文摘
We classify the simple even lattices of square free level and signature \((2,n), n \ge 4\) . A lattice is called simple if the space of cusp forms of weight \(1+n/2\) for the dual Weil representation of the lattice is trivial. For a simple lattice every formal principal part obeying obvious conditions is the principal part of a vector valued modular form. Using this, we determine all holomorphic Borcherds products of singular weight (arising from vector valued modular forms with non-negative principal part) for the simple lattices. We construct the corresponding vector valued modular forms by eta products and compute expansions of the automorphic products at different cusps.