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Constant sign and sign changing NLS ground states on noncompact metric graphs

Colette De Coster, Simone Dovetta, Damien Galant, Enrico Serra and Christophe Troestler

Vol. 19 (2026), No. 2, 203–240
Abstract

We investigate existence and nonexistence of action ground states and nodal action ground states for the nonlinear Schrödinger equation on noncompact metric graphs with mixed homogeneous Kirchhoff and Dirichlet boundary conditions. We first obtain abstract sufficient conditions for existence, typical of problems with lack of compactness, in terms of “levels at infinity” for the action functional associated with the problems. Then we analyze in detail two relevant classes of graphs. For noncompact graphs with at least one half-line, we detect purely topological sharp conditions preventing the existence of ground states or of nodal ground states. We also investigate analogous conditions of metrical nature. The negative results are complemented by several sufficient conditions to ensure existence, either of topological or metrical nature, or a combination of the two. For graphs with infinitely many edges, all bounded, we focus on periodic graphs and infinite trees. In these cases, our results completely describe the phenomenology. Furthermore, we study nodal domains and nodal sets of nodal ground states and we show that the situation on graphs can be totally different from that on domains of N.

Keywords
nonlinear Schrödinger, ground states, nodal solutions, least action, constrained minimization
Mathematical Subject Classification
Primary: 35Q55, 35R02, 49J40, 58E30
Milestones
Received: 25 September 2023
Revised: 25 September 2024
Accepted: 1 February 2025
Published: 22 January 2026
Authors
Colette De Coster
Université Polytechnique Hauts-de-France
INSA Hauts-de-France
CERAMATHS - Laboratoire de Matériaux Céramiques et de Mathématiques
F-59313 Valenciennes
France
Simone Dovetta
Dipartimento di Scienze Matematiche “G. L. Lagrange”
Politecnico di Torino
Torino
Italy
Damien Galant
Département de Mathématiques
Université de Mons
Mons
Belgium
Université Polytechnique Hauts-de-France
INSA Hauts-de-France
CERAMATHS - Laboratoire de Matériaux Céramiques et de Mathématiques
F-59313 Valenciennes
France
Department of Mathematics
Brown University
Providence, RI
United States
Enrico Serra
Dipartimento di Scienze Matematiche “G. L. Lagrange”
Politecnico di Torino
Torino
Italy
Christophe Troestler
Département de Mathématiques
Université de Mons
Mons
Belgium

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