5,851 research outputs found
The Decay Properties of the 1^{-+} Hybrid State
Within the framework of the QCD sum rules, we consider the three-point
correlation function, work at the limit q^2 -> 0 and m_\pi -> 0, and pick out
the singular term ~ {1\over q^2} to extract the pionic coupling constants of
the 1^{-+} hybrid meson. Then we calculate the decay widths of different modes.
The decay width of the S-wave modes b_1 \pi, f_1\pi increases quickly as the
hybrid meson mass and decay momentum increase. But for the low mass hybrid
meson around 1.6 GeV, the P-wave decay mode \rho \pi is very important and its
width is around 180 MeV, while the widths of \eta \pi and \eta^\prime \pi are
strongly suppressed. We suggest the experimental search of \pi_1(1600) through
the decay chains at BESIII: e^+e^- -> J/\psi(\psi') -> \pi_1 +\gamma or e^+e^-
-> J/\psi(\psi') -> \pi_1 +\rho where the \pi_1 state can be reconstructed
through the decay modes \pi_1 -> \rho\pi -> \pi^+\pi^-\pi^0 or \pi_1 ->
f_1(1285)\pi^0. It is also interesting to look for \pi_1 using the available
BELLE/BABAR data through the process e^+e^- -> \gamma^\ast -> \rho\pi_1,
b_1\pi_1, \gamma \pi_1 etc.Comment: one reference correcte
The I^G J^{PC}=1^- 1^{-+} Tetraquark States
We study the tetraquark states with I^G J^{PC}=1^- 1^{-+} in the QCD sum
rule. After exhausting all possible flavor structures, we analyses both the SVZ
and finite energy sum rules. Both approaches lead to a mass around 1.6 GeV for
the state with the quark contents q q q_bar q_bar, and around 2.0 GeV for the
state with the quark contents q s q_bar s_bar. The flavor structure 3_bar *
6_bar + 6 * 3 is preferred. Our analysis strongly indicates that both pi1(1600)
and pi1(2015) are also compatible with the exotic tetraquark interpretation,
which are sometimes labeled as candidates of the 1^{-+} hybrid mesons. Moreover
one of their dominant decay modes is a pair of axial-vector and pseudoscalar
mesons such as b1(1235) pi, which is sometimes considered as the characteristic
decay mode of the hybrid mesons.Comment: 18 pages, 14 figures, revised version to appear in Phys. Rev.
Exotic Tetraquark ud bar[s] bar[s] of J^P=0^+ in the QCD Sum Rule
We study a QCD sum rule analysis for an exotic tetraquark ud bar[s] bar[s] of
J^P=0^+ and I = 1. We construct q q bar[q] bar[q] currents in a local product
form and find that there are five independent currents for this channel. Due to
high dimensional nature of the current, it is not easy to form a good sum rule
when using a single current. This means that we do not find any sum rule window
to extract reliable results, due to the insufficient convergence of the OPE and
to the exceptional important role of QCD continuum. Then we examine sum rules
by using currents of linear combinations of two currents among the independent
ones. We find two reasonable cases that predict a mass of the tetraquark around
1.5 GeV.Comment: 15 pages, 8 figures, revised versio
Light Scalar Tetraquark Mesons in the QCD Sum Rule
We study the lowest-lying scalar mesons in the QCD sum rule by considering
them as tetraquark states. We find that there are five independent currents for
each state with a certain flavor structure. By forming linear combinations, we
find that some mixed currents give reliable QCD sum rules. Among various
tetraquark currents, we consider those which are constructed by the diquarks
having anti-symmetric and symmetric flavor structures. That the results of the
QCD sum rule derived from the two types of currents are similar suggests that
the tetraquark states can have a large mixing between different flavor
structures.Comment: 18 pages, 5 figures; reference added, minor corrections; version to
appear in Phys.Rev.
Next-to-leading order QCD corrections to the top quark associated with production via model-independent flavor-changing neutral-current couplings at hadron colliders
We present the complete next-to-leading order (NLO) QCD corrections to the
top quark associated with production induced by model-independent
and flavor-changing neutral-current (FCNC) couplings at hadron
colliders, respectively. We also consider the mixing effects between the
and FCNC couplings for this process. Our results show that,
for the couplings, the NLO QCD corrections can enhance the total
cross sections by about 50% and 40% at the Tevatron and LHC, respectively.
Including the contributions from the , FCNC couplings and their
mixing effects, the NLO QCD corrections can enhance the total cross sections by
about 50% for the and FCNC couplings, and by about the 80% for
the and FCNC couplings at the LHC, respectively. Moreover, the
NLO corrections reduce the dependence of the total cross section on the
renormalization and factorization scale significantly. We also evaluate the NLO
corrections for several important kinematic distributions.Comment: 25 pages, 16 figure
Next-to-leading order QCD corrections to the top quark decay via the Flavor-Changing Neutral-Current operators with mixing effects
In this paper detailed calculations of the complete
corrections to top quark decay widths are presented
(). Besides describing in detail the calculations in our previous
paper (arXiv:0810.3889), we also include the mixing effects of the
Flavor-Changing Neutral-Current (FCNC) operators for and , which were not considered in our previous paper. The results for are the same as in our previous paper. But the mixing effects can either
be large or small, and increase or decrease the branching ratios for and , depending on the values of the anomalous couplings
(,
and ).Comment: 21 pages, 12 figure
Implementation of quantum gates based on geometric phases accumulated in the eigenstates of periodic invariant operators
We propose a new strategy to physically implement a universal set of quantum
gates based on geometric phases accumulated in the nondegenerate eigenstates of
a designated invariant operator in a periodic physical system. The system is
driven to evolve in such a way that the dynamical phase shifts of the invariant
operator eigenstates are the same (or {\it mod} ) while the corresponding
geometric phases are nontrivial.
We illustrate how this strategy to work in a simple but typical NMR-type
qubit system.Comment: 4 page
Current-induced Spin Polarization in Two-Dimensional Hole Gas
We investigate the current-induced spin polarization in the two-dimensional
hole gas (2DHG) with the structure inversion asymmetry. By using the
perturbation theory, we re-derive the effective -cubic Rashba Hamiltonian
for 2DHG and the generalized spin operators accordingly. Then based on the
linear response theory we calculate the current-induced spin polarization both
analytically and numerically with the disorder effect considered. We have found
that, quite different from the two-dimensional electron gas, the spin
polarization in 2DHG depends linearly on Fermi energy in the low doping regime,
and with increasing Fermi energy, the spin polarization may be suppressed and
even changes its sign. We predict a pronounced peak of the spin polarization in
2DHG once the Fermi level is somewhere between minimum points of two spin-split
branches of the lowest light-hole subband. We discuss the possibility of
measurements in experiments as regards the temperature and the width of quantum
wells.Comment: 13 pages, 8 figures, submitted to PR
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