# A Question about the associahedron/amplituhedron

1. Aug 1, 2018

### nrqed

If anyone here has worked on the associahedron and/or amplituhedron, I would like your input. I am focusing now on the paper by Nima Arkani-Hamed et al, "Scattering Forms and the Positive Geometry of Kinematics, Color an the Worldsheet".

The key step to define the kinematic associahedron is to impose $X_{ij} \geq 0$ and also the impose the $c_{ij} > 0$. They do this without giving any motivation at all. I know that it gives the correct answer in the end, but I wonder if there is any way to motivate these choices, from a physics point of view (or short of that, from a mathematical point of view). It would be nice to get some intuition about what leads to these choices, other than "because it gives the correct final answer".

Thank you!

2. Aug 2, 2018

### MathematicalPhysicist

How do they know what is the correct answer?

3. Aug 2, 2018

### nrqed

The scattering form restricted to the associahedron reproduces the correct amplitude. Or, alternatively, the volume of the dual associahedron gives the correct amplitude.