TOPICS
Search

Weil-Petersson Volume


The Weil-Petersson volume of the moduli space M_(g,n)(L_1,...,L_n) of genus-g hyperbolic surfaces with n labeled boundary components of lengths L_i is

 V_(g,n)(L)=1/((3g-3+n)!)int_(M_(g,n)(L))omega_(WP)^(3g-3+n),

where omega_(WP) is the Weil-Petersson symplectic form and 2g-2+n>0. In Fenchel-Nielsen coordinates with length and twist variables l_i,tau_i, its normalization is omega_(WP)=sum_(i=1)^(3g-3+n)dl_i ^ dtau_i. The integral uses orbifold volume, and a boundary length 0 represents a cusp (Mirzakhani 2007). Write V_(g,n)=V_(g,n)(0,...,0).

For fixed n, Li and Wang (2026) reported

 V_(g,n)∼((2g-3+n)!(4pi^2)^(2g-3+n))/(sqrt(pig))

as g->infty, identifying the normalization constant as 1/sqrt(pi). Li and Wang (2026) also reported a moving-saddle expansion uniform over all n>=0, with relative error O(1/g) at leading order and exp(-asqrt(g)) after optimal truncation, for some a>0. The fixed-n formula displayed above is not the uniform leading term. The full uniformity and normalization arguments require independent assessment. Li and Wang (2026) report AI assistance with mathematical derivation and verification.

Li and Wang (2026) further reported a limiting primitive unoriented length spectrum for a random surface drawn from the probability measure given by normalized Weil-Petersson volume on M_(g,n) as g->infty and n/sqrt(g)->c in (0,infty). The limit is a Poisson background of intensity (cosht-1)dt/t together with independent clusters given by the complete primitive spectra of pairs of pants having two cusps. The waist lengths of those two-cusp pairs of pants form a Poisson process with intensity c^2sinh(s/2)ds/(8pi^2). The clusters retain correlations, so the full limit is not Poisson. This extension is subject to the same independent-assessment qualification as the volume asymptotics.


See also

Moduli Space

Explore with Wolfram|Alpha

References

Li, Z. and Wang, Q. "Uniform Large-Genus Asymptotics of Weil-Petersson Volumes." 29 Oct 2026. https://arxiv.org/abs/2610.35492.Mirzakhani, M. "Simple Geodesics and Weil-Petersson Volumes of Moduli Spaces of Bordered Riemann Surfaces." Invent. Math. 167, 179-222, 2007. https://doi.org/10.1007/s00222-006-0013-2.

Cite this as:

Weisstein, Eric W. "Weil-Petersson Volume." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Weil-PeterssonVolume.html

Subject classifications