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Main Author: Hedenmalm, Haakan
Format: Preprint
Published: 2026
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Online Access:https://arxiv.org/abs/2603.03868
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author Hedenmalm, Haakan
author_facet Hedenmalm, Haakan
contents We study the Klein-Gordon equation in one spatial and one temporal dimension. Physically, this equation describes the wave function of a relativistic spinless boson with positive rest mass. Mathematically, this is the most elementary hyperbolic partial differential equation, after the wave equation itself. Relative to the origin, the spacetime splits according to the light cones, and we find four quarter-planes, two of which are timelike while the remaining two are spacelike. Not unexpectedly, the solutions behave quite differently in the two types of quarter-planes. It turns out that the spacelike quarter-planes exhibit a Liouville phenomenon, where insufficient growth forces the solutions to display a certain kind of symmetry, where the values on the two linear edges are in a one-to-one relation. This phenomenon shares features with the classical Liouville theorem as well as the Phragmen-Lindelof principle for harmonic functions.
format Preprint
id arxiv_https___arxiv_org_abs_2603_03868
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Liouville phenomenon for the Klein-Gordon equation in 1+1 dimensions
Hedenmalm, Haakan
Analysis of PDEs
35L10, 35Q40, 35B53
We study the Klein-Gordon equation in one spatial and one temporal dimension. Physically, this equation describes the wave function of a relativistic spinless boson with positive rest mass. Mathematically, this is the most elementary hyperbolic partial differential equation, after the wave equation itself. Relative to the origin, the spacetime splits according to the light cones, and we find four quarter-planes, two of which are timelike while the remaining two are spacelike. Not unexpectedly, the solutions behave quite differently in the two types of quarter-planes. It turns out that the spacelike quarter-planes exhibit a Liouville phenomenon, where insufficient growth forces the solutions to display a certain kind of symmetry, where the values on the two linear edges are in a one-to-one relation. This phenomenon shares features with the classical Liouville theorem as well as the Phragmen-Lindelof principle for harmonic functions.
title Liouville phenomenon for the Klein-Gordon equation in 1+1 dimensions
topic Analysis of PDEs
35L10, 35Q40, 35B53
url https://arxiv.org/abs/2603.03868