7,753 research outputs found
Scattering of Massless Particles: Scalars, Gluons and Gravitons
In a recent note we presented a compact formula for the complete tree-level
S-matrix of pure Yang-Mills and gravity theories in arbitrary spacetime
dimension. In this paper we show that a natural formulation also exists for a
massless colored cubic scalar theory. In Yang-Mills, the formula is an integral
over the space of n marked points on a sphere and has as integrand two factors.
The first factor is a combination of Parke-Taylor-like terms dressed with U(N)
color structures while the second is a Pfaffian. The S-matrix of a U(N)xU(N')
cubic scalar theory is obtained by simply replacing the Pfaffian with a U(N')
version of the previous U(N) factor. Given that gravity amplitudes are obtained
by replacing the U(N) factor in Yang-Mills by a second Pfaffian, we are led to
a natural color-kinematics correspondence. An expansion of the integrand of the
scalar theory leads to sums over trivalent graphs and are directly related to
the KLT matrix. We find a connection to the BCJ color-kinematics duality as
well as a new proof of the BCJ doubling property that gives rise to gravity
amplitudes. We end by considering a special kinematic point where the partial
amplitude simply counts the number of color-ordered planar trivalent trees,
which equals a Catalan number. The scattering equations simplify dramatically
and are equivalent to a special Y-system with solutions related to roots of
Chebyshev polynomials.Comment: 31 page
Einstein-Yang-Mills Scattering Amplitudes From Scattering Equations
We present the building blocks that can be combined to produce tree-level
S-matrix elements of a variety of theories with various spins mixed in
arbitrary dimensions. The new formulas for the scattering of massless
particles are given by integrals over the positions of points on a sphere
restricted to satisfy the scattering equations. As applications, we obtain all
single-trace amplitudes in Einstein--Yang--Mills (EYM) theory, and
generalizations to include scalars. Also in EYM but extended by a B-field and a
dilaton, we present all double-trace gluon amplitudes. The building blocks are
made of Pfaffians and Parke--Taylor-like factors of subsets of particle labels.Comment: 18 pages. References and a new section on double-trace gluon
amplitudes added in v
Higgs Inflation, Reheating and Gravitino Production in No-Scale Supersymmetric GUTs
We extend our previous study of supersymmetric Higgs inflation in the context
of no-scale supergravity and grand unification, to include models based on the
flipped SU(5) and the Pati-Salam group. Like the previous SU(5) GUT model,
these yield a class of inflation models whose inflation predictions interpolate
between those of the quadratic chaotic inflation and Starobinsky-like
inflation, while avoiding tension with proton decay limits. We further analyse
the reheating process in these models, and derive the number of e-folds, which
is independent of the reheating temperature. We derive the corresponding
predictions for the scalar tilt and the tensor-to-scalar ratio in cosmic
microwave background perturbations, as well as discussing the gravitino
production following inflation.Comment: JCAP Final Version. 23pp, 3 Figs. Only minor refinements, references
adde
Casting Light on Dark Matter
The prospects for detecting a candidate supersymmetric dark matter particle
at the LHC are reviewed, and compared with the prospects for direct and
indirect searches for astrophysical dark matter. The discussion is based on a
frequentist analysis of the preferred regions of the Minimal supersymmetric
extension of the Standard Model with universal soft supersymmetry breaking (the
CMSSM). LHC searches may have good chances to observe supersymmetry in the near
future - and so may direct searches for astrophysical dark matter particles,
whereas indirect searches may require greater sensitivity, at least within the
CMSSM.Comment: 16 pages, 13 figures, contribution to the proceedings of the LEAP
2011 Conferenc
On the Interpretation of Gravitational Corrections to Gauge Couplings
Several recent papers discuss gravitational corrections to gauge couplings
that depend quadratically on the energy. In the framework of the
background-field approach, these correspond in general to adding to the
effective action terms quadratic in the field strength but with higher-order
space-time derivatives. We observe that such terms can be removed by
appropriate local field redefinitions, and do not contribute to physical
scattering-matrix elements. We illustrate this observation in the context of
open string theory, where the effective action includes, among other terms, the
well-known Born-Infeld form of non-linear electrodynamics. We conclude that the
quadratically energy-dependent gravitational corrections are \emph{not}
physical in the sense of contributing to the running of a physically-measurable
gauge coupling, or of unifying couplings as in string theory.Comment: 4 page
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