8,393 research outputs found
The hidden-charm pentaquark and tetraquark states
In the past decade many charmonium-like states were observed experimentally.
Especially those charged charmonium-like states and bottomonium-like
states can not be accommodated within the naive quark model. These
charged states are good candidates of either the hidden-charm tetraquark
states or molecules composed of a pair of charmed mesons. Recently, the LHCb
Collaboration discovered two hidden-charm pentaquark states, which are also
beyond the quark model. In this work, we review the current experimental
progress and investigate various theoretical interpretations of these
candidates of the multiquark states. We list the puzzles and theoretical
challenges of these models when confronted with the experimental data. We also
discuss possible future measurements which may distinguish the theoretical
schemes on the underlying structures of the hidden-charm multiquark states.Comment: Review accepted by Physics Reports, 152 pages, 66 figures, and 29
table
Common wave behavior for mergers and acquisitions in OECD countries? a unique analysis using new Markov switching panel model approach
This paper investigates whether or not there is co-waved merger and acquisition (M&A) activity in 26 OECD countries. We apply the Markov Switching model to panel data (MSP hereafter), an approach which has not previously been attempted. Two distinct regimes are recognized in emerge from M&A data: the wave merger regime and normal merger regime. Our MSP captures the co-wave pattern of the sample countries and has a much better fit than either the univariate Markov Switching model or the conventional linear panel model.
Mass spectra of Zc and Zb exotic states as hadron molecules
We construct charmonium-like and bottomonium-like molecular interpolating
currents with quantum numbers J(PC)=1(+-) in a systematic way, including both
color singlet-singlet and color octet-octet structures. Using these
interpolating currents, we calculate two-point correlation functions and
perform QCD sum rule analyses to obtain mass spectra of the charmonium-like and
bottomonium-like molecular states. Masses of the charmonium-like q_bar c c_bar
q molecular states for these various currents are extracted in the range
3.85-4.22 GeV, which are in good agreement with observed masses of the Zc
resonances. Our numerical results suggest a possible landscape of hadronic
molecule interpretations of the newly-observed Zc states. Mass spectra of the
bottomonium-like q_bar b b_bar q molecular states are similarly obtained in the
range 9.92-10.48 GeV, which support the interpretation of the Zb(10610) meson
as a molecular state within theoretical uncertainties. Possible decay channels
of these molecular states are also discussed.Comment: 15 pages, 3 figures, 2 tables, accepted by PR
The Possible J^{PC}=0^{--} Exotic State
In order to explore the possible existence of the exotic state, we
have constructed the tetraquark interpolating operators systematically. As a
byproduct, we notice the tetraquark operators without derivatives do
not exist. The special Lorentz structure of the currents forbids the
four-quark correction to the spectral density. Now the gluon condensate is the
dominant power correction. Within the framework of the finite energy sum rule,
none of the seven interpolating currents supports a resonant signal. Therefore
we conclude that the exotic state does not exist below 2 GeV, which is
consistent with the current experimental observations.Comment: 12 pages, 27 figure
Imputing unknown competitor marketing activity with a Hidden Markov Chain
We demonstrate on a case study with two competing products at a bank how one
can use a Hidden Markov Chain (HMC) to estimate missing information on a
competitor's marketing activity. The idea is that given time series with sales
volumes for products A and B and marketing expenditures for product A, as well
as suitable predictors of sales for products A and B, we can infer at each
point in time whether it is likely or not that marketing activities took place
for product B. The method is successful in identifying the presence or absence
of marketing activity for product B about 84% of the time. We allude to the
issue of whether, if one can infer marketing activity about product B from
knowledge of marketing activity for product A and of sales volumes of both
products, the reverse might be possible and one might be able to impute
marketing activity for product A from knowledge of that of product B. This
leads to a concept of symmetric imputation of competing marketing activity. The
exposition in this paper aims to be accessible and relevant to practitioners
Establishing low-lying doubly charmed baryons
We systematically study the -wave doubly charmed baryons using the method
of QCD sum rules. Our results suggest that the recently
observed by LHCb can be well identified as the -wave state of
. We study its relevant state, whose mass is
predicted to be around 3.7 GeV. We also systematically study the -wave
doubly charmed baryons, whose masses are predicted to be around 4.1 GeV.
Especially, there can be several excited doubly charmed baryons in this energy
region, and we suggest to search for them in order to study the fine structure
of the strong interaction.Comment: 6 pages, 2 figures, 1 table; A mistake was found when evaluating
decay constants of the S-wave charmed baryons. The conclusion is not change
Radial Angular Momentum Transfer and Magnetic Barrier for Short-Type Gamma-Ray Burst Central Engine Activity
Soft extended emission (EE) following initial hard spikes up to 100 seconds
was observed with {\em Swift}/BAT for about half of short-type gamma-ray bursts
(SGRBs). This challenges the conversional central engine models of SGRBs, i.e.,
compact star merger models. In the framework of the black hole-neutron star
merger models, we study the roles of the radial angular momentum transfer in
the disk and the magnetic barrier around the black hole for the activity of
SGRB central engines. We show that the radial angular momentum transfer may
significantly prolong the lifetime of the accretion process and multiple
episodes may be switched by the magnetic barrier. Our numerical calculations
based on the models of the neutrino-dominated accretion flows suggest that the
disk mass is critical for producing the observed EE. In case of the mass being
, our model can reproduce the observed timescale and
luminosity of both the main and EE episodes in a reasonable parameter set. The
predicted luminosity of the EE component is lower than the observed EE with
about one order of magnitude and the timescale is shorter than 20 seconds if
the disk mass being . {\em Swift}/BAT-like instruments may
be not sensitive enough to detect the EE component in this case. We argue that
the EE component would be a probe for merger process and disk formation for
compact star mergers.Comment: 9 pages, 3 figures, accepted for publication in Ap
Doubly hidden-charm/bottom tetraquark states
We study the mass spectra for the and
tetraquark states by developing a moment sum rule method. Our results show that
the tetraquarks lie below the threshold of
. They are probably stable and very narrow. The masses
for the doubly hidden-charm states are higher than the
spontaneous dissociation thresholds of two charmonium mesons. We suggest to
search for such states in the and
channels.Comment: 8 pages, 2 figures. More references added. Conference proceedings for
6th International Conference on New Frontiers in Physics (ICNFP 2017), Crete,
Greece, 17-29 Aug, 201
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