7,232 research outputs found
Expanding Einstein-Yang-Mills by Yang-Mills in CHY frame
Using the Cachazo-He-Yuan (CHY) formalism, we prove a recursive expansion of
tree level single trace Einstein-Yang-Mills (EYM) amplitudes with arbitrary
number of gluons and gravitons, which is valid for general spacetime dimensions
and any helicity configurations. The recursion is written in terms of
fewer-graviton EYM amplitudes and pure Yang-Mills (YM) amplitudes, which can be
further carried out until we reach an expansion in terms of pure YM amplitudes
in Kleiss-Kuijf (KK) basis. Our expansion then generates naturally a spanning
tree structure rooted on gluons whose vertices are gravitons. We further
propose a set of graph theoretical rules based on spanning trees that evaluate
directly the pure YM expansion coefficients.Comment: 36 pages, 3 captioned figures; v2: more details added, revised and
published versio
A search for sterile neutrinos with the latest cosmological observations
We report the result of a search for sterile neutrinos with the latest
cosmological observations. Both cases of massless and massive sterile neutrinos
are considered in the CDM cosmology. The cosmological observations
used in this work include the Planck 2015 temperature and polarization data,
the baryon acoustic oscillation data, the Hubble constant direct measurement
data, the Planck Sunyaev-Zeldovich cluster counts data, the Planck lensing
data, and the cosmic shear data. We find that the current observational data
give a hint of the existence of massless sterile neutrino (as dark radiation)
at the 1.44 level, and the consideration of an extra massless sterile
neutrino can indeed relieve the tension between observations and improve the
cosmological fit. For the case of massive sterile neutrino, the observations
give a rather tight upper limit on the mass, which implies that actually a
massless sterile neutrino is more favored. Our result is consistent with the
recent result of neutrino oscillation experiment done by the Daya Bay and MINOS
collaborations, as well as the recent result of cosmic ray experiment done by
the IceCube collaboration.Comment: 16 pages, 4 figures; accepted for publication in Eur. Phys. J.
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