Non Self-conjugate Strings, Singular Strings and Rigged Configurations   in the Heisenberg Model
  We observe a different type of complex solutions in the isotropic spin-1/2 Heisenberg chain starting from N=12, where the central rapidity of some of the odd-length strings becomes complex making not all the strings self-conjugate individually. We show that there are at most (N-2)/2 singular solutions for M=4, M=5 down-spins and at most (N^2-6N+8)/8 singular solutions for M=6, M=7 down-spins in an even-length chain with N \geq 2M. Correspondence of the non self-conjugate string solutions and the singular string solutions to the rigged configurations has also been shown. 
Tetsuo Deguchi, Pulak Ranjan Giri
hep-th cond-mat.str-el math-ph math.MP nlin.SI