Spin Forces Research Articles

Large-scale quantum field theory calculations on supercomputers

Large-scale calculations are used to evaluate the spin forces among quarks, from first principles. Applications to hadronic spectroscopy are discussed.

Spin anisotropy of ferromagnetic slabs and overlayers (invited)

We calculate the spin anisotropy of ferromagnetic monolayers of Fe, Ni, V, and Co. We find the easy direction of magnetization is perpendicular to the plane of the monolayer for Fe and V, but in the plane for Ni and Co. The result for Fe explains why spin splitting but no spin polarization is observed in recent photoemission experiments on Fe monolayers. For thicker ferromagnetic slabs, the depolarization energy will quickly overwhelm the spin anisotropy and force the moment into the plane of the slab. This is illustrated by calculations for thicker slabs of Fe. Preliminary calculations of the anisotropy of a monolayer of Fe on Ag indicate that the Ag must be treated fully relativistically.

Isospin nonconservation in nucleon-nucleon scattering by a color force.

A recently performed high accuracy measurement indicates the existence of a spin and isospin nonconserving force in neutron-proton scattering. One origin of this effect can be the influence of the up and down quark mass difference on the one gluon exchange spin-orbit force. We include this effect in a resonating group calculation, and find that its contribution is very small compared to that conventional meson-exchange forces.

SPIN AND QUARK MASS EFFECTS IN QCD SPECTROSCOPY

Spin forces are flavour dependent. They also induce large effects through chiral breaking. Isospin breaking also can be large. We discuss using QCD methods a variety of effects that are large and can be measured at LEAR.

Electric versus scalar confinement

I show that if 〈 r −1d V shortrange( r)/d r〉 p > 0, 〈 r −1d V conf.( r)/d r〉 p > 0 then within the Fermi-Breit approach the 1 1p 1 masses of the c c and b b systems are bounded by 3558.4 < M(1 1 p 1 suc c ) < 3605 MeV, 9901.2 < M(1 1 p 1 b b ) < 9917 MeV in case forces are generated by electric confinement. On the other hand, if the confining potential generates spin forces by a scalar gluon exchange then I show that M(1 1 p 1 c c ) <3558.4 MeV, M(1 1 p 1 b b < 9901.2 meV so that the measurement of the 1 1 p 1 c c and/or 1 1 p 1 b b masses could decide between these two alternatives.

1,3,5-Trineopentylbenzene and Related 1,3,5-Trialkylbenzenes Containing Groups with Both Steric and Conjugative Effects. 1H NMR Band Shape and 13C Spin Lattice Relaxation Time Measurements and Force Field Calculations.

Dans le cas des (trineopentyl-2,4,6) styrenes le groupe methylvinylique en β-cis est responsable de la haute barriere a la rotation interne (74 kJ mol −1 ) observee. Lorsque le groupe est en position trans la barriere est inferieure a 20 kJ mol −1 . Pour les benzaldehydes et les benzaldehydes imine (N-methyl) la limite superieure de la barriere est inferieure a 20 kJ mol −1

Bag Models of Hadrons

We believe further progress in the bag model must come from a better understanding of QCD. The bag theory is basically a simple model of the vacuum. A ''perturbative'' vacuum of finite extent is found inside the bag, while the ''true'' vacuum is found outside. The formation of the bag can be viewed as a phase change between the two types of vacuum. In what sense does QCD support this view. There have been many recent attempts to characterize the QCD vacuum. Of particular relevance to the bag model is recent work by Hansson et al. They set out to determine the structure of the vacuum wave function by using a variational argument. Their ''trial'' wave function was inspired by the bag model, but their intention was to describe general features of QCD. Their work starts from the realization that with the usual perturbative model of the vacuum a J /sup PC/ = 0/sup + +/ glueball state can be made with m/sup 2/ < 0. This result implies that the simple vacuum is not the true vacuum. A negative squared mass occurs in the simple model, because the spin force between two gluons paired into a color singlet, spinmore » scalar state is strongly attractive. The potential energy of attraction can overcome the kinetic energy needed to create the two gluons. Such a situation was encountered in the calculation of the lightest bag model 0/sup + +/ glueball (C. B. Thorn, unpublished), which leads to a state with m/sup 2/ < 0 when c.m. corrections are included (65). Hansson et al show that the perturbative vacuum can lower its energy by filling up with scalar glueballs. They calculate the energy of glueballs containing two and four gluons and find that the energy of the four-gluon state is higher. Therefore the vacuum energy reaches a minimum when the glueballs start to overlap.« less

Gamow-Teller strength function forZr90: Effects of spin and isospin exchange forces, and ground-state correlations

