27 research outputs found
Random versus holographic fluctuations of the background metric. II. Note on the dark energies arising due to microstructure of space-time
Over the last few years a certain class of dark-energy models decaying
inversely proportional to the square of the horizon distance emerged on the
basis either of Heisenberg uncertainty relations or of the uncertainty relation
between the four-volume and the cosmological constant. The very nature of these
dark energies is understood to be the same, namely it is the energy of
background space/metric fluctuations. Putting together these uncertainty
relations one finds that the model of random fluctuations of the background
metric is favored over the holographic one.Comment: 3 page
Cell-type-specific modulation of feedback inhibition by serotonin in the hippocampus
Midbrain raphe nuclei provide strong serotonergic projections to the hippocampus, in which serotonin (5-HT) exerts differential effects mediated by multiple 5-HT receptor subtypes. The functional relevance of this diversity of information processing is poorly understood. Here we show that serotonin via 5-HT(1B) heteroreceptors substantially reduces synaptic excitation of cholecystokinin-expressing interneurons in area CA1 of the rat hippocampus, in contrast to parvalbumin-expressing basket cells. The reduction is input specific, affecting only glutamatergic synaptic transmission originating from CA1 pyramidal cells. As a result, serotonin selectively decreases feedback inhibition via 5-HT(1B) receptor activation and subsequently increases the integration time window for spike generation in CA1 pyramidal cells. Our data imply an important role for serotonergic modulation of GABAergic action in subcortical control of hippocampal output
Another Two Dark Energy Models Motivated from Karolyhazy Uncertainty Relation
The Krolyhzy uncertainty relation
indicates that there exists the minimal detectable cell over the
region in Minkowski spacetime. Due to the energy-time uncertainty
relation, the energy of the cell can not be less .
Then we get a new energy density of metric fluctuations of Minkowski spacetime
as . Motivated by the energy density, we propose two new dark
energy models. One model is characterized by the age of the universe and the
other is characterized by the conformal age of the universe. We find that in
the two models, the dark energy mimics a cosmological constant in the late
time.Comment: 10 pages, 5 figures, References are adde
Entropy-Corrected New Agegraphic Dark Energy Model in Horava-Lifshitz Gravity
In this work, we have considered the entropy-corrected new agegraphic dark
energy (ECNADE) model in Horava-Lifshitz gravity in FRW universe. We have
discussed the correspondence between ECNADE and other dark energy models such
as DBI-essence,Yang-Mills dark energy, Chameleon field, Non-linear
electrodynamics field and hessence dark energy in the context of
Horava-Lifshitz gravity and reconstructed the potentials and the dynamics of
the scalar field theory which describe the ECNADE.Comment: 12 page
Restoring New Agegraphic Dark Energy in RS II Braneworld
Motivated by recent works [1,2], we investigate new agegraphic model of dark
energy in the framework of RS II braneworld. We also include the case of
variable gravitational constant in our model. Furthermore, we establish
correspondence between the new agegraphic dark energy with other dark energy
candidates based on scalar fields.Comment: 13 pages, accepted for publication in IJT
Interacting Agegraphic Dark Energy
A new dark energy model, named "agegraphic dark energy", has been proposed
recently, based on the so-called K\'{a}rolyh\'{a}zy uncertainty relation, which
arises from quantum mechanics together with general relativity. In this note,
we extend the original agegraphic dark energy model by including the
interaction between agegraphic dark energy and pressureless (dark) matter. In
the interacting agegraphic dark energy model, there are many interesting
features different from the original agegraphic dark energy model and
holographic dark energy model. The similarity and difference between agegraphic
dark energy and holographic dark energy are also discussed.Comment: 10 pages, 5 figures, revtex4; v2: references added; v3: accepted by
Eur. Phys. J. C; v4: published versio
The accelerated scaling attractor solution of the interacting agegraphic dark energy in Brans-Dicke theory
We investigate the interacting agegraphic dark energy in Brans-Dicke theory
and introduce a new series general forms of dark sector coupling. As examples,
we select three cases involving a linear interaction form (Model I) and two
nonlinear interaction form (Model II and Model III). Our conclusions show that
the accelerated scaling attractor solutions do exist in these models. We also
find that these interacting agegraphic dark energy modes are consistent with
the observational data. The difference in these models is that nonlinear
interaction forms give more approached evolution to the standard CDM
model than the linear one. Our work implies that the nonlinear interaction
forms should be payed more attention.Comment: 9 pages, 10 figures, accepted in Eur. Phys. J.
Interacting entropy-corrected new agegraphic dark energy in Brans-Dicke cosmology
Motivated by a recent work of one of us [1], we extend it by using quantum
(or entropy) corrected new agegraphic dark energy in the Brans-Dicke cosmology.
The correction terms are motivated from the loop quantum gravity which is one
of the competitive theories of quantum gravity. Taking the non-flat background
spacetime along with the conformal age of the universe as the length scale, we
derive the dynamical equation of state of dark energy and the deceleration
parameter. An important consequence of this study is the phantom divide
scenario with entropy-corrected new agegraphic dark energy. Moreover, we assume
a system of dark matter, radiation and dark energy, while the later interacts
only with dark matter. We obtain some essential expressions related with dark
energy dynamics. The cosmic coincidence problem is also resolved in our model.Comment: 16 pages, no figure, accepted for publication in Gen. Relativ. Gra
Inflation and late time acceleration in braneworld cosmological models with varying brane tension
Braneworld models with variable brane tension introduce a new
degree of freedom that allows for evolving gravitational and cosmological
constants, the latter being a natural candidate for dark energy. We consider a
thermodynamic interpretation of the varying brane tension models, by showing
that the field equations with variable can be interpreted as
describing matter creation in a cosmological framework. The particle creation
rate is determined by the variation rate of the brane tension, as well as by
the brane-bulk energy-matter transfer rate. We investigate the effect of a
variable brane tension on the cosmological evolution of the Universe, in the
framework of a particular model in which the brane tension is an exponentially
dependent function of the scale factor. The resulting cosmology shows the
presence of an initial inflationary expansion, followed by a decelerating
phase, and by a smooth transition towards a late accelerated de Sitter type
expansion. The varying brane tension is also responsible for the generation of
the matter in the Universe (reheating period). The physical constraints on the
model parameters, resulted from the observational cosmological data, are also
investigated.Comment: 25 pages, 8 figures, accepted for publication in European Physical
Journal
Agegraphic dark energy as a quintessence
Recently, a dark energy model characterized by the age of the universe,
dubbed ``agegraphic dark energy'', was proposed by Cai. In this paper, a
connection between the quintessence scalar-field and the agegraphic dark energy
is established, and accordingly, the potential of the agegraphic quintessence
field is constructed.Comment: 9 pages, 3 figures; accepted by Eur. Phys. J.