248,444 research outputs found

### Possible signatures for tetraquarks from the decays of $a_0(980)$, $a_0(1450)$

Based on the recent proposal for the tetraquarks with the mixing scheme, we
investigate fall-apart decays of $a_0(980), a_0(1450)$ into two lowest-lying
mesons. This mixing scheme suggests that $a_0(980)$ and $a_0(1450)$ are the
tetraquarks with the mixtures of two spin configurations of diquark and
antidiquark. Due to the relative sign differences in the mixtures, the
couplings of fall-apart decays into two mesons are strongly enhanced for
$a_0(980)$ but suppressed for $a_0(1450)$. We report that this expectation is
supported by their experimental decays. In particular, the ratios of the
associated partial decay widths, which depend on some kinematical factors and
the couplings, are found to be around $\Gamma [a_0(980)\rightarrow \pi
\eta]/\Gamma [a_0(1450)\rightarrow \pi \eta] = 2.51-2.54$, $\Gamma
[a_0(980)\rightarrow K\bar{K}]/\Gamma [a_0(1450)\rightarrow K\bar{K}] =
0.52-0.89$, which seems to agree with the experimental ratios reasonably well.
This agreement can be interpreted as the tetraquark signatures for $a_0(980),
a_0(1450)$.Comment: 6 pages, no figures, more references are added, the version to be
published in EPJ

### Semidirect Product Groups, Vacuum Alignment and Tribimaximal Neutrino Mixing

The neutrino oscillation data are in very good agreement with the
tribimaximal mixing pattern: \sin^2\theta_{23}=1/2, \sin^2\theta_{12}=1/3, and
\sin^2\theta_{13}=0. Attempts to generate this pattern based on finite family
symmetry groups typically assume that the family symmetry is broken to
different subgroups in the charged lepton and the neutrino mass matrices. This
leads to a technical problem, where the cross-couplings between the Higgs
fields responsible for the two symmetry breaking chains force their vacuum
expectation values to align, upsetting the desired breaking pattern. Here, we
present a class of models based on the semidirect product group (S_3)^4 \rtimes
A_4, where the lepton families belong to representations which are not
faithful. In effect, the Higgs sector knows about the full symmetry while the
lepton sector knows only about the A_4 factor group. This can solve the
alignment problem without altering the desired properties of the family
symmetry. Inclusion of quarks into the framework is straightforward, and leads
to small and arbitrary CKM mixing angles. Supersymmetry is not essential for
our proposal, but the model presented is easily supersymmetrized, in which case
the same family symmetry solves the SUSY flavor problem.Comment: Typos fixed, 26 pages in LaTe

### Z_{12-I} Orbifold Compactification toward SUSY Standard Model

We explain the orbifold compactification in string models and present a
Z_{12-I} orbifold compactification toward supersymmetric standard models. We
also point out an effective R-parity from this string construction. The VEVs of
gauge singlets are chosen such that phenomenological constraints are satisfied.Comment: 13 pages with 5 figure. Talk presented at "CTP Symposium on SUSY at
LHC", Cairo, 11-14 March 200

### Norm Estimates for the Difference Between Bochner's Integral and the Convex Combination of Function's Values

Norm estimates are developed between the Bochner integral of a vector-valued
function in Banach spaces having the Radon-Nikodym property and the convex
combination of function values taken on a division of the interval [a,b]

### 20 K superconductivity in heavily electron doped surface layer of FeSe bulk crystal

A superconducting transition temperature Tc as high as 100 K was recently
discovered in 1 monolayer (1ML) FeSe grown on SrTiO3 (STO). The discovery
immediately ignited efforts to identify the mechanism for the dramatically
enhanced Tc from its bulk value of 7 K. Currently, there are two main views on
the origin of the enhanced Tc; in the first view, the enhancement comes from an
interfacial effect while in the other it is from excess electrons with strong
correlation strength. The issue is controversial and there are evidences that
support each view. Finding the origin of the Tc enhancement could be the key to
achieving even higher Tc and to identifying the microscopic mechanism for the
superconductivity in iron-based materials. Here, we report the observation of
20 K superconductivity in the electron doped surface layer of FeSe. The
electronic state of the surface layer possesses all the key spectroscopic
aspects of the 1ML FeSe on STO. Without any interface effect, the surface layer
state is found to have a moderate Tc of 20 K with a smaller gap opening of 4
meV. Our results clearly show that excess electrons with strong correlation
strength alone cannot induce the maximum Tc, which in turn strongly suggests
need for an interfacial effect to reach the enhanced Tc found in 1ML FeSe/STO.Comment: 5 pages, 4 figure

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