Shell-model calculations of the Gamow-Teller strength function for $^{90}\mathrm{Zr}$ have been performed utilizing a realistic finite-range two-body interaction in a model space consisting of the $2p$ and $1g$ shells. The effects of admixtures of two-particle two-hole excitations in $^{90}\mathrm{Nb}$, mostly due to the spin and isospin exchange components of the nucleon-nucleon force, are discussed. Ground state correlations in $^{90}\mathrm{Zr}$ are also added via seniority-zero two-proton excitations from the $2p$ shell into the $1{g}_{\frac{9}{2}}$ shell. With the correlations the Gamow-Teller strength function is in good agreement with the experimental results and accounts for essentially all of the observed dispersion of strength. The inclusion of these correlations does not, however, produce either a displacement of Gamow-Teller strength to higher excitation energies, or a significant change in the total strength. Thus, they cannot account for the observed Gamow-Teller quenching. The quenching factor derived by a comparison of our calculated results with experiment is 0.52.NUCLEAR STRUCTURE $^{90}\mathrm{Zr}$ calculated Gamow-Teller strength function. Analyzed contributions from two-particle two-hole admixtures in the $1g$-shell and parent ground-state correlations.

De Sitter and Poincaré gauge-invariant fermion lagrangians and gravity

We present a new fermion lagrangian which possesses exact symmetry under the local de Sitter group. The lagrangian involves new “scale gauge fields” related to the newtonian force and the usual Yang-Mills “phase gauge fields” related to a new “gravitational spin force” between two fermions. Generalization of the usual gauge theory for external symmetry groups is also discussed.

Two-phase measurements of saltating turbulent boundary layer flow

Mean wind and particle speed measurements as functions of heigh were made for a saltating turbulent boundary layer flow. An exponential dependence of particle flux with height above the surface was found independent of windspeed and particle size. Particle-speed distributions as functions of height above the surface were measured for experiments conducted at two ambient pressures: atmospheric pressure and approximately 1% atmospheric pressure. The wind was shown to be a more efficient mover of particles at atmospheric pressure. High-speed motion pictures of saltating ground walnut shells (of diameter 500–1500 μm and density 1.1 g/cm 3) were taken in an environmental wind tunnel to simulate the planetary boundary layer. These experiments verify the existence and magnitude of particle spin rates proposed by White & Schulz (1977). There was remarkable agreement between numerical trajectory solutions, including the spin effect, and the filmed trajectories. An observation was made that not all particles spin exclusively in the vertical longitudinal plane (in the direction of flow). At low pressures (0.6 kPa) the effect of spin forces on the particle's trajectory was shown to have little influence and was verified by a theoretical force ration balance of spin to drag force.

Rigorous inequalities in non-relativistic quantum mechanics with applications to quarkonium spectroscopy

We show that for a concave (convex) potential ( l 2 > l 1 > 0) |R 1 S (0)| 2≷2l 1(l 1(l 1+1)〉 1 r 3 〈 1l 1 ≷2l 2(l 2+1)〉 1 r 3 〈 1l 2 , ∂ ∂m ( 1 m 〉 1 r 3 〈 1l)≷0 , 〉 1 r ν 〈 1 S > 〉 1 r ν 〈 2 S , 〉r ν〈 1 S < 〉r ν〈 2 S . If, in addition, (d 2/d r 2)( rV) > 0, then ( m M ) 1 3 < El 2(M) − El 1(M) El 2(m) − El 1(m) ⩽ M m , (M > m) . Further, if the confining potential V c( r) generates spin forces by an admixture of scalar and vector gluon exchanges, then it is shown that the vector fraction must be less than 0.4. In this case a number of rigorous bounds are derived some of which are M J ψ − M η c > 55 MeV, 3344 < M( 1P c 1) ⩽ 3526.1 MeV , Mϒ − Mη b > 23.6 MeV, Mη′ b − Mη b > 550 MeV , Mψ − Mη′ c > 18 MeV . The possibility of V c( r) generating spin forces by scalar gluon exchange alone is also considered in some detail and it is shown that in this case M( 3P b 2 − M( 3P b 2) < 0.8(M ( 3P b 2)− M( 3P b 0)) , M( 3D c 2) − 2 5 M( 3D c 3) − 3 5 M( 3D c 1) < 12.7 MeV , M( 3P b 1) − M( 3P b 0) < 9 8 (M ϒ − Mη b) .

Spin forces in mesons made up of quarks of different mass

With the help of a variational method we apply the standard Coulomb + Linear potential to the analysis of mesons constructed from quarks of different mass. Fine and hyperfine splittings are discussed, with particular emphasis on their asymptotic behaviour. Striking differences in this behaviour are predicted to occur compared with the case of mesons built up from equal mass quarks, with the spin-orbit mixing force playing here a fundamental role. Such predictions may be tested within the bottom $$(b\bar u)$$ meson family. Our considerations are also extended to the strange and charmed mesons. Our model favours ak(O+) below theK * (1.430), and predicts a partial inversion in the ordering of theP-wave states of the charmed mesons $$(c\bar u)$$ .

