Recently my teacher told me that there are many ways of deriving the Gell-Mann-Okubo mass formula by using group representation theory (by using dynamical group etc). Where can I read about these ways?
One place you could look for a rather neat derivation (that I haven't really found elsewhere) is Lecture 38 and 39 from the series that Sidney Coleman gave at Harvard in 1976. The series is available online at the Harvard physics website. He says he learnt that method himself from Smorodinsky (Russian mathematician) at the Dubna conference (probably in the mid sixties). It uses the 33 element of the octet, as well as the co-factor matrix.