In mathematics, the Weil–Petersson metric is a Kähler metric on the Teichmüller space T_g,n of genus g Riemann surfaces with n marked points. It was introduced by André Weil (1958, 1979) using the Petersson inner product on forms on a Riemann surface (introduced by Hans Petersson).

If a point of Teichmüller space is represented by a Riemann surface R, then the cotangent space at that point can be identified with the space of quadratic differentials at R. Since the Riemann surface has a natural hyperbolic metric, at least if it has negative Euler characteristic, one can define a Hermitian inner product on the space of quadratic differentials by integrating over the Riemann surface. This induces a Hermitian inner product on the tangent space to each point of Teichmüller space, and hence a Riemannian metric.

Weil (1958) stated, and Ahlfors (1961) proved, that the Weil–Petersson metric is a Kähler metric. Ahlfors (1961b) proved that it has negative holomorphic sectional, scalar, and Ricci curvatures. The Weil–Petersson metric is usually not complete.

The Weil–Petersson metric can be defined in a similar way for some moduli spaces of higher-dimensional varieties.

• Ramanujan–Petersson conjecture

• Ahlfors, Lars V. (1961), "Some remarks on Teichmüller's space of Riemann surfaces", Annals of Mathematics, Second Series, 74 (1): 171–191, doi:10.2307/1970309, hdl:2027/mdp.39015095258003, JSTOR 1970309, MR 0204641
• Ahlfors, Lars V. (1961b), "Curvature properties of Teichmüller's space", Journal d'Analyse Mathématique, 9: 161–176, doi:10.1007/BF02795342, hdl:2027/mdp.39015095248350, MR 0136730, S2CID 124921349
• Weil, André (1958), "Modules des surfaces de Riemann", Séminaire Bourbaki; 10e année: 1957/1958. Textes des conférences; Exposés 152à 168; 2e éd.corrigée, Exposé 168 (in French), Paris: Secrétariat Mathématique, pp. 413–419, MR 0124485, Zbl 0084.28102
• Weil, André (1979) [1958], "On the moduli of Riemann surfaces", Scientific works. Collected papers. Vol. II (1951--1964), Berlin, New York: Springer-Verlag, pp. 381–389, ISBN 978-0-387-90330-9, MR 0537935
• Wolpert, Scott A. (2001) [1994], "Weil–Petersson_metric", Encyclopedia of Mathematics, EMS Press
• Wolpert, Scott A. (2009), "The Weil-Petersson metric geometry", in Papadopoulos, Athanase (ed.), Handbook of Teichmüller theory. Vol. II, IRMA Lect. Math. Theor. Phys., vol. 13, Eur. Math. Soc., Zürich, pp. 47–64, arXiv:0801.0175, doi:10.4171/055-1/2, ISBN 978-3-03719-055-5, MR 2497791
• Wolpert, Scott A. (2010), Families of Riemann Surfaces and Weil-Petersson Geometry, CBMS Reg. Conf. Series in Math., vol. 113, Amer. Math. Soc., Providence, Rhode Island, arXiv:1202.4078, doi:10.1090/cbms/113, ISBN 978-0-8218-4986-6, MR 2641916, S2CID 7880175

• Weil-Petersson metric on nLab