title: Counting rule for Nambu-Goldstone modes in nonrelativistic systems.
abstract: The counting rule for Nambu-Goldstone modes is discussed using Mori's projection operator method in nonrelativistic systems at zero and finite temperatures. We show that the number of Nambu-Goldstone modes is equal to the number of broken charges, Q(a), minus half the rank of the expectation value of [Q(a), Q(b)].
authors.affiliation: Mathematical Physics Laboratory, RIKEN Nishina Center, Saitama 351-0198, Japan.
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Hidaka