316 research outputs found
Photon Polarization in the b->s gamma processes in the Left-Right Symmetric Model
The circular-polarization of the photon in the radiative B decays is
dominantly left-handed in the Standard Model (SM), but the right-handed
polarization may be enhanced in some new physics models with right-handed
currents, such as the Left-Right Symmetric Model (LRSM). In this article, we
investigate how large this wrong polarization could be within the allowed
parameter space of the LRSM. We show that in LRSM, the right-handed
polarization of the photon in the processes could be largely
enhanced by the mixing contributions because of the helicity flip on
the internal top quark line of the penguin diagrams and the enhancement by the
CKM factor . We discuss the sensitivity of the proposed
methods to determine the photon polarization to the LRSM as well
as their complementary role compared to the direct search of right-handed
charged gauge bosons at LHC.Comment: 30pages, 5 figures, published version; references adde
Implications on the first observation of charm CPV at LHCb
Very recently, the LHCb Collaboration observed the violation (CPV) in
the charm sector for the first time, with .
This result is consistent with our prediction of obtained in the factorization-assisted
topological-amplitude (FAT) approach in [PRD86,036012(2012)]. It implies that
the current understanding of the penguin dynamics in charm decays in the
Standard Model is reasonable. Motivated by the success of the FAT approach, we
further suggest to measure the decay, which is the next
potential mode to reveal the CPV of the same order as .Comment: 10 page
Determination of mixing angle through decays
We study decays, the quark content of
and the mixing angle of and . We calculate not only the
factorizable contribution in QCD facorization scheme but also the
nonfactorizable hard spectator corrections in QCDF and pQCD approach. We get
consistent result with the experimental data of and
predict the branching ratio of . We suggest two ways
to determine mixing angle . Using the experimental
measured branching ratio of , we can get the
mixing angle with some theoretical uncertainties. We
suggest another way to determine mixing angle using both
of experimental measured decay branching ratios to avoid theoretical uncertainties.Comment: arXiv admin note: substantial text overlap with arXiv:0707.263
Branching ratios and direct CP asymmetries in decays
We propose a theoretical framework for analyzing two-body nonleptonic
meson decays, based on the factorization of short-distance (long-distance)
dynamics into Wilson coefficients (hadronic matrix elements of four-fermion
operators). The parametrization of hadronic matrix elements in terms of several
nonperturbative quantities is demonstrated for the decays,
denoting a pseudoscalar meson. We consider the evolution of Wilson coefficients
with energy release in individual decay modes, and the Glauber strong phase
associated with the pion in nonfactorizable annihilation amplitudes, that is
attributed to the unique role of the pion as a Nambu-Goldstone boson and a
quark-anti-quark bound state simultaneously. The above inputs improve the
global fit to the branching ratios involving the meson, and resolves
the long-standing puzzle from the and
branching ratios, respectively. Combining short-distance dynamics associated
with penguin operators and the hadronic parameters determined from the global
fit to branching ratios, we predict direct CP asymmetries, to which the quark
loops and the scalar penguin annihilation give dominant contributions. In
particular, we predict , lower than the LHCb and CDF data.Comment: 17 pages, 3 figures, matches published versio
Branching ratios and direct CP asymmetries in decays
We study the two-body hadronic decays, where () denotes a
pseudoscalar (vector) meson, in the factorization-assisted
topological-amplitude approach proposed in our previous work. This approach is
based on the factorization of short-distance and long-distance dynamics into
Wilson coefficients and hadronic matrix elements of four-fermion operators,
respectively, with the latter being parametrized in terms of several
nonperturbative quantities. We further take into account the -
mixing effect, which improves the global fit to the branching ratios involving
the and mesons. Combining short-distance dynamics associated
with penguin operators and the hadronic parameters determined from the global
fit to branching ratios, we predict direct asymmetries. In particular, the
direct asymmetries in the , , and decays are found to be of , which can be
observed at the LHCb or future Belle II experiment. We also predict the
asymmetry observables of some neutral meson decays.Comment: 16 pages, 2 figure
Charged lepton flavor violating Higgs decays at future colliders
After the discovery of the Higgs boson, several future experiments have been
proposed to study the Higgs boson properties, including two circular lepton
colliders, the CEPC and the FCC-ee, and one linear lepton collider, the ILC. We
evaluate the precision reach of these colliders in measuring the branching
ratios of the charged lepton flavor violating Higgs decays ,
and . The expected upper bounds on the
branching ratios given by the circular (linear) colliders are found to be
, and at 95\% CL, which are improved by
one to two orders compared to the current experimental bounds. We also discuss
the constraints that these upper bounds set on certain theory parameters,
including the charged lepton flavor violating Higgs couplings, the
corresponding parameters in the type-III 2HDM, and the new physics cut-off
scales in the SMEFT, in RS models and in models with heavy neutrinos.Comment: 20 pages, 2 figures (extend the CEPC study to the FCC-ee and the ILC,
and to match the published version
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