Extracting explicit conjugating paths for subsurface-deformation Hamiltonian flows

Determine an explicit procedure to compute, from a given G-invariant multi-function f: G^k → R and its variation function F, the boundary-conjugating paths g_i^t ∈ G (with g_i^0 = e) that cover the Hamiltonian flow of the induced function f_{\underline{\alpha}} on the character variety Hom(π1(S), G)//G in the case where the supporting subsurface S_0 is a fully separating m-holed sphere. Specifically, for each component S_i adjacent to S_0 along boundary curve c_i, derive g_i^t directly from f and F so that the flow Xi_ρ(t)(γ) = g_i^t ρ_i(γ) (g_i^t)^{-1} realizes the Hamiltonian dynamics on the restriction to Γ_i = π1(S_i).

Background

The paper shows that Hamiltonian flows of functions on surface-group character varieties induced by G-invariant multi-functions are subsurface deformations supported on appropriate subsurfaces. In the special case where the supporting subsurface S_0 is a fully separating m-holed sphere, the authors prove that the Hamiltonian flow can be covered by paths of conjugations along the boundary curves, i.e., by elements g_it ∈ G that conjugate the restricted representations on each complementary component S_i.

While this geometric description is established, the authors note that obtaining explicit expressions for these conjugating paths is nontrivial in practice. Although they compute some examples, they identify a gap: a systematic method to extract g_it from the data of the invariant multi-function f and its variation function F is currently lacking. Addressing this would enhance the practical computability of Hamiltonian flows and deepen understanding of their dynamics in concrete settings.

References

It is in general difficult to write explicit paths of conjugating matrices $g_it$; even though we have computed a few explicit examples, it is an open question how to extract information on the $g_it$ out of the function $f$ and its variation function $F$.

Invariant multi-functions and Hamiltonian flows for surface group representations  (2410.05154 - Camacho-Cadena et al., 2024) in Section “Subsurface deformations”, paragraph immediately following Corollary \ref{cor : hamiltonian flow for fully separating subsurface}