4,780 research outputs found
K-essential Leptogenesis
K-essence is a possible candidate for dark energy of the Universe. In this
paper we consider couplings of k-essence to the matter fields of the standard
electroweak theory and study the effects of the cosmological CPT violation
induced by the CPT violating {\bf Ether} during the evolution of the k-essence
scalar field on the laboratory experiments and baryogenesis. Our results show
that the matter and antimatter asymmetry can be naturally explained {\it via}
leptogenesis without conflicting with the experimental limits on CPT violation
test. The mechanism for baryogenesis proposed in this paper provides a unified
picture for dark energy and baryon matter of our Universe and allows an almost
degenerate neutrino mass pattern with a predicted rate on the neutrinoless
double beta decays accessible to the experimental sensitivity in the near
future.Comment: 6 pages, 1 figure. To appear in Phys. Lett.
A Comparison of Quintessence and Nonlinear Born-Infeld Scalar Field Using Gold Supernova data
We study the Non-Linear Born-Infeld(NLBI) scalar field model and quintessence
model with two different potentials( and ). We
investigate the differences between those two models. We explore the equation
of state parameter w and the evolution of scale factor in both NLBI
scalar field and quintessence model. The present age of universe and the
transition redshift are also obtained. We use the Gold dataset of 157 SN-Ia to
constrain the parameters of the two models. All the results show that NLBI
model is slightly superior to quintessence model.Comment: 17 pages, 10 figures, some references adde
Current-driven Magnetization Reversal in a Ferromagnetic Semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As Tunnel Junction
Current-driven magnetization reversal in a ferromagnetic semiconductor based
(Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K.
Magnetoresistance measurements combined with current pulse application on a
rectangular 1.5 x 0.3 um^2 device revealed that magnetization switching occurs
at low critical current densities of 1.1 - 2.2 x 10^5 A/cm^2 despite the
presence of spin-orbit interaction in the p-type semiconductor system. Possible
mechanisms responsible for the effect are discussed.Comment: 16 pages, 4 figure
The Weak Energy Condition and the Expansion History of the Universe
We examine flat models containing a dark matter component and an arbitrary
dark energy component, subject only to the constraint that the dark energy
satisfies the weak energy condition. We determine the constraints that these
conditions place on the evolution of the Hubble parameter with redshift, H(z),
and on the scaling of the coordinate distance with redshift, r(z).
Observational constraints on H(z) are used to derive an upper bound on the
current matter density. We demonstrate how the weak energy condition constrains
fitting functions for r(z).Comment: 5 pages, 3 figures, references and discussion adde
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
Negative A-plates for broadband wide-view liquid crystal displays
Negative A-plates fabricated by mechanically stretching polystyrene are studied and their physical properties evaluated. A molecular model is developed to explain the underlying physical mechanisms. An example of a broadband wide-view liquid crystal display including a negative A-plate for phase compensation is illustrated
Contradiction between strong lensing statistics and a feedback solution to the cusp/core problem
Standard cosmology has many successes on large scales, but faces some
fundamental difficulties on small, galactic scales. One such difficulty is the
cusp/core problem. High resolution observations of the rotation curves for dark
matter dominated low surface brightness (LSB) galaxies imply that galactic dark
matter halos have a density profile with a flat central core, whereas N-body
structure formation simulations predict a divergent (cuspy) density profile at
the center. It has been proposed that this problem can be resolved by stellar
feedback driving turbulent gas motion that erases the initial cusp. However,
strong gravitational lensing prefers a cuspy density profile for galactic
halos. In this paper, we use the most recent high resolution observations of
the rotation curves of LSB galaxies to fit the core size as a function of halo
mass, and compare the resultant lensing probability to the observational
results for the well defined combined sample of the Cosmic Lens All-Sky Survey
(CLASS) and Jodrell Bank/Very Large Array Astrometric Survey (JVAS). The
lensing probabilities based on such density profiles are too low to match the
observed lensing in CLASS/JVAS. High baryon densities in the galaxies that
dominate the lensing statistics can reconcile this discrepancy, but only if
they steepen the mass profile rather than making it more shallow. This places
contradictory demands upon the effects of baryons on the central mass profiles
of galaxies.Comment: 8 pages, 3 figures. Largely improved compared with the version 1 to
reflect the referees' reports, conclusions unchanged. Published in Research
in Astronomy and Astrophysics (RAA
Revisit of Coulomb effects on pi^{-}/pi^{+} ratio in heavy-ion collisions
It is shown that the large ratio at low pion energies
recently observed in the reaction of Au+Au at GeV at SIS/GSI
is due to the strong Coulomb field of the reaction system.Comment: LaTex, 7 pages, 4 figures are available from the Author upon request,
Phys. Lett. B in press
Non-minimally coupled f(R) Cosmology
We investigate the consequences of non-minimal gravitational coupling to
matter and study how it differs from the case of minimal coupling by choosing
certain simple forms for the nature of coupling, The values of the parameters
are specified at (present epoch) and the equations are evolved backwards
to calculate the evolution of cosmological parameters. We find that the Hubble
parameter evolves more slowly in non-minimal coupling case as compared to the
minimal coupling case. In both the cases, the universe accelerates around
present time, and enters the decelerating regime in the past. Using the latest
Union2 dataset for supernova Type Ia observations as well as the data for
baryon acoustic oscillation (BAO) from SDSS observations, we constraint the
parameters of Linder exponential model in the two different approaches. We find
that there is a upper bound on model parameter in minimal coupling. But for
non-minimal coupling case, there is range of allowed values for the model
parameter.Comment: 7 pages, Latex style, 8 eps figure
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