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Conan Gillis

Publications and source records attributed to Conan Gillis.

6 recordsLinked to original sources
arXiv2026

Conjugator Lengths and Isoperimetric functions

We show that for any recognizing $S$-machine $\textbf{S}$ with superadditive time function $f$, there exists a finitely presented group whose conjugator length function is quadratic and whose Dehn function grows like the square of $f$. This result is dual to that of a previous paper of the authors, which constructed a family of groups with cubic Dehn function that have various conjugator length functions. We thereby give the first known example of a finitely presented group whose conjugator length function is recursive, but whose Word and Conjugacy Problems are both undecidable. This answers an analogue of a question of Rips. Moreover, given a finitely presented group $G$ with decidable Word Problem, we obtain a finitely presented group with decidable Conjugacy Problem whose Dehn function grows faster than that of $G$. Finally, combining this result with its dual, for a wide array of pairs of functions $(f,g)$ we furnish an example of a finitely presented group with Dehn function equivalent to $f$ and conjugator length function equivalent to $g$. This shows that the two invariants are very strongly independent and making significant progress on a question of Bridson, Riley, and Sale.

math.GR↗
arXiv2026

Conjugator Length in Finitely Presented Groups

The conjugator length function of a finitely generated group is the function $f$ so that $f(n)$ is the minimal upper bound on the length of a word realizing the conjugacy of two words of length at most $n$. We study herein the spectrum of functions which can be realized as the conjugator length function of a finitely presented group, showing that it contains every function that can be realized as the Dehn function of a finitely presented group. In particular, given a real number $\alpha\geq2$ which is computable in double-exponential time, we show there exists a finitely presented group whose conjugator length function is asymptotically equivalent to $n^\alpha$. This yields a substantial refinement to results of Bridson and Riley. We attain this result through the computational model of $S$-machines, achieving the more general result that any sufficiently large function which can be realized as the time function of an $S$-machine can also be realized as the conjugator length function of a finitely presented group. Finally, we use the constructed groups to explore the relationship between the conjugator length function, the Dehn function, and the annular Dehn function in finitely presented groups.

math.GR↗
arXiv2025

Conjugator Length in the Baumslag-Gersten Group

We show that the conjugator length function of the Baumslag-Gersten group is equivalent to a tower of exponentials of height $\lfloor \log_2n\rfloor$ -- in particular it grows faster than any tower of exponentials of fixed height. We ask whether any one-relator group has a larger conjugator length function than the Baumslag-Gersten group. Along the way, we also show that the conjugator length function of the $m$-th iterated Baumslag-Solitar groups is equivalent to the $(m-1)$-times iterated exponential function.

math.GR↗
arXiv2025

Distinguishing Filling Invariants Associated to Conjugacy in Groups

Brick and Corson introduced annular Dehn functions in 1998 to quantify the conjugacy problem for finitely generated groups and gave the fundamental relationships between it, the Dehn function, and the conjugator length function. We furnish the theory with diverse examples groups. In particular, we show that these three invariants are independent -- no two of the three functions determine the other.

math.GR↗
arXiv2024

Conjugacy in Miller's Groups

In 1971 C.F.\ Miller associated to every finitely presented group $G$ a free-by-free group $M(G)$ known as the Miller Machine, whose conjugacy problem is closely related to the conjugacy and word problems of $G$. We quantify this relationship, and look to fully understand the conjugacy problem of $M(G)$; namely, we reduce the conjugacy problem in $M(G)$ to a strong form of list conjugacy in $G$, which we term iso-computational list conjugacy. As an application, we show that if $G$ is finite, the conjugacy problem for $M(G)$ is in $\mathsf{PSPACE}$.

math.GR↗