Scattering Amplitudes and the Positive Grassmannian
read the original abstract
We establish a direct connection between scattering amplitudes in planar four-dimensional theories and a remarkable mathematical structure known as the positive Grassmannian. The central physical idea is to focus on on-shell diagrams as objects of fundamental importance to scattering amplitudes. We show that the all-loop integrand in N=4 SYM is naturally represented in this way. On-shell diagrams in this theory are intimately tied to a variety of mathematical objects, ranging from a new graphical representation of permutations to a beautiful stratification of the Grassmannian G(k,n) which generalizes the notion of a simplex in projective space. All physically important operations involving on-shell diagrams map to canonical operations on permutations; in particular, BCFW deformations correspond to adjacent transpositions. Each cell of the positive Grassmannian is naturally endowed with positive coordinates and an invariant measure which determines the on-shell function associated with the diagram. This understanding allows us to classify and compute all on-shell diagrams, and give a geometric understanding for all the non-trivial relations among them. Yangian invariance of scattering amplitudes is transparently represented by diffeomorphisms of G(k,n) which preserve the positive structure. Scattering amplitudes in (1+1)-dimensional integrable systems and the ABJM theory in (2+1) dimensions can both be understood as special cases of these ideas. On-shell diagrams in theories with less (or no) supersymmetry are associated with exactly the same structures in the Grassmannian, but with a measure deformed by a factor encoding ultraviolet singularities. The Grassmannian representation of on-shell processes also gives a new understanding of the all-loop integrand for scattering amplitudes, presenting all integrands in a novel dLog form which directly reflects the underlying positive structure.
This paper has not been read by Pith yet.
Forward citations
Cited by 9 Pith papers
-
The Conformal Grassmannian: A Symplectic Bi-Grassmannian for $CFT_ 4$ Correlators
A new symplectic bi-Grassmannian representation encodes CFT4 Wightman correlators via integrals over mutually symplectically orthogonal n-planes aligned with kinematics, reproducing known 2- and 3-point structures com...
-
Emergent Features in $U(N) \times U(\tilde{N})$ Bi-adjoint Cubic Theory
A planar scattering potential in bi-adjoint φ³ theory reproduces Dolan-Goddard massive equations, counts invariants via Ferrers shapes, and interprets U(1) decoupling as Catalan and Narayana recursions.
-
Loop integrals in de Sitter spacetime: The parity-split IBP system and $\mathrm{d}\log$-form differential equations
A parity-split IBP system for n-propagator families in de Sitter space is identified, along with a conjecture that dlog-form differential equations extend to dS integrands with Hankel functions, verified for the one-l...
-
Kinematics, cluster algebras and Feynman integrals
Cluster algebras for planar conformal kinematics are identified as G(4,n) subalgebras and used to bootstrap the symbol of an 8-point three-loop wheel integral via D3 and new algebraic letters.
-
Tree Amplitudes with Charged Matter in Pure Gauge Theory
A new Mathematica package computes tree amplitudes with arbitrary gauge bosons and arbitrarily charged massless fermions by reducing distinct-flavor partial amplitudes to linear combinations of single-flavor supersymm...
-
QFT in Klein space
Authors construct canonical and path-integral quantizations for QFT in Klein space using extra modes, deriving correlation functions that match Minkowski space via analytical continuation.
-
Recursive construction for expansions of tree Yang-Mills amplitudes from soft theorem
A recursive construction expands tree YM amplitudes to YMS and BAS amplitudes from soft theorems while preserving gauge invariance at each step.
-
New recursive construction for tree NLSM and SG amplitudes, and new understanding of enhanced Adler zero
Recursive construction of off-shell NLSM and SG tree amplitudes from bootstrapped low-point ones via universal soft behaviors, automatically producing enhanced Adler zeros on-shell.
-
Expanding single trace YMS amplitudes with gauge invariant coefficients
A recursive expansion of single-trace YMS amplitudes is built from soft theorems; the result is gauge invariant, permutation symmetric, and equivalent to the Cheung-Mangan covariant color-kinematic duality construction.
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.