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http://hdl.handle.net/2440/12353
Thu, 28 Apr 2016 19:52:30 GMT2016-04-28T19:52:30ZIsospin distributions in the proton and the Gottfried sum rule from leptoproduction of hadrons
http://hdl.handle.net/2440/98464
Title: Isospin distributions in the proton and the Gottfried sum rule from leptoproduction of hadrons
Author: Levelt, J.; Mulders, P.J.; Schreiber, A.W.
Abstract: We investigate the implications for the production of hadrons of the asymmetry in the proton sea distribution, i.e. ū(x)≠ d̄(x), found recently by the New Muon Collaboration. The resulting “deviations” in the cross sections for the production of charged pions and, more general, charged hadrons are of the same order of magnitude as those in inclusive processes. Hence semi-inclusive data can provide an additional check on the Gottfried sum rule.Tue, 01 Jan 1991 00:00:00 GMThttp://hdl.handle.net/2440/984641991-01-01T00:00:00ZFirst-order variational calculation of form factor in a scalar nucleon-meson theory
http://hdl.handle.net/2440/98463
Title: First-order variational calculation of form factor in a scalar nucleon-meson theory
Author: Schreiber, A.W.; Rosenfelder, R.
Abstract: We investigate a relativistic quantum field theory in the particle representation using a non-perturbative variational technique. The theory is that of two massive scalar particles, ‘nucleons’ and ‘mesons’, interacting via a Yukawa coupling. We calculate the general Euclidean Green function involving two external nucleons and an arbitrary number of external mesons in the quenched approximation for the nucleons. The non-perturbative renormalization and truncation is done in a consistent manner and results in the same variational functional independent of the number of external mesons. We check that the calculation agrees with one-loop perturbation theory for small couplings. As an illustration the special case of meson absorption on the nucleon is considered in detail. We derive the radius of the dressed particle and numerically investigate the vertex function after analytic continuation to Minkowski space.Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/2440/984631996-01-01T00:00:00ZVariational calculation of relativistic meson-nucleon scattering in zeroth order
http://hdl.handle.net/2440/98462
Title: Variational calculation of relativistic meson-nucleon scattering in zeroth order
Author: Schreiber, A.W.; Rosenfelder, R.; Alexandrou, C.
Abstract: We extend the polaron variational treatment previously developed for the propagator to the case where one nucleon and n external mesons are present. Using the particle representation of the scalar Wick-Cutkosky model this is done in lowest order of an expansion of the exact action around a retarded quadratic trial action. In particular, we evaluate the form factor for scattering of mesons from the scalar nucleon and determine the radius of the dressed particle. After analytic continuation to Minkowski space we study elastic meson-nucleon scattering both analytically and numerically near threshold and show that it is essential to incorporate the correct behaviour of the retardation function at large proper times. Only if this is done the optical theorem is approximately fulfilled over a range of energies and coupling constants.Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/2440/984621996-01-01T00:00:00ZAstrophysical implications of the binary black hole merger GW150914
http://hdl.handle.net/2440/98461
Title: Astrophysical implications of the binary black hole merger GW150914
Author: Abbott, B.P.; Abbott, R.; Abbott, T.D.; Abernathy, M.R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R.X.; Adya, V.B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O.D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; et al.
Abstract: The discovery of the gravitational-wave (GW) source GW150914 with the Advanced LIGO detectors provides the first observational evidence for the existence of binary black hole (BH) systems that inspiral and merge within the age of the universe. Such BH mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively "heavy" BHs ($\gtrsim 25$ ${M}_{\odot }$) can form in nature. This discovery implies relatively weak massive-star winds and thus the formation of GW150914 in an environment with a metallicity lower than about 1/2 of the solar value. The rate of binary-BH (BBH) mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions ($\gtrsim 1$ Gpc−3 yr−1) from both types of formation models. The low measured redshift ($z\simeq 0.1$) of GW150914 and the low inferred metallicity of the stellar progenitor imply either BBH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/2440/984612016-01-01T00:00:00Z