Spin forces in harmonic model of confinement

The nonrelativistic expansion of the mass operator of the Leutwyler-Stern covariant oscillator equations supplemented by the short distance gluon exchange contribution has been performed. The resulting operator of the Fermi-Breit type reveals a rich spin—dependent structure which might be suitable for the description of quarkonium. Its energy spectrum of order (v/c)2 is compared to the fully relativistic spectrum of the original mass operator. The differences for higher lying states of charmonium (e.g. ψ′) are as large as 100 MeV, demonstrating the importance of higher-order relativistic effects. The non-relativistic bound state equation with long-range confining and spin-dependent forces and short-distance Coulombic terms is proposed and solved numerically.

Lower bounds on [formula omitted] and Mϒ - Mηb

We prove that for a concave (convex) potential |R 1 S (0)| 2 > (<) 4 〈 1 r 3 〉 1 P and ( ϖ ϖμ )(μ −1 〈1/r 3〉 1 P ) > (<) 0 , from where it follows that M J ψ − M η c > 94.5 MeV in case the confining potential generates spin forces by scalar exchange only. It is further shown that M ϒ − M ηb > 14.7 MeV and [3M( 3 P 2P b ) − 2M( 3 P 0 b − M( 3 P 2 b )] > 20 GeV .

Variational calculations of models of nuclear and neutron matter

We report results of variational calculations of models of nuclear matter in which the nuclear interaction is approximated by a sum of central, spin, isospin and tensor forces. The models are based on realistic potentials such as those of Reid, Bethe-Johnson, Hamada-Johnston, and Gammel-Thaler. The correlation operator in the variational wave function contains central, spin, isospin and tensor terms. We briefly review the Fermi-hypernetted-chain, and single-operator-chain (SOC) methods used to calculate the energy expectation value. The energies obtained for these simple models by various variational and reaction matrix calculations seem to be in reasonable agreement. Results with the SOC approximation for the ν 3 model of neutron matter, in which the interaction has only central and spin components, are also reported. These are in good agreement with the energies obtained by summing multiple operator chains.

Variations on a theme of nuclear matter

The authors review new techniques developed to apply the variational method to the nuclear matter problem. The variational wave function is taken to be ($S{\ensuremath{\Pi}}_{i&lt;j}{\mathrm{F}}_{\mathrm{ij}}$) $\ensuremath{\Phi}$; the correlation operators ${\mathrm{F}}_{\mathrm{ij}}$ can in principle induce central, backflow, spin isospin, tensor, etc. correlations, and $\ensuremath{\Phi}$ is the ideal Fermi gas wave function. The application of diagrammatic cluster expansion and chain summation techniques to calculate expectation values with such wave functions is discussed in detail. The authors also give a brief overview of various other approaches to the calculation of the binding energies of quantum fluids, and a comparison of results for simple systems such ad helium liquids. Results obtained by various methods for simplified models of nuclear matter, which include central, spin, isospin, and tensor forces, have converged significantly in recent months. Results obtained with more realistic models which include the spin-orbit potentials are also discussed. The potential models considered so far either give too little binding or too high equilibrium density.

What do the baryonium data tell us about the nucleon-antinucleon potential?

A phenomenological analysis of the baryonium data is made and it is shown that the form of the NN potential is quite restricted. In the case where spin forces are assumed to be generated by vector exchange a sum rule for p levels follows which predicts the 11p1 level of baryonium around 1820 MeV. Radiative decay widths have also been calculated and are found to be between 20 and 50 keV.

Almost degenerate P-wave charmed-bottom meson multiplet as a test of scalar confinement

We show that if the quarkonium confining potential generates spin forces via scalar exchange, then the P-wave charmed-bottom meson multiplet is almost degenerate. The hyperfine splittings for various non self-conjugate mesons have also been estimated. It is also shown that contrary to the recent claim of Schnitzer the F-type P-meson multiplet is not inverted.

What does the data tell us about the quark-antiquark potential?

In view of the failure of the standard charmonium models to explain ψ−η c and 3 PJ splittings, I consider various possible modifications to these models. In particular, I show that for power-law potentials the spin forces are most likely generated through the admixture of scalar-vector-Pauli moment exchanges and that this model can be tested by measuring the 1p 1 mass. I also show that if instantons really generate a large spin-spin force, then the 1p 1 mass must be as low as 3250–3270 MeV.

Instantons and Spin Forces between Massive Quarks

A generalization of Wilson's loop prescription to include spin is proposed. Instantons are shown to generate a spin-spin interaction between quarks. The large splitting between $\frac{J}{\ensuremath{\psi}}(3100)$ and ${\ensuremath{\eta}}_{c}(2830)$ may, in fact, be dominated by this mechanism and thus may provide a vivid demonstration of the physical effects of instantons. Heuristic arguments are presented which explain the sign and form of the interaction.