Lorentzian polynomials from polytope projections

Abstract

Lorentzian polynomials, recently introduced by Brändén and Huh, generalize the notion of log-concavity of sequences to homogeneous polynomials whose supports are integer points of generalized permutahedra. Brändén and Huh show that normalizations of polynomials equaling integer point transforms of generalized permutahedra are Lorentzian; moreover, normalizations of certain projections of integer point transforms of generalized permutahedra with zero-one vertices are also Lorentzian. Taking this polytopal perspective further, we show that normalizations of certain projections of integer point transforms of flow polytopes (which, before projection, are not Lorentzian), are also Lorentzian.

14 pages