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atyy
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Ben Niehoff said:The funny rainbow picture is just the artist's imaginative illustration after hearing the physicists attempt to describe what they've done in simple language.
The original paper is here:
http://arxiv.org/abs/1212.5605
The paper doesn't seem to use the word "amplituhedron". Natalie Wolchover's article https://www.simonsfoundation.org/quanta/20130917-a-jewel-at-the-heart-of-quantum-physics/ seems to indicate it's a different thing from the positive Grassmannian.
"The physicists hoped that the amplitude of a scattering process would emerge purely and inevitably from geometry, but locality and unitarity were dictating which pieces of the positive Grassmannian to add together to get it. They wondered whether the amplitude was “the answer to some particular mathematical question,” said Trnka, a post-doctoral researcher at the California Institute of Technology. “And it is,” he said."
"Arkani-Hamed and Trnka discovered that the scattering amplitude equals the volume of a brand-new mathematical object — the amplituhedron."