258 research outputs found
Gauged Q ball in a piecewise parabolic potential
Q ball solutions are considered within the theory of a complex scalar field
with a gauged
U(1) symmetry and a parabolic-type potential. In the thin-walled limit, we
show explicitly that there is a maximum size for these objects because of the
repulsive Coulomb force. The size of Q ball will increase with the decrease of
local minimum of the potential. And when the two minima degenerate, the energy
stored within the surface of the Q ball becomes significant.
Furthermore, we find an analytic expression for gauged Q ball, which is
beyond the conventional thin-walled limit.Comment: 1 figure
Exponential Cardassian Universe
The expectation of explaining cosmological observations without requiring new
energy sources is forsooth worthy of investigation. In this letter, a new kind
of Cardassian models, called exponential Cardassian models, for the late-time
universe are investigated in the context of the spatially flat FRW universe
scenario. We fit the exponential Cardassian models to current type Ia
supernovae data and find they are consistent with the observations.
Furthermore, we point out that the equation-of-state parameter for the
effective dark fluid component in exponential Cardassian models can naturally
cross the cosmological constant divide that observations favor mildly
without introducing exotic material that destroy the weak energy condition.Comment: 14 pages, 5 eps figures, using Latex with elsart.cls; references
added ; typos corrected and a dicussion on the CMB spectrum effect is adde
On the Quintessence with Abelian and Non-abelian Symmetry
We study the perturbations on both "radial" and "angular" components of the
quintessence with an internal abelian and non-abelian symmetry. The properties
of the perturbation on the "radial" component depend on the specific potential
of the model and is similiar for both abelian and non-abelian case. We show
that the consine-type potential is very interesting for the O(\textit{N})
quintessence model and also give a critical condition of instability for the
potential. While the properties of perturbations on "angular" components depend
on whether the internal symmetry is abelian or non-abelian, which we have
discussed respectively. In the non-abelian case, the fluctuation of the
"angular" component will increase rapidly with time while in the abelian case
it will not.Comment: 15 pages, to be published in Int. J. Mod. Phys.
Revisiting the parametrization of Equation of State of Dark Energy via SNIa Data
In this paper, we revisit the parameterizations of the equation of state of
dark energy and point out that comparing merely the of different
fittings may not be optimal for choosing the "best" parametrization. Another
figure of merit for evaluating different parametrizations based on the area of
the band is proposed. In light of the analysis of some two-parameter
parameterizations and models based on available SNIa data, the area of
band seems to be a good figure of merit, especially in the situation that the
value of for different parametrizations are very close.
Therefore, we argue that both the area of the band and should be synthetically considered for choosing a better parametrization
of dark energy in the future experiments.Comment: 7 pages, contains 5 figures and 2 tables, accepted for publication in
MNRA
Quasinormal modes of stringy black holes
String theory is a promising candidate for a fundamental quantum theory of
all interactions including Einstein gravity. Some solutions in string theory
can be interpreted as black holes. Using the semi-analytic method and WKB
method,the quasinormal modes(QNMs)of 1+1 dimensional black hole in string
theory are studied.The QNMs of 1+3 dimensional black hole in string theory are
also calculated through numerical approach.The numerical investigation has
shown that the late time gravitational oscillation of the black hole under an
external perturbaton is dominated by certain QNMs.Comment: 2 figure
Effects of Water Stress on Germination and Growth of Wheat, Photosynthetic Efficiency and Accumulation of Metabolites
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