707 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

    Light Front Theory Of Nuclear Matter

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    A relativistic light front formulation of nuclear dynamics is applied to infinite nuclear matter. A hadronic meson-baryon Lagrangian, consistent with chiral symmetry, leads to a nuclear eigenvalue problem which is solved, including nucleon-nucleon (NN) correlations, in the one-boson-exchange approximation for the NN potential. The nuclear matter saturation properties are reasonably well reproduced, with a compression modulus of 180 MeV. We find that there are about 0.05 excess pions per nucleon.Comment: 6 pages, Revtex, one figure; version resubmitted to Phys. Lett.

    Medium Effects in rho-Meson Photoproduction

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    We compute dilepton invariant mass spectra from the decays of rho mesons produced by photon reactions off nuclei. Our calculations employ a realistic model for the rho photoproduction amplitude on the nucleon which provides fair agreement with measured cross sections. Medium effects are implemented via an earlier constructed rho propagator based on hadronic many-body theory. At incoming photon energies of 1.5 -3 GeV as used by the CLAS experiment at JLAB, the average density probed for iron targets is estimated at about half saturation density. At the pertinent rho-meson 3-momenta the predicted medium effects on the rho propagator are rather moderate. The resulting dilepton spectra approximately agree with recent CLAS data.Comment: One numerical error corrected, conclusions unchange

    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

    Low-momentum interactions for nuclei

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    We show how the renormalization group is used to construct a low-momentum nucleon-nucleon interaction V_{low k}, which unifies all potential models used in nuclear structure calculations. V_{low k} can be directly applied to the nuclear shell model or to nucleonic matter without a G matrix resummation. It is argued that V_{low k} parameterizes a high-order chiral effective field theory two-nucleon force. We use cutoff dependence as a tool to assess the error in the truncation of nuclear forces to two-nucleon interactions and introduce a low-momentum three-nucleon force, which regulates A=3,4 binding energies. The adjusted three-nucleon interaction is perturbative for small cutoffs. In contrast to other precision interactions, the error due to missing many-body forces can be estimated, when V_{low k} and the corresponding three-nucleon force are used in nuclear structure calculations and the cutoff is varied.Comment: 10 pages, 5 figures, talk at INT workshop on Nuclear Forces and the Quantum Many-Body Problem, Seattle, October 200

    Neutrino and axion emissivities of neutron stars from nucleon-nucleon scattering data

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    Neutrino and axion production in neutron stars occurs mainly as bremsstrahlung from nucleon-nucleon (NN) scattering. The energy radiated via neutrinos or axions is typically very small compared to other scales in the two-nucleon system. The rate of emission of such "soft" radiation is directly related to the on-shell NN amplitude, and thereby to the NN experimental data. This facilitates the model-independent calculation of the neutrino and axion radiation rates which is presented here. We find that the resultant rates are a factor of four below earlier estimates based on a one-pion-exchange NN amplitude.Comment: 5 pages, 2 figures, revtex, uses epsfig.sty. Revised version has minor modifications to the text and references, as well as some changes to the numerical results. The conclusions are unchange

    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
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