  A Littelmann path model is constructed for crystals pertaining to a not
necessarily symmetrizable Borcherds-Cartan matrix. Here one must overcome
several combinatorial problems coming from the imaginary simple roots. The main
results are an isomorphism theorem and a character formula of
Borcherds-Kac-Weyl type for the crystals. In the symmetrizable case, the
isomorphism theorem implies that the crystals constructed by this path model
coincide with those of Jeong, Kang, Kashiwara and Shin obtained by taking the
limit at q=0 in the quantized enveloping algebra.

Representation Theory