Decompositions of amplituhedra
Annales de l’Institut Henri Poincaré D, Tome 7 (2020) no. 3, pp. 303-363.
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The (tree) amplituhedron 𝒜n,k,m is the image in the Grassmannian Grk,k+m of the totally nonnegative Grassmannian Grk,n0, under a (map induced by a) linear map which is totally positive. It was introduced by Arkani-Hamed and Trnka in 2013 in order to give a geometric basis for the computation of scattering amplitudes in planar 𝒩=4 supersymmetric Yang–Mills theory. In the case relevant to physics (m=4), there is a collection of recursively-defined 4k-dimensional BCFW cells in Grk,n0, whose images conjecturally "triangulate" the amplituhedron – that is, their images are disjoint and cover a dense subset of 𝒜n,k,4. In this paper, we approach this problem by first giving an explicit (as opposed to recursive) description of the BCFW cells. We then develop sign-variational tools which we use to prove that when k=2, the images of these cells are disjoint in 𝒜n,k,4. We also conjecture that for arbitrary even m, there is a decomposition of the amplituhedron 𝒜n,k,m involving precisely Mk,n-k-m,m2 top-dimensional cells (of dimension km), where M(a,b,c) is the number of plane partitions contained in an a×b×c box. This agrees with the fact that when m=4, the number of BCFW cells is the Narayana number Nn-3,k+1=1n-3n-3k+1n-3k.

Accepté le :
Publié le :
DOI : 10.4171/aihpd/87
Classification : 05-XX, 14-XX, 15-XX, 81-XX
Mots-clés : Amplituhedron, scattering amplitude, totally nonnegative Grassmannian, BCFW recursion, Narayana number, plane partition
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     author = {Karp, Steven N. and Williams, Lauren K. and Zhang, Yan X},
     title = {Decompositions of amplituhedra},
     journal = {Annales de l{\textquoteright}Institut Henri Poincar\'e D},
     pages = {303--363},
     volume = {7},
     number = {3},
     year = {2020},
     doi = {10.4171/aihpd/87},
     mrnumber = {4152617},
     zbl = {1470.81048},
     language = {en},
     url = {https://www.numdam.org/articles/10.4171/aihpd/87/}
}
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Karp, Steven N.; Williams, Lauren K.; Zhang, Yan X. Decompositions of amplituhedra. Annales de l’Institut Henri Poincaré D, Tome 7 (2020) no. 3, pp. 303-363. doi : 10.4171/aihpd/87. https://www.numdam.org/articles/10.4171/aihpd/87/

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