Friedmann cosmology with decaying vacuum density in Brans-Dicke theory

In this paper, we study Friedmann cosmology with time-varying vacuum energy density in the context of Brans-Dicke theory. We consider an isotropic and homogeneous flat space, filled with a matter-dominated perfect fluid and a dynamical cosmological term Λ(t), obeying the equation of state of the vacuum. As the exact nature of a possible time-varying vacuum is yet to be found, we explore Λ(t) given by the phenomenological law Λ(t)=λ+σH, where λ and σ are positive constants. We solve the model and then focus on two different cases ΛH1 and ΛH2 by assuming Λ=λ and Λ=σH, respectively. Notice that ΛH1 is the analog of the standard ΛCDM, but within the Brans-Dicke cosmology. We find the analytical solution of the main cosmological functions such as the Hubble parameter, the scale factor, deceleration and equation of state parameters for these models. In order to test the viability of the cosmological scenarios, we perform two sets of joint observational analyses of the recent Type Ia supernova data (Pantheon), observational measurements of Hubble parameter data, Baryon acoustic oscillation/Cosmic microwave background data and Local Hubble constant for each model. For the sake of comparison, the same data analysis is performed for the ΛCDM model. Each model shows a transition from decelerated phase to accelerated phase and can be viewed as an effective quintessence behavior. Using the model selection criteria AIC and BIC to distinguish from existing dark energy models, we find that the Brans-Dicke analog of the Λ-cosmology (i.e. our model ΛH1) performs at a level comparable to the standard ΛCDM, whereas ΛH2 is less favoured

Some anisotropic universes in the presence of imperfect fluid coupling with spatial curvature

We consider Bianchi VI spacetime, which also can be reduced to Bianchi types VI0-V-III-I. We initially consider the most general form of the energy-momentum tensor which yields anisotropic stress and heat flow. We then derive an energy-momentum tensor that couples with the spatial curvature in a way so as to cancel out the terms that arise due to the spatial curvature in the evolution equations of the Einstein field equations. We obtain exact solutions for the universes indefinetly expanding with constant mean deceleration parameter. The solutions are beriefly discussed for each Bianchi type. The dynamics of the models and fluid are examined briefly, and the models that can approach to isotropy are determined. We conclude that even if the observed universe is almost isotropic, this does not necessarily imply the isotropy of the fluid (e.g., dark energy) affecting the evolution of the universe within the context of general relativity.Comment: 17 pages, no figures; to appear in International Journal of Theoretical Physics; in this version (which is more concise) an equation added, some references updated and adde

Synthesis and antimicrobial evaluation of 1,4-disubstituted 1,2,3-triazoles with aromatic ester functionality

AbstractA series of 1,4-disubstituted 1,2,3-triazoles having p-substituted aromatic ester functionality were synthesized via Cu(I) catalysed click reaction between p-substituted benzoic acid prop-2-ynyl esters and aralkyl azides. The synthesized triazoles were characterized by IR, 1H NMR, 13C NMR and mass spectral techniques. These compounds were evaluated for their antimicrobial activity against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Mycobacterium tuberculosis, Candida albicans, Aspergillus niger and Aspergillus flavus by two fold serial dilution method. Some of the synthesized 1,4-disubstituted 1,2,3-triazoles possess comparable or even better antibacterial, antitubercular and antifungal activities than reference drugs against tested bacterial, mycobacterial and fungal strains, respectively

Bianchi type-II cosmological model: some remarks

Within the framework of Bianchi type-II (BII) cosmological model the behavior of matter distribution has been considered. It is shown that the non-zero off-diagonal component of Einstein tensor implies some severe restriction on the choice of matter distribution. In particular for a locally rotationally symmetric Bianchi type-II (LRS BII) space-time it is proved that the matter distribution should be strictly isotropic if the corresponding matter field possesses only non-zero diagonal components of the energy-momentum tensor.Comment: 3 page

Response to challenge infection in sheep selected for resistance and susceptibility to Haemonchus contortus

