Scale Invariance via a Phase of Slow Expansion

We consider a cosmological scenario in which a scale-invariant spectrum of curvature perturbations is generated by a rapidly-evolving equation of state on a slowly expanding background. This scenario generalizes the "adiabatic ekpyrotic" mechanism proposed recently in arXiv:0910.2230. Whereas the original proposal assumed a slowly contracting background, the present work shows that the mechanism works equally well on an expanding background. This greatly expands the realm of broader cosmological scenarios in which this mechanism can be embedded. We present a phase space analysis and show that both the expanding and contracting versions of the scenario are dynamical attractors, with the expanding branch having a broader basin of attraction. In both cases, a finite range of scale invariant modes can be generated within the regime of validity of perturbation theory.Comment: 34 pages, 5 figure

Strong Coupling Problem with Time-Varying Sound Speed

For a single scalar field with unit sound speed minimally coupled to Einstein gravity, there are exactly three distinct cosmological solutions which produce a scale invariant spectrum of curvature perturbations in a dynamical attractor background, assuming vacuum initial conditions: slow-roll inflation; a slowly contracting adiabatic ekpyrotic phase, described by a rapidly-varying equation of state; and an adiabatic ekpyrotic phase on a slowly expanding background. Of these three, only inflation remains weakly coupled over a wide range of modes, the other scenarios can produce at most 12 e-folds of scale invariant and gaussian modes. In this paper, we investigate how allowing the speed of sound of fluctuations to evolve in time affects this classification. While in the presence of a variable sound speed there are many more scenarios which are scale invariant at the level of the two-point function, they generically suffer from strong coupling problems similar to those in the canonical case. There is, however, an exceptional case with superluminal sound speed, which suppresses non-gaussianities and somewhat alleviates strong coupling issues. We focus on a particular realization of this limit and show these scenarios are constrained and only able to produce at most 28 e-folds of scale invariant and gaussian perturbations. A similar bound should hold more generally --- the condition results from the combined requirements of matching the observed amplitude of curvature perturbations, demanding that the Hubble parameter remain sub-Planckian and keeping non-gaussianities under control. We therefore conclude that inflation remains the unique scenario, assuming a single degree of freedom on an attractor background, capable of producing arbitrarily many scale invariant modes while remaining weakly coupled. Alternative mechanisms must inevitably be unstable or rely on multiple degrees of freedom.Comment: 23 pages, 1 figure, v2: minor edits, version to appear in PR

Consistency Relations for the Conformal Mechanism

We systematically derive the consistency relations associated to the non-linearly realized symmetries of theories with spontaneously broken conformal symmetry but with a linearly-realized de Sitter subalgebra. These identities relate (N+1)-point correlation functions with a soft external Goldstone to N-point functions. These relations have direct implications for the recently proposed conformal mechanism for generating density perturbations in the early universe. We study the observational consequences, in particular a novel one-loop contribution to the four-point function, relevant for the stochastic scale-dependent bias and CMB mu-distortion.Comment: 34 pages, 3 figures. v2: minor changes, version appearing in JCA

Beyond the Cosmological Standard Model

After a decade and a half of research motivated by the accelerating universe, theory and experiment have a reached a certain level of maturity. The development of theoretical models beyond \Lambda, or smooth dark energy, often called modified gravity, has led to broader insights into a path forward, and a host of observational and experimental tests have been developed. In this review we present the current state of the field and describe a framework for anticipating developments in the next decade. We identify the guiding principles for rigorous and consistent modifications of the standard model, and discuss the prospects for empirical tests. We begin by reviewing attempts to consistently modify Einstein gravity in the infrared, focusing on the notion that additional degrees of freedom introduced by the modification must screen themselves from local tests of gravity. We categorize screening mechanisms into three broad classes: mechanisms which become active in regions of high Newtonian potential, those in which first derivatives become important, and those for which second derivatives are important. Examples of the first class, such as f(R) gravity, employ the familiar chameleon or symmetron mechanisms, whereas examples of the last class are galileon and massive gravity theories, employing the Vainshtein mechanism. In each case, we describe the theories as effective theories. We describe experimental tests, summarizing laboratory and solar system tests and describing in some detail astrophysical and cosmological tests. We discuss future tests which will be sensitive to different signatures of new physics in the gravitational sector. Parts that are more relevant to theorists vs. observers/experimentalists are clearly indicated, in the hope that this will serve as a useful reference for both audiences, as well as helping those interested in bridging the gap between them.Comment: 175 pages, 24 figures. v2: Minor corrections, added references. Review article, comments welcom

DBI Realizations of the Pseudo-Conformal Universe and Galilean Genesis Scenarios

The pseudo-conformal universe is an alternative to inflation in which the early universe is described by a conformal field theory on approximately flat space-time. The fields develop time-dependent expectation values, spontaneously breaking the conformal symmetries to a de Sitter subalgebra, and fields of conformal weight zero acquire a scale invariant spectrum of perturbations. In this paper, we show that the pseudo-conformal scenario can be naturally realized within theories that would ordinarily be of interest for DBI inflation, such as the world-volume theory of a probe brane in an AdS bulk space-time. In this approach, the weight zero spectator field can be associated with a geometric flat direction in the bulk, and its scale invariance is protected by a shift symmetry.Comment: 34 page

Effective Management of Flatulence

Probiotics and rifaximin (Xifaxan) have been shown to reduce total number of flatus episodes and associated discomfort. (Strength of Recommendation [SOR]: B, based on small randomized controlled trials [RCTs]). Oral alpha-galactosidase (Beano) has been shown to reduce volume of flatus associated with fermentable carbohydrates and high-fiber diets. (SOR: B, based on small RCTs). Oral bismuth subsalicylate (Pepto-Bismol) and odor-reducing external devices containing activated charcoal have shown benefit in reducing flatus-associated odor. (SOR: C, based on disease-oriented evidence). Evidence for oral activated charcoal and simethicone has been inconsistent and does not support their use. (SOR: B, based on multiple small RCTs)

Coupling Infrastructure Resilience and Flood Risk Assessment for a Coastal Urban Watershed

This thesis sheds light on coupling potential flood risk and drainage infrastructure resilience of low-lying areas of a coastal urban watershed to flood hazards and subsequent multi-scale impacts of those hazards via detailed modeling frameworks. Physically based models along with statistical models are employed to highlight the complexity for characterizing flood risk while evaluating such risk under various levels of adaptive capacity from traditional flood management techniques to low impact development (LID), as a first step to conduct resilience assessment. Findings indicate that the coupling flood risk and infrastructure resilience is achievable by the careful formulation of flood risk associated with a resilience metric, which is a function of the hazard(s) considered, vulnerability and adaptive capacity. The results also give insights into improving existing methodologies for municipalities in flood management practices such as incorporating multi-criteria flood risk evaluation that includes resilience

Gendered Impact Assessment on Food Securing Upgrading Strategies: Results from Three Methodological Approaches

In developing countries, rural women and men play different roles in guaranteeