Critical Coupling in (1+1)-Dimensional Light-Front ${\varphi }^4$ Theory. II -effects of non-diagonal interactionof non-diagonal interactions-

Spontaneous symmetry breaking in (1+1)-dimensional ${\varphi }^4$ theory is studied with discretized light-front quantization. Taking effects of non-diagonal interactions into account, the first few terms of the commutation relations $[a_0,a_n]$ are recalculated in the $\mathrm{\hslash }$ expansion. Our result of the critical coupling is still consistent with the equal-time result $22{\mu }^2\mathrm{/}\mathrm{\hslash }\le {\lambda }_{\mathrm{c}\mathrm{r}}\le 55.5{\mu }^2\mathrm{/}\mathrm{\hslash }$. We also have examined effects of regarding the ratio of the bare coupling constant to a renormalized mass as an independent parameter in the $\mathrm{\hslash }$ expansion.