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Shannon entropy for harmonic metrics on cyclic Higgs bundles II

Differential Geometry 2025-08-19 v1 Complex Variables

Abstract

Let XX be a Riemann surface and KXXK_X \rightarrow X the canonical bundle. For each integer r2r \geq 2, each qH0(KXr)q \in H^0(K_X^r), and each choice of the square root KX1/2K_X^{1/2} of the canonical bundle, we obtain a Higgs bundle, which is called a cyclic Higgs bundle. A diagonal harmonic metric h=(h1,,hr)h = (h_1, \dots, h_r) on a cyclic Higgs bundle yields r1r-1-Hermitian metrics H1,,Hr1H_1, \dots, H_{r-1} on KX1XK_X^{-1} \rightarrow X, while h1h_1, hrh_r, and qq yield a degenerate Hermitian metric HrH_r on KX1XK_X^{-1}\rightarrow X. The rr-differential qq induces a subharmonic weight function ϕq=1rlogq\phi_q=\frac{1}{r}\log|q| on KXK_X, and the diagonal harmonic metric depends solely on this weight function. In the previous papers, the author studied the extension of harmonic metrics associated with arbitrary subharmonic weight function φ\varphi, which also constructs Hermitian metrics H1,,HrH_1,\dots, H_r on KX1XK_X^{-1}\rightarrow X. Especially, the author introduced a function called entropy that quantifies the degree of mutual misalignment of the metrics H1,,HrH_1,\dots, H_r. In this paper, by analogy with the canonical ensemble in statistical mechanics, we further introduce the quantity which we call free energy. When H1,,Hr1H_1,\dots, H_{r-1} are all complete and satisfy a condition concerning their approximation, we give a sufficient condition for the free energy to decrease at each point, and when r=2,3r=2,3 we also give a sufficient condition for the entropy to increase at each point. Furthermore, on the unit disc D\mathbb{D}, when is C2C^2 outside a compact subset, we provide, from the perspective of entropy and free energy, necessary and sufficient conditions for the function eφh1hDe^\varphi h_\ast^{-1} \otimes h_{\mathbb{D}} to be bounded, where hDh_{\mathbb{D}} denotes the Hermitian metric induced by the Poincar\'e metric. This result extends the work of Wan, Benoist-Hulin, Labourie-Toulisse, and Dai-Li.

Keywords

Cite

@article{arxiv.2508.12844,
  title  = {Shannon entropy for harmonic metrics on cyclic Higgs bundles II},
  author = {Natsuo Miyatake},
  journal= {arXiv preprint arXiv:2508.12844},
  year   = {2025}
}

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