<p>We introduce a natural cell decomposition of a closed oriented surface associated with a pants decomposition, and an explicit groupoid cocycle on the cell decomposition which represents each point of the Teichmüller space <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10711_2025_1016_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathcal {T}}_g\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="script">T</mi> <mi>g</mi> </msub> </math></EquationSource> </InlineEquation>. We call it the <i>standard cocycle</i> of the point of <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10711_2025_1016_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathcal {T}}_g\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="script">T</mi> <mi>g</mi> </msub> </math></EquationSource> </InlineEquation>. As an application of the explicit description of the standard cocycle, we obtain a topological proof of Wolpert’s formula for the Weil-Petersson symplectic form in terms of the Fenchel-Nielsen coordinates associated with the pants decomposition.</p>

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A topological proof of Wolpert’s formula for the Weil-Petersson symplectic form in terms of the Fenchel-Nielsen coordinates

  • Nariya Kawazumi

摘要

We introduce a natural cell decomposition of a closed oriented surface associated with a pants decomposition, and an explicit groupoid cocycle on the cell decomposition which represents each point of the Teichmüller space \({\mathcal {T}}_g\) T g . We call it the standard cocycle of the point of \({\mathcal {T}}_g\) T g . As an application of the explicit description of the standard cocycle, we obtain a topological proof of Wolpert’s formula for the Weil-Petersson symplectic form in terms of the Fenchel-Nielsen coordinates associated with the pants decomposition.