New source of charge-symmetry violation in the nucleon-nucleon system

Abstract

Within the framework of the cloudy bag model we show that the small difference of up- and down-quark masses leads to a small increase in the ${\pi }^0\mathrm{nn}$ coupling constant relative to ${\pi }^0\mathrm{pp}$. There may be many experimental consequences of this observation but, as an example, $\left|a_{\mathrm{nn}}\mathrm{}\right|-\left|\mathrm{}{a}_{\mathrm{pp}}\right|\cong 0.3$ fm because of this effect.