  In 1974 Dashen, Hasslacher and Neveu calculated the leading quantum
correction to the mass of the kink in the scalar $\phi^4$ theory in 1+1
dimensions. The derivation relies on the identification of the perturbations
about the kink as solutions of the Poschl-Teller (PT) theory. They regularize
the theory by placing it in a periodic box, although the kink is not itself
periodic. They also require an ad hoc identification of plane wave and PT
states which is difficult to interpret in the decompactified limit. We rederive
the mass using the kink operator to recast this problem in terms of the PT
Hamiltonian which we explicitly diagonalize using its exact eigenstates. We
normal order from the beginning, rendering our theory finite so that no
compactification is necessary. In our final expression for the kink mass, the
form of the PT potential disappears, suggesting that our mass formula applies
to other quantum solitons.
