87 research outputs found
Reheating mechanism of Curvaton with Nonminimal Derivative Coupling to Gravity
In this paper, we continue our study on the curvaton model with nonminimal
derivative coupling (NDC) to Einstein gravity proposed in our previous work,
focusing on the reheating mechanism. We found that according to whether the
curvaton has dominated the background after the end of inflation, it will have
two different behaviors of evolution, which should be the general property of
curvaton with nonminimal couplings. This will cause diffferent rates of
particle creation, which goes on via the parametric resonance process. The
reheating temperature is estimated for both cases in which reheating completes
before and after curvaton domination, and the constraints are quite loose
compared to that of overproduction of gravitino. Finally we investigated the
evolution of curvature perturbation during reheating. We have shown both
analytically and numerically that the curvature perturbation will not blow up
during the resonance process.Comment: 10 pages, 8 figures. corrections are made to match the published
versio
Statistics of X-ray flares of Sagittarius A*: evidence for solar-like self-organized criticality phenomenon
X-ray flares have routinely been observed from the supermassive black hole,
Sagittarius A (Sgr A), at our Galactic center. The nature of
these flares remains largely unclear, despite of many theoretical models. In
this paper, we study the statistical properties of the Sgr A X-ray
flares, by fitting the count rate (CR) distribution and the structure function
(SF) of the light curve with a Markov Chain Monte Carlo (MCMC) method. With the
3 million second \textit{Chandra} observations accumulated in the Sgr A
X-ray Visionary Project, we construct the theoretical light curves through
Monte Carlo simulations. We find that the keV X-ray light curve can be
decomposed into a quiescent component with a constant count rate of
count s and a flare component with a power-law
fluence distribution with . The duration-fluence correlation can also be modelled as a
power-law with (
confidence). These statistical properties are consistent with the theoretical
prediction of the self-organized criticality (SOC) system with the spatial
dimension . We suggest that the X-ray flares represent plasmoid
ejections driven by magnetic reconnection (similar to solar flares) in the
accretion flow onto the black hole.Comment: to appear in Ap
Fabrication of CMC-g-PAM Superporous Polymer Monoliths via Eco-Friendly Pickering-MIPEs for Superior Adsorption of Methyl Violet and Methylene Blue
A series of superporous carboxymethylcellulose-graft-poly(acrylamide)/palygorskite (CMC-g-PAM/Pal) polymer monoliths presenting interconnected pore structure and excellent adsorption properties were prepared by one-step free-radical grafting polymerization reaction of CMC and acrylamide (AM) in the oil-in-water (O/W) Pickering-medium internal phase emulsions (Pickering-MIPEs) composed of non-toxic edible oil as a dispersion phase and natural Pal nanorods as stabilizers. The effects of Pal dosage, AM dosage, and co-surfactant Tween-20 (T-20) on the pore structures of the monoliths were studied. It was revealed that the well-defined pores were formed when the dosages of Pal and T-20 are 9–14 and 3%, respectively. The porous monolith can rapidly adsorb 1,585 mg/g of methyl violet (MV) and 1,625 mg/g of methylene blue (MB). After the monolith was regenerated by adsorption-desorption process for five times, the adsorption capacities still reached 92.1% (for MV) and 93.5% (for MB) of the initial maximum adsorption capacities. The adsorption process was fitted with Langmuir adsorption isotherm model and pseudo-second-order adsorption kinetic model very well, which indicate that mono-layer chemical adsorption mainly contribute to the high-capacity adsorption for dyes. The superporous polymer monolith prepared from eco-friendly Pickering-MIPEs shows good adsorption capacity and fast adsorption rate, which is potential adsorbent for the decontamination of dye-containing wastewater
A String-Inspired Quintom Model Of Dark Energy
We propose in this paper a quintom model of dark energy with a single scalar
field given by the lagrangian . In the limit of 0 our model reduces to the
effective low energy lagrangian of tachyon considered in the literature. We
study the cosmological evolution of this model, and show explicitly the
behaviors of the equation of state crossing the cosmological constant boundary.Comment: 6 pages, 4 figures, accepted by PL
Reconstruction of f(R) models with Scale-invariant Power Spectrum
Following our previous work in [JCAP 1206, 041 (2012)], in this paper, we
continue our study of reconstructing modified gravity models that can be
connected to a single scalar field in general relativity via conformal
transformation, which lead to scale-invariant power spectrum in the early
universe. With modified gravity, one does not need to introduce extra
scalar, the nature of which are to be explained. Different from general
nonminimal coupling theory, the behavior of the theory has been fixed by
its counterpart in Einstein frame, and thus have one to one correspondence.
Numerical plots of the functional form of as well as the evolution of
in terms of cosmic time are also presented.Comment: 8 pages, 4 figures, 1 tabl
Oscillating universe with quintom matter
In this paper, we study the possibility of building a model of the
oscillating universe with quintom matter in the framework of 4-dimensional
Friedmann-Robertson-Walker background. Taking the two-scalar-field quintom
model as an example, we find in the model parameter space there are five
different types of solutions which correspond to: (I) a cyclic universe with
the minimal and maximal values of the scale factor remaining the same in every
cycle, (II) an oscillating universe with its minimal and maximal values of the
scale factor increasing cycle by cycle, (III) an oscillating universe with its
minimal and maximal values of the scale factor decreasing cycle by cycle, (IV)
an oscillating universe with its scale factor always increasing, and (V) an
oscillating universe with its scale factor always decreasing.Comment: 14 pages, 6 figures, accepted by PL
Avoiding the Big-Rip Jeopardy in a Quintom Dark Energy Model with Higher Derivatives
In the framework of a single scalar field quintom model with higher
derivative, we construct in this paper a dark energy model of which the
equation of state (EOS) crosses over the cosmological constant boundary.
Interestingly during the evolution of the universe happens just for a
period of time with a distinguished feature that starts with a value above
-1, transits into . This avoids the Big Rip
jeopardy induced by .Comment: 7 pages, 3 figure
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