9,295 research outputs found
Revisiting Agegraphic Dark Energy in Brans-Dicke Cosmology
We explore a spatially homogeneous and isotropic Friedmann-Robertson-Walker
(FRW) universe which is filled with agegraphic dark energy (ADE) with mutual
interaction with pressureless dark matter in the background of Brans-Dicke (BD)
theory. We consider both original and new type of agegraphic dark energy (NADE)
and further assume the sign of the interaction term can change during the
history of the Universe. We obtain the equation of state parameter, the
deceleration parameter and the evolutionary equation for the sign-changeable
interacting ADE and NADE in BD theory. We find that, in both models, the
equation of state parameter, , cannot cross the phantom line, although
they can predict the Universe evolution from the early deceleration phase to
the late time acceleration, compatible with observations. We also investigate
the sound stability of these models and find out that both models cannot show a
signal of stability for different model parameters.Comment: 10 pages, 14 figure
Some faces of Smarandache semigroups' concept in transformation semigroups' approach
In the following text, the main aim is to distinguish some relations between Smarad-
che semigroups and (topological) transformation semigroups areas. We will see that a transformation group is not distal if and only if its enveloping semigroup is a Smarandache semigroup. Moreover we will find a classifying of minimal right ideals of the enveloping semigroup of a transformation semigroup
Stability of HDE model with sign-changeable interaction in Brans-Dicke theory
We consider the Brans-Dicke (BD) theory of gravity and explore the
cosmological implications of the sign-changeable interacting holographic dark
energy (HDE) model in the background of Friedmann-Robertson-Walker (FRW)
universe. As the system's infrared (IR) cutoff, we choose the future event
horizon, the Granda-Oliveros (GO) and the Ricci cutoffs. For each cutoff, we
obtain the density parameter, the equation of state (EoS) and the deceleration
parameter of the system. In case of future event horizon, we find out that the
EoS parameter, , can cross the phantom line, as a result the transition
from deceleration to acceleration expansion of the universe can be achieved
provided the model parameters are chosen suitably. Then, we investigate the
instability of the sign-changeable interacting HDE model against perturbations
in BD theory. For this purpose, we study the squared sound speed whose
sign determines the stability of the model. When the model is
unstable against perturbation. For future event horizon cutoff, our universe
can be stable () depending on the model parameters. Then, we focus
on GO and Ricci cutoffs and find out that although other features of these two
cutoffs seem to be consistent with observations, they cannot leads to stable
dominated universe, except in special case with GO cutoff. Our studies confirm
that for the sign-changeable HDE model in the setup of BD cosmology, the event
horizon is the most suitable horizon which can passes all conditions and leads
to a stable DE dominated universe.Comment: 19pages, 22figure
Lifting 1/4-BPS States on K3 and Mathieu Moonshine
The elliptic genus of K3 is an index for the 1/4-BPS states of its sigma
model. At the torus orbifold point there is an accidental degeneracy of such
states. We blow up the orbifold fixed points using conformal perturbation
theory, and find that this fully lifts the accidental degeneracy of the 1/4-BPS
states with h=1. At a generic point near the Kummer surface the elliptic genus
thus measures not just their index, but counts the actual number of these BPS
states. We comment on the implication of this for symmetry surfing and Mathieu
moonshine.Comment: 29+5 pp, a sign mistake corrected in eqs. (3.14) and (4.20), footnote
6 added to clarify this point, references adde
Interval valued intuitionistic -fuzzy -submodules
On the basis of the concept of the interval valued intuitionistic fuzzy sets
introduced by K.Atanassov, the notion of interval valued intuitionistic fuzzy
-submodules of an -module with respect to -norm and -norm
is given and the characteristic properties are described. The homomorphic
image and the inverse image are investigated.In particular, the connections
between interval valued intuitionistic -fuzzy -submodules and
interval valued intuitionistic -fuzzy submodules are discussed
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