Light-meson masses in an unquenched quark model

TL;DR

This study calculates light meson masses using an unquenched quark model that includes both quark-antiquark and four-quark components, addressing issues in traditional models by modifying the quark-pair creation mechanism.

Contribution

It introduces modifications to the $^3P_0$ quark-pair creation operator to produce more realistic meson mass shifts in an unquenched quark model.

Findings

Mass shifts are reduced to 10-20% of hadron masses with the new model.

Large negative mass shifts in traditional models are mitigated.

The approach provides a more valid description of light meson masses.

Abstract

We perform a coupled-channels calculation of the masses of light mesons with the quantum numbers $IJ^{P=-}$, $(I,J)=0,1$, by including $q\bar{q}$ and $(q\bar{q})^2$ components in a nonrelativistic chiral quark model. The coupling between two- and four-quark configurations is realized through a $^3P_0$ quark-pair creation model. With the usual form of this operator, the mass shifts are large and negative, an outcome which raises serious issues of validity for the quenched quark model. Herein, therefore, we introduce some improvements of the $^3P_0$ operator in order to reduce the size of the mass shifts. By introducing two simple factors, physically well motivated, the coupling between $q\bar{q}$ and $(q\bar{q})^2$ components is weakened, producing mass shifts that are around 10-20% of hadron bare masses.