This article considers a class of nonlinear ordinary differential equations (ODEs) whose general solutions possess a natural boundary in the complex plane and admit special solutions that are automorphic under the action of subgroups of the modular group P$ \text{SL}_2(\mathbb{Z}) $. Specifically, a $ 3 \times 3 $ matrix valued system known as the Darboux-Halphen 9 (DH9) system and its fifth-order reduction to the DH5 system are discussed. These systems arise as reductions of the self-dual Yang-Mills equations of mathematical physics. It is shown that the equations discovered by J. Chazy (1908) and V. Ramamani (1970) are embedded in the DH5 system.
Citation: S. Chakravarty, P. Guha. The DH5 system and the Chazy and Ramamani equations[J]. AIMS Mathematics, 2025, 10(3): 6318-6337. doi: 10.3934/math.2025288
This article considers a class of nonlinear ordinary differential equations (ODEs) whose general solutions possess a natural boundary in the complex plane and admit special solutions that are automorphic under the action of subgroups of the modular group P$ \text{SL}_2(\mathbb{Z}) $. Specifically, a $ 3 \times 3 $ matrix valued system known as the Darboux-Halphen 9 (DH9) system and its fifth-order reduction to the DH5 system are discussed. These systems arise as reductions of the self-dual Yang-Mills equations of mathematical physics. It is shown that the equations discovered by J. Chazy (1908) and V. Ramamani (1970) are embedded in the DH5 system.
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