332690
The role of non‐spesctator interactions in charm and bottom decays
The role of annihilation and exchange diagrams in charmed messon, Λc+ and B‐meson decays is analyzed.
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.
121312073
Gluon enhancements in charmed-meson decays
We address tests of nonspectator diagrams in charmed-meson decays. In particular, we explore the consequences of a model in which such diagrams are enhanced by the emission of a single gluon. For a lifetime ratio tau(D/sup +/)/tau(D/sup 0/)=5, we predict (i) tau(F/sup +/)/tau(D/sup +/) approx. = 0.6, (ii) an enhanced ..delta..S=0 rate for D/sup +/, (iii) a substantial multipion branching fraction for the F/sup +/, (iv) an F/sup +/ ..-->.. tau/sup +/..nu.. branching fraction of order 10 --20%, and (v) restrictive bounds on the D/sup 0/ ..-->.. K-bar/sup 0/..pi../sup 0/ mode.
119880793
Optimized perturbation theory in the Gross-Neveu model
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.
117188910
The renormalization‐scheme‐dependence problem and its solution
I explain, in ‘‘uncompromising’’ terms, the solution to the renormalization‐scheme‐dependence problem.
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.
14438221
The tensor-kinetic field in nuclear collisions
The role of the tensor terms in the Skyrme interaction is studied for their effect in dynamic calculations where non-zero contributions to the mean-field may arise, even when the starting nucleus, or nuclei are even-even and have no active time-odd potentials in the ground state. We study collisions in the test-bed 16O-16O system, and give a qualitative analysis of the behaviour of the time-odd tensor-kinetic density, which only appears in the mean field Hamiltonian in the presence of the tensor force. We find an axial excitation of this density is induced by a collision.
31581119
The TDHF code Sky3D
The nuclear mean-field model based on Skyrme forces or related density functionals has found widespread application to the description of nuclear ground states, collective vibrational excitations, and heavy-ion collisions. The code Sky3D solves the static or dynamic equations on a three-dimensional Cartesian mesh with isolated or periodic boundary conditions and no further symmetry assumptions. Pairing can be included in the BCS approximation for the static case. The code is implemented with a view to allow easy modifications for including additional physics or special analysis of the results.
17333676
Isoscalar and Isovector Giant Monopole Resonances from a Continuum Hartree-Fock Method
We motivate and summarise some recent results in the application of formally exact boundary conditions in nuclear time-dependent Hartree-Fock calculations, mak- ing use of Laplace transformations to calculate the values of the wave functions at the boundaries. We have realised the method in the case of giant monopole resonances of spherically-symmetric nuclei, and present strength functions of 16 O and 40 Ca using a sim- plified version of the Skyrme force, showing that no artefacts from discretisation occur as contaminatnts
17501117
Cause of the charge radius isotope shift at the $N$=126 shell gap
We discuss the mechanism causing the ‘kink’ in the charge radius isotope shift at the N = 126 shell closure. The occupation of the 1 i 11/2 neutron orbital is the decisive factor for reproducing the experimentally observed kink. We investigate whether this orbital is occupied or not by different Skyrme effective interactions as neutrons are added above the shell closure. Our results demonstrate that several factors can cause an appreciable occupation of the 1 i 11/2 neutron orbital, including the magnitude of the spin-orbit field, and the isoscalar effective mass of the Skyrme interaction. The symmetry energy of the effective interaction has little influence upon its ability to reproduce the kink.