446 research outputs found

    An “Untrammeled Right”? The McCarran Immigration Subcommittee and the Origins of Presidential Authority to Suspend and Restrict Alien Entry Under §1182(f)

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    The language of Section 212(e) of the 1952 Immigration and Nationality Act, 8 U.S.C. §1182(f), contains a sweeping authorization of presidential discretion to suspend and restrict alien entry into the United States. Senator Pat McCarran (D-NV) first introduced the subsection in 1950 as part of the omnibus immigration bill drafted by his Judiciary Committee’s immigration subcommittee. The specific origins of the language and the original intent behind the subsection remain missing pieces in the extensive scholarly literature on the 1952 INA and legislative history as explored by the courts. This article reveals that the subcommittee modeled the subsection on the sixth proviso of the 1917 Immigration Act, the May 1918 Wartime Measure, and a selective interpretation of Supreme Court precedent. The article reveals further that the original intent behind the subsection was to close perceived loopholes in existing law enabling entry by displaced persons and Communist governmental officials

    Many-Body Corrections to Charged-Current Neutrino Absorption Rates in Nuclear Matter

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    Including nucleon--nucleon correlations due to both Fermi statistics and nuclear forces, we have developed a general formalism for calculating the charged--current neutrino--nucleon absorption rates in nuclear matter. We find that at one half nuclear density many--body effects alone suppress the rates by a factor of two and that the suppression factors increase to ∌\sim5 at 4×10144\times10^{14} g cm−3^{-3}. The associated increase in the neutrino--matter mean--free--paths parallels that found for neutral--current interactions and opens up interesting possibilities in the context of the delayed supernova mechanism and protoneutron star cooling.Comment: 11 pages, APS REVTeX format, 1 PostScript figure, uuencoded compressed, and tarred, submitted to Physical Review Letter

    Modern nucleon-nucleon potentials and symmetry energy in infinite matter

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    We study the symmetry energy in infinite nuclear matter employing a non-relativistic Brueckner-Hartree-Fock approach and using various new nucleon-nucleon (NN) potentials, which fit np and pp scattering data very accurately. The potential models we employ are the recent versions of the Nijmegen group, Nijm-I, Nijm-II and Reid93, the Argonne V18V_{18} potential and the CD-Bonn potential. All these potentials yield a symmetry energy which increases with density, resolving a discrepancy that existed for older NN potentials. The origin of remaining differences is discussed.Comment: 17 pages, 10 figures included, elsevier latex style epsart.st

    Transport coefficients of O(N) scalar field theories close to the critical point

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    We investigate the critical dynamics of O(N)-symmetric scalar field theories to determine the critical exponents of transport coefficients as a second-order phase transition is approached from the symmetric phase. A set of stochastic equations of motion for the slow modes is formulated, and the long wavelength dynamics is examined for an arbitrary number of field components, NN, in the framework of the dynamical renormalization group within the Ï”\epsilon expansion. We find that for a single component scalar field theory, N=1, the system reduces to the model C of critical dynamics, whereas for N>1N>1 the model G is effectively restored owing to dominance of O(N)-symmetric charge fluctuations. In both cases, the shear viscosity remains finite in the critical region. On the other hand, we find that the bulk viscosity diverges as the correlation length squared, for N=1, while it remains finite for N>1N>1.Comment: revised for publication in PR

    Vector Meson Photoproduction with an Effective Lagrangian in the Quark Model

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    A quark model approach to the photoproduction of vector mesons off nucleons is proposed. Its starting point is an effective Lagrangian of the interaction between the vector meson and the quarks inside the baryon, which generates the non-diffractive s- and u- channel resonance contributions. Additional t-channel π0\pi^0 and σ\sigma exchanges are included for the ω\omega and ρ0\rho^0 production respectively to account for the large diffractive behavior in the small tt region as suggested by Friman and Soyeur. The numerical results are presented for the ω\omega and ρ\rho productions in four isospin channels with the same set of parameters, and they are in good agreement with the available data not only in ω\omega and ρ0\rho^0 productions but also in the charged ρ\rho productions where the additional t-channel σ\sigma exchange does not contribute so that it provides an important test to this approach. The investigation is also extended to the ϕ\phi photoproduction, and the initial results show that the non-diffractive behavior of the ϕ\phi productions in the large tt region can be described by the s- and u- channel contributions with significantly smaller coupling constants, which is consistent with the findings in the similar studies in the QHD framework. The numerical investigation has also shown that polarization observables are essential for identifying so-called "missing resonances".Comment: 36 pages, 10 PS figures, extended version of nucl-th/9711061 and nucl-th/9803021, submitted to PR

    Study of possible \omega bound states in nuclei with the (\gamma,p) reaction

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    We perform calculations for \omega production in nuclei by means of the (\gamma,p) reaction for photon energies and proton angles suited to running and future experiments in present Laboratories. For some cases of possible \omega optical potentials we find clear peaks which could be observable provided a good resolution in the \omega energy is available. We also study the inclusive production of \pi^0 \gamma in nuclei around the \omega energy and find a double hump structure for the energy spectra, with a peak around a \pi^0 \gamma energy of m_{\omega}-100 MeV, which could easily be misidentified by a signal of a bound \omega state in nuclei, while it is due to a different scaling of the uncorrelated \pi^0 \gamma production and \omega production with subsequent \pi^0 \gamma decay.Comment: 19 pages, 10 figure

    Meson - nucleon vertex form factors at finite temperature

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    In this paper the dependence of meson-nucleon-nucleon vertex form factors is studied as a function of termperature. The results are obtained starting from a zero temperature Bonn potential. The temperature dependence of the vertex form factors and radii is studied in the thermofield dynamics, a real-time operator formalism of finite temperature field theory. It is anticipated that these results will have an impact on the study of relativistic heavy-ion collisions as the critical temperature for the phase transition from hadronic to quark-gluon system is approached.Comment: 19 pages, Revtex, 11 figures (Ps), 171k

    An isotopic effect in phi photoproduction at a few GeV

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    A distinct isotopic effect in phi photoproduction at 2-5 GeV region is identified by examining the production amplitudes due to Pomeron-exchange and meson-exchange mechanisms. This effect is mainly caused by the pi-eta interference constrained by SU(3) symmetry and the isotopic structure of the gamma NN coupling in the direct phi-radiation amplitude. It can be tested experimentally by measuring differences in the polarization observables between the gamma-p and gamma-n reactions.Comment: 11 pages, 6 figure
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