We study the
P
cs
(
4459
)
0
recently observed by LHCb using the method of QCD sum rules. Our results support its interpretation as the
D
¯
∗
Ξ
c
hadronic molecular state of either
J
P
=
1
/
2
-
or
3
.../
2
-
. Within the hadronic molecular picture, the three LHCb experiments observing
P
c
and
P
cs
states (Aaij et al., Phys Rev Lett 115:072001, 2015; Aaij et al., Phys Rev Lett 122:222001, 2019; Aaij et al.,
arXiv:2012.10380
hep-ex, 2012) can be well understood as a whole. This strongly supports the existence of hadronic molecules, whose studies can significantly improve our understanding on the construction of the subatomic world. To verify this picture, we propose to further investigate the
P
cs
(
4459
)
0
to examine whether it can be separated into two states, and to search for the
D
¯
Ξ
c
molecular state of
J
P
=
1
/
2
-
.
We find that several thresholds can contribute to the enhancements of the newly observed heavy pentaquark candidates Pc+(4380) and Pc+(4450) via the anomalous triangle singularity (ATS) transitions ...in the specific kinematics of Λb→J/ψK−p. Apart from the observed two peaks we find that another peaks around 4.5 GeV can also be produced by the ATS. We also show that the Σc(⁎) can be produced at leading order in Λb decay. This process is different from the triangle diagram and its threshold enhancement only appears as CUSP effects if there is no pole structure or the ATS involved. The threshold interaction associated with the presence of the ATS turns out to be a general phenomenon and plays a crucial role in the understanding of candidates for exotic states.
The rapid development of topological photonics and acoustics calls for accurate understanding of band topology in classical waves, which is not yet achieved in many situations. Here, we present the ...Wilson-loop approach for exact numerical calculation of the topological invariants for several photonic/sonic crystals. We demonstrate that these topological photonic/sonic crystals are topological crystalline insulators with fragile topology, a feature which has been ignored in previous studies. We further discuss the bulk-edge correspondence in these systems with emphasis on symmetry broken on the edges.
The spectrum of hadrons is the manifestation of color confinement of quantum chromodynamics. Hadronic resonances correspond to poles of the S-matrix. Since 2003, lots of new hadron resonant ...structures were discovered in the mass regions from light mesons to hadrons containing a pair of a heavy quark and an antiquark. Many of them are candidates of exotic hadrons, and they are usually observed as peaks in invariant mass distributions. However, the S-matrix also has kinematical singularities due to the on-shellness of intermediate particles for a process, such as two-body thresholds and triangle singularities (TSs), and they can produce peaks as well. On the one hand, such singularities may be misidentified as resonances; on the other hand, they can be used as tools for precision measurements. In this paper, we review the threshold cusps and various triangle singularities in hadronic reactions, paying attention to their manifestations in phenomena related to exotic hadron candidates.
Topological insulators with unique edge states have revolutionized the understanding of solid-state materials. Recently, higher-order topological insulators (HOTIs), which host both gapped edge ...states and in-gap corner/hinge states, protected concurrently by band topology, were predicted and observed in experiments, unveiling a new horizon beyond the conventional bulk-edge correspondence. However, the control and manifestation of band topology in a hierarchy of dimensions, which is at the heart of HOTIs, have not yet been witnessed. Here, we propose theoretically and observe experimentally that tunable two-dimensional sonic crystals can be versatile systems to visualize and harness higher-order topology. In our systems, the two-dimensional acoustic bands mimic the quantum spin Hall effect, while the resultant one-dimensional helical edge states are gapped due to broken space-symmetry and carry quantized Zak phases, which then lead to zero-dimensional topological corner states. We demonstrate that topological transitions in the bulk and edges can be triggered independently by tuning the geometry of the sonic crystals. With complementary experiments and theories, our study reveals rich physics in HOTIs, opening a new route towards tunable topological metamaterials where novel applications, such as the topological transfer of acoustic energy among two-, one- and zero-dimensional modes, can be achieved.By tuning the geometry of a two-dimensional sonic crystal, its one-dimensional helical edge states become gapped and zero-dimensional topological corner states emerge. The band topology is thus manifested in a hierarchy of dimensions.
