Crystals and total positivity on orientable surfaces

Thomas Lam, Pavlo Pylyavskyy

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10 Scopus citations


We develop a combinatorial model of networks on orientable surfaces, and study weight and homology generating functions of paths and cycles in these networks. Network transformations preserving these generating functions are investigated. We describe in terms of our model the crystal structure and R-matrix of the affine geometric crystal of products of symmetric and dual symmetric powers of type A. Local realizations of the R-matrix and crystal actions are used to construct a double affine geometric crystal on a torus, generalizing the commutation result of Kajiwara et al. (Lett Math Phys, 60(3):211-219, 2002) and an observation of Berenstein and Kazhdan (MSJ Mem, 17:1-9, 2007). We show that our model on a cylinder gives a decomposition and parametrization of the totally non-negative part of the rational unipotent loop group of GLn.

Original languageEnglish (US)
Pages (from-to)173-235
Number of pages63
JournalSelecta Mathematica, New Series
Issue number1
StatePublished - Mar 2013

Bibliographical note

Funding Information:
T. Lam was supported by NSF grant DMS-0652641 and DMS-0901111, and by a Sloan Fellowship. P. Pylyavskyy was supported by NSF grant DMS-0757165.


  • Boundary measurements
  • Geometric crystals
  • Loop groups
  • Networks on surfaces
  • Total positivity


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