Shocks, instability, and the twenty networks of infinite geodesics in the Directed Landscape

Fuente: arXiv
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Autori principali: Rassoul-Agha, Firas, Sweeney, Mikhail
Natura: Preprint
Pubblicazione: 2026
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author Rassoul-Agha, Firas
Sweeney, Mikhail
author_facet Rassoul-Agha, Firas
Sweeney, Mikhail
contents For stochastic Hamilton-Jacobi (SHJ) equations, instability points are the space-time locations where two eternal solutions with the same asymptotic velocity differ. Another fundamental structure in such equations is shocks, which are the space-time locations where the velocity field is discontinuous. In this work, we study the KPZ fixed point, the central object of the KPZ universality class, which can be viewed as a prototype--albeit degenerate--of an inviscid SHJ equation in one spatial dimension. We describe the geometric structure of the instability region and give a detailed and precise analysis of its interplay with the shock structures of the two eternal solutions. We show that these shock structures allow one to reconstruct the instability region. Along the way, we obtain a complete classification of all possible configurations of semi-infinite geodesics emanating from arbitrary space-time points, in the directed landscape--the random environment in which the KPZ fixed point evolves.
format Preprint
id arxiv_https___arxiv_org_abs_2604_12963
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Shocks, instability, and the twenty networks of infinite geodesics in the Directed Landscape
Rassoul-Agha, Firas
Sweeney, Mikhail
Probability
60K35, 60K37, 37H05, 37H30, 37L55, 35F21, 35R60
For stochastic Hamilton-Jacobi (SHJ) equations, instability points are the space-time locations where two eternal solutions with the same asymptotic velocity differ. Another fundamental structure in such equations is shocks, which are the space-time locations where the velocity field is discontinuous. In this work, we study the KPZ fixed point, the central object of the KPZ universality class, which can be viewed as a prototype--albeit degenerate--of an inviscid SHJ equation in one spatial dimension. We describe the geometric structure of the instability region and give a detailed and precise analysis of its interplay with the shock structures of the two eternal solutions. We show that these shock structures allow one to reconstruct the instability region. Along the way, we obtain a complete classification of all possible configurations of semi-infinite geodesics emanating from arbitrary space-time points, in the directed landscape--the random environment in which the KPZ fixed point evolves.
title Shocks, instability, and the twenty networks of infinite geodesics in the Directed Landscape
topic Probability
60K35, 60K37, 37H05, 37H30, 37L55, 35F21, 35R60
url https://arxiv.org/abs/2604.12963