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.
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
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.
14288023
HYDRODYNAMICS OF THE VACUUM
Hydrodynamics is the appropriate "effective theory" for describing any fluid medium at sufficiently long length scales. This paper treats the vacuum as such a medium and derives the corresponding hydrodynamic equations. Unlike a normal medium the vacuum has no linear sound-wave regime; disturbances always "propagate" nonlinearly. For an "empty vacuum" the hydrodynamic equations are familiar ones (shallow water-wave equations) and they describe an experimentally observed phenomenon — the spreading of a clump of zero-temperature atoms into empty space. The "Higgs vacuum" case is much stranger; pressure and energy density, and hence time and space, exchange roles. The speed of sound is formally infinite, rather than zero as in the empty vacuum. Higher-derivative corrections to the vacuum hydrodynamic equations are also considered. In the empty-vacuum case the corrections are of quantum origin and the post-hydrodynamic description corresponds to the Gross–Pitaevskii equation. We conjecture the form of the post-hydrodynamic corrections in the Higgs case. In the (1+1)-dimensional case the equations possess remarkable "soliton" solutions and appear to constitute a new exactly integrable system.
123053533
Scale-scheme ambiguities in the Brodsky-Lepage-Mackenzie procedure
Abstract The recently proposed method of Brodsky, Lepage and Mackenzie for “eliminating scale ambiguities in perturbative QCD” yields different results in different renormalization schemes. We show that one cannot make a scheme-independent separation of fermion loop effects from other types of higher-order correction. The case of ϒ decay is discussed particularly.
118692296
Applying Optimized Perturbation Theory to QCD at Low Energies
We discuss the use of the optimization procedure based on the Principle of Minimal Sensitivity to the third-order calculation of {\mbox{${R_{e^+e^-}}$}}. The effective coupling constant remains finite allowing us to apply the Poggio-Quinn-Weinberg smearing method down to energies below 1 GeV, where we find good agreement between theory and experiment. The couplant freezes to a value of $\alpha_s/\pi = 0.26$ at zero energy which is in remarkable concordance with values obtained phenomenologically.
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.