[institut] [phys4phys] Group for Gravitation, Particle and Fields on-line seminar, Friday 11 March 2022

[Marija Dimitrijevic Ciric]

Dear colleagues,

You are cordially invited to the online seminar of the Group for 
Gravitation, Particles and Fields, which will be held on Friday, 11 
March 2022 at 11:00 via the BigBlueButton platform (link is given 
below).


The talk entitled

Landau Singularities in Planar Massless Theories

will be given by Igor Prlina (PhD from Brown University 2019).

Abstract: In this work we present our contribution to the method of 
using Landau singularities for probing scattering amplitudes in planar 
massless quantum field theories. We start by proposing a simple 
geometric algorithm for determining the complete set of branch points of 
amplitudes in planar N = 4 super-Yang-Mills theory directly from the 
amplituhedron, without resorting to any particular representation in 
terms of local Feynman integrals. This represents a step towards 
translating integrands directly into integrals. In particular, the 
algorithm provides information about the symbol alphabets of general 
amplitudes. First we illustrate the algorithm applied to the one-and 
two-loop MHV amplitudes. Then we demonstrate how to use the 
reformulation of amplituhedra in terms of 'sign flips' in order to 
streamline the application of this algorithm to amplitudes of any 
helicity. In this way we recover the known branch points of all one-loop 
amplitudes, and we find an 'emergent positivity' on boundaries of 
amplituhedra. Lastly, we look beyond planar N = 4 super-Yang-Mills 
theory, and analyze Landau singularities of general massless planar 
theories. In massless quantum field theories the Landau equations are 
invariant under graph operations familiar from the theory of electrical 
circuits. Using a theorem on the Y-∆ reducibility of planar circuits we 
prove that the set of first-type Landau singularities of an n-particle 
scattering amplitude in any massless planar theory, in any spacetime 
dimension D, at any finite loop order in perturbation theory, is a 
subset of those of a certain n-particle ⌊(n−2)^2/4⌋-loop "ziggurat" 
graph. We determine this singularity locus explicitly for D = 4 and n = 
6 and find that it corresponds precisely to the vanishing of the symbol 
letters familiar from the hexagon bootstrap in SYM theory. Further 
implications for SYM theory are discussed.



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Time: March 11, 2022 11:00 Belgrade

https://gravityserver.ipb.ac.rs/b/mar-xoo-t1v-vwn

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Best regards,

Marija Dimitrijevic Ciric

University of Belgrade
Faculty of Physics
Studentski trg 12-16
11000 Belgrade
Serbia