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 ∣
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.
119880793
Optimized perturbation theory in the Gross-Neveu model
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.
117188910
The renormalization‐scheme‐dependence problem and its solution
I explain, in ‘‘uncompromising’’ terms, the solution to the renormalization‐scheme‐dependence problem.
120633210
Comments on the Sterman-Weinberg jet formula
Abstract A simple derivation of the Sterman-Weinberg jet formula (the QCD perturbation theory formula for the 2-jet cross section) is described. Conditions on the jet parameters ϵ and δ for this formula to be applicable are discussed and the corrections to the formula up to O(ϵ 2 ), O(δ 2 ) are presented.
118367914
Unrestricted Skyrme-tensor time-dependent Hartree-Fock model and its application to the nuclear response from spherical to triaxial nuclei
The nuclear time-dependent Hartree-Fock model formulated in three-dimensional space, based on the full standard Skyrme energy density functional complemented with the tensor force, is presented. Full self-consistency is achieved by the model. The application to the isovector giant dipole resonance is discussed in the linear limit, ranging from spherical nuclei (16O and 120Sn) to systems displaying axial or triaxial deformation (24Mg, 28Si, 178Os, 190W and 238U). Particular attention is paid to the spin-dependent terms from the central sector of the functional, recently included together with the tensor. They turn out to be capable of producing a qualitative change on the strength distribution in this channel. The effect on the deformation properties is also discussed. The quantitative effects on the linear response are small and, overall, the giant dipole energy remains unaffected. Calculations are compared to predictions from the (quasi)-particle random-phase approximation and experimental data where available, finding good agreement
121521132
Nuclear Matter and Neutron Star Properties Calculated with a Separable Monopole Interaction
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.
15682173
Density distributions of superheavy nuclei
We employed the Skyrme-Hartree-Fock model to investigate the density distributions and their dependence on nuclear shapes and isospins in the superheavy mass region. Different Skyrme forces were used for the calculations with a special comparison to the experimental data in Pb-208. The ground-state deformations, nuclear radii, neutron-skin thicknesses and alpha-decay energies were also calculated. Density distributions were discussed with the calculations of single-particle wave functions and shell fillings. Calculations show that deformations have considerable effects on the density distributions, with a detailed discussion on the (292)120 nucleus. Earlier predictions of remarkably low central density are not supported when deformation is allowed for.
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.