Negative type inequalities arise in the study of embedding properties of metric spaces, but they often reduce to intractable combinatorial problems. In this paper we study more quantitative versions of these inequalities involving the so-called
p -negative type gap. In particular, we focus our attention on the class of finite ultrametric spaces which are important in areas such as phylogenetics and data mining. Let
(X,d) be a given finite ultrametric space with minimum non-zero distance
α. Then the
p -negative type gap
ΓX(p) of
(X,d) is positive for all
p≥0. In this paper we compute the value of the limit
It turns out that this value is positive and it may be given explicitly by an elegant combinatorial formula. This formula allows us to characterize when the ratio
ΓX(p)/αp is a constant independent of
p . The determination of
c73a4ca6738f064e" title="Click to view the MathML source">ΓX(∞) also leads to new, asymptotically sharp, families of enhanced
p -negative type inequalities for
(X,d). Indeed, suppose that
G∈(0,ΓX(∞)). Then, for all sufficiently large
p, the inequality
holds for each finite subset
{z1,…,zn}⊆X, and each scalar
n -tuple
ζ=(ζ1,…,ζn)∈Rn that satisfies
ζ1+⋯+ζn=0. Notably, these results do not extend to general finite metric spaces.