56,207 research outputs found
Evolution of magnetic component in Yang-Mills condensate dark energy models
The evolution of the electric and magnetic components in an effective
Yang-Mills condensate dark energy model is investigated. If the electric field
is dominant, the magnetic component disappears with the expansion of the
Universe. The total YM condensate tracks the radiation in the earlier Universe,
and later it becomes thus is similar to the cosmological constant.
So the cosmic coincidence problem can be avoided in this model. However, if the
magnetic field is dominant, holds for all time, suggesting that it
cannot be a candidate for the dark energy in this case.Comment: 12 pages, 4 figures, minor typos correcte
Yang-Mills condensate dark energy coupled with matter and radiation
The coincidence problem is studied for the dark energy model of effective
Yang-Mills condensate in a flat expanding universe during the matter-dominated
stage. The YMC energy is taken to represent the dark energy, which
is coupled either with the matter, or with both the matter and the radiation
components. The effective YM Lagrangian is completely determined by quantum
field theory up to 1-loop order. It is found that under very generic initial
conditions and for a variety of forms of coupling, the existence of the scaling
solution during the early stages and the subsequent exit from the scaling
regime are inevitable. The transition to the accelerating stage always occurs
around a redshift . Moreover, when the Yang-Mills
condensate transfers energy into matter or into both matter and radiation, the
equation of state of the Yang-Mills condensate can cross over -1 around
, and takes on a current value . This is consistent with
the recent preliminary observations on supernovae Ia. Therefore, the
coincidence problem can be naturally solved in the effective YMC dark energy
models.Comment: 24 pages, 18 figure
The State Equation of the Yang-Mills field Dark Energy Models
In this paper, we study the possibility of building Yang-Mills(YM) field dark
energy models with equation of state (EoS) crossing -1, and find that it can
not be realized by the single YM field models, no matter what kind of
lagrangian or initial condition. But the states of and
all can be naturally got in this kind of models. The former is like
a quintessence field, and the latter is like a phantom field. This makes that
one can build a model with two YM fields, in which one with the initial state
of , and the other with . We give an example model of
this kind, and find that its EoS is larger than -1 in the past and less than -1
at the present time. We also find that this change must be from to
, and it will go to the critical state of with the expansion
of the Universe, which character is same with the single YM field models, and
the Big Rip is naturally avoided.Comment: 20 pages, 4 figures. minor typos correcte
Possible discovery of the r-process characteristics in the abundances of metal-rich barium stars
We study the abundance distributions of a sample of metal-rich barium stars
provided by Pereira et al. (2011) to investigate the s- and r-process
nucleosynthesis in the metal-rich environment. We compared the theoretical
results predicted by a parametric model with the observed abundances of the
metal-rich barium stars. We found that six barium stars have a significant
r-process characteristic, and we divided the barium stars into two groups: the
r-rich barium stars (, [La/Nd]\,) and normal barium stars. The
behavior of the r-rich barium stars seems more like that of the metal-poor
r-rich and CEMP-r/s stars. We suggest that the most possible formation
mechanism for these stars is the s-process pollution, although their abundance
patterns can be fitted very well when the pre-enrichment hypothesis is
included. The fact that we can not explain them well using the s-process
nucleosynthesis alone may be due to our incomplete knowledge on the production
of Nd, Eu, and other relevant elements by the s-process in metal-rich and super
metal-rich environments (see details in Pereira et al. 2011).Comment: 5 pages, 5 figures, accepted for publication in A&
Discussion on Event Horizon and Quantum Ergosphere of Evaporating Black Holes in a Tunnelling Framework
In this paper, with the Parikh-Wilczek tunnelling framework the positions of
the event horizon of the Vaidya black hole and the Vaidya-Bonner black hole are
calculated respectively. We find that the event horizon and the apparent
horizon of these two black holes correspond respectively to the two turning
points of the Hawking radiation tunnelling barrier. That is, the quantum
ergosphere coincides with the tunnelling barrier. Our calculation also implies
that the Hawking radiation comes from the apparent horizon.Comment: 8 page
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