Biangular Lines Revisited

Abstract

Line systems passing through the origin of the d-dimensional Euclidean space admitting exactly two distinct angles are called biangular. It is shown that the maximum cardinality of biangular lines is at least $$2(d-1)(d-2)$$ 2 ( d - 1 ) ( d - 2 ) , and this result is sharp for $$d\in \{4,5,6\}$$ d ∈ { 4 , 5 , 6 } . Connections to binary codes, few-distance sets, and association schemes are explored, along with their multiangular generalization.