New York Journal of Mathematics
Volume 30 (2024), 561-582


Leo Benard, Vincent Florens, and Adrien Rodau

A slope invariant and the A-polynomial of knots

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Published: April 15, 2024.
Keywords: knot theory, A-polynomial, Reidemeister torsion.
Subject [2010]: Primary: 57K10, Secondary: 57K14, Tertiary: 57K31.

The A-polynomial is a knot invariant related to the space of SL2(C) representations of the knot group. In this paper our interests lies in the logarithmic Gauss map of the A-polynomial. We develop a homological point of view on this function by extending the constructions of Degtyarev, the second author and Lecuona to the setting of non-abelian representations. It defines a rational function on the character variety, which unifies various known invariants such as the change of curves in the Reidemeister function, the modulus of boundary-parabolic representations, the boundary slope of some incompressible surfaces embedded in the exterior of the knot K or equivalently the slopes of the sides of the Newton polygon of the A-polynomial AK. We also present a method to compute this invariant in terms of Alexander matrices and Fox calculus.


This paper has been written while Leo Benard was a member of the Research Training Group 2491 "Fourier Analysis and Spectral Theory", University of Gottingen. He thanks the Research Group, and in particular Thomas Schick, for the time he spent there. The authors thank Julien Marche, Stepan Yu. Orevkov and Joan Porti for related conversations.

Author information

Leo Benard
Institut de Mathematiques de Marseille
Aix-Marseille Universite
Marseille, France


Vincent Florens
Universite de Pau
Pau, France


Adrien Rodau
Univ. Lille, CNRS
UMR 8524 - Laboratoire Paul Painleve
F-59000 Lille, France