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 ${\ensuremath{\pi}}^{0}\mathrm{nn}$ coupling constant relative to ${\ensuremath{\pi}}^{0}\mathrm{pp}$. There may be many experimental consequences of this observation but, as an example, $|{a}_{\mathrm{nn}}|\ensuremath{-}|{a}_{\mathrm{pp}}|\ensuremath{\cong}0.3$ fm because of this effect.