Buryak–Rossi–Shadrin bihamiltonian conjecture for the DR hierarchy

Let VV be the state space of a homogeneous cohomological field theory with homogeneous basis e1,,eNe_1,\ldots,e_N, metric (ηαβ)(\eta^{\alpha\beta}), degrees degeα=qα\deg e_\alpha=q_\alpha, and parameters rγr^\gamma defined by r=rγeγ\overline r=r^\gamma e_\gamma. Set

μ=diag(μ1,,μN),μα=qαδ2,\mu=\operatorname{diag}(\mu_1,\ldots,\mu_N),\qquad \mu_\alpha=q_\alpha-\frac{\delta}{2},

and let KDRK^\mathrm{DR} be the matrix differential operator defined from the DR hierarchy. Define

Aαβ:=ηβνc0,3(eνeαr).A^\beta_\alpha:=\eta^{\beta\nu}c_{0,3}(e_\nu\otimes e_\alpha\otimes\overline r).

For the DR Hamiltonians gα,d\overline g_{\alpha,d}, let {,}KDR\{\cdot,\cdot\}_{K^\mathrm{DR}} and {,}η1x\{\cdot,\cdot\}_{\eta^{-1}\partial_x} denote the brackets induced by KDRK^\mathrm{DR} and the first Poisson operator η1x\eta^{-1}\partial_x, respectively.

Buryak–Rossi–Shadrin's conjecture. The operator KDRK^\mathrm{DR} is Poisson and compatible with η1x\eta^{-1}\partial_x. It endows the DR hierarchy with a bihamiltonian structure satisfying

{,gα,d}KDR=(d+32+μα){,gα,d+1}η1x+Aαβ{,gβ,d}η1x,d1.\left\{\cdot,\overline g_{\alpha,d}\right\}_{K^\mathrm{DR}}=\left(d+\frac{3}{2}+\mu_\alpha\right)\left\{\cdot,\overline g_{\alpha,d+1}\right\}_{\eta^{-1}\partial_x}+A^\beta_\alpha\left\{\cdot,\overline g_{\beta,d}\right\}_{\eta^{-1}\partial_x},\qquad d\geq -1.

This conjecture proposes a second compatible Poisson structure for the DR hierarchy, making it bihamiltonian and providing a recursion among its Hamiltonian flows. The supplied text does not state whether it has been proved or disproved.

Sources & referencesView supporting material

Primary source

Alexandr Buryak and Paolo Rossi, “Bihamiltonian structure of the DR hierarchy in the semisimple case”, arXiv:2408.12397 (2025).

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