Dark Matter, Modified Gravity and the Mass of the Neutrino

It has been suggested that Einstein's theory of General Relativity can be modified to accomodate mismatches between the gravitational field and luminous matter on a wide range of scales. Covariant theories of modified gravity generically predict the existence of extra degrees of freedom which may be interpreted as dark matter. We study a subclass of these theories where the overall energy density in these extra degrees of freedom is subdominant relative to the baryon density and show that they favour the presence of massive neutrinos. For some specific cases (such as a flat Universes with a cosmological constant) one finds a conservative lower bound on the neutrinos mass of $m_\nu>0.31$ eV.Comment: 5 pages, 2 figures, 2 tables, submitted to Phys. Rev.

Recognizing the importance of chronic disease in driving healthcare expenditure in Tanzania: analysis of panel data from 1991 to 2010

Despite the growing chronic disease burden in low- and middle-income countries, there are significant gaps in our understanding of the financial impact of these illnesses on households. As countries make progress towards universal health coverage, specific information is needed about how chronic disease care drives health expenditure over time, and how this spending differs from spending on acute disease care

Dark energy after GW170817, revisited

We revisit the status of scalar-tensor theories with applications to dark energy in the aftermath of the gravitational wave signal GW170817 and its optical counterpart GRB170817A. At the level of the cosmological background, we identify a class of theories, previously declared unviable in this context, whose anomalous gravitational wave speed is proportional to the scalar equation of motion. As long as the scalar field is assumed not to couple directly to matter, this raises the possibility of compatibility with the gravitational wave data, for any cosmological sources, thanks to the scalar dynamics. This newly "rescued" class of theories includes examples of generalised quintic galileons from Horndeski theories. Despite the promise of this leading order result, we show that the loophole ultimately fails when we include the effect of large scale inhomogeneities.Comment: Updated with corrections to the gravitational wave propagation coming from higher order terms in the presence of large scale inhomogeneities. These close off any remaining loopholes. References adde

The cosmological behavior of Bekenstein's modified theory of gravity

We study the background cosmology governed by the Tensor-Vector-Scalar theory of gravity proposed by Bekenstein. We consider a broad family of potentials that lead to modified gravity and calculate the evolution of the field variables both numerically and analytically. We find a range of possible behaviors, from scaling to the late time domination of either the additional gravitational degrees of freedom or the background fluid.Comment: 10 pages, 8 figures, A few typos corrected in the text and figures. Version published in PR

Comparing Public and Provider Preferences for Setting Healthcare Priorities: Evidence from Kuwait

As attempts are made to allocate health resources more efficiently, understanding the acceptability of these changes is essential. This study aims to compare the priorities of the public with those of health service providers in Kuwait. It also aims to compare the perceptions of both groups regarding key health policies in the country. Members of the general public and a sample of health service providers, including physicians, dentists, nurses, and technicians, were randomly selected to complete a structured, self-administered questionnaire. They were asked to rank health services by their perceived importance, rank preferred sources of additional health funding, and share their perceptions of the current allocation of health resources, including current healthcare spending choices and the adequacy of total resources allocated to healthcare. They were also asked for their perception of the current local policies on sending patients abroad for certain types of treatments and the policy of providing private health insurance for retirees. The response rate was above 75% for both groups. A higher tax on cigarettes was preferred by 73% of service providers as a source of additional funding for healthcare services, while 59% of the general public group chose the same option. When asked about the sufficiency of public sector health funding, 26.5% of the general public thought that resources were sufficient to meet all healthcare needs, compared with 40% of service providers. The belief that the public should be offered more opportunities to influence health resource allocation was held by 56% of the general public and 75% of service providers. More than half of the respondents from both groups believed that the policy on sending patients abroad was expensive, misused, and politically driven. Almost 64% of the general public stated that the provision of private health insurance for retirees was a ‘good’ policy, while only 34% of service providers agreed with this statement. This study showed similarities and differences between the general public and health service providers’ preferences. Both groups showed a preference for treating the young rather than the old. The general public preferred more expensive health services that had immediate effects rather than health promotion activities with delayed benefits and health services for the elderly. These findings suggest that the general public may not accept common allocative efficiency improvements in public health spending unless the challenges in this sector and the gains from reallocation are clearly communicated

The linear growth rate of structure in Parametrized Post Friedmannian Universes

A possible solution to the dark energy problem is that Einstein's theory of general relativity is modified. A suite of models have been proposed that, in general, are unable to predict the correct amount of large scale structure in the distribution of galaxies or anisotropies in the Cosmic Microwave Background. It has been argued, however, that it should be possible to constrain a general class of theories of modified gravity by focusing on properties such as the growing mode, gravitational slip and the effective, time varying Newton's constant. We show that assuming certain physical requirements such as stability, metricity and gauge invariance, it is possible to come up with consistency conditions between these various parameters. In this paper we focus on theories which have, at most, 2nd derivatives in the metric variables and find restrictions that shed light on current and future experimental constraints without having to resort to a (as yet unknown) complete theory of modified gravity. We claim that future measurements of the growth of structure on small scales (i.e. from 1-200 h^{-1} Mpc) may lead to tight constraints on both dark energy and modified theories of gravity.Comment: 15 Pages, 11 Figure

The initial conditions of the universe: how much isocurvature is allowed?

We investigate the constraints imposed by the current data on correlated mixtures of adiabatic and non-adiabatic primordial perturbations. We discover subtle flat directions in parameter space that tolerate large (~60%) contributions of non-adiabatic fluctuations. In particular, larger values of the baryon density and a spectral tilt are allowed. The cancellations in the degenerate directions are explored and the role of priors elucidated.Comment: 4 pages, 4 figures. Submitted to PR

Learning Online: A Case Study Exploring Student Perceptions and Experience of a Course in Economic Evaluation

This study explored the perceptions and experiences of a group of students enrolled in an online course in Economic Evaluation. A mixed methods approach was adopted for the data collection, and thematic analysis was used to synthesize the data collected and highlight key findings. The participants identified several positive and negative perceived attributes of online learning, many of which are well documented in the literature. In addition, after exposure to the course, participants reported several factors that affected their learning experience on this course, some of which have not yet been reported in the wider literature. The five main factors affecting learning on this course include; 1) Pace of learning in an online environment, 2) Learning style, 3) Immediacy of feedback, 4) Method of content delivery, and 5) Issues around navigating content. These findings could help improve online teaching practice and learning quality in future courses

Parametrized post-Friedmannian framework for interacting dark energy theories

We present the most general parametrization of models of dark energy in the form of a scalar field which is explicitly coupled to dark matter. We follow and extend the parametrized post-Friedmannian approach, previously applied to modified gravity theories, in order to include interacting dark energy. We demonstrate its use through a number of worked examples and show how the initially large parameter space of free functions can be significantly reduced and constrained to include only a few nonzero coefficients. This paves the way for a model-independent approach to classify and test interacting dark energy theories