Cosmological applications in Kaluza-Klein theory

The field equations of Kaluza-Klein (KK) theory have been applied in the domain of cosmology. These equations are solved for a flat universe by taking the gravitational and the cosmological constants as a function of time t. We use Taylor's expansion of cosmological function, $\Lambda(t)$, up to the first order of the time $t$. The cosmological parameters are calculated and some cosmological problems are discussed.Comment: 14 pages Latex, 5 figures, one table. arXiv admin note: text overlap with arXiv:gr-qc/9805018 and arXiv:astro-ph/980526

Equation of state for Universe from similarity symmetries

In this paper we proposed to use the group of analysis of symmetries of the dynamical system to describe the evolution of the Universe. This methods is used in searching for the unknown equation of state. It is shown that group of symmetries enforce the form of the equation of state for noninteracting scaling multifluids. We showed that symmetries give rise the equation of state in the form $p=-\Lambda+w_{1}\rho(a)+w_{2}a^{\beta}+0$ and energy density $\rho=\Lambda+\rho_{01}a^{-3(1+w)}+\rho_{02}a^{\beta}+\rho_{03}a^{-3}$, which is commonly used in cosmology. The FRW model filled with scaling fluid (called homological) is confronted with the observations of distant type Ia supernovae. We found the class of model parameters admissible by the statistical analysis of SNIa data. We showed that the model with scaling fluid fits well to supernovae data. We found that $\Omega_{\text{m},0} \simeq 0.4$ and $n \simeq -1$ ($\beta = -3n$), which can correspond to (hyper) phantom fluid, and to a high density universe. However if we assume prior that $\Omega_{\text{m},0}=0.3$ then the favoured model is close to concordance $\Lambda$CDM model. Our results predict that in the considered model with scaling fluids distant type Ia supernovae should be brighter than in $\Lambda$CDM model, while intermediate distant SNIa should be fainter than in $\Lambda$CDM model. We also investigate whether the model with scaling fluid is actually preferred by data over $\Lambda$CDM model. As a result we find from the Akaike model selection criterion prefers the model with noninteracting scaling fluid.Comment: accepted for publication versio

Reconstruction of the equation of state for the cyclic universes in homogeneous and isotropic cosmology

We study the cosmological evolutions of the equation of state (EoS) for the universe in the homogeneous and isotropic Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) space-time. In particular, we reconstruct the cyclic universes by using the Weierstrass and Jacobian elliptic functions. It is explicitly illustrated that in several models the universe always stays in the non-phantom (quintessence) phase, whereas there also exist models in which the crossing of the phantom divide can be realized in the reconstructed cyclic universes.Comment: 29 pages, 8 figures, version accepted for publication in Central European Journal of Physic

Dark Energy and Gravity

I review the problem of dark energy focusing on the cosmological constant as the candidate and discuss its implications for the nature of gravity. Part 1 briefly overviews the currently popular `concordance cosmology' and summarises the evidence for dark energy. It also provides the observational and theoretical arguments in favour of the cosmological constant as the candidate and emphasises why no other approach really solves the conceptual problems usually attributed to the cosmological constant. Part 2 describes some of the approaches to understand the nature of the cosmological constant and attempts to extract the key ingredients which must be present in any viable solution. I argue that (i)the cosmological constant problem cannot be satisfactorily solved until gravitational action is made invariant under the shift of the matter lagrangian by a constant and (ii) this cannot happen if the metric is the dynamical variable. Hence the cosmological constant problem essentially has to do with our (mis)understanding of the nature of gravity. Part 3 discusses an alternative perspective on gravity in which the action is explicitly invariant under the above transformation. Extremizing this action leads to an equation determining the background geometry which gives Einstein's theory at the lowest order with Lanczos-Lovelock type corrections. (Condensed abstract).Comment: Invited Review for a special Gen.Rel.Grav. issue on Dark Energy, edited by G.F.R.Ellis, R.Maartens and H.Nicolai; revtex; 22 pages; 2 figure

