Generalized Chaplygin Gas Model: Dark Energy - Dark Matter Unification and CMBR Constraints

The generalized Chaplygin gas (GCG) model allows for an unified description of the recent accelerated expansion of the Universe and the evolution of energy density perturbations. This dark energy - dark matter unification is achieved through an exotic background fluid whose equation of state is given by $p = - A/\rho^{\alpha}$, where $A$ is a positive constant and $0 < \alpha \le 1$. Stringent constraints on the model parameters can be obtained from recent WMAP and BOOMERanG bounds on the locations of the first few peaks and troughs of the Cosmic Microwave Background Radiation (CMBR) power spectrum as well as SNe Ia data.Comment: 9 pages, 2 figures; essay selected for an honorable mention by the Gravity Research Foundation, 200

Nonlinear evolution of dark matter and dark energy in the Chaplygin-gas cosmology

The hypothesis that dark matter and dark energy are unified through the Chaplygin gas is reexamined. Using generalizations of the spherical model which incorporate effects of the acoustic horizon we show that an initially perturbative Chaplygin gas evolves into a mixed system containing cold dark matter-like gravitational condensate.Comment: 11 pages, 3 figures, substantial revision, title changed, content changed, added references, to appear in JCA

General solutions of Einstein's spherically symmetric gravitational equations with junction conditions

Einstein's spherically symmetric interior gravitational equations are investigated. Following Synge's procedure, the most general solution of the equations is furnished in case $T^{1}_{1}$ and $T^{4}_{4}$ are prescribed. The existence of a total mass function, $M(r,t)$, is rigorously proved. Under suitable restrictions on the total mass function, the Schwarzschild mass $M(r,t)=m$, implicitly defines the boundary of the spherical body as $r=B(t)$. Both Synge's junction conditions as well as the continuity of the second fundamental form are examined and solved in a general manner. The weak energy conditions for an \emph{arbitrary boost} are also considered. The most general solution of the spherically symmetric anisotropic fluid model satisfying both junction conditions is furnished. In the final section, various exotic solutions are explored using the developed scheme including gravitational instantons, interior $T$-domains and $D$-dimensional generalizations.Comment: 23 pages, 1 figure, uses AMS packages. Updated version has corrected typos as well as added comments and extension regarding ISLD junction conditions. Accepted for publication in Journal of Mathematical Physic

Deviation From \Lambda CDM With Cosmic Strings Networks

In this work, we consider a network of cosmic strings to explain possible deviation from \Lambda CDM behaviour. We use different observational data to constrain the model and show that a small but non zero contribution from the string network is allowed by the observational data which can result in a reasonable departure from \Lambda CDM evolution. But by calculating the Bayesian Evidence, we show that the present data still strongly favour the concordance \Lambda CDM model irrespective of the choice of the prior.Comment: 15 Pages, Latex Style, 4 eps figures, Revised Version, Accepted for publication in European Physical Journal

Large scale structure and the generalised Chaplygin gas as dark energy

The growth of large scale structure is studied in a universe containing both cold dark matter (CDM) and generalized Chaplygin gas (GCg). GCg is assumed to contribute only to the background evolution of the universe while the CDM component collapses and forms structures. We present some new analytical as well as numerical results for linear and non-linear growth in such model. The model passes the standard cosmological distance test without the need of a cosmological constant (LCDM). But we find that the scenario is severely constrained by current observations of large scale structure. Any small deviations of the GCg parameters away from the standard Lambda dominated cosmology (LCDM) produces substantial suppression for the growth of structures.Comment: 6 pages, matches version accepted for publication in Phys.Rev.D (in press

Declining free healthcare and rising treatment costs in India: an analysis of national sample surveys 1986-2004

The article focuses on trends in health-seeking behaviour of people and choosing between government and private sources, reasons for not accessing health care and the cost of treatment by examining three rounds of NSS data on health care use and morbidity pattern during 1986–87, 1995–96 and 2004. With variation across states, treatment-seeking from public providers has declined and preference for private providers has increased over the period. Although overall health-seeking behaviour has improved for both males and females, a significant percentage of people, more in rural than urban areas, do not seek treatment due to lack of accessibility and consider that the illness is not serious enough to require treatment. The financial reason for not seeking treatment was also an important issue in rural areas. There has also been change in the cost of health care over time. While the health care cost has increased, the gap between the public and the private has reduced, owing to perhaps increased cost of treatment in public health facilities following the levying of user-fees and curtailing distribution of free medicine. Practically all states reported decline in availability of free both out-patient and in-patient care. The article concludes with supporting the adaptation of innovative public-private partnership in health sector for various services realizing the limitations of the state provision of health, particularly in rural and remote areas, and the growing preference of consumers for private health providers. As effectiveness of public spending also depends on the choice of health interventions, target population and technical efficiency partnering with private health providers could work towards reducing the health inequalities in the country

Cosmic coincidence problem and variable constants of physics

The standard model of cosmology is investigated using time dependent cosmological constant $\Lambda$ and Newton's gravitational constant $G$. The total energy content is described by the modified Chaplygin gas equation of state. It is found that the time dependent constants coupled with the modified Chaplygin gas interpolate between the earlier matter to the later dark energy dominated phase of the universe. We also achieve a convergence of parameter $\omega\to-1$, with minute fluctuations, showing an evolving $\omega$. Thus our model fairly alleviates the cosmic coincidence problem which demands $\omega=-1$ at present time.Comment: 27 pages, 15 figure

The economics and politics of women's rights

Women’s rights and economic development are highly correlated. Today, the discrepancy between the legal rights of women and men is much larger in developing compared to developed countries. Historically, even in countries that are now rich women had few rights before economic development took off. Is development the cause of expanding women’s rights, or conversely, do women’s rights facilitate development? We argue that there is truth to both hypotheses. The literature on the economic consequences of women’s rights documents that more rights for women lead to more spending on health and children, which should benefit development. The politicaleconomy literature on the evolution of women’s rights finds that technological change increased the costs of patriarchy for men, and thus contributed to expanding women’s rights. Combining these perspectives, we discuss the theory of Doepke and Tertilt (2009), where an increase in the return to human capital induces men to vote for women’s rights, which in turn promotes growth in human capital and income per capita

Entropy perturbations in quartessence Chaplygin models

We show that entropy perturbations can eliminate instabilities and oscillations, in the mass power spectrum of the quartessence Chaplygin models. Our results enlarge the current parameter space of models compatible with large scale structure and cosmic microwave background (CMB) observations.Comment: references added, one figure corrected, results unchange

Observational Constraints on Chaplygin Quartessence: Background Results

We derive the constraints set by several experiments on the quartessence Chaplygin model (QCM). In this scenario, a single fluid component drives the Universe from a nonrelativistic matter-dominated phase to an accelerated expansion phase behaving, first, like dark matter and in a more recent epoch like dark energy. We consider current data from SNIa experiments, statistics of gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in galaxy clusters. We investigate the constraints from this data set on flat Chaplygin quartessence cosmologies. The observables considered here are dependent essentially on the background geometry, and not on the specific form of the QCM fluctuations. We obtain the confidence region on the two parameters of the model from a combined analysis of all the above tests. We find that the best-fit occurs close to the $\Lambda$CDM limit ($\alpha=0$). The standard Chaplygin quartessence ($\alpha=1$) is also allowed by the data, but only at the $\sim2\sigma$ level.Comment: Replaced to match the published version, references update