Positive Burau eigenvalue conjecture for order-preserving braids

From papers

Let BnB_n be the braid group on nn strands, let E\mathbb{E} be the relevant ordered field with quadratic form QQ, and let

ρ:βGLn1(Z[t±1])\rho:\beta \to \operatorname{GL}_{n-1}(\mathbb{Z}[t^{\pm 1}])

be the reduced Burau representation. A braid βBn\beta\in B_n is order-preserving if it preserves an ordering of the free or surface group under consideration. Positive Burau eigenvalue conjecture. If βBn\beta\in B_n is an order-preserving braid, then ρ(β)\rho(\beta) has at least one positive eigenvalue in (E,Q)(\mathbb{E},Q). This would provide a partial converse to the criterion that positive Burau eigenvalues imply order preservation; the full converse is indicated to be false by the examples discussed in the paper.

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Sources & referencesView supporting material

Primary source

Jonathan Johnson and Khanh Le, “Order-Preserving outer automorphisms of free and surface groups”, arXiv:2501.18847 (2026).

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