1,095 research outputs found
Consistency Conditions on S-Matrix of Spin 1 Massless Particles
Motivated by new techniques in the computation of scattering amplitudes of
massless particles in four dimensions, like BCFW recursion relations, the
question of how much structure of the S-matrix can be determined from purely
S-matrix arguments has received new attention. The BCFW recursion relations for
massless particles of spin 1 and 2 imply that the whole tree-level S-matrix can
be determined in terms of three-particle amplitudes (evaluated at complex
momenta). However, the known proofs of the validity of the relations rely on
the Lagrangian of the theory, either by using Feynman diagrams explicitly or by
studying the effective theory at large complex momenta. This means that a
purely S-matrix theoretic proof of the relations is still missing. The aim of
this paper is to provide such a proof for spin 1 particles by extending the
four-particle test introduced by P. Benincasa and F. Cachazo in
arXiv:0705.4305[hep-th] to all particles. We show how n-particle tests imply
that the rational function built from the BCFW recursion relations possesses
all the correct factorization channels including holomorphic and
anti-holomorphic collinear limits. This in turn implies that they give the
correct S-matrix of the theory.Comment: 24 pages, 4 figure
One-Loop Amplitudes Of Gluons In SQCD
One-loop amplitudes of gluons in supersymmetric Yang-Mills are
four-dimensional cut-constructible. This means that they can be determined from
their unitarity cuts. We present a new systematic procedure to explicitly carry
out any finite unitarity cut integral. The procedure naturally separates the
contributions from bubble, triangle and box scalar integrals. This technique
allows the systematic calculation of N=1 amplitudes of gluons. As an
application we compute all next-to-MHV six-gluon amplitudes in N=1
super-Yang-Mills.Comment: 49 pages, 4 figures, harvmac. v2: references added, typos fixed. v3:
corrections to 3-mass-triangle coefficients, footnote 6 added,
acknowledgments added. v4: a typo in formulas for the 3-mass-triangle
coefficient is corrected, acknowledgments adde
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
A note on the boundary contribution with bad deformation in gauge theory
Motivated by recently progresses in the study of BCFW recursion relation with
nonzero boundary contributions for theories with scalars and
fermions\cite{Bofeng}, in this short note we continue the study of boundary
contributions of gauge theory with the bad deformation. Unlike cases with
scalars or fermions, it is hard to use Feynman diagrams directly to obtain
boundary contributions, thus we propose another method based on the SYM theory. Using this method, we are able to write down a useful
on-shell recursion relation to calculate boundary contributions from related
theories. Our result shows the cut-constructibility of gauge theory even with
the bad deformation in some generalized sense.Comment: 16 pages, 7 figure
Integrand reduction of one-loop scattering amplitudes through Laurent series expansion
We present a semi-analytic method for the integrand reduction of one-loop
amplitudes, based on the systematic application of the Laurent expansions to
the integrand-decomposition. In the asymptotic limit, the coefficients of the
master integrals are the solutions of a diagonal system of equations, properly
corrected by counterterms whose parametric form is konwn a priori. The Laurent
expansion of the integrand is implemented through polynomial division. The
extension of the integrand-reduction to the case of numerators with rank larger
than the number of propagators is discussed as well.Comment: v2: Published version: references and two appendices added. v3:
Eq.(6.11) corrected, Appendix B updated accordingl
On-Shell Recursion Relations for Generic Theories
We show that on-shell recursion relations hold for tree amplitudes in generic
two derivative theories of multiple particle species and diverse spins. For
example, in a gauge theory coupled to scalars and fermions, any amplitude with
at least one gluon obeys a recursion relation. In (super)gravity coupled to
scalars and fermions, the same holds for any amplitude with at least one
graviton. This result pertains to a broad class of theories, including QCD, N=4
SYM, and N=8 supergravity.Comment: 19 pages, 3 figure
Multi-frequency, Multi-Epoch Study of Mrk 501: Hints for a two-component nature of the emission
Since the detection of very high energy (VHE) -rays from Mrk 501, its
broad band emission of radiation was mostly and quite effectively modeled using
one zone emission scenario. However, broadband spectral and flux variability
studies enabled by the multiwavelength campaigns carried out during the recent
years have revealed rather complex behavior of Mrk 501. The observed emission
from Mrk 501 could be due to a complex superposition of multiple emission
zones. Moreover new evidences of detection of very hard intrinsic -ray
spectra obtained from {\it Fermi}--LAT observations have challenged the
theories about origin of VHE -rays. Our studies based on {\it
Fermi}--LAT data indicate the existence of two separate components in the
spectrum, one for low energy -rays and the other for high energy
-rays. Using multiwaveband data from several ground and space based
instruments, in addition to HAGAR data, the spectral energy distribution of
Mrk~501 is obtained for various flux states observed during 2011. In the
present work, this observed broadband spectral energy distribution is
reproduced with a leptonic, multi-zone Synchrotron Self-Compton model.Comment: Published in Astrophysical Journal (ApJ
Superconformal Multi-Black Hole Moduli Spaces in Four Dimensions
Quantum mechanics on the moduli space of N supersymmetric Reissner-Nordstrom
black holes is shown to admit 4 supersymmetries using an unconventional
supermultiplet which contains 3N bosons and 4N fermions. A near-horizon limit
is found in which the quantum mechanics of widely separated black holes
decouples from that of strongly-interacting, near-coincident black holes. This
near-horizon theory is shown to have an enhanced D(2,1;0) superconformal
symmetry. The bosonic symmetries are SL(2,R) conformal symmetry and SU(2)xSU(2)
R-symmetry arising from spatial rotations and the R-symmetry of N=2
supergravity.Comment: 23 pages, harvmac. v2: many typos fixe
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