Showing 4051 - 4100 of 7406 Items
Date: 2019-09-21
Creator: Kenneth A. Dennison, Thomas W. Baumgarte, Stuart L. Shapiro
Access: Open access
- The ‘direct collapse’ scenario has emerged as a promising evolutionary track for the formation of supermassive black holes early in the Universe. In an idealized version of such a scenario, a uniformly rotating supermassive star spinning at the mass-shedding (Keplerian) limit collapses gravitationally after it reaches a critical configuration. Under the assumption that the gas is dominated by radiation pressure, this critical configuration is characterized by unique values of the dimensionless parameters J/M2 and Rp/M, where J is the angular momentum, Rp the polar radius, and M the mass. Motivated by a previous perturbative treatment, we adopt a fully non-linear approach to evaluate the effects of gas pressure on these dimensionless parameters for a large range of masses. We find that gas pressure has a significant effect on the critical configuration even for stellar masses as large as M ~ 106 MO. We also calibrate two approximate treatments of the gas pressure perturbation in a comparison with the exact treatment, and find that one commonly used approximation in particular results in increasing deviations from the exact treatment as the mass decreases, and the effects of gas pressure increase. The other approximation, however, proves to be quite robust for all masses M >~ 104 MO.
Date: 1993-01-01
Creator: M. Procario, S. Yang, D. S. Akerib, B. Barish, M., Chadha, S. Chan, D. F. Cowen, G. Eigen, J. S. Miller, J. Urheim, A. J. Weinstein, D. Acosta, M. Athanas, G. Masek, B. Ong, H. Paar, M. Sivertz, A. Bean, J. Gronberg, R. Kutschke, S. Menary, R. J. Morrison, S. Nakanishi, H. N. Nelson, T. K. Nelson, J. D. Richman, H. Tajima, D. Schmidt, D. Sperka, M. S. Witherell, R. Ballest
Access: Open access
- Using the CLEO II detector at CESR we have studied D0 decays into final states with a K̄0 or K̄*0, and have measured branching ratios for the decay modes D0→(K̄0K̄*0)π0,η, η′. These results are compared with predictions of various charm decay models, and contributions of final-state interactions are discussed. © 1993 The American Physical Society.
Date: 1993-01-01
Creator: S. Sanghera, T. Skwarnicki, R. Stroynowski, M. Artuso, M., Goldberg, N. Horwitz, R. Kennett, G. C. Moneti, F. Muheim, S. Playfer, Y. Rozen, P. Rubin, S. Stone, M. Thulasidas, W. M. Yao, G. Zhu, A. V. Barnes, J. Bartelt, S. E. Csorna, Z. Egyed, V. Jain, P. Sheldon, D. S. Akerib, B. Barish, M. Chadha, D. F. Cowen, G. Eigen, J. S. Miller, J. Urheim, A. J. Weinstein, D. Acosta
Access: Open access
- We present a measurement of the lepton decay asymmetry Afb in the reaction B̄→D*l-ν̄l using data collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR). The value of Afb confirms that the chirality of the weak interaction is predominantly left-handed in b→c transitions as expected in the standard model, if it is assumed that the lepton current is also left-handed. Using Afb and the previously determined branching ratio, q2 distribution, and D* polarization, we obtain the first measurement of the form-factor ratios that are used to describe this semileptonic decay. © 1993 The American Physical Society.
Date: 2014-09-01
Creator: Stephen G. Naculich
Access: Open access
- Abstract: We generalize the scattering equations to include both massless and massive particles. We construct an expression for the tree-level n-point amplitude with n − 2 gluons or gravitons and a pair of massive scalars in arbitrary spacetime dimension as a sum over the (n − 3)! solutions of the scattering equations, à la Cachazo, He, and Yuan. We derive the BCJ relations obeyed by these massive amplitudes.
Date: 2003-08-01
Creator: Mark Battle, Michael Bender, Melissa B. Hendricks, David T. Ho, Robert, Mika, Galen McKinley, Song Miao Fan, Tegan Blaine, Ralph F. Keeling
Access: Open access
- The Ar/N2 ratio of air measured at 6 globally distributed sites shows annual cycles with amplitudes of 12 to 37 parts in 106. Summertime maxima reflect the atmospheric Ar enrichment driven by seasonal warming and degassing of the oceans. Paired models of air-sea heat fluxes and atmospheric tracer transport predict seasonal cycles in the Ar/N2 ratio that agree with observations, within uncertainties.