Recently LHCb declared a new structure
X
(6900) in the final state di-
J
/
ψ
which is popularly regarded as a
cc
-
c
¯
c
¯
tetraquark state. Within the Bethe–Salpeter (B–S) framework we study the ...possible
cc
-
c
¯
c
¯
bound states and the interaction between diquark (
cc
) and antidiquark (
c
¯
c
¯
). In this work
cc
(
c
¯
c
¯
) is treated as a color anti-triplet (triplet) axial-vector so the quantum numbers of
cc
-
c
¯
c
¯
bound state are
0
+
,
1
+
and
2
+
. Learning from the interaction in meson case and using the effective coupling we suggest the interaction kernel for the diquark and antidiquark system. Then we deduce the B–S equations for different quantum numbers. Solving these equations numerically we find the spectra of some excited states can be close to the mass of
X
(6900) when we assign appropriate values for parameter
κ
introduced in the interaction (kernel). We also briefly calculate the spectra of
bb
-
b
¯
b
¯
bound states. Future measurement of
bb
-
b
¯
b
¯
state will help us to determine the exact form of effective interaction.
Weyl semimetals (WSMs)
exhibit phenomena such as Fermi arc surface states, pseudo-gauge fields and quantum anomalies that arise from topological band degeneracy in crystalline solids for electrons
...and metamaterials for photons
and phonons
. Here we report a higher-order Weyl semimetal (HOWSM) in a phononic system that exhibits topologically protected boundary states in multiple dimensions. We created the physical realization of the HOWSM in a chiral phononic crystal with uniaxial screw symmetry. Using acoustic pump-probe spectroscopies, we observed coexisting chiral Fermi arc states on two-dimensional surfaces and dispersive hinge arc states on one-dimensional hinge boundaries. These topological boundary states link the projections of the Weyl points (WPs) in different dimensions and directions, and hence demonstrate the higher-order topological physics
in WSMs. Our study further establishes the fundamental connection between higher-order topology and Weyl physics in crystalline materials and should stimulate further work on other potential materials, such as higher-order topological nodal-line semimetals.
We investigate the possible rescattering effects which may contribute to the process B+→J/ψϕK+. It is shown that the ψ′ϕ rescattering via the ψ′K1 loop can simulate the structure of X(4700). The cusp ...effect due to the Ds⁎+Ds− rescattering may possibly simulate the X(4140) structure, but it depends on the cusp model parameters. If the quantum numbers of X(4274) (X(4500)) are 1++ (0++), it is hard to ascribe the observation of X(4274) and X(4500) to the P-wave threshold rescattering effects, which implies that X(4274) and X(4500) could be genuine resonances. We also suggest that X(4274) may be the conventional orbitally excited state χc1(3P).
We investigate the anomalous triangle singularity (ATS) and its possible manifestations in various processes. We show that the ATS should have important impact on our understanding of the nature of ...some newly observed threshold states. Discussions on how to distinguish the ATS phenomena from genuine dynamic pole structures are presented.
Sea surface temperature (SST) prediction has raised considerable attention in various ocean-related fields. However, these methods were only limited to the time-sequence prediction of some isolated ...points, and their spatial linkage was not considered. Furthermore, these studies only predict the temperature of sea surface, but the subsurface temperature in the inner ocean is much more important. In this letter, we propose a model of multilayer convolutional long- and short-term memory (M-convLSTM) to predict 3-D ocean temperature, comprising convolutional neural networks (CNNs), long- and short-term memory (LSTM), and multiple layer stacking to consider the horizontal and vertical temperature variations from sea surface to subsurface to be about 2000 m below. Global marine environment observation data (ARGO) are used to conduct the prediction of 3-D ocean temperature in this letter, and the results demonstrate the overall good accuracy of forecast and ARGO data.
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