Paper · Oct 9, 2026

Direct proofs for spaces with cyclic parallel Ricci tensor

Fengyuan Zhang

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Abstract

We give direct proofs of rigidity results for gradient Ricci solitons, compact quasi-Einstein manifolds with boundary, and critical spaces with cyclic parallel Ricci tensor. For solitons and quasi-Einstein manifolds, successive traces of first-order pointwise identities yield quadratic equations for the Ricci tensor and its modification. These equations imply radial flatness and radial -flatness, respectively, and the corresponding global rigidity theorems apply. For critical spaces, comparison of two expressions for the Laplacian of the Hessian gives a pointwise tensor identity whose scalar contraction yields a weighted divergence formula. Integration then gives the vacuum static, CPE, and Miao–Tam conclusions. The same comparison also proves Ricci parallelism pointwise for solitons and quasi-Einstein manifolds.

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  1. The rigity of spaces with cyclic parallel Ricci tensor

    Fengyuan Zhang PDF

    Topics Almost & η-Ricci solitons, Einstein metrics, Boundaries & non-compact · Same author Fengyuan Zhang · Shared terms “cyclic parallel”, “parallel Ricci”, “Ricci tensor”

  2. Quasi-Einstein Metrics and a curvature identity associated with the Ricci flow

    Atreyee Bhattacharya and Sayoojya Prakash PDF

    Topics Almost & η-Ricci solitons, Einstein metrics, Stability & uniqueness · Shared terms “quasi Einstein”, “identity”, “gradient Ricci”

  3. -Ricci Solitons on Kenmotsu 3-Manifolds

    K. De and U. C. De PDF

    Topics Almost & η-Ricci solitons, Ricci solitons · Shared terms “cyclic parallel”, “parallel Ricci”, “Ricci tensor”

  4. The extended quasi-Einstein manifolds with generalised Ricci solitons

    Zhiming Huang, Weijun Lu and Fuhong Su PDF

    Topics Almost & η-Ricci solitons, Einstein metrics, Ricci solitons · Shared terms “quasi Einstein”

  5. Almost Gradient Ricci Solitons on Static Spacetime

    Akhilesh Yadav and Tarun Saxena PDF

    Topics Almost & η-Ricci solitons, Einstein metrics, Boundaries & non-compact · Shared terms “vacuum static”, “gradient Ricci”

  6. Back to almost Ricci solitons

    Vladimir Rovenski, Sergey Stepanov and Irina Tsyganok PDF

    Topics Almost & η-Ricci solitons, Einstein metrics, Ricci solitons · Shared terms “Ricci tensor”

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

    Samuel Belo PDF

    Topics Almost & η-Ricci solitons, Einstein metrics, Ricci solitons · Shared terms “quasi Einstein”, “compact quasi”

  8. Almost Ricci solitons on Finsler spaces

    Qiaoling Xia PDF

    Topics Almost & η-Ricci solitons, Einstein metrics, Stability & uniqueness · Shared terms “gradient Ricci”

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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. 11B.1
    Ricci SolitonsBook 11B · Solitons, Compactness and Singularities

    Self-similar solutions: the Gaussian, cylinders, the cigar and the Bryant soliton.

  2. 12B.2
    The Asymptotic Soliton and Three-Dimensional ShrinkersBook 12B · κ-Solutions and Surgery

    Perelman's Proposition 11.2 proved with Morgan and Tian: the reduced-length bounds on κ-solutions, the limit of rescalings, the equality case, and the classification of shrinking solitons in dimensions two and three.