102,077 research outputs found
Dark Energy: a Brief Review
The problem of dark energy is briefly reviewed in both theoretical and
observational aspects. In the theoretical aspect, dark energy scenarios are
classified into symmetry, anthropic principle, tuning mechanism, modified
gravity, quantum cosmology, holographic principle, back-reaction and
phenomenological types. In the observational aspect, we introduce cosmic
probes, dark energy related projects, observational constraints on theoretical
models and model independent reconstructions.Comment: 19 pages, invited review article to appear in the special issue of
"Frontiers of Physics" dedicated to "High energy astrophysics", an shortened
version of our previous article arXiv:1103.587
The study of light invisible particles in decays
In this paper, we study the light scalar and pseudoscalar invisible particles
in the flavor changing neutral current processes of the meson. Effective
operators are introduced to describe the couplings between quarks and light
invisible particles. The Wilson coefficients are extracted from the
experimental results of the and mesons, which are used to predict the
upper limits of the branching fractions of the similar decay processes for the
meson. The hadronic transition matrix element is calculated with the
instantaneously approximated Bethe-Salpeter method. The upper limits of the
branching fractions when taking different values are presented. It is
found that at some region of , the channel has the largest upper limit which is of the order of
, and for , the largest value of the
upper limits can achieve the order of . Other decay modes, such as
and ,
are also considered.Comment: 24 pages, 35 figure
Weak Decays of Doubly-Heavy Tetraquarks
We study the weak decays of exotic tetraquark states
with two heavy quarks. Under the SU(3) symmetry for light quarks, these
tetraquarks can be classified into an octet plus a singlet: . We will concentrate on the octet tetraquarks with
, and study their weak decays, both semileptonic and nonleptonic.
Hadron-level effective Hamiltonian is constructed according to the irreducible
representations of the SU(3) group. Expanding the Hamiltonian, we obtain the
decay amplitudes parameterized in terms of a few irreducible quantities. Based
on these amplitudes, relations for decay widths are derived, which can be
tested in future. We also give a list of golden channels that can be used to
look for these states at various colliders.Comment: 14 pages,3 figure
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