Biquaternions and ADHM Construction of Non-Compact SL(2,C) Yang-Mills   Instantons
  We extend quaternion calculation in the ADHM construction of Sp(1) (=SU(2)) self-dual Yang-Mills (SDYM) instantons to the case of biquaternion. We use the biconjugate operation of biquaternion first introduced by Hamilton to construct the non-compact SL(2,C) k-instantons. The number of moduli for SL(2,C) k-instantons is found to be twice of that of Sp(1), 16k-6. These new SL(2,C) instanton solutions contain the SL(2,C) (M,N) instanton solutions constructed previously as a subset. The structures of singularities or jumping lines of the complete SL(2,C) k=1,2,3 instantons with 10,26,42 moduli parameters are particularly investigated. The existence of singular structures of the SL(2,C) k-instantons is mathematically consistent with recent results of solutions of complex ADHM equations. It may also help to clearify the long standing global singularity problems associated with Backlund transformations of SU(2) instantons. 
Sheng-Hong Lai, Jen-Chi Lee and I-Hsun Tsai
hep-th math-ph math.MP nlin.SI