Speaker
Veljko Dmitrasinovic
(Institute of Physics Belgrade)
Description
The nucleon $\Sigma$ term's large "observed" value (> 55 MeV) has long been interpreted as a sign of hidden strangeness in the nucleon. We have calculated the $\Sigma_{\pi N}$ term on the basis of mixing of chiral multiplets, and using known constraints on the current quark masses $m_{u}^{0}, m_{d}^{0}$ and the flavor-singlet and isostriplet axial couplings. We show that the $[(1,1/2)\oplus (1/2,1)]$ chiral multiplet, that is necessary for the reproduction of the isotriplet axial coupling, makes a contribution enhanced by a factor of $\frac{19}{3}\simeq 6.33$, due to $SU_L(2) \times SU_R(2)$ algebra, that leads to $\Sigma_{\pi N} \geq \left(1 + \frac{16}{3} \sin^2 \theta \right){3 \over 2} \left(m_{u}^{0} + m_{d}^{0}\right) = 60$ MeV, in general accord with ``experimental'' values of $\Sigma_{\pi N}$. The chiral mixing angle $\theta$ is given by $\sin^2\theta = \frac{3}{8}\left(g_A^{(0)} + g_A^{(3)}\right)$, where $g_A^{(0)} = 0.33 \pm 0.08$, or $0.28 \pm 0.16$, and $g_A^{(3)} = 1.267$, are the flavor singlet and the isotriplet axial couplings, respectively. These results show there is no need for $q^4 {\bar q}$ components, and in particular, no need for an $s \bar s$ component in the nucleon.
Primary author
Veljko Dmitrasinovic
(Institute of Physics Belgrade)
