A nonlinear evolution equation, i psi(t)+psi(xx)-i lambda(psipsi(x)-p
si(x))psi = 0, which we name the chiral nonlinear Schrodinger (CNLS)
equation is studied. The CNLS equation has two kinds of progressive wa
ve solutions; bright soliton for lambda upsilon > 0 and dark soliton f
or lambda upsilon < 0, where upsilon is the velocity of the envelop. T
he bright soliton corresponds to the particle while the dark soliton i
s interpreted as the hole. (C) 1998 Elsevier Science Ltd. All rights r
eserved.