14,864 research outputs found
A power-law coupled three-form dark energy model
We consider a field theory model of coupled dark energy which treats dark
energy as a three-form field and dark matter as a spinor field. By assuming the
effective mass of dark matter as a power-law function of the three-form field
and neglecting the potential term of dark energy, we obtain three solutions of
the autonomous system of evolution equations, including a de Sitter attractor,
a tracking solution and an approximate solution. To understand the strength of
the coupling, we confront the model with the latest Type Ia Supernova (SN Ia),
Baryon Acoustic Oscillations (BAO) and Cosmic Microwave Backround (CMB)
radiation observations, with the conclusion that the combination of these three
databases marginalized over the present dark matter density parameter
and the present three-form field gives stringent
constraints on the coupling constant, (
confidence level), by which we give out the model applicable parameter range.Comment: 16 pages, 5 figures, refernces added, Eur. Phys. J. C (2018
Transformation of \u3cem\u3eTetrahymena thermophila\u3c/em\u3e with Hypermethylated rRNA Genes
The extrachromosomal rRNA genes (rDNA) of Tetrahymena thermophila contain 0.4% N6-methyladenine. C3 strain rDNA was isolated, hypermethylated in vitro, and microinjected into B strain host cells. Clonal cell lines were established, and transformants were selected on the basis of resistance to paromomycin, conferred by the injected rDNA. The effects of methylation by three enzymes which methylate the sequence 5\u27-NAT-3\u27, the dam, EcoRI, and ClaI methylases, were tested. Hypermethylation of the injected rDNA had no effect on transformation efficiency relative to mock-methylated controls. The injected C3 strain rDNA efficiently replaced host rDNA as the major constituent of the population of rDNA molecules. Hypermethylation of the injected DNA was not maintained through 20 to 25 cell generations
A Complementary Third Law for Black Hole Thermodynamics
There are some examples in the literature, in which despite the fact that the
underlying theory or model does not impose a lower bound on the size of black
holes, the final temperature under Hawking evaporation is nevertheless finite
and nonzero. We show that under some loose conditions, the black hole is
necessarily an effective remnant, in the sense that its evaporation time is
infinite. That is, the final state that there is nonzero finite temperature
despite having no black hole remaining cannot be realized. We discuss the
limitations, subtleties, and the implications of this result, which is
reminiscent of the third law of black hole thermodynamics, but with the roles
of temperature and size interchanged. We therefore refer to our result as the
"complementary third law" for black hole thermodynamics.Comment: 10 pages, 5 figures; improved and published versio
Studies on X(4260) and X(4660) particles
Studies on the X(4260) and X(4660) resonant states in an effective lagrangian
approach are reviewed. Using a Breit--Wigner propagator to describe their
propagation, we find that the X(4260) has a sizable coupling to the
channel, while other couplings are found to be negligible.
Besides, it couples much stronger to than to : As an approximate result for
X(4660), we obtain that the ratio of
. Finally, taking X(3872) as an example, we also point out a possible way to
extend the previous method to a more general one in the effective lagrangian
approach.Comment: Talk given by H. Q. Zheng at "Xth Quark Confinement and the Hadron
Spectrum", October 8-12, 2012, TUM Campus Garching, Munich, Germany. 6 pages,
3 figures, 3 table
Nonfactorizable decay and QCD factorization
We study the unexpectedly large rate for the factorization-forbidden decay
within the QCD factorization approach. We use a non-zero
gluon mass to regularize the infrared divergences in vertex corrections. The
end-point singularities arising from spectator corrections are regularized and
carefully estimated by the off-shellness of quarks. We find that the
contributions arising from the vertex and leading-twist spectator corrections
are numerically small, and the twist-3 spectator contribution with chiral
enhancement and linear end-point singularity becomes dominant. With reasonable
choices for the parameters, the branching ratio for decay is
estimated to be in the range , which is compatible with
the Belle and BaBar data.Comment: Appendix added; it is emphasized that in the dominant twist-3
spectator corrections the end-point singularity contributions may be
estimated by the off-shellness of the charm quark (by the binding energy in
charmonium) and the gluon (by the transverse momentum of the light quark in
the kaon
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