Paper · Oct 25, 2022

Harmonic spinors in the Ricci flow

Julius Baldauf

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Abstract

This paper studies the Ricci flow on closed manifolds admitting harmonic spinors. It is shown that Perelman's Ricci flow entropy can be expressed in terms of the energy of harmonic spinors in all dimensions, and in four dimensions, in terms of the energy of Seiberg-Witten monopoles. Consequently, Ricci flow is the gradient flow of these energies. The proof relies on a weighted version of the monopole equations, introduced here. Further, a sharp parabolic Hitchin-Thorpe inequality for simply-connected, spin 4-manifolds is proven. From this, it follows that the normalized Ricci flow on any exotic K3 surface must become singular.

Comments: 19 pages

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The 8 papers on this site closest to this one, judged by the topics they share, the words and phrases in their titles and abstracts, and their authors. They are not its citations, but a map of the work around it. Papers here go back to 2021, plus the canon.

Connected papers This paper in the centre and the 8 papers closest to it around it, in date order clockwise from the top. The closer a paper sits to the centre, the stronger the connection. This paper On a dichotomy of the curvature decay of steady Ricci soliton (Pak-Yeung Chan and Bo Zhu, 2021)6Chan 2021 Parallel spinor flows on three-dimensional Cauchy hypersurfaces (Ángel Murcia and C. S. Shahbazi, 2021)3Murcia 2021 Spinors and mass on weighted manifolds (Julius Baldauf and Tristan Ozuch, 2022)2Baldauf 2022 On Euler characteristic and Hitchin-Thorpe inequality for four-dimensional compact Ricci solitons (Xu Cheng, Ernani Ribeiro and Detang Zhou, 2022)1Cheng 2022 The spinorial energy for asymptotically Euclidean Ricci flow (Julius Baldauf and Tristan Ozuch, 2022)4Baldauf 2022 Classification of Gradient Ricci solitons with harmonic Weyl curvature (Jongsu Kim, 2023)7Kim 2023 Local Existence Of The Symplectic Gradient Flow On The Hyperkähler Four-dimensional Flat Torus (Pinsard Morel Lucas, 2025)5Lucas 2025 Diameter estimates and Hitchin-Thorpe inequality for four-dimensional compact Quasi-Einstein manifolds (Samuel Belo, 2026)8Belo 2026
Closer to the centre: more closely connected. Clockwise from the top: oldest to newest. Ricci flowWider flowsalso connected to each other
  1. On Euler characteristic and Hitchin-Thorpe inequality for four-dimensional compact Ricci solitons

    Xu Cheng, Ernani Ribeiro and Detang Zhou PDF

    Topics 4-manifolds · Shared terms “Thorpe inequality”, “Hitchin Thorpe”

  2. Spinors and mass on weighted manifolds

    Julius Baldauf and Tristan Ozuch PDF

    Topics Ricci flow · Same author Julius Baldauf · Shared terms “Witten”, “gradient flow”, “Perelman”

  3. Parallel spinor flows on three-dimensional Cauchy hypersurfaces

    Ángel Murcia and C. S. Shahbazi PDF

    Topics Ricci-flat & Calabi–Yau, 4-manifolds · Shared terms “simply connected”, “admitting”

  4. The spinorial energy for asymptotically Euclidean Ricci flow

    Julius Baldauf and Tristan Ozuch PDF

    Topics Ricci flow · Same author Julius Baldauf · Shared terms “gradient flow”, “Perelman”

  5. Local Existence Of The Symplectic Gradient Flow On The Hyperkähler Four-dimensional Flat Torus

    Pinsard Morel Lucas PDF

    Topics Ricci-flat & Calabi–Yau, 4-manifolds · Shared terms “gradient flow”

  6. On a dichotomy of the curvature decay of steady Ricci soliton

    Pak-Yeung Chan and Bo Zhu PDF

    Topics Ricci-flat & Calabi–Yau, 4-manifolds

  7. Diameter estimates and Hitchin-Thorpe inequality for four-dimensional compact Quasi-Einstein manifolds

    Samuel Belo PDF

    Topics 4-manifolds · Shared terms “Thorpe inequality”, “Hitchin Thorpe”

Read around it

Background reading

The guides for the topics of this paper: what each idea is, why it matters, and the papers to read first.

In the guidebook

  1. 5A.5
    Uniformization and the Two-Dimensional Ricci FlowBook 5A · Complex Analysis and Conformal Geometry

    Constant-curvature metrics on surfaces, and Ricci flow as a heat equation for the conformal factor.

  2. 10A.12
    Curve Shortening and Minimal DiscsBook 10A · Three-Manifolds and Geometrization

    How loops shrink under curvature, how the discs they bound lose area, and Perelman's extinction estimate.

  3. 11A.1
    The Equation and Its First SolutionsBook 11A · The Ricci Flow: Existence and Maximum Principles

    A heat equation for the metric: spheres, cylinders and scaling.