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Hidden-Charm Tetraquarks and Charged Zc States
Experimentally several charged axial-vector hidden-charm states were
reported. Within the framework of the color-magnetic interaction, we have
systematically considered the mass spectrum of the hidden-charm and
hidden-bottom tetraquark states. It is impossible to accommodate all the three
charged states , and within the axial vector
tetraquark spectrum simultaneously. Not all these three states are tetraquark
candidates. Moreover, the eigenvector of the chromomagnetic interaction
contains valuable information of the decay pattern of the tetraquark states.
The dominant decay mode of the lowest axial vector tetraquark state is while its and modes are strongly suppressed,
which is in contrast with the fact that the dominant decay mode of
and is and respectively. We emphasize
that all the available experimental information indicates that is a
very promising candidate of the lowest axial vector hidden-charm tetraquark
state
Zero sound in a two-dimensional dipolar Fermi gas
We study zero sound in a weakly interacting 2D gas of single-component
fermionic dipoles (polar molecules or atoms with a large magnetic moment)
tilted with respect to the plane of their translational motion. It is shown
that the propagation of zero sound is provided by both mean field and many-body
(beyond mean field) effects, and the anisotropy of the sound velocity is the
same as the one of the Fermi velocity. The damping of zero sound modes can be
much slower than that of quasiparticle excitations of the same energy. One thus
has wide possibilities for the observation of zero sound modes in experiments
with 2D fermionic dipoles, although the zero sound peak in the structure
function is very close to the particle-hole continuum.Comment: 15 pages, 2 figure
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