31,632 research outputs found
Weak Decays of Doubly-Heavy Tetraquarks
We study the weak decays of exotic tetraquark states
with two heavy quarks. Under the SU(3) symmetry for light quarks, these
tetraquarks can be classified into an octet plus a singlet: . We will concentrate on the octet tetraquarks with
, and study their weak decays, both semileptonic and nonleptonic.
Hadron-level effective Hamiltonian is constructed according to the irreducible
representations of the SU(3) group. Expanding the Hamiltonian, we obtain the
decay amplitudes parameterized in terms of a few irreducible quantities. Based
on these amplitudes, relations for decay widths are derived, which can be
tested in future. We also give a list of golden channels that can be used to
look for these states at various colliders.Comment: 14 pages,3 figure
Transverse emission of isospin ratios as a probe of high-density symmetry energy in isotopic nuclear reactions
Transverse emission of preequilibrium nucleons, light clusters (complex
particles) and charged pions from the isotopic Sn+Sn
reactions at a beam energy of 400\emph{A} MeV, to extract the high-density
behavior of nuclear symmetry energy, are investigated within an isospin and
momentum dependent transport model. Specifically, the double ratios of
neutron/proton, triton/helium-3 and in the squeeze-out domain
are analyzed systematically, which have the advantage of reducing the influence
of the Coulomb force and less systematic errors. It is found that the
transverse momentum distribution of isospin ratios strongly depend on the
stiffness of nuclear symmetry energy, which would be a nice observable to
extract the high-density symmetry energy. The collision centrality and the mass
splitting of neutron and proton in nuclear medium play a significant role on
the distribution structure of the ratios, but does not change the influence of
symmetry energy on the spectrum.Comment: 5 figures, 13 page
Designer Topological Insulators in Superlattices
Gapless Dirac surface states are protected at the interface of topological
and normal band insulators. In a binary superlattice bearing such interfaces,
we establish that valley-dependent dimerization of symmetry-unrelated Dirac
surface states can be exploited to induce topological quantum phase
transitions. This mechanism leads to a rich phase diagram that allows us to
design strong, weak, and crystalline topological insulators. Our ab initio
simulations further demonstrate this mechanism in [111] and [110] superlattices
of calcium and tin tellurides.Comment: 5 pages, 4 figure
Giant and tunable valley degeneracy splitting in MoTe2
Monolayer transition-metal dichalcogenides possess a pair of degenerate
helical valleys in the band structure that exhibit fascinating optical valley
polarization. Optical valley polarization, however, is limited by carrier
lifetimes of these materials. Lifting the valley degeneracy is therefore an
attractive route for achieving valley polarization. It is very challenging to
achieve appreciable valley degeneracy splitting with applied magnetic field. We
propose a strategy to create giant splitting of the valley degeneracy by
proximity-induced Zeeman effect. As a demonstration, our first principles
calculations of monolayer MoTe on a EuO substrate show that valley
splitting over 300 meV can be generated. The proximity coupling also makes
interband transition energies valley dependent, enabling valley selection by
optical frequency tuning in addition to circular polarization. The valley
splitting in the heterostructure is also continuously tunable by rotating
substrate magnetization. The giant and tunable valley splitting adds a readily
accessible dimension to the valley-spin physics with rich and interesting
experimental consequences, and offers a practical avenue for exploring device
paradigms based on the intrinsic degrees of freedom of electrons.Comment: 8 pages, 5 figures, 1 tabl
The geometric mean is a Bernstein function
In the paper, the authors establish, by using Cauchy integral formula in the
theory of complex functions, an integral representation for the geometric mean
of positive numbers. From this integral representation, the geometric mean
is proved to be a Bernstein function and a new proof of the well known AG
inequality is provided.Comment: 10 page
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