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Article

Lorentzian Kac-Moody algebras with Weyl groups of 2-reflections

Proceedings of the London Mathematical Society. 2018. Vol. 116. No. 3. P. 485-533.
Gritsenko V., Nikulin V. V.

We describe a new large  class of  Lorentzian Kac--Moody algebras. For all ranks, we classify 2-reflective hyperbolic lattices $S$ with the group of 2-reflections of finite volume and with a lattice Weyl vector.  They define the corresponding hyperbolic Kac--Moody algebras of restricted arithmetic type which are graded by S. For most of them, we construct Lorentzian Kac--Moody algebras which give their automorphic corrections: they are graded by the S, have the same simple real roots, but their denominator identities are given by automorphic forms with 2-reflective divisors. We give exact constructions of these automorphic forms as Borcherds products and, in some cases, as additive Jacobi liftings.