Constraints on cosmological models from strong gravitational lensing systems

Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structure, formation, and evolution). Using the gravitational lensing theory and cluster mass distribution model, we try to collect a relatively complete observational data concerning the Hubble constant independent ratio between two angular diameter distances $D_{ds}/D_s$ from various large systematic gravitational lens surveys and lensing by galaxy clusters combined with X-ray observations, and check the possibility to use it in the future as complementary to other cosmological probes. On one hand, strongly gravitationally lensed quasar-galaxy systems create such a new opportunity by combining stellar kinematics (central velocity dispersion measurements) with lensing geometry (Einstein radius determination from position of images). We apply such a method to a combined gravitational lens data set including 70 data points from Sloan Lens ACS (SLACS) and Lens Structure and Dynamics survey (LSD). On the other hand, a new sample of 10 lensing galaxy clusters with redshifts ranging from 0.1 to 0.6 carefully selected from strong gravitational lensing systems with both X-ray satellite observations and optical giant luminous arcs, is also used to constrain three dark energy models ($\Lambda$CDM, constant $w$ and CPL) under a flat universe assumption. For the full sample ($n=80$) and the restricted sample ($n=46$) including 36 two-image lenses and 10 strong lensing arcs, we obtain relatively good fitting values of basic cosmological parameters, which generally agree with the results already known in the literature. This results encourages further development of this method and its use on larger samples obtained in the future.Comment: 22 pages, 5 figures, 2 tables; accepted by JCA

Role of eosinophils in anaphylactic reactions related to hormonal alterations

This essay deals with enzymatic causation of anaphylactic reactions,and with the role which eoinophils play in anaphylaxis.Since anaphylactic reaions represent non-specific stress stimuli,their primary symptomatology is intermingled with the secondary manifestations from stress stimulation.The chief aim of the present thesis is to demonstrate ,that a group of manifestations which bear the name mq of anaphylaxis or allergy,are signs and symptoms which result from the different pathogenetic origins.A tentative effort is made to segregade the anaphylactic manifestations according to their primary pathogeneti factors.A thorough review is not,therefore, intended to be made of any of the three main problems:eosinophils, enzymatic theory of anaphylaxis,or hormonal involvement in anaphylaxis. It is, however, intended to demonstrate a close interdependence and causal relation ship between disturbed enzymatic proteolysis and horonal discrasia.The title "... anaphylactic reactions related to hormonal alterations" may be misleading, because only one particular hormonal involvement (pituitary-adrenal response) in anaphylactic reactions is discussed, although many other endocrinopathies may be closely connected with allergy.The enzymatic theory of anaphylaxis was recjected. many years ago,for lack of conclusive evidence and because some experimental findings contradicted he rationale of this theory.By taking advantage of new developments in histo- chemistry and modern knowledge of sub-microscopical cellular structure, this thesis attempts to produce a new evidence in support of the enzymatic theory;furthermore,it endeavours to answer the objections previously advanced by antagonists of this theory.If,however,the enzymatic theory of anaphylaxis is now to be accepted, its original form requires substantial modifications in accordance with modern views,and this is another aim of this thesis.For purely mnemonic reasons the whole essay is divided into three main chapters followed by "General conclusions ".In each chapter stress has been laid on one particular object; to make the presentation of this object more comprehensive,certain facts and theories are repeated in each chapter.The terminology used for the designation of the intracellular proteolytic enzymes is based in principle on that accepted by M.Bergmenn (1942), with some modifications .Pepsinase, pepsin-like proteinase or Cathepsine I, are synonyms, and they denominate an enzyme whose proteolytic activity is similar to that of the gastric pepsin.Trypsinase, trypsin-like proteinase, or Cathepsine II,are synonyms, and they denominate an enzyme whose proteolytic activity is similar to that of intestinal trypsin. The intracellular proteinases, however,are not entirely identical with the corresponding proteolytic enzymes of alimentary canal (see page 24