13,357 research outputs found
A unification of RDE model and XCDM model
In this Letter, we propose a new generalized Ricci dark energy (NGR) model to
unify Ricci dark energy (RDE) and XCDM. Our model can distinguish between RDE
and XCDM by introducing a parameter called weight factor. When
, NGR model becomes the usual RDE model. The XCDM model is
corresponding to . Moreover, NGR model permits the situation where
neither nor . We then perform a statefinder analysis on NGR
model to see how effects the trajectory on the plane.
In order to know the value of , we constrain NGR model with latest
observations including type Ia supernovae (SNe Ia) from Union2 set (557 data),
baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan
Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and cosmic
microwave background (CMB) observation from the 7-year Wilkinson Microwave
Anisotropy Probe (WMAP7) results. With Markov Chain Monte Carlo (MCMC) method,
the constraint result is
=, which
manifests the observations prefer a XCDM universe rather than RDE model. It
seems RDE model is ruled out in NGR scenario within regions.
Furthermore, we compare it with some of successful cosmological models using
AIC information criterion. NGR model seems to be a good choice for describing
the universe.Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in PL
Constraints on f(R) cosmologies from strong gravitational lensing systems
f(R) gravity is thought to be an alternative to dark energy which can explain
the acceleration of the universe. It has been tested by different observations
including type Ia supernovae (SNIa), the cosmic microwave background (CMB), the
baryon acoustic oscillations (BAO) and so on. In this Letter, we use the Hubble
constant independent ratio between two angular diameter distances
to constrain f(R) model in Palatini approach . These data are from various large systematic
lensing surveys and lensing by galaxy clusters combined with X-ray
observations. We also combine the lensing data with CMB and BAO, which gives a
stringent constraint. The best-fit results are
or using lensing data only. When combined
with CMB and BAO, the best-fit results are or
. If we further fix (corresponding
to CDM), the best-fit value for is
= for the
lensing analysis and
= for the
combined data, respectively. Our results show that CDM model is within
1 range.Comment: 9 pages, 2 figures, 2 table
On the valence bond solid in the presence of Dzyaloshinskii-Moriya interaction
We examine the stability of the valence bond solid (VBS) phase against the
Dzyaloshinskii-Moriya (DM) interaction in the bipartite lattice. Despite the
VBS is vulnerable against the antiferromagnetic interaction, for example in the
Q-J model proposed by Sandvik, where the quantum phase transition occurs at
, we found that on the contrary the VBS is very stable against
the DM interaction. The quantum phase transition does not occur until D/Q goes
to infinity, where D is the strength of the DM interaction. The VBS in the ALKT
model and the Haldane gap system also exhibit the same property.Comment: 5 pages and 5 figure
Effect of interaction with neutrons in matter on flavor conversion of super-light sterile neutrino with active neutrino
A super-light sterile neutrino was proposed to explain the absence of the
expected upturn of the survival probability of low energy solar boron
neutrinos. This is because this super-light sterile neutrino can oscillate
efficiently with electron neutrino through a MSW resonance happened in Sun. One
may naturally expect that a similar resonance should happen for neutrinos
propagating in Earth matter. We study the flavor conversion of this super-light
sterile neutrino with active neutrinos in Earth matter. We find that the
scenario of the super-light sterile neutrino can easily pass through possible
constraints from experiments which can test the Earth matter effect in
oscillation of neutrinos. Interestinlgy, we find that this is because the
naively expected resonant conversion disappears or is significantly suppressed
due to the presence of a potential which arises from neutral current
interaction of neutrino with neutrons in matter. In contrast, the neutron
number density in the Sun is negligible and the effect of is effectively
switched off. This enables the MSW resonance in Sun needed in oscillation of
the super-light sterile neutrino with solar electron neutrinos. It's
interesting to note that it is the different situation in the Sun and in the
Earth that makes effectively turned off and turned on respectively. This
observation makes the scenario of the super-light sterile neutrino quite
interesting.Comment: 22 pages, 10 figure
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