30,875 research outputs found
History of the tether concept and tether missions: a review
This paper introduces history of space tethers, including tether concepts and tether missions, and attempts to provide a source of references for historical understanding of space tethers. Several concepts of space tethers since the original concept has been conceived are listed in the literature, as well as a summary of interesting applications, and a research of space tethers is given. With the aim of implementing scientific experiments in aerospace, several space tether missions which have been delivered for aerospace application are introduced in the literature.</jats:p
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
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