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The Monster Lie algebra $\frak m $, which admits an action of the Monster finite simple group $\mathbb{M}$, was introduced by Borcherds as part of his work on the Conway--Norton Monstrous Moonshine conjecture. Here we construct an analog~$G(\frak m)$ of a Lie group or Kac--Moody group, associated to~$\frak m$. The group~$G(\frak m)$ is given by generators and relations, analogous to a construction of a Kac--Moody group given by Tits. In the absence of local nilpotence of the adjoint representation of $\frak m$, we introduce the notion of pro-summability of an infinite sum of operators. We use this to construct a complete pro-unipotent group $\Uhp$ of automorphisms of a completion $\widehat{\mathfrak{m}}=\frak n^-\ \oplus\ \frak h\ \oplus\ \widehat{\frak n}^+$ of~$\mathfrak{m}$, where $\widehat{\frak n}^+$ is the formal product of the positive root spaces of $\frak m$. The elements of $\widehat{U}^+$ are pro-summable infinite series with constant term 1. The group $\widehat{U}^+$ has a subgroup~$\widehat{U}^+_\text{im}$, which is an analog of a complete unipotent group corresponding to the positive imaginary roots of~$\frak m$.We construct analogs $\text{Exp}: \widehat{\mathfrak{n}}^+\to\widehat{U}^+$ and $\text{Ad} :\widehat{U}^+ \to \Aut(\widehat{\frak{n}}^+)$ of the classical exponential map and adjoint representation. We show that the action of $\mathbb{M}$ on $\mathfrak m$ induces an action of~$\mathbb{M}$ on~$\widehat{\frak m}$, and that this in turn induces an action of $\mathbb{M}$ on~$\widehat{U}^+$. We also show that the action of $\mathbb{M}$ on $\widehat{\mathfrak n}^+$ is compatible with the action of $\widehat{U}^+$ on $\widehat{\mathfrak n}^+$.

The Monster Lie algebra $\mathfrak m$ is a quotient of the physical space of the vertex algebra $V=V^\natural\otimes V_{1,1}$, where $V^\natural$ is the Moonshine module vertex operator algebra of Frenkel, Lepowsky, and Meurman, and $V_{1,1}$ is the vertex algebra corresponding to the rank 2 even unimodular lattice $\textrm{II}_{1,1}$. We construct vertex algebra elements that project to bases for subalgebras of $\mathfrak m$ isomorphic to $\mathfrak{gl}_{2}$, corresponding to each imaginary simple root, denoted $(1,j)$ for $j>0$. Our method requires the existence of pairs of primary vectors in $V^{\natural}$ satisfying some natural conditions, which we prove. We show that the action of the Monster finite simple group $\mathbb{M}$ on the subspace of primary vectors in $V^\natural$ induces an $\mathbb{M}$-action on the set of $\mathfrak{gl}_2$ subalgebras corresponding to a fixed imaginary simple root. We use the generating function for dimensions of subspaces of primary vectors of $V^\natural$ to prove that this action is non-trivial for small values of $j$., Comment: Final version, to appear in the Journal of Pure and Applied Algebra

We describe various approaches to constructing groups which may serve as Lie group analogs for the monster Lie algebra of Borcherds., Comment: To appear in Letters in Math. Phys

The three point current algebra $\mathfrak{sl}(2,\mathcal R)$ where $\mathcal R=\mathbb C[t,t^{-1},u\,|\,u^2=t^2+4t ]$ and three-point Virasoro algebra both act on a previously constructed Fock space. In this paper we prove that the semi-direct product, i.e. the gauge algebra acts on the Fock space as well., Comment: arXiv admin note: text overlap with arXiv:1303.6973, arXiv:1502.04102, arXiv:1309.7316

We define a 3-point Virasoro algebra, and construct a representation of it on a previously defined Fock space for the 3-point affine algebra $\mathfrak{sl}(2, \mathcal R) \oplus\left( \Omega_{\mathcal R}/d{\mathcal R}\right)$., Comment: arXiv admin note: text overlap with arXiv:1303.6973, arXiv:1309.7316

We provide formulas for computing the cocycles on a 3-point Witt algebra Der(R), using an isomorphism between two 3-point algebras Der(R) and Der(S), where the cocycle is already defined. These cocycles can be used to construct universal central extensions and the 3-point Virasoro, which are useful for the representation theory of a 3-point current algebra. The computations determining the cocycles on Der(R) involve elegant applications of the Chu-Vandermonde convolution and other identities for sums of binomial coefficients.

