Markov chain Monte Carlo analysis of Bianchi VII_h models

We have extended the analysis of Jaffe et al. to a complete Markov chain Monte Carlo (MCMC) study of the Bianchi type ${\rm VII_h}$ models including a dark energy density, using 1-year and 3-year Wilkinson Microwave Anisotropy Probe (WMAP) cosmic microwave background (CMB) data. Since we perform the analysis in a Bayesian framework our entire inference is contained in the multidimensional posterior distribution from which we can extract marginalised parameter constraints and the comparative Bayesian evidence. Treating the left-handed Bianchi CMB anisotropy as a template centred upon the `cold-spot' in the southern hemisphere, the parameter estimates derived for the total energy density, `tightness' and vorticity from 3-year data are found to be: $\Omega_{tot} = 0.43\pm 0.04$, $h = 0.32^{+0.02}_{-0.13}$, $\omega = 9.7^{+1.6}_{-1.5}\times 10^{-10}$ with orientation $\gamma = {337^{\circ}}^{+17}_{-23}$). This template is preferred by a factor of roughly unity in log-evidence over a concordance cosmology alone. A Bianchi type template is supported by the data only if its position on the sky is heavily restricted. The low total energy density of the preferred template, implies a geometry that is incompatible with cosmologies inferred from recent CMB observations. Jaffe et al. found that extending the Bianchi model to include a term in $\Omega_{\Lambda}$ creates a degeneracy in the $\Omega_m - \Omega_{\Lambda}$ plane. We explore this region fully by MCMC and find that the degenerate likelihood contours do not intersect areas of parameter space that 1 or 3 year WMAP data would prefer at any significance above $2\sigma$. Thus we can confirm that a physical Bianchi ${\rm VII_h}$ model is not responsible for this signature.Comment: 8 pages, 10 figures, significant update to include more accurate results and conclusions to match version accepted by MNRA

Ultrasound Investigations of Orbital Quadrupolar Ordering in UPd_3

For a high-quality single crystal of UPd_3 we present the relevant elastic constants and ultrasonic attenuation data. In addition to the magnetic phase transition at T_2=4.4 +/- 0.1K and the quadrupolar transition at T_1~6.8K, we find orbital ordering at T_0=7.6 +/- 0.1K concomitant with a symmetry change from hexagonal to orthorhombic. A striking feature is the splitting of the phase transition at T_1 into a second-order transition at T_{+1}=6.9 +/- 0.05K and a first-order transition at T_{-1}=6.7 +/- 0.05K. For the four phase transitions, the quadrupolar order parameters and the respective symmetry changes are specified.Comment: 14 pages (RevTex), 3 eps-figures, accepted by PR

How isotropic is the Universe?

A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of $(\sigma_V/H)_0 < 4.7 \times 10^{-11}$ (95% CI), which is an order of magnitude tighter than previous Planck results that used CMB temperature only. We also place upper limits on other modes of anisotropic expansion, with the weakest limit arising from the regular tensor mode, $(\sigma_{T,\rm reg}/H)_0<1.0 \times 10^{-6}$ (95% CI). Including all degrees of freedom simultaneously for the first time, anisotropic expansion of the Universe is strongly disfavoured, with odds of 121,000:1 against.Comment: 6 pages, 1 figure, v2: replaced with version accepted by PR

Optimal filters for detecting cosmic bubble collisions

A number of well-motivated extensions of the LCDM concordance cosmological model postulate the existence of a population of sources embedded in the cosmic microwave background (CMB). One such example is the signature of cosmic bubble collisions which arise in models of eternal inflation. The most unambiguous way to test these scenarios is to evaluate the full posterior probability distribution of the global parameters defining the theory; however, a direct evaluation is computationally impractical on large datasets, such as those obtained by the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck. A method to approximate the full posterior has been developed recently, which requires as an input a set of candidate sources which are most likely to give the largest contribution to the likelihood. In this article, we present an improved algorithm for detecting candidate sources using optimal filters, and apply it to detect candidate bubble collision signatures in WMAP 7-year observations. We show both theoretically and through simulations that this algorithm provides an enhancement in sensitivity over previous methods by a factor of approximately two. Moreover, no other filter-based approach can provide a superior enhancement of these signatures. Applying our algorithm to WMAP 7-year observations, we detect eight new candidate bubble collision signatures for follow-up analysis.Comment: 12 pages, 6 figures, replaced to match version accepted by PR

Acute reduction in secretory immunoglobulin A following smoking cessation

Smokers report an increase in upper respiratory infections in the early phase of stopping smoking. One possible cause is a depletion in secretory immunoglobulin A (S-IgA) which has been observed in one study. The present study sought to establish this finding in smokers using nicotine patches. Ninety-two smokers, trying to stop smoking, were assessed whilst smoking and for up to six weeks of abstinence. All smokers were prescribed 15 mg 16-h nicotine patches. Among abstinent smokers, changes in S-IgA and saliva volume were assessed. During the preliminary analyses, we observed that for the pre-smoking cessation measure a longer time since the last cigarette was significantly related to Lower S-IgA levels (P = 0.006). Consequently, the main analysis, of changes in S-IgA from pre-cessation to post-cessation, was confined to those who had smoked within 0.5-1.5 h of the pre-cessation measure (n = 51). There was a significant decline in S-IgA, relative to pre-smoking abstinence levels, following abstinence of one day (P = 0.027), but Levels returned to pre-abstinence values after one week. There was no evidence of any significant changes in saliva volume following smoking cessation, relative to pre-cessation levels. Users of 15 mg patches are likely to experience a decline in S-IgA levels on the first day of smoking cessation, independent of saliva volumes, and this decline in S-IgA is Likely to occur acutely, within the first few hours of smoking abstinence. This acute drop in S-IgA appears to stem from a factor other than depletion of nicotine from the body. The observed decrease in S-IgA may help to explain the increased susceptibility of smokers to upper respiratory tract infections in the immediate post-cessation period. (C) 2004 Elsevier Ltd. ALL rights reserved

A framework for testing isotropy with the cosmic microwave background

We present a new framework for testing the isotropy of the Universe using cosmic microwave background data, building on the nested-sampling ANICOSMO code. Uniquely, we are able to constrain the scalar, vector and tensor degrees of freedom alike; previous studies only considered the vector mode (linked to vorticity). We employ Bianchi type VII$_h$ cosmologies to model the anisotropic Universe, from which other types may be obtained by taking suitable limits. In a separate development, we improve the statistical analysis by including the effect of Bianchi power in the high-$\ell$, as well as the low-$\ell$, likelihood. To understand the effect of all these changes, we apply our new techniques to WMAP data. We find no evidence for anisotropy, constraining shear in the vector mode to $(\sigma_V/H)_0 < 1.7 \times 10^{-10}$ (95% CL). For the first time, we place limits on the tensor mode; unlike other modes, the tensor shear can grow from a near-isotropic early Universe. The limit on this type of shear is $(\sigma_{T,\rm reg}/H)_0 < 2.4 \times 10^{-7}$ (95% CL).Comment: 11 pages, 6 figures, v3: minor modifications to match version accepted by MNRA