Physics Letters B 756 (2016) 180–187
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Elimination and recursions in the scattering equations
Carlos Cardona
a
, Chrysostomos Kalousios
b,∗
a
Physics Division, National Center for Theoretical Sciences, National Tsing-Hua University, Hsinchu, 30013 Taiwan, ROC
b
ICTP South American Institute for Fundamental Research, Instituto de Física Teórica, UNESP – Universidade Estadual Paulista, R. Dr. Bento T. Ferraz 271 – Bl. II,
01140-070, São Paulo, SP, Brazil
a r t i c l e i n f o a b s t r a c t
Article history:
Received
12 January 2016
Accepted
1 March 2016
Available
online 4 March 2016
Editor: M.
Cveti
ˇ
c
Keywords:
Scattering
amplitudes
Scattering
equations
Elimination
theory
We use the elimination theory to explicitly construct the (n − 3)! order polynomial in one of the variables
of the scattering equations. The answer can be given either in terms of a determinant of Sylvester type
of dimension (n − 3)! or a determinant of Bézout type of dimension (n − 4)!. We present a recursive
formula for the Sylvester determinant. Expansion of the determinants yields expressions in terms of
Plücker coordinates. Elimination of the rest of the variables of the scattering equations is also presented.
© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
The last decade a great amount of progress has been made in our understanding of scattering amplitudes for massless theories starting
with the revolutionary work of Witten [1] on four dimensional scattering amplitudes in twistor space. In 2013 a new formulation for the
computation of the tree level S-matrix of massless particles in any dimension was proposed in a series of papers by Cachazo, He and
Yuan (CHY) [2–6]. The formalism was proven for Yang–Mills and scalars in [7]. By defining a map from the space of kinematic invariants
of the scattering of n massless particles to the space of punctures over a Riemann sphere, CHY found the so-called scattering equations,
f
a
≡
n
b=a
k
a
· k
b
σ
a
− σ
b
= 0, a = 1, 2,...,n, (1)
where k
a
denotes the momentum of the ath particle and σ
b
the position of the bth puncture on the sphere. Those equations have appeared
previously in different contexts, particularly in the work of Fairlie and Roberts [8–10] and in the study of the high energy behavior of
scattering of strings by Gross and Mende [11] (see also [12–16]). In this work we use the polynomial form of (1) that was presented in
[17] and which can be written as
S⊂ A, |S|=m
k
2
S
σ
S
= 0, 2 ≤ m ≤ n − 2, (2)
where A = 1, 2,...,n and the sum runs over all subsets of S with m elements. Furthermore,
k
S
=
a∈S
k
a
, σ
S
=
b∈S
σ
b
. (3)
According to CHY, massless scattering at tree level in arbitrary dimensions can in general be described by the contour integral
A
n
=
d
n
σ
vol SL(2, C)
σ
ij
σ
jk
σ
ki
a=i, j,k
δ( f
a
) I
n
(k, , σ ), (4)
*
Corresponding author.
E-mail
addresses: carlosandres@mx.nthu.edu.tw (C. Cardona), ckalousi@ift.unesp.br (C. Kalousios).
http://dx.doi.org/10.1016/j.physletb.2016.03.003
0370-2693/
© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.