14158568
How do sound waves in a Bose-Einstein condensate move so fast?
Low-momentum excitations of a dilute Bose-Einstein condensate behave as phonons and move at a finite velocity ${v}_{s}.$ Yet the atoms making up the phonon excitation each move very slowly; ${v}_{a}=p/\stackrel{\ensuremath{\rightarrow}}{m}0.$ A simple ``cartoon picture'' is suggested to understand this phenomenon intuitively. It implies a relation ${v}_{s}{/v}_{a}\ensuremath{\approx}{N}_{\mathrm{ex}},$ where ${N}_{\mathrm{ex}}$ is the number of excited atoms making up the phonon. This relation does indeed follow from the standard Bogoliubov theory.
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.
119880793
Optimized perturbation theory in the Gross-Neveu model
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.
117188910
The renormalization‐scheme‐dependence problem and its solution
I explain, in ‘‘uncompromising’’ terms, the solution to the renormalization‐scheme‐dependence problem.
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.
17867643
Shape Evolution in the Neutron-Rich Tungsten Region
Recent experimental data on the low-lying states in {sup 190}W show a change in the E(4{sub 1}{sup +})/E(2{sub 1}{sup +}) behavior compared to less neutron-rich neighbors. Self-consistent axially-deformed Hartree-Fock calculations, using a separable monopole interaction, of nuclei in the vicinity of {sup 190}W are performed to systematically examine the evolution of ground state quadrupole deformations. It is found that the neutron number N=116 causes a coexistence of oblate and prolate shapes, with a weak dependence on proton number, thereby hindering the development of these isotones as well-deformed rotors.
5363509
Role of boundary conditions in dynamic studies of nuclear giant resonances and collisions.
Absorbing boundary conditions are often employed in time-dependent mean-field calculations to cope with the problem of emitted particles which would otherwise return back onto the system and falsify the dynamical evolution. We scrutinize two widely used methods, imaginary potentials and gradual attenuation by a mask function. To that end, we consider breathing oscillations of a nucleus computed on a radial one-dimensional grid in coordinate space. The most critical test case is the computation of resonance spectra in the (linear) domain of small amplitude motion. Absorbing bounds turn out to provide a reliable alternative to fully fledged continuum random phase approximation (RPA) calculations, although rather large absorbing bounds are required to simulate reliably well continuum conditions. We also investigate the computation of observables in the nonlinear domain. This regime turns out to be less demanding. Smaller absorbing margin suffice to achieve the wanted absorption effect.
11864210
Configuration dependence of K-forbidden transition rates from three-quasiparticle isomers
Reduced hindrance factors for K-forbidden E2 transitions from two- and three-quasiparticle isomers in the Aapprox =180 deformed region are compared. Evidence is presented that when all three quasiparticles are of the same nucleon type (proton or neutron) there is a strong dependence of the E2 reduced hindrance factor on the isomer excitation energy.
5450319
GIANT RESONANCES FROM TDHF
A method of calculating giant resonance strength functions using Time-Dependent Hartree-Fock techniques is described. An application to isoscalar giant monopole resonances in spherical nuclei is made, thus allowing a comparison between independent 1-, 2- and 3-Dimensional computer codes.
6132493
Mass Distributions Beyond TDHF
The mass distributions for giant dipole resonances in 32S and 132Sn decaying through particle emission and for deep‐inelastic collisions between 16O nuclei have been investigated by implementing the Balian‐Veneroni variational technique based upon a three‐dimensional time‐dependent Hartree‐Fock code with realistic Skyrme interactions. The mass distributions obtained have been shown to be significantly larger than the standard TDHF results.