R. L. Wilson | Searcharxiv

arXiv1995

On Hopf algebras and the elimination theorem for free Lie algebras

The elimination theorem for free Lie algebras, a general principle which describes the structure of a free Lie algebra in terms of free Lie subalgebras, has been recently used by E. Jurisich to prove that R. Borcherds' ``Monster Lie algebra'' has certain large free Lie subalgebras, illuminating part of Borcherds' proof that the moonshine module vertex operator algebra obeys the Conway-Norton conjectures. In the present expository note, we explain how the elimination theorem has a very simple and natural generalization to, and formulation in terms of, Hopf algebras. This fact already follows from general results contained in unpublished 1972 work, unknown to us when we wrote this note, of R. Block and P. Leroux.

q-alg↗

arXiv1994

Realizations of the Monster Lie algebra

We study aspects of the theory of generalized Kac-Moody Lie algebras (or Borcherds algebras) and their standard modules. It is shown how such an algebra with no mutually orthogonal imaginary simple roots, including Borcherds' Monster Lie algebra $\frak m$, can be naturally constructed from a certain Kac-Moody subalgebra and a module for it. We observe that certain generalized Verma (induced) modules for generalized Kac-Moody algebras are standard modules and hence irreducible. In particular, starting from the moonshine module for the Monster group $M$, we construct a certain $\{frak gl}_2$- and $M$-module, the tensor algebra over which carries a natural structure of irreducible module for $\frak m$, which is realized as an explicitly prescribed $M$-covariant Lie algebra of operators on this tensor algebra. The existence of large free subalgebras of $\frak m$ is further exploited to provide a simplification of Borcherds' proof of the Conway-Norton conjectures for the McKay-Thompson series of the moonshine module. The coefficients of these series are shown to satisfy natural recursion relations (replication formulas) equivalent to, but different from, those obtained by Borcherds.

hep-th↗