## Tohoku Mathematical Journal

### On the universal deformations for ${\rm SL}_2$-representations of knot groups

#### Abstract

Based on the analogies between knot theory and number theory, we study a deformation theory for ${\rm SL}_2$-representations of knot groups, following after Mazur's deformation theory of Galois representations. Firstly, by employing the pseudo-${\rm SL}_2$-representations, we prove the existence of the universal deformation of a given ${\rm SL}_2$-representation of a finitely generated group $\Pi$ over a perfect field $k$ whose characteristic is not 2. We then show its connection with the character scheme for ${\rm SL}_2$-representations of $\Pi$ when $k$ is an algebraically closed field. We investigate examples concerning Riley representations of 2-bridge knot groups and give explicit forms of the universal deformations. Finally we discuss the universal deformation of the holonomy representation of a hyperbolic knot group in connection with Thurston's theory on deformations of hyperbolic structures.

#### Article information

Source
Tohoku Math. J. (2), Volume 69, Number 1 (2017), 67-84.

Dates
First available in Project Euclid: 26 April 2017

Permanent link to this document
https://projecteuclid.org/euclid.tmj/1493172129

Digital Object Identifier
doi:10.2748/tmj/1493172129

Mathematical Reviews number (MathSciNet)
MR3640015

Zentralblatt MATH identifier
06726842

#### Citation

Morishita, Masanori; Takakura, Yu; Terashima, Yuji; Ueki, Jun. On the universal deformations for ${\rm SL}_2$-representations of knot groups. Tohoku Math. J. (2) 69 (2017), no. 1, 67--84. doi:10.2748/tmj/1493172129. https://projecteuclid.org/euclid.tmj/1493172129

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