Magnetoresistance of the Double-Exchange Model in Infinite Dimension

Double-exchange model in infinite dimension is studied as the strong Hund's coupling limit $J\to\infty$ of the Kondo lattice model. Several quantities such as Green's function and the d.c.\ conductivity are calculated in analytical forms. Magnetoresistance in lightly doped (La,Sr)MnO$_3$ is reproduced very well.