Using the classical Lazard's elimination theorem, we obtain a decomposition theorem for Lie algebras defined by generators and relations of a certain type. This is a preprint version of the paper appearing in Communications in Algebra Volume 32, Issue 10, 2004.

It is shown that any generalized Kac-Moody Lie algebra g that has no mutually orthogonal imaginary simple roots can be written as the vector space direct sum of a Kac-Moody subalgebra and subalgebras isomorphic to free Lie algebras over certain modules for the Kac-Moody subalgebra. Also included is a detailed discussion of Borcherds' construction of the Monster Lie algebra from a vertex algebra and an elementary proof of Borcherds' theorem relating Lie algebras with `an almost positive definite bilinear form' to generalized Kac-Moody algebras. (Preprint version 1996), Comment: Preprint version (from 1996) of the published paper

We construct a new representation of the infinite rank Lie algebra $a_{\infty}$ with central charge $c=1$ on the Fock space $\mathit{F^{\otimes \frac{1}{2}}}$ of a single neutral fermion. We show that $\mathit{F^{\otimes \frac{1}{2}}}$ is a direct sum of irreducible integrable highest weight modules for $a_{\infty}$ with central charge $c=1$. We prove that as $a_{\infty}$ modules $\mathit{F^{\otimes \frac{1}{2}}}$ is isomorphic to the Fock space $\mathit{F^{\otimes 1}}$ of the charged free fermions. As a corollary we obtain the decompositions of certain irreducible highest weight modules for $d_{\infty}$ with central charge $c=\frac{1}{2}$ into irreducible highest weight modules for $d_{\infty}$ with central charge $c=1$., Comment: Contribution to the XXIst International Conference on Integrable Systems and Quantum symmetries (ISQS-21), Prague, Czech Republic, 2013

In this paper we study fields satisfying $N$-point locality and their properties. We obtain residue formulae for $N$-point local fields in terms of derivatives of delta functions and Bell polynomials. We introduce the notion of the space of descendants of $N$-point local fields which includes normal ordered products and coefficients of operator product expansions. We show that examples of $N$-point local fields include the vertex operators generating the boson-fermion correspondences of type B, C and D-A. We apply the normal ordered products of these vertex operators to the setting of the representation theory of the double-infinite rank Lie algebras $b_{\infty}, c_{\infty}, d_{\infty}$. Finally, we show that the field theory generated by $N$-point local fields and their descendants has a structure of a twisted vertex algebra., Comment: long version with additional details and proofs

We describe the universal central extension of the three point current algebra $\mathfrak{sl}(2,\mathcal R)$ where $\mathcal R=\mathbb C[t,t^{-1},u\,|\,u^2=t^2+4t ]$ and construct realizations of it in terms of sums of partial differential operators., Comment: arXiv admin note: text overlap with arXiv:0902.1273. This version has a correction to a scalar in Cor 2.3. The representations of the algebra are unaffected

The authors construct a Wakimoto type realization of toroidal $\mathfrak{sl}_{n+1}$ The representation constructed in this paper utilizes non-commuting differential operators acting on the tensor product of two polynomial rings in many commuting variables., Comment: 65 pages

We give a summary of R. Borcherds' solution (with some modifications) to the following part of the Conway-Norton conjectures: Given the Monster simple group and Frenkel-Lepowsky-Meurman's moonshine module for the group, prove the equality between the graded characters of the elements of the Monster group acting on the module (i.e., the McKay-Thompson series) and the modular functions provided by Conway and Norton. The equality is established using the homology of a certain subalgebra of the monster Lie algebra, and the Euler-Poincare identity., Comment: First presented at Moonshine - the first quarter century and beyond.A Workshop on the Moonshine Conjectures and Vertex Algebras ICMS, 5 - 13 July 2004

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., Comment: 32 pages