Amplitudes for massive vector and scalar bosons in spontaneously-broken gauge theory from the CHY representation

In the formulation of Cachazo, He, and Yuan, tree-level amplitudes for massless particles in gauge theory and gravity can be expressed as rational functions of the Lorentz invariants $k_a \cdot k_b$, $\epsilon_a \cdot k_b$, and $\epsilon_a \cdot \epsilon_b$, valid in any number of spacetime dimensions. We use dimensional reduction of higher-dimensional amplitudes of particles with internal momentum $\kappa$ to obtain amplitudes for massive particles in lower dimensions. In the case of gauge theory, we argue that these massive amplitudes belong to a theory in which the gauge symmetry is spontaneously broken by an adjoint Higgs field. Consequently, we show that tree-level $n$-point amplitudes containing massive vector and scalar bosons in this theory can be obtained by simply replacing $k_a \cdot k_b$ with $k_a \cdot k_b - \kappa_a \kappa_b$ in the corresponding massless amplitudes, where the masses of the particles are given by $|\kappa_a|$.Comment: 7 pages, no figures; v2: added paragraph, published versio

Scattering equations and BCJ relations for gauge and gravitational amplitudes with massive scalar particles

We generalize the scattering equations to include both massless and massive particles. We construct an expression for the tree-level n-point amplitude with n-2 gluons or gravitons and a pair of massive scalars in arbitrary spacetime dimension as a sum over the (n-3)! solutions of the scattering equations, a la Cachazo, He, and Yuan. We derive the BCJ relations obeyed by these massive amplitudes.Comment: 22 pages. v2: clarification of eqs. (5.5) and (5.6

Scattering equations and virtuous kinematic numerators and dual-trace functions

Inspired by recent developments on scattering equations, we present a constructive procedure for computing symmetric, amplitude-encoded, BCJ numerators for n-point gauge-theory amplitudes, thus satisfying the three virtues identified by Broedel and Carrasco. We also develop a constructive procedure for computing symmetric, amplitude-encoded dual-trace functions (tau) for n-point amplitudes. These can be used to obtain symmetric kinematic numerators that automatically satisfy color-kinematic duality. The S_n symmetry of n-point gravity amplitudes formed from these symmetric dual-trace functions is completely manifest. Explicit expressions for four- and five-point amplitudes are presented.Comment: 24 pages; v2: minor sign corrections, added references; v3: minor corrections, published versio

Large-N Universality of the Two-Dimensional Yang-Mills String

We exhibit the gauge-group independence (``universality'') of all normalized non-intersecting Wilson loop expectation values in the large N limit of two-dimensional Yang-Mills theory. This universality is most easily understood via the string theory reformulation of these gauge theories. By constructing an isomorphism between the string maps contributing to normalized Wilson loop expectation values in the different theories, we prove the large N universality of these observables on any surface. The string calculation of the Wilson loop expectation value on the sphere also leads to an indication of the large N phase transition separating strong- and weak-coupling phases.Comment: 18 pages, phyzzx macro, no figure

Level-rank duality of untwisted and twisted D-branes of the so(N)_K WZW model

We analyze the level-rank duality of untwisted and epsilon-twisted D-branes of the so(N)_K WZW model. Untwisted D-branes of so(N)_K are characterized by integrable tensor and spinor representations of so(N)_K. Level-rank duality maps untwisted so(N)_K D-branes corresponding to (equivalence classes of) tensor representations onto those of so(K)_N. The epsilon-twisted D-branes of so(2n)_2k are characterized by (a subset of) integrable tensor and spinor representations of so(2n-1)_2k+1. Level-rank duality maps spinor epsilon-twisted so(2n)_2k D-branes onto those of so(2k)_2n. For both untwisted and epsilon-twisted D-branes, we prove that the spectrum of an open string ending on these D-branes is isomorphic to the spectrum of an open string ending on the level-rank-dual D-branes.Comment: 18 page

IR divergences and Regge limits of subleading-color contributions to the four-gluon amplitude in N=4 SYM Theory

We derive a compact all-loop-order expression for the IR-divergent part of the N=4 SYM four-gluon amplitude, which includes both planar and all subleading-color contributions, based on the assumption that the higher-loop soft anomalous dimension matrices are proportional to the one-loop soft anomalous dimension matrix, as has been recently conjectured. We also consider the Regge limit of the four-gluon amplitude, and we present evidence that the leading logarithmic growth of the subleading-color amplitudes is less severe than that of the planar amplitudes. We examine possible 1/N^2 corrections to the gluon Regge trajectory, previously obtained in the planar limit from the BDS ansatz. The double-trace amplitudes have Regge behavior as well, with a nonsense-choosing Regge trajectory and a Regge cut which first emerges at three loops.Comment: 29 pages; v2: corrections to sections 5.1 and 5.2, references added; v3: clarification in introduction, references added; v4: published versio

Quantum Corrections to Deep Bags

Nontopological solitons, or ``bags,'' can arise when fermions acquire their mass through a Yukawa coupling to some scalar field. Bags have played an important role in models of baryons, nuclei, and more recently, in the idea that a Higgs condensate may form around a very heavy top quark. It has been claimed that deep bags, which correspond to tightly-bound states of fermions, will form when the Yukawa coupling is strong. Quantum corrections, however, are significant in this regime. We examine the effects of these quantum corrections on the formation of nontopological solitons in an exactly solvable large-$N$ model. We find that quantum bags differ dramatically from those of the classical theory. In particular, for large Yukawa coupling, the bags remain shallow and the fermions weakly bound.Comment: Talk given at the XXVI Int. Conf. on High Energy Physics, August, 1992 LATEX file, 7 pages + 2 figures available upon request, JHU-TIPAC-92002

KLT-type relations for QCD and bicolor amplitudes from color-factor symmetry

Color-factor symmetry is used to derive a KLT-type relation for tree-level QCD amplitudes containing gluons and an arbitrary number of massive or massless quark-antiquark pairs, generalizing the expression for Yang-Mills amplitudes originally postulated by Bern, De Freitas, and Wong. An explicit expression is given for all amplitudes with two or fewer quark-antiquark pairs in terms of the (modified) momentum kernel. We also introduce the bicolor scalar theory, the "zeroth copy" of QCD, containing massless biadjoint scalars and massive bifundamental scalars, generalizing the biadjoint scalar theory of Cachazo, He, and Yuan. We derive KLT-type relations for tree-level amplitudes of biadjoint and bicolor theories using the color-factor symmetry possessed by these theories.Comment: 24 pages, 2 figures; v2: added referenc