Multicritical Edge Statistics for the Momenta of Fermions in Nonharmonic Traps

We compute the joint statistics of the momenta p₈ of N noninteracting fermions in a trap, near the Fermi edge, with a particular focus on the largest one p₌₀ₗ. For a 1D harmonic trap, momenta and positions play a symmetric role, and hence the joint statistics of momenta are identical to that of the positions. In particular, p₌₀ₗ, as x₌₀ₗ, is distributed according to the Tracy-Widom distribution. Here we show that novel "momentum edge statistics" emerge when the curvature of the potential vanishes, i. e. , for "flat traps" near their minimum, with V (x) ∼x^2n and n>1. These are based on generalizations of the Airy kernel that we obtain explicitly. The fluctuations of p₌₀ₗ are governed by new universal distributions determined from the nth member of the second Painlevé hierarchy of nonlinear differential equations, with connections to multicritical random matrix models. Finite temperature extensions and possible experimental signatures in cold atoms are discussed.