3,194 research outputs found
Highly excited and exotic fully-strange tetraquark states
Some hadrons have the exotic quantum numbers that the traditional
mesons and baryons can not reach, such as , etc. We investigate for the first
time the exotic quantum number , and study the fully-strange
tetraquark states with such an exotic quantum number. We systematically
construct all the diquark-antidiquark interpolating currents, and apply the
method of QCD sum rules to calculate both the diagonal and off-diagonal
correlation functions. The obtained results are used to construct three mixing
currents that are nearly non-correlated, and we use one of them to extract the
mass of the lowest-lying state to be GeV. We apply the
Fierz rearrangement to transform this mixing current to be the combination of
three meson-meson currents, and the obtained Fierz identity suggests that this
state dominantly decays into the -wave
channel. This fully-strange tetraquark state of is a purely
exotic hadron to be potentially observed in future particle experiments.Comment: 8 pages, 7 figures, 1 table, revised version to be published in EPJ
A potential superhard material m-BCN
We here propose a new superhard material m-BCN with comparable Vickers hardness to cBN by the use of first-principles calculations. The calculations show that the mentioned m-BCN is a thermodynamically and kinetically stable semiconductor. Hydrostatic calculation shows that it is anisotropic and its incompressibility is very close to c-BN. Structural analysis shows that its excellent mechanical property and thermodynamically stability are inherited from diamond and cBN. These results provide a new clue to find new superhard phase.Запропоновано новий надтвердий матеріал m-BCN, твердість за Віккерсом якого за розрахунками за першими принципами порівняна з твердістю cBN. Розрахунки показали, що згаданий m-BCN за термодинамічними і кінетичними показниками є стабільним напівпровідником. Гідростатичний розрахунок показав, що він є анізотропним і його нестисливість дуже близька до нестисливості cBN. Структурний аналіз показав, що його відмінні механічні властивості і термодинамічна стабільність успадковані від алмаза і cBN. Дані результати забезпечують нову схему пошуку нових надтвердих фаз.Предложен новый сверхтвердый материал m-BCN, твердость по Виккерсу которого по расчетам по первым принципам сравнима с твердостью cBN. Расчеты показывают, что упомянутый m-BCN по термодинамическим и кинетическим показателям является стабильным полупроводником. Гидростатический расчет показал, что он анизотропный и его несжимаемость очень близка к несжимаемости cBN. Структурный анализ показал, что его отличные механические свойства и термодинамическая стабильность унаследованы от алмаза и cBN. Данные результаты обеспечивают новую схему поиска новых сверхтвердых фаз
Cooling mechanical resonators to quantum ground state from room temperature
Ground-state cooling of mesoscopic mechanical resonators is a fundamental
requirement for test of quantum theory and for implementation of quantum
information. We analyze the cavity optomechanical cooling limits in the
intermediate coupling regime, where the light-enhanced optomechanical coupling
strength is comparable with the cavity decay rate. It is found that in this
regime the cooling breaks through the limits in both the strong and weak
coupling regimes. The lowest cooling limit is derived analytically at the
optimal conditions of cavity decay rate and coupling strength. In essence,
cooling to the quantum ground state requires , with being the mechanical quality factor and
being the thermal phonon number. Remarkably, ground-state
cooling is achievable starting from room temperature, when mechanical
-frequency product , and both of the
cavity decay rate and the coupling strength exceed the thermal decoherence
rate. Our study provides a general framework for optimizing the backaction
cooling of mesoscopic mechanical resonators
QCD sum rule studies on the tetraquark states of
We apply the method of QCD sum rules to study the
tetraquark states of . We construct all the relevant tetraquark currents, and find that there are only two independent
ones. We use them to further construct two weakly-correlated mixed currents.
One of them leads to reliable QCD sum rule results and the mass is extracted to
be GeV, suggesting that the or the
can be explained as the tetraquark state of .
To verify this interpretation, we propose to further study the invariant mass spectra of the decays in BESIII to examine whether there exists the
resonance.Comment: 8 pages, 6 figures, suggestions and comments are welcom
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