INVESTIGATING THE BPS SPECTRUM OF NONCRITICAL E-N STRINGS

We use the effective action of the E-n non-critical strings to study i ts BPS spectrum for 0 less than or equal to n less than or equal to 8, We show how to introduce mass parameters, or Wilson lines, into the e ffective action, and then perform the appropriate asymptotic expansion s that yield the BPS spectrum, The result is the E-n character expansi on of the spectrum, and is equivalent to performing the mirror map on a Calabi-Yau with up to nine Kahler moduli. This enables a much more d etailed examination of the E-n structure of the theory, and provides e xtensive checks on the effective action description of the non-critica l string, We extract some universal (E-n-independent) information conc erning the degeneracies of BPS excitations. (C) 1997 Published by Else vier Science B.V.