what is meant isospin asymmetry for nuclear matter ?
"Isospin [symmetry] is violated by the fact that the masses of the up and down quarks are different, as well as by their different electric charges.
Because this violation is only a small effect in most processes that involve the strong interactions, isospin symmetry remains a useful calculational tool, and its violation introduces corrections to the isospin-symmetric results."
for more details, see http://en.wikipedia.org/wiki/Asymmetry#Isospin_violation
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