150 research outputs found
Boundary Contributions Using Fermion Pair Deformation
Continuing the study of boundary BCFW recursion relation of tree level
amplitudes initiated in \cite{Feng:2009ei}, we consider boundary contributions
coming from fermion pair deformation. We present the general strategy for these
boundary contributions and demonstrate calculations using two examples, i.e,
the standard QCD and deformed QCD with anomalous magnetic momentum coupling. As
a by-product, we have extended BCFW recursion relation to off-shell gluon
current, where because off-shell gluon current is not gauge invariant, a new
feature must be cooperated.Comment: 26 pages, 4 figure
Single Cut Integration
We present an analytic technique for evaluating single cuts for one-loop
integrands, where exactly one propagator is taken to be on shell. Our method
extends the double-cut integration formalism of one-loop amplitudes to the
single-cut case. We argue that single cuts give meaningful information about
amplitudes when taken at the integrand level. We discuss applications to the
computation of tadpole coefficients.Comment: v2: corrected typo in abstrac
General Split Helicity Gluon Tree Amplitudes in Open Twistor String Theory
We evaluate all split helicity gluon tree amplitudes in open twistor string
theory. We show that these amplitudes satisfy the BCFW recurrence relations
restricted to the split helicity case and, hence, that these amplitudes agree
with those of gauge theory. To do this we make a particular choice of the
sextic constraints in the link variables that determine the poles contributing
to the contour integral expression for the amplitudes. Using the residue
theorem to re-express this integral in terms of contributions from poles at
rational values of the link variables, which we determine, we evaluate the
amplitudes explicitly, regaining the gauge theory results of Britto et al.Comment: 30 pages, minor misprints correcte
Spinor Helicity and Dual Conformal Symmetry in Ten Dimensions
The spinor helicity formalism in four dimensions has become a very useful
tool both for understanding the structure of amplitudes and also for practical
numerical computation of amplitudes. Recently, there has been some discussion
of an extension of this formalism to higher dimensions. We describe a
particular implementation of the spinor-helicity method in ten dimensions.
Using this tool, we study the tree-level S-matrix of ten dimensional super
Yang-Mills theory, and prove that the theory enjoys a dual conformal symmetry.
Implications for four-dimensional computations are discussed.Comment: 24 pages, 1 figure
Monodromy--like Relations for Finite Loop Amplitudes
We investigate the existence of relations for finite one-loop amplitudes in
Yang-Mills theory. Using a diagrammatic formalism and a remarkable connection
between tree and loop level, we deduce sequences of amplitude relations for any
number of external legs.Comment: 24 pages, 6 figures, v2 typos corrected, reference adde
On General BCJ Relation at One-loop Level in Yang-Mills Theory
BCJ relation reveals a dual between color structures and kinematic structure
and can be used to reduce the number of independent color-ordered amplitudes at
tree level. Refer to the loop-level in Yang-Mills theory, we investigate the
similar BCJ relation in this paper. Four-point 1-loop example in N = 4 SYM can
hint about the relation of integrands. Five-point example implies that the
general formula can be proven by unitary- cut method. We will then prove a
'general' BCJ relation for 1-loop integrands by D-dimension unitary cut, which
can be regarded as a non-trivial generalization of the (fundamental)BCJ
relation given by Boels and Isermann in [arXiv:1109.5888 [hep-th]] and
[arXiv:1110.4462 [hep-th]].Comment: 18 pages, 6 figure
Note on New KLT relations
In this short note, we present two results about KLT relations discussed in
recent several papers. Our first result is the re-derivation of Mason-Skinner
MHV amplitude by applying the S_{n-3} permutation symmetric KLT relations
directly to MHV amplitude. Our second result is the equivalence proof of the
newly discovered S_{n-2} permutation symmetric KLT relations and the well-known
S_{n-3} permutation symmetric KLT relations. Although both formulas have been
shown to be correct by BCFW recursion relations, our result is the first direct
check using the regularized definition of the new formula.Comment: 15 Pages; v2: minor correction
Note on Bonus Relations for N=8 Supergravity Tree Amplitudes
We study the application of non-trivial relations between gravity tree
amplitudes, the bonus relations, to all tree-level amplitudes in N=8
supergravity. We show that the relations can be used to simplify explicit
formulae of supergravity tree amplitudes, by reducing the known form as a sum
of (n-2)! permutations obtained by solving on-shell recursion relations, to a
new form as a (n-3)!-permutation sum. We demonstrate the simplification by
explicit calculations of the next-to-maximally helicity violating (NMHV) and
next-to-next-to-maximally helicity violating (N^2MHV) amplitudes, and provide a
general pattern of bonus coefficients for all tree-level amplitudes.Comment: 21 pages, 9 figures; v2, minor changes, references adde
Next-to-leading order QCD predictions for W+W+jj production at the LHC
Because the LHC is a proton-proton collider, sizable production of two
positively charged W-bosons in association with two jets is possible. This
process leads to a distinct signature of same sign high-pt leptons, missing
energy and jets. We compute the NLO QCD corrections to the QCD-mediated part of
pp -> W+W+jj. These corrections reduce the dependence of the production
cross-section on the renormalization and factorization scale to about +- 10
percent. We find that a large number of W+W+jj events contain a relatively hard
third jet. The presence of this jet should help to either pick up the W+W+jj
signal or to reject it as an unwanted background.Comment: 15 pages, 5 (lovely) figures, v3 accepted for publication in JHEP,
corrects tables in appendi
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