi^4 theory, and on variations in the details of our estimation method, which goes beyond conventional Pade approximants by estimating and correcting for subasymptotic deviations from exact results.Comment: 11 pages, LaTeX, including 2 figures in 3 ps files; requires epsfig.sty; added comparison with recent exact result

    The neural correlates of semantic richness : Evidence from an fMRI study of word learning

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    We investigated the neural correlates of concrete nouns with either many or few semantic features. A group of 21 participants underwent two days of training and were then asked to categorize 40 newly learned words and a set of matched familiar words as living or nonliving in an MRI scanner. Our results showed that the most reliable effects of semantic richness were located in the left angular gyrus (AG) and middle temporal gyrus (MTG), where activation was higher for semantically rich than poor words. Other areas showing the same pattern included bilateral precuneus and posterior cingulate gyrus. Our findings support the view that AG and anterior MTG, as part of the multimodal network, play a significant role in representing and integrating semantic features from different input modalities. We propose that activation in bilateral precuneus and posterior cingulate gyrus reflects interplay between AG and episodic memory systems during semantic retrieval

    Corrections to Bino Annihilation II: One-Loop Contribution to B~B~Z\widetilde B \widetilde B \to Z^*

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    We calculate the one-loop contribution to the bino annihilation rate due to the process B~B~Z\widetilde B \widetilde B \to Z^*, which vanishes at tree level.Comment: 8 pages in LaTex plus 5 postscript figures (included), UCSBTH--94--02, UMN--TH--1233/9

    Calculations of Neutralino-Stau Coannihilation Channels and the Cosmologically Relevant Region of MSSM Parameter Space

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    Assuming that the lightest supersymmetric particle (LSP) is the lightest neutralino, we present a detailed exploration of neutralino-stau coannihilation channels, including analytical expressions and numerical results. We also include neutralino coannihilations with the selectron and smuon. We evaluate the implications of coannihilations for the cosmological relic density of the LSP, which is assumed to be stable, in the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the soft supersymmetry-breaking parameters are universal at the supergravity GUT scale. We evaluate the changes due to coannihilations in the region of the MSSM parameter space that is consistent with the cosmological upper limit on the relic LSP density. In particular, we find that the upper limit on the mass of the neutralino is increased from about 200 GeV to about 600 GeV in the CMSSM, and estimate a qualitatively similar increase for gauginos in the general MSSM.Comment: 38 pages in LaTeX, including 25 encapsulated postscript figures. Added small clarification in the text, corrected some typos in the appendix. Figures and conclusions unchange

    Phases in the MSSM, Electric Dipole Moments and Cosmological Dark Matter

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    We consider the effect of CP violating phases in the MSSM on the relic density of the lightest supersymmetric particle (LSP). In particular, we find that the upper limits on the LSP mass are relaxed when phases in the MSSM are allowed to take non-zero values when the LSP is predominantly a gaugino (bino). Previous limits of \mb \la 250 GeV for Ωh2<0.25\Omega h^2 < 0.25 can be relaxed to \mb \la 650 GeV. We also consider the additional constraints imposed by the neutron and electron electric dipole moments induced by these phases. Though there is some restriction on the phases, the bino mass may still be as large as \sim 350 GeV and certain phases can be arbitrarily large.Comment: 10 pages in LaTeX, with 4 Postscript figures (included

    What predicts a successful smoking cessation attempt?

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    Quit date abstinence (strength of recommendation [SOR]: B, based on low-quality randomized controlled trial [RCT] of healthy subjects) and refraining from tobacco products within the first 2 weeks after an attempt (SOR: A, based on 2 RCTs) predict long-term abstinence from smoking. Inconsistent studies variously identify being married, a diagnosis of coronary artery disease (CAD) within the past 2 years, a higher education level, advanced age, and social status (such as being a homeowner) as factors correlated with successful smoking cessation (SOR: C, based on prospective cohort studies with conflicting results)

    The Evolution of the Optical and Near-Infrared Galaxy Luminosity Functions and Luminosity Densities to z~2

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    Using Hubble Space Telescope and ground-based U through K- band photometry from the Great Observatories Origins Deep Survey (GOODS), we measure the evolution of the luminosity function and luminosity density in the rest-frame optical (UBR) to z ~ 2, bridging the poorly explored ``redshift desert'' between z~1 and z~2. We also use deep near-infrared observations to measure the evolution in the rest-frame J-band to z~1. Compared to local measurements from the SDSS, we find a brightening of the characteristic magnitude, (M*), by ~2.1, \~0.8 and ~0.7 mag between z=0.1 and z=1.9, in U, B, and R bands, respectively. The evolution of M* in the J-band is in the opposite sense, showing a dimming between redshifts z=0.4 and z=0.9. This is consistent with a scenario in which the mean star formation rate in galaxies was higher in the past, while the mean stellar mass was lower, in qualitative agreement with hierarchical galaxy formation models. We find that the shape of the luminosity function is strongly dependent on spectral type and that there is strong evolution with redshift in the relative contribution from the different spectral types to the luminosity density. We find good agreement in the luminosity function derived from an R-selected and a K-selected sample at z~1, suggesting that optically selected surveys of similar depth (R < 24) are not missing a significant fraction of objects at this redshift relative to a near-infrared-selected sample. We compare the rest-frame B-band luminosity functions from z~0--2 with the predictions of a semi-analytic hierarchical model of galaxy formation, and find qualitatively good agreement. In particular, the model predicts at least as many optically luminous galaxies at z~1--2 as are implied by our observations.Comment: 43 pages; 15 Figures; 5 Tables, Accepted for publication in Ap.
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