The current status of observational cosmology

Observational cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation. The transition to precision cosmology has been spearheaded by measurements of the anisotropy in the cosmic microwave background (CMB) over the past decade. Observations of the large scale structure in the distribution of galaxies, high red-shift supernova, have provided the required complementary information. We review the current status of cosmological parameter estimates from joint analysis of CMB anisotropy and large scale structure (LSS) data. We also sound a note of caution on overstating the successes achieved thus far.Comment: 13 pages, 3 figures, Latex style files included, To appear in the proceedings of ICGC-04. Minor rewording in the abstract and introductio

Non-Gaussianity and direction dependent systematics in HST key project data

Two new statistics, namely $\Delta_\chi^2$ and $\Delta_\chi$, based on extreme value theory, were derived in \cite{gupta08,gupta10}. We use these statistics to study direction dependence in the HST key project data which provides the most precise measurement of the Hubble constant. We also study the non-Gaussianity in this data set using these statistics. Our results for $\Delta_\chi^2$ show that the significance of direction dependent systematics is restricted to well below one $\sigma$ confidence limit, however, presence of non-Gaussian features is subtle. On the other hand $\Delta_\chi$ statistic, which is more sensitive to direction dependence, shows direction dependence systematics to be at slightly higher confidence level, and the presence of non-Gaussian features at a level similar to the $\Delta_\chi^2$ statistic.Comment: 6 pages, 4 figures; accepted for publication in MNRA

Instrumental and sensory characterisation of oleogels for cosmetic use

Oleogels are semisolid systems consisting of an oleogelator (gelling agent) and a lipophilic liquid phase. Despite having some distinct advantages (e.g. absence of preservatives or surfactants), the use of oleogels in cosmetic products is still sporadic. The aim of this study was to compare the effects of different types of oleogelators on instrumental and sensory properties of oleogels made with common emollient types: hydrocarbon, synthetic ester and natural oil

Direction Dependence in Supernova Data: Constraining Isotropy

We revise and extend the extreme value statistic, introduced in \cite{gup08}, to study directional dependence in the high redshift supernova data; arising either from departures from the cosmological principle or due to direction dependent statistical systematics in e data. We introduce a likelihood function that analytically marginalises over the Hubble constant, and use it to extend our previous statistic. We also introduce a new statistic that is sensitive to direction dependence arising from living off-centre inside a large void, as well as previously mentioned reasons for anisotropy. We show that for large data sets this statistic has a limiting form that can be computed analytically. We apply our statistics to the gold data sets from \cite{rie04} and \cite{rie07}, as in our previous work. Our revision and extension of previous statistic shows that 1) the effect of marginalsing over Hubble constant instead of using its best fit value has only a marginal effect on our results. However, correction of errors in our previous work reduce the level of non-Gaussianity in the 2004 gold data that was found in our earlier work. The revised results for the 2007 gold data show that the data is consistent with isotropy and Gaussianity. Our second statistic confirms these results.Comment: 8 pages, 6 figures. Accepted for publication in MNRA

Decoding X-ray observations from centres of galaxy clusters using MCMC

We correct for the use of electron densities instead of total gas density in the pressure fits which were used to derive the local free-fall times (t$_{\rm ff}$) in the original paper

Is there Supernova Evidence for Dark Energy Metamorphosis ?

We reconstruct the equation of state $w(z)$ of dark energy (DE) using a recently released data set containing 172 type Ia supernovae without assuming the prior $w(z) \geq -1$ (in contrast to previous studies). We find that dark energy evolves rapidly and metamorphoses from dust-like behaviour at high $z$ ($w \simeq 0$ at $z \sim 1$) to a strongly negative equation of state at present (w \lleq -1 at $z \simeq 0$). Dark energy metamorphosis appears to be a robust phenomenon which manifests for a large variety of SNe data samples provided one does not invoke the weak energy prior $\rho + p \geq 0$. Invoking this prior considerably weakens the rate of growth of $w(z)$. These results demonstrate that dark energy with an evolving equation of state provides a compelling alternative to a cosmological constant if data are analysed in a prior-free manner and the weak energy condition is not imposed by hand.Comment: 20 pages, 21 figures. Discussions enhanced. Appendix added on error propagation with new figures. References updated. Main results unchanged. Accepted for publication in MNRA