Duke Mathematical Journal

FI-modules and stability for representations of symmetric groups

Thomas Church, Jordan S. Ellenberg, and Benson Farb

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In this paper we introduce and develop the theory of FI-modules. We apply this theory to obtain new theorems about:

• the cohomology of the configuration space of n distinct ordered points on an arbitrary (connected, oriented) manifold;

• the diagonal coinvariant algebra on r sets of n variables;

• the cohomology and tautological ring of the moduli space of n -pointed curves;

• the space of polynomials on rank varieties of n × n matrices;

• the subalgebra of the cohomology of the genus n Torelli group generated by H 1 ;

and more. The symmetric group S n acts on each of these vector spaces. In most cases almost nothing is known about the characters of these representations, or even their dimensions. We prove that in each fixed degree the character is given, for n large enough, by a polynomial in the cycle-counting functions that is independent of n . In particular, the dimension is eventually a polynomial in n . In this framework, representation stability (in the sense of Church–Farb) for a sequence of S n -representations is converted to a finite generation property for a single FI-module.

Article information

Duke Math. J., Volume 164, Number 9 (2015), 1833-1910.

Received: 14 July 2013
Revised: 5 September 2014
First available in Project Euclid: 15 June 2015

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Mathematical Reviews number (MathSciNet)

Zentralblatt MATH identifier

Primary: 55N25: Homology with local coefficients, equivariant cohomology
Secondary: 05E10: Combinatorial aspects of representation theory [See also 20C30] 20J06: Cohomology of groups

FI-modules representations symmetric groups


Church, Thomas; Ellenberg, Jordan S.; Farb, Benson. FI-modules and stability for representations of symmetric groups. Duke Math. J. 164 (2015), no. 9, 1833--1910. doi:10.1215/00127094-3120274. https://projecteuclid.org/euclid.dmj/1434377462

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