3,644 research outputs found
Test of conformal gravity with astrophysical observations
Since it can describe the rotation curves of galaxies without dark matter and
can give rise to accelerated expansion, conformal gravity attracts much
attention recently. As a theory of modified gravity, it is important to test
conformal gravity with astrophysical observations. Here we constrain conformal
gravity with SNIa and Hubble parameter data and investigate whether it suffers
from an age problem with the age of APM~08279+5255. We find conformal gravity
can accommodate the age of APM~08279+5255 at 3 deviation, unlike most
of dark energy models which suffer from an age problem.Comment: 6 pages, 2 figure
The puzzle of anomalously large isospin violations in
The BES-III Collaboration recently report the observation of anomalously
large isospin violations in , where the in the invariant mass
spectrum appears to be much narrower ( 10 MeV) than the peak width
(50 MeV) measured in other processes. We show that a mechanism, named as
triangle singularity (TS), can produce a narrow enhancement between the charged
and neutral thresholds, i.e., . It can also
lead to different invariant mass spectra for
and , which can possibly explain the long-standing puzzle
about the need for two close states and in
and , respectively. The TS could be a key to our
understanding of the nature of and advance our knowledge
about the mixing between and .Comment: 4 pages and 7 eps figures; Journal-matched versio
Spectral properties of Sturm-Liouville operators on infinite metric graphs
This paper mainly deals with the Sturm-Liouville operator \begin{equation*}
\mathbf{H}=\frac{1}{w(x)}\left( -\frac{\mathrm{d}}{\mathrm{d}x}p(x)\frac{
\mathrm{d}}{\mathrm{d}x}+q(x)\right) ,\text{ }x\in \Gamma \end{equation*}
acting in where is a metric graph.
We establish a relationship between the bottom of the spectrum and the positive
solutions of quantum graphs, which is a generalization of the classical
Allegretto-Piepenbrink theorem. Moreover, we prove the Persson-type theorem,
which characterizes the infimum of the essential spectrum
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