Off-shell extended graphic rule and the expansion of Berends-Giele currents in Yang-Mills theory

Abstract

Tree-level color-ordered Yang-Mills (YM) amplitudes can be decomposed in terms of (n − 2)! bi-scalar (BS) amplitudes, whose expansion coefficients form a basis of Bern-Carrasco-Johansson (BCJ) numerators. By the help of the recursive expansion of Einstein-Yang-Mills (EYM) amplitudes, the BCJ numerators are given by polynomial functions of Lorentz contractions which are conveniently described by graphic rule. In this work, we extend the expansion of YM amplitudes to off-shell level. We define different types of off-shell extended numerators that can be generated by graphs. By the use of these extended numerators, we propose a general decomposition formula of off-shell Berends-Giele currents in YM. This formula consists of three terms: (i). an effective current which is expanded as a combination of the Berends-Giele currents in BS theory (The expansion coefficients are one type of off-shell extended numerators) (ii). a term proportional to the total momentum of on-shell lines and (iii). a term expressed by the sum of lower point Berends-Giele currents in which some polarizations and momenta are replaced by vectors proportional to off-shell momenta appropriately. In the on-shell limit, the last two terms vanish while the decomposition of effective current precisely reproduces the decomposition of on-shell YM amplitudes with the expected coefficients (BCJ numerators in DDM basis). We further symmetrize these coefficients such that the Lie symmetries are satisfied. These symmetric BCJ numerators simultaneously satisfy the relabeling property of external lines and the algebraic properties (antisymmetry and Jacobi identity).

Snowmass White Paper: the Double Copy and its Applications

“…A particularly important class is given by Yang-Mills-Einstein theories, some simple supergravities which include non-abelian gauge interactions. Aside from the double-copy method [463,487,[571][572][573][574][575][576][577], a variety of approaches have been employed in studying the amplitudes in these theories, facilitating contact between closely-related subfields [41,[578][579][580][581][582][583][584][585][586][587][588][589].…”

A Type of Unifying Relation in (A)dS Spacetime

“…As a semi-on-shell method, Berends-Giele (BG) currents [5] are popular because of their recursive character. In recent years, many techniques based on BG currents have been developed [6][7][8][9][10][11][12][13][14][15][16][17]. However, the research of BG currents in (A)dS is still very scarce.…”

One-loop off-shell amplitudes from classical equations of motion

“…This construction, however, cannot be easily extended to gluon loops because of the gauge symmetry: lifting the on-shell condition in gauge fields is a non-trivial task. In this case, a concrete solution has only recently been found in [10], following an extensive procedure using graphic rules in pure Yang-Mills.…”