123143461
Interacting holographic dark energy with variable deceleration parameter and tachyon scalar field dark energy model in LRS Bianchi type-II universe
In this work, we have considered the spatially homogeneous and anisotropic Bianchi type-II universe filled with two interacting fluids; dark matter and holographic dark energy components. Assuming the proportionality relation between one of the components of shear scalar and expansion scalar which yields time dependent deceleration parameter, an exact solution to Einstein’s field equations in Bianchi type-II line element is obtained. We have investigated geometric and kinematics properties of the model and the behaviour of the holographic dark energy. It is observed that the mean anisotropic parameter is uniform through the whole evolution of the universe and the coincidence parameter increases with increasing time. The solutions are also found to be in good agreement with the results of recent observations. We have applied the statefinder diagnostics method to study the behaviour of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. We have also established a correspondence between the holographic dark energy model and the tachyon scalar field dark energy model. We have reconstructed the potential and the dynamics of the tachyon scalar field, which describes accelerated expansion of the universe.
122930946
Holographic dark energy model with linearly varying deceleration parameter and generalised Chaplygin gas dark energy model in Bianchi type-I universe
The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein’s field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations.
122369912
Interacting holographic dark energy with variable deceleration parameter and accreting black holes in Bianchi type-V universe
In this paper, we have considered the spatially homogeneous and anisotropic Bianchi type-V space time filled with two interacting fluids; dark matter and a hypothetical isotropic fluid as the holographic dark energy components. To obtain an exact solution of the Einstein’s field equations, we used the assumption of time dependent deceleration parameter. We have investigated geometric and kinematic properties of the model. It is observed that the anisotropy parameter of the universe approaches to zero and the universe achieve flatness for large cosmic time. We have shown that this expanding solution is stable against the perturbation with respect to anisotropic spatial directions. We have also studied the evolution of the mass of a black hole embedded in a universe which interacts with a combination of dark matter and dark energy, considering that in the vicinity of the black hole the metric is of Schwarzschild type. We found that the black hole mass increases with the evolution of the universe, and on later epochs the increase in mass stops as dark energy accretion takes over. The results are found to be consistent with recent cosmological observations.
121622669
Holographic dark energy model with variable deceleration parameter, cosmic coincidence and the future singularity of the Kantowski-Sachs universe
The present work deals with a spatially homogeneous and anisotropic Kantowski-Sachs space time filled with two minimally interacting fluids; dark matter and a hypothetical anisotropic fluid as the holographic dark energy components. To obtain an exact solution of the Einstein’s field equations, we used the assumption of linearly varying deceleration parameter. We have investigated geometric and kinematic properties of the model and the role of the anisotropic holographic dark energy in the evolution of the Kantowski-Sachs universe. Under the suitable condition, it is observed that the anisotropy parameter of the universe and the skewness parameter of the holographic dark energy approaches to zero for large cosmic time and the universe can achieve flatness for some particular moments throughout its entire lifetime. Results show that the coincidence parameter $( \Re= \frac{\rho_{\varLambda}}{\rho_{M}} )$ increases with increasing time and a big rip type future singularity will occur for this model. We have also applied the statefinder diagnostics method to study the behavior of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. Since in this model, the universe has a finite life time and passes through a significant time when the dark energy and the matter energy densities are roughly comparable, so considering $\frac{1}{ \Re_{0}} <\Re < \Re_{0}$, where ℜ0 is any fixed ratio, we have calculated the fraction of total life time of the universe when the universe passes through the coincidental stage for this future singularity. The results are found to be consistent with recent cosmological observations.
121582631
Dark energy, cosmic coincidence and future singularity of the universe
Dark energy model with the equation of state $$p_{DE} =-\rho _{DE} -A\rho _{DE}^\alpha $$, is characterised by four finite life time future singularity of the universe for different values of the parameter $$A$$ and $$\alpha $$ [Nojiri et al. in Phys Rev D 71:063004, 2005]. Since from the matter dominated era to the dark energy dominated era the ratio of the dark energy density to the matter energy density increases as the universe expand for these future singularities, the universe passes through a significant time when the dark energy density and the matter energy density are nearly comparable. Considering $$\frac{1}{r_0 }<r=\frac{\rho _{DE} }{\rho _M }<r_0 $$, where $$r_0$$ is any fixed ratio, we calculate the fraction of total life time of the universe when the universe passes through the coincidental stage for these singularities. It has been found that the fractional time varies as $$\alpha $$ varies within the range for which these finite life time future singularities occur and the fraction is smaller for smaller values of $$r_0 $$. Importance of the fractional time and observational limits onto the values of the parameter $$A$$ and $$\alpha $$ has also been discussed.
122825702
Holographic Dark Energy Model with Quintessence in Bianchi Type-I Space-Time
In this paper, we have studied a homogeneous and anisotropic universe filled with matter and holographic dark energy components. Assuming deceleration parameter to be a constant, an exact solution to Einstein’s field equations in axially symmetric Bianchi type-I line element is obtained. A correspondence between the holographic dark energy models with the quintessence dark energy models is also established. Quintessence potential and the dynamics of the quintessence scalar field are reconstructed, which describe accelerated expansion of the universe.
121294545
Gauge theories with strong coupling in four dimensions
Abstract The long distance behavior of singlet current correlation functions of gauge theories on a lattice are found approximately using the renormalization group. For strong coupling the behavior is similar to that found in the lattice massive Schwinger model.
117009870
Energy loss due to field fluctuations in a two-stream QCD plasma
We derive the expression for the collisional energy loss in two stream plasma induced by the fluctuating chromoelectric field. It is revealed that the main contribution here comes from the unstable modes which grow exponentially with time. A strong direction dependence of the energy loss has also been demonstrated.
119200237
Finsler metrics and CPT
The role of Finsler-like metrics in situations where Lorentz symmetry breaking and also CPT violation are discussed. Various physical instances of such metrics both in quantum gravity and analogue systems are discussed. Both differences and similarities between the cases will be emphasised. In particular the medium of D-particles that arise in string theory will be examined. In this case the breaking of Lorentz invariance, at the level of quantum fluctuations, together with concomitant CPT in certain situations will be analysed. In particular it will be shown correlations for neutral meson pairs will be modified and a new contribution to baryogenesis will appear.
8253414
The omega effect for neutral mesons
The possible role of decoherence due to space-time foam is discussed within the context of two models, one based on string/brane theory. and the other based on properties of black hole horizons in general relativity. It is argued that the density matrix satisfies a dissipative master equation, primarily from the study of renormalization group flows in non-critical string theory. This interpretation of the zero mode of the Liouville field as time leads necessarily to the CPT operator being ill defined. One striking consequence is that the quantum mechanical correlations of pair states of neutral mesons produced in meson factories are changed from the usual EPR state. The magnitude of this departure from EPR correlations is characterised by a parameter ω. The predicted value of ω is very small or zero. However it is shown explicitly that the the non-vanishing of ω is only a feature of the model based on string/brane theory.
54602717
Experience with the TRIUMF Main Tank Vacuum Control System
The TRIUMF Main Tank Vacuum Control System was upgraded in 1984. The earlier system, which consisted of a collection of hardwired relay logic boxes housed in three standard instrumentation racks, was replaced with a compact and flexible microprocessor-based control system. The user interface, previously distributed over the three racks, was consolidated into a single hardwired control and mimic panel. Since 1984, the Main Tank Vacuum System has undergone a series of changes in configuration and vacuum pumping hardware with necessary changes being implemented in the control system logic. Corresponding changes to the user interface were sometimes difficult to implement and in time exhausted the spare input/output capacity which had been built in to the panel. The availability of inexpensive personal computers with adequate graphics capability and the ease of modifying, or adding to a programmable user interface precipitated the retirement of the hardwired panel and its replacement by a PC-based graphics user interface. System configuration, safety considerations, the hardware and the software implementation using the 'C' programming language are described. The evolution of the control system and its performance, both over the years and in adapting to the vacuum system changes, are discussed.<<ETX>>