• Accepted Paper

Edge dynamics of covariant higher-rank Chern-Simons theory of fractons

Erica Bertolini, Matteo Carrega, Nicola Maggiore, Daniel Sacco Shaikh, and Maria Florencia Semino

Phys. Rev. D - Accepted 6 November, 2026

DOI: https://doi.org/10.1103/s4lh-2jvz

Abstract

We study the covariant higher-rank Chern-Simons theory of fractons in (2+1) dimensions in the presence of a planar boundary. The differential generator associated with the scalar gauge symmetry singles out a single scalar Ward combination of the functional field equations. Its zeroth and first normal moments give two integrated boundary identities. The zeroth moment yields a traceless rank-two current obeying a fractonic double-divergence conservation law and a higher-rank Kac-Moody algebra. The first moment makes the normal-tangential field wi=h2i explicit and yields an ordinarily conserved vector current with a standard U(1) Kac-Moody algebra. Functional differentiation also produces a mixed equal-time bulk-boundary commutator between the spatial components w1 and h11: it is non-vanishing at finite normal distance and vanishes in the intrinsic boundary limit. The equal-time commutators of the boundary current with the spatial components of the gauge-invariant field strength vanish, so microcausality is satisfied; when the boundary parameters are such that the two boundary sectors decouple, the corresponding retarded response vanishes at all times. Locally, the boundary constraints are solved by wi=∂iχ and hij=∂i∂jξ+ηijϕ. When the boundary parameters are such that the two sectors decouple, the induced action is the direct sum of a chiral boson in the wi sector and a higher-rank sector in which ϕ is auxiliary and ψ=∂1ξ is the propagating field. The latter has a non-chiral Luttinger-liquid description on its positive-energy branch and admits a chiral reduction. The bulk boundary conditions determine the velocity and positivity branch of the wi mode, while the compatibility analysis in the hij sector selects the positive-energy chiral branch. On the matched positive-energy branch the two chiral modes co-propagate, with orientation opposite to the sign of κ. We also identify the extrinsic-curvature terms through which non-planar geometry enters the projected gauge transformations and can consequently modify the boundary conditions and edge dynamics.

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