17579087
The Banks-Zaks Expansion and "Freezing" in Perturbative QCD
The recent calculation of the four-loop beta function in QCD provides further evidence that the Banks-Zaks expansion in 16half-n_f is sufficiently well behaved to be useful even for n_f=2 light flavours. This expansion inherently predicts "freezing" of the QCD couplant at low energies as a perturbative effect. We consider the e+e- and Bjorken-sum-rule cases as examples.
36677369
Spin transfer in hyperon production.
The polarization transfer coefficient DNN provides a sensitive test of present quark recombination models of hyperon production. In this paper we present preliminary results from a recent measurement of DNN in the reaction p↘Be → Λ↘X at the Brookhaven AGS using the newly available polarized proton beam at incident momenta of 13 and 18 GeV/c.
120633210
Comments on the Sterman-Weinberg jet formula
Abstract A simple derivation of the Sterman-Weinberg jet formula (the QCD perturbation theory formula for the 2-jet cross section) is described. Conditions on the jet parameters ϵ and δ for this formula to be applicable are discussed and the corrections to the formula up to O(ϵ 2 ), O(δ 2 ) are presented.
117188910
The renormalization‐scheme‐dependence problem and its solution
I explain, in ‘‘uncompromising’’ terms, the solution to the renormalization‐scheme‐dependence problem.
119880793
Optimized perturbation theory in the Gross-Neveu model
119665196
Sense and nonsense in the renormalization-scheme-dependence problem
Abstract I discuss in detail the issues involved in the renormalization-scheme-dependence problem in perturbative QCD. The problem is not to find a good universal scheme; nor is it a question of how to make coefficients small. The problem is that finite-order results depend on the choice of scheme, even though it is “arbitrary” (in that the exact result is scheme independent). Only the “principle of minimal sensitivity” approach gets to the heart of the problem, and attempts to reconcile this contradiction. I explain the motivation for this approach, defend it against recent criticisms, and explain to what extent it provides a solution to the problem.
14447155
Charge radius isotope shift across the N=126 shell gap.
We revisit the problem of the kink in the charge radius shift of neutron-rich even isotopes near the N=126 shell closure. We show that the ability of a Skyrme force to reproduce the isotope shift is determined by the occupation of the neutron 1i(11/2) orbital beyond N=126 and the corresponding change it causes to deeply-bound protons orbitals with a principal quantum number of 1. Given the observed position of the single-particle energies, one must either ensure occupation is allowed through correlations, or not demand that the single-particle energies agree with experimental values at the mean-field level.
5363509
Role of boundary conditions in dynamic studies of nuclear giant resonances and collisions.
Absorbing boundary conditions are often employed in time-dependent mean-field calculations to cope with the problem of emitted particles which would otherwise return back onto the system and falsify the dynamical evolution. We scrutinize two widely used methods, imaginary potentials and gradual attenuation by a mask function. To that end, we consider breathing oscillations of a nucleus computed on a radial one-dimensional grid in coordinate space. The most critical test case is the computation of resonance spectra in the (linear) domain of small amplitude motion. Absorbing bounds turn out to provide a reliable alternative to fully fledged continuum random phase approximation (RPA) calculations, although rather large absorbing bounds are required to simulate reliably well continuum conditions. We also investigate the computation of observables in the nonlinear domain. This regime turns out to be less demanding. Smaller absorbing margin suffice to achieve the wanted absorption effect.
17867643
Shape Evolution in the Neutron-Rich Tungsten Region
Recent experimental data on the low-lying states in {sup 190}W show a change in the E(4{sub 1}{sup +})/E(2{sub 1}{sup +}) behavior compared to less neutron-rich neighbors. Self-consistent axially-deformed Hartree-Fock calculations, using a separable monopole interaction, of nuclei in the vicinity of {sup 190}W are performed to systematically examine the evolution of ground state quadrupole deformations. It is found that the neutron number N=116 causes a coexistence of oblate and prolate shapes, with a weak dependence on proton number, thereby hindering the development of these isotones as well-deformed rotors.
14658401
Dipole giant resonances in deformed heavy nuclei
The spectral distribution of isovector dipole strength is computed using the time-dependent Skyrme-Hartree-Fock method with subsequent spectral analysis. The calculations are done without any imposed symmetry restriction, allowing any nuclear shape to be dealt with. The scheme is used to study the deformation dependence of giant resonances and its interplay with Landau fragmentation (owing to 1ph states). Results are shown for the chain of Nd isotopes, superdeformed {sup 152}Dy, triaxial {sup 188}Os, and {sup 238}U.
14308528
Mass dispersions from giant dipole resonances using the Balian–Vénéroni variational approach
The Balian–Veneroni variational approach has been implemented using a three-dimensional time-dependent Hartree–Fock (TDHF) code with realistic Skyrme interactions and used to investigate the mass dispersions from giant dipole resonances in 32S and 132Sn decaying through particle emission. The fluctuations obtained are shown to be quantitatively larger than the standard TDHF results.