# Advances in Nuclear Physics: Volume 13 by A. W. Thomas (auth.), J. W. Negele, Erich Vogt (eds.)

By A. W. Thomas (auth.), J. W. Negele, Erich Vogt (eds.)

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1). 0 -2/3 -1/3 From DeG + 75. 3. The Axial Current The accurate prediction of the axial coupling constant, gA, is certainly one of the major successes of the MIT bag model. It is a direct consequence of the correct, relativistic treatment of the quarks. In view of the importance of the axial current in our later development of a chiral-symmetric model of hadronic structure, we shall discuss the calculation of gA in detail. First, we briefly review the standard phenomenological treatment of weak interactions.

105) is then linear in 0: as shown in Fig. 4. Clearly, if either g or qq is large enough, it is possible that the minimum energy will occur at a = 0 rather than a = a v ' In this region the quark and sigma fields obey coupled linear equations (Ci . 108) k where a o is the time-independent, mean a-field. Same typical solutions of these equations are plotted in Fig. 5. 'IfJ eventually vanishes as r - * 00 so that asymptotically areturns to its usual vacuum expectation value. Inside, however, a is very small and the quarks are essentially free (a(O) s::::!

Nonzero Quark Masses If the strange quark was massless, the other members of the nuc1eon octet, namely the E, A, and 8, would all be degenerate with the nuc1eon. From prebag phenomenology one might expect that giving the strange quark a mass would solve the problem and that is indeed the case. We might add that there is presently no understanding of the quark mass problem; these can only be regarded as free parameters of the theory (see, however, CT 74, Fri 77, Gun+ 77, Wei 77). 9). Inside the bag we then have (Bar 75, DeG+ 75) (- i"y .