Not AvailableA study was undertaken to compare the host response on single and trickle infections of H. contortus in Malpura lambs selected for either resistance or susceptibility to H. contortus. Twelve Malpura male lambs (6 each from resistant - R and susceptible - S lines; 9-12 months old) were used during two periods of 10 weeks: single and trickle infections with an interval of three weeks. The host response was measured in terms of body weight, faecal egg count, haematological and biochemical characters for 10 weeks post challenge. Over the period of 10 weeks, a gain of 0.3 kg was recorded in lambs of R-line compared to a loss of 4.1 kg in S-line on single challenge. However, on trickle infection both the groups exhibited gain (5.7 kg in R-line and 5.2 kg in S-line) in body weight. On majority of occasions intensity of infection was lower in R-line compared to S line. Non-significant variation was observed in haemoglobin (Hb) and packed cell volume (PCV) among both the lines on single challenge. However, significant (P<0.05/0.001) variations among divergent lines (lower Hb value in S-line compared to R-line) were observed on trickle challenge. In both the forms of challenge, plasma pepsinogen level revealed non-significant variation. On slaughter, the mean number of adult H. contortus in abomasum varied non-significantly between 498.7±40.1 (R-line) and 576.7±270.1 (S-line). The worm length remained more or less similar in both the lines. Correlation between log FEC and body weight was significant (P<0.05) only in S line. Log FEC showed significantly (P<0.001) negative correlation with Hb and PCV in both the lines on single challenge. The correlation between log FEC and plasma pepsinogen level was significantly (P<0.05) negative in both the lines on trickle challenge. It was concluded that the animals selected for resistance can tolerate parasite challenge effectively with reduced intensity of infection, higher body weight gain and reduced pathogenic effect.ICAR-CSWRI Avikanaga

Non-Vacuum Bianchi Types I and V in f(R) Gravity

In a recent paper \cite{1}, we have studied the vacuum solutions of Bianchi types I and V spacetimes in the framework of metric f(R) gravity. Here we extend this work to perfect fluid solutions. For this purpose, we take stiff matter to find energy density and pressure of the universe. In particular, we find two exact solutions in each case which correspond to two models of the universe. The first solution gives a singular model while the second solution provides a non-singular model. The physical behavior of these models has been discussed using some physical quantities. Also, the function of the Ricci scalar is evaluated.Comment: 15 pages, accepted for publication in Gen. Realtiv. Gravi

Bulk Viscous LRS Biachi-I Universe with variable GG and decaying Λ\Lambda

The present study deals with spatially homogeneous and totally anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological model with variable $G$ and $\Lambda$ in presence of imperfect fluid. To get the deterministic model of Universe, we assume that the expansion $(\theta)$ in the model is proportional to shear $(\sigma)$. This condition leads to $A=\ell B^{n}$, where $A$,\;$B$ are metric potential. The cosmological constant $\Lambda$ is found to be decreasing function of time and it approaches a small positive value at late time which is supported by recent Supernovae Ia (SN Ia) observations. Also it is evident that the distance modulus curve of derived model matches with observations perfectly.Comment: 11 pages, 4 figures and 1 table, Accepted for publication in Astrophysics and Space Scienc

Warped Tachyonic Inflation in Type IIB Flux Compactifications and the Open-String Completeness Conjecture

We consider a cosmological scenario within the KKLT framework for moduli stabilization in string theory. The universal open string tachyon of decaying non-BPS D-brane configurations is proposed to drive eternal topological inflation. Flux-induced `warping' can provide the small slow-roll parameters needed for successful inflation. Constraints on the parameter space leading to sufficient number of e-folds, exit from inflation, density perturbations and stabilization of the Kahler modulus are investigated. The conditions are difficult to satisfy in Klebanov-Strassler throats but can be satisfied in T^3 fibrations and other generic Calabi-Yau manifolds. This requires large volume and magnetic fluxes on the D-brane. The end of inflation may or may not lead to cosmic strings depending on the original non-BPS configuration. A careful investigation of initial conditions leading to a phenomenologically viable model for inflation is carried out. The initial conditions are chosen on the basis of Sen's open string completeness conjecture. We find time symmetrical bounce solutions without initial singularities for k=1 FRW models which are correlated with an inflationary period. Singular big-bang/big-crunch solutions also exist but do not lead to inflation. There is an intriguing correlation between having an inflationary universe in 4 dimensions and 6 compact dimensions or a big-crunch singularity and decompactification.Comment: 43 pages, 9 figures. v3: Typos correcte

Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter

The Bianchi type III dark energy models with constant deceleration parameter are investigated. The equation of state parameter $\omega$ is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical aspect of the dark energy models are discussed.Comment: 12 pages, 2 figures, Accepted version of IJT