118367914
Unrestricted Skyrme-tensor time-dependent Hartree-Fock model and its application to the nuclear response from spherical to triaxial nuclei
The nuclear time-dependent Hartree-Fock model formulated in three-dimensional space, based on the full standard Skyrme energy density functional complemented with the tensor force, is presented. Full self-consistency is achieved by the model. The application to the isovector giant dipole resonance is discussed in the linear limit, ranging from spherical nuclei (16O and 120Sn) to systems displaying axial or triaxial deformation (24Mg, 28Si, 178Os, 190W and 238U). Particular attention is paid to the spin-dependent terms from the central sector of the functional, recently included together with the tensor. They turn out to be capable of producing a qualitative change on the strength distribution in this channel. The effect on the deformation properties is also discussed. The quantitative effects on the linear response are small and, overall, the giant dipole energy remains unaffected. Calculations are compared to predictions from the (quasi)-particle random-phase approximation and experimental data where available, finding good agreement
122193074
The effect of the tensor force on the predicted stability of superheavy nuclei
The effect of the tensor component of the Skyrme effective nucleon-nucleon interaction on the single-particle structure in superheavy elements is studied. A selection of the available Skyrme forces has been chosen and their predictions for the proton and neutron shell closures investigated. The inclusion of the tensor term with realistic coupling strength parameters leads to a small increase in the spin-orbit splitting between the proton 2f7/2 and 2f5/2 partners, opening the Z=114 shell gap over a wide range of nuclei. The Z=126 shell gap, predicted by these models in the absence of the tensor term, is found to be stongly dependent on neutron number with a Z=138 gap opening for large neutron numbers, having a consequent implication for the synthesis of neutron-rich superheavy elements. The predicted neutron shell structures remain largely unchanged by inclusion of the tensor component.
118393197
Single-particle dissipation in TDHF studied from a phase-space perspective
N. Loebl, A. S. Umar, J.A. Maruhn, P.-G. Reinhard, P.D. Stevenson, and V. E., Oberacker Institut fuer Theoretische Physik, Universitaet Frankfurt, D-60438 Frankfurt, Germany Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA Institut fuer Theoretische Physik II, Universitaet Erlangen-Nuernberg, D-91058 Erlangen, Germany and Department of Physics, University of Surrey, Guildford, GU2 7XH, UK (Dated: August 30, 2012)
16956676
Continuum time-dependent Hartree-Fock method for giant resonances in spherical nuclei
This paper deals with the solution of the spherically symmetric time-dependent Hartree-Fock approximation applied in the case of nuclear giant monopole resonances in the small and large amplitude regimes. The problem is spatially unbounded as the resonance state is in the continuum. The practical requirement to perform the calculation in a finite-sized spatial region results in a difficulty with the spatial boundary conditions. Here we propose an absorbing boundary condition scheme to handle the conflict. The derivation, via a Laplace transform method, and implementation is described. The accuracy and efficiency of the scheme is tested and the results presented to support the case that they are a effective way of handling the artificial boundary. © 2013 American Physical Society.
117963510
Mass distributions in a variational model
The time-dependent Hartree-Fock approach may be derived from a variational principle and a Slater Determinant wavefunction Ansatz. It gives a good description of nuclear processes in which one-body collisions dominate and has been applied with success to giant resonances and collisions around the barrier. It is inherently unable to give a good description of two-body observables. A variational principle, due to Balian and Veneroni has been proposed which can be geared to good reproduction of two-body observables. Keeping the Slater Determinant Ansatz, and restricting the two-body observables to be the squares of one-body observables, the procedure can be implemented as a modification of the time-dependent Hartree-Fock procedure. Applications, using the Skyrme effective interaction, are presented for the mass distributions of fragments following de-excitation of the giant dipole resonance in 32 S. An illustration of the method's use in collisions is given.
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.
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.
118692296
Applying Optimized Perturbation Theory to QCD at Low Energies
We discuss the use of the optimization procedure based on the Principle of Minimal Sensitivity to the third-order calculation of {\mbox{${R_{e^+e^-}}$}}. The effective coupling constant remains finite allowing us to apply the Poggio-Quinn-Weinberg smearing method down to energies below 1 GeV, where we find good agreement between theory and experiment. The couplant freezes to a value of $\alpha_s/\pi = 0.26$ at zero energy which is in remarkable concordance with values obtained phenomenologically.
119264999
Optimization of QCD perturbation theory: Results for Re+e− at fourth order
Abstract Physical quantities in QCD are independent of renormalization scheme (RS), but that exact invariance is spoiled by truncations of the perturbation series. “Optimization” corresponds to making the perturbative approximant, at any given order, locally invariant under small RS changes. A solution of the resulting optimization equations is presented. It allows an efficient algorithm for finding the optimized result. Example results for R e + e − = 3 ∑ q i 2 ( 1 + R ) to fourth order (NNNLO) are given that show nice convergence, even down to arbitrarily low energies. The Q = 0 “freezing” behavior, R = 0.3 ± 0.3 , found at third order is confirmed and made more precise; R = 0.2 ± 0.1 . Low-energy results in the MS ¯ scheme, by contrast, show the typical pathologies of a non-convergent asymptotic series.
123053533
Scale-scheme ambiguities in the Brodsky-Lepage-Mackenzie procedure
Abstract The recently proposed method of Brodsky, Lepage and Mackenzie for “eliminating scale ambiguities in perturbative QCD” yields different results in different renormalization schemes. We show that one cannot make a scheme-independent separation of fermion loop effects from other types of higher-order correction. The case of ϒ decay is discussed particularly.
121132984
Hadron-nucleus scattering as a function of nuclear size☆
Abstract High-energy hadron-nucleus collisions, when viewed in terms of nuclear size, exhibit a remarkable simplicity. The data suggest that nuclear matter is extremely opaque to hadrons, and that fast-forward hadrons ( x ≳0.3) arise solely from peripheral collisions. This picture naturally explains why the production ratios of different hadron species are target independent at large x .