Twisted Sector Yukawa Couplings For The ZM×ZN{\bf Z}_M\times {\bf Z}_N Orbifolds

The moduli dependent Yukawa couplings between twisted sectors of ${\bf Z}_M\times {\bf Z}_N$ Coxeter orbifolds are studied.Comment: 40 pages, SUSX-TH-92/1

Yukawa Couplings involving Excited Twisted Sector States for ZN{\bf Z}_N and ZM×ZN{\bf Z}_M\times {\bf Z}_N Orbifolds

We study the Yukawa couplings among excited twist fields which might arise in the low-energy effective field theory obtained by compactifying the heterotic string on ${\bf Z}_N$ and ${\bf Z}_M\times {\bf Z}_N$ orbifolds.Comment: SUSX--TH--93/12, 31 page