16803754
Self-consistent description of dysprosium isotopes in the doubly midshell region
Dy in the framework of density-dependent Hartree-Fockcalculations with BCS pairing correlations. Further deformed Hartree-Fock with angular-momentum projectionand band-mixing calculations explore the yrast spectra of the nuclides approaching the neutron midshell.Predictions of high-K states in the doubly midshell nucleus
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.
121929671
Nuclear matter and neutron star properties calculated with the skyrme interaction
The effective Skyrme interaction has been used extensively in mean-field models for several decades and many different parametrizations of the interaction have been proposed. All of these give similar agreement with the experimental observables of nuclear ground states as well as with the properties of infinite symmetric nuclear matter at the saturation density n0. However, when applied over a wider range of densities (up to ∼3n0) they predict widely varying behavior for the observables of both symmetric and asymmetric nuclear matter. A particularly relevant example of naturally occurring asymmetric nuclear matter is the material of which neutron stars are composed. At around nuclear matter density, this can be well represented as a mixture of neutrons, protons, electrons, and muons (n+p+e+μ matter) in β-equilibrium, and these densities turn out to be the key ones for determining the properties of neutron-star models with masses near to the widely used “canonical” value of 1.4M⊙. By constructing equations of state for neutron-star matter using the different Skyrme parametrizations, calculating corresponding neutron-star models and then comparing these with observational data, an additional constraint can be obtained for the values of the Skyrme parameters. Such a constraint is particularly relevant because the parametrizations are initially determined by fitting to the properties of doubly closed-shell nuclei and it is an open question how suitable they then are for nuclei with high values of isospin, such as those at the neutron drip-line and beyond. The neutron-star environment provides an invaluable testing ground for this. We have carried out an investigation of 87 different Skyrme parametrizations in order to examine how successful they are in predicting the expected properties of infinite nuclear matter and generating plausible neutron-star models. This is the first systematic study of the predictions of the various Skyrme parametrizations for the density dependence of the characteristic observables of nuclear matter; the density dependence of the symmetry energy for β-equilibrium matter turns out to be a crucial property for indicating which Skyrme parameter sets will apply equally well for finite nuclei and for neutron-star matter. Only 27 of the 87 parametrizations investigated pass the test of giving satisfactory neutron-star models and we present a list of these.
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.
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)
6712657
FURTHER LATTICE EVIDENCE FOR A LARGE RESCALING OF THE HIGGS CONDENSATE
Using a high-statistics lattice simulation of the Ising limit of (λΦ4)4 theory, we have measured the susceptibility and propagator in the broken phase. We confirm our earlier finding of a discrepancy between the field rescaling implied by the propagator data and that implied by the susceptibility. The discrepancy becomes worse as one goes closer to the continuum limit; thus, it cannot be explained by residual perturbative effects. The data are consistent with an unconventional description of symmetry breaking and "triviality" in which the rescaling factor for the finite-momentum fluctuations tends to unity, but the rescaling factor for the condensate becomes larger and larger as one approaches the continuum limit. In the standard model this changes the interpretation of the Fermi-constant scale and its relation to the Higgs mass.
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.
122449480
An introduction to the renormalization-scheme ambiguity of perturbation theory
2592138
Vacuum Hydrodynamics
The Higgs vacuum – with its constant background field – is not ‘empty’ but is a kind of medium. Any ordinary medium, viewed at sufficiently long length scales, has a hydrodynamic description and can propagate sound waves. The vacuum medium is unusual; the speed of sound is formally infinite and there is no linear sound-wave regime. Instead, long-wavelength disturbances are described by some intrinsically nonlinear hydrodynamic equations. The purpose of this Letter is more to raise questions than to answer them. The premise is that the vacuum of the Standard Model, with its non-zero background field 〈φ〉 6 = 0, is a kind of medium [1]. The only other assumption is that a “mean free path” scale λmfp exists and is finite. (While λmfp must be long compared to particle-physics length scales, whether it is a millimeter or an astronomical or cosmological scale is another question.) My point is that at sufficiently long length scales L ≫ λmfp any fluid medium can be described by hydrodynamics (see, for example, [2, 3, 4]). That is, it can be treated as an ideal fluid up to corrections of order λmfp/L [5]. In the hydrodynamic regime the only relevant modes are those directly linked to conservation laws. In particular, energy-momentum conservation equations lead directly to longitudinal pressure waves — sound waves. Let us briefly review the derivation. The energy-momentum tensor for a perfect fluid has the form [c = 1, gμν = diag(1,−1,−1,−1)] T μν = (E + P )uu − Pg , (1) where E is the energy density, P is the pressure, and uμ is the flow 4-velocity u = (u0, ~u), with u 2 0 − ~u = 1. (2) The energy-momentum conservation equation ∂μT μν = 0 yields ∂ ∂t [ (E + P )u0 ] + ∂ ∂xj [ (E + P )uu0 ] − ∂P ∂t = 0, (3) ∂ ∂t [ (E + P )u0u ] + ∂ ∂xj [ (E + P )uu ] + ∂P ∂xi = 0. (4) Consider a small perturbation about a static, homogeneous equilibrium state E0, P0, ~u = 0. If the pressure variation δP and the energy variation δE are sufficiently small they must be proportional, with their ratio fixed by the thermodynamic derivative ∂P ∂E ∣
119042764
Resolution of the lambda phi**4 puzzle and a 2-TeV Higgs boson
We argue that massless (lambda Phi^4)_4 is "trivial" without being entirely trivial. It has a non-trivial effective potential which leads to spontaneous symmetry breaking, but the particle excitations above the broken vacuum are non-interacting. The key to this picture is the realization that the constant background field (the mode with zero 4-momentum) renormalizes differently from the fluctuation field (the finite-momentum modes). This picture reconciles rigorous results and lattice calculations with one-loop and Gaussian-approximation analyses. Because of "triviality", these latter two methods should be effectively exact. Indeed, they yield the same renormalized effective potential and the same relation m_h^2 = 8 pi^2 v^2 between the particle mass and the physical vacuum expectation value. This relation predicts a Higgs mass m_h about 2 TeV in the standard model. The non-interacting nature of the scalar sector implies, by the equivalence theorem, that Higgs and gauge bosons interact only weakly, through their gauge and Yukawa couplings.