123614631
Pushing nuclei to the extreme
The ancient Greek philosopher Epicurus reportedly said that "atoms come together in different order and position, like the letters which, though they are few, produce innumerable words". Much the same could be said of the way that neutrons and protons form atomic nuclei. The nucleus is at the heart of every atom and makes up essentially all of its mass. Yet there is still a surprising amount we do not know about the behaviour of nuclei.
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.
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)
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.
122752251
Comment on ''An alternative implementation of the 'principle of minimal sensitivity'''
I explain that the difficulties encountered by Wrigley in the preceding paper arise only because he is attempting to find the stationary value of an undefined function.
121158451
Resolution of the renormalisation-scheme ambiguity in perturbative QCD
Abstract Next-to-leading-order QCD predictions depend on the arbitrary choice of renormalisation scheme. I resolve this ambiguity and show how to find the unique, optimum prediction, given the result in some arbitrary, initial scheme.
118504036
Response to Brodsky and Lu's Letter "On the Self-Consistency of Scale-Setting Methods
The claim that the Principle of Minimal Sensitivity is "disfavored" because it does not satisfy certain "self-consistency requirements" is meaningless, and shows a basic misunderstanding of the renormalization-scheme-dependence problem.
18791932
Gaussian effective potential for the U(1) Higgs model
In order to investigate the Higgs mechanism nonperturbatively, we compute the Gaussian effective potential of the U(1) Higgs model (“scalar electrodynamics”). We show that the same simple result is obtained in three different formalisms. A general covariant gauge is used, with Landau gauge proving to be optimal. The renormalization generalizes the “autonomous” renormalization for λϕ4 theory and requires a particular relationship between the bare gauge coupling eB and the bare scalar self-coupling λB. When both couplings are small, then λ is proportional to e4 and the scalar/vector mass-squared ratio is of order e2, as in the classic 1-loop analysis of Coleman and Weinberg. However, as λ increases, e reaches a maximum value and then decreases, and in this “nonperturbative” regime the Higgs scalar can be much heavier than the vector boson. We compare our results to the autonomously renormalized 1-loop effective potential, finding close agreement in the physical predictions. The main phenomenological implication is a Higgs mass of about 2 TeV.