  In order to numerically study electron correlation effects in multi-orbital
systems, we propose a new type of discrete transformation for the exchange
(Hund's coupling) and pair-hopping interactions to be used in the dynamical
mean field theory + quantum Monte Carlo method. The transformation, which is
real and exact, turns out to suppress the sign problem in a wide parameter
region including non-half-filled bands. This enables us to obtain the dominant
pairing symmetry in the double-orbital Hubbard model, which shows that the
spin-triplet, orbital-antisymmetric pairing that exploits Hund's coupling is
stable in a wide region of the band filling.
