16434094
Skyrme Interaction and Nuclear Matter Constraints
This paper presents a detailed assessment of the ability of the 240 Skyrme interaction parameter sets in the literature to satisfy a series of criteria derived from macroscopic properties of nuclear matter in the vicinity of nuclear saturation density at zero temperature and their density dependence, derived by the liquid-drop model, in experiments with giant resonances and heavy-ion collisions. The objective is to identify those parametrizations which best satisfy the current understanding of the physics of nuclear matter over a wide range of applications. Out of the 240 models, only 16 are shown to satisfy all these constraints. Additional, more microscopic, constraints on the density dependence of the neutron and proton effective mass β-equilibrium matter, Landau parameters of symmetric and pure neutron nuclear matter, and observational data on high- and low-mass cold neutron stars further reduce this number to 5, a very small group of recommended Skyrme parametrizations to be used in future applications of the Skyrme interaction of nuclear-matter-related observables. Full information on partial fulfillment of individual constraints by all Skyrme models considered is given. The results are discussed in terms of the physical interpretation of the Skyrme interaction and the validity of its use in mean-field models. Future work on application of the Skyrme forces, selected on the basis of variables of nuclear matter, in the Hartree-Fock calculation of properties of finite nuclei, is outlined.
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)
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.
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.
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.
122699564
Optimized Perturbation Theory
Conventional perturbation theory gives different results in different renormalization schemes, a problem which is especially serious in quantum chromodynamics (QCD). I propose a theoretical resolution of this ambiguity which uses the full renormalization-group invariance of the theory. The idea is that, in any kind of approximation scheme which does not respect the known invariances of the exact result, the "optimum" approximant is the one that is "most invariant," i.e., least sensitive to variations in the unphysical parameters. I discuss this principle in several examples, including the Halliday-Suranyi expansion for the anharmonic oscillator. Turning to massless field theories, I identify the unphysical variables which label a particular renormalization scheme as the renormalization point $\ensuremath{\mu}$, and the $\ensuremath{\beta}$-function coefficients. I describe how perturbative approximations depend on these unphysical variables, and show how to find the stationary point which represents the "optimum" result. Certain renormalization-scheme invariants, in one-to-one correspondence with the perturbation-series coefficients, arise naturally in the analysis. An application to the $e$,$\ensuremath{\mu}$ magnetic moments in QED provides a partial test of these ideas, with encouraging results. I suggest possible further theoretical developments, and advocate the method as a sound basis for quantitative QCD phenomenology.
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 .
119348427
The lambda Phi^4 Miracle: lattice data and the zero-point potential
Recent lattice data for the effective potential of lambda Phi^4 theory fits the massless one-loop formula with amazing precision. Any corrections are at least 100 times smaller than is reasonable, perturbatively. This is strong evidence for the "exactness conjecture" of Consoli and Stevenson.
16467069
Response to Tarrach's "Mode Dependent Field Renormalization and Triviality"
We respond to Tarrach's criticisms (hep-th/9511034) of our work on lambda Phi^4 theory. Tarrach does not discuss the same renormalization procedure that we do. He also relies on results from perturbation theory that are not valid. There is no "infrared divergence" or unphysical behaviour associated with the zero-momentum limit of our effective action.
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.