Harmonic oscillator force between heavy quarks

TL;DR

This paper develops a renormalization group approach to derive an effective Hamiltonian for heavy quarkonia in QCD, revealing a harmonic oscillator potential that could aid in understanding quarkonium spectra.

Contribution

It introduces a new method to calculate effective light-front Hamiltonians for heavy quarkonia, including a harmonic oscillator term from gluon exchange effects.

Findings

Derived a Hamiltonian with Coulomb and harmonic oscillator potentials.

Identified a spin-independent harmonic oscillator term with a calculable frequency.

The harmonic oscillator term is largely independent of the gluon mass ansatz.

Abstract

A renormalization group procedure for effective particles is applied to quantum chromodynamics of one flavor of quarks with large mass m in order to calculate light-front Hamiltonians for heavy quarkonia, H_lambda, using perturbative expansion in the coupling constant alpha_lambda. lambda is the renormalization group parameter with the interpretation of an inverse of the spatial size of the color charge distribution in the effective quarks and gluons. The eigenvalue equation for H_lambda couples quark-anti-quark states with sectors of a larger number of constituents. The coupling to states with more than one effective gluon, and interactions in the quark-anti-quark-gluon sector, are removed at the price of introducing an ansatz for the gluon mass, mu^2. The simplified equation is used to evaluate a new Hamiltonian of order alpha_lambda that acts only in the effective quark-anti-quark sector and in the non-relativistic limit turns out to contain the Coulomb term with Breit-Fermi orrections and spin-independent harmonic oscillator term with frequency omega = [(4/3)(alpha_lambda/pi)]^1/2 lambda (lambda/m)^2 (pi/1152)^1/4. The latter originates from the hole excavated in the overlapping quark self-interaction gluon clouds by the exchange of effective gluons between the quarks. The new term is largely independent of the details of mu^2 and in principle can fit into the ball park of phenomenology. The first approximation can be improved by including more terms in H_lambda and solving the eigenvalue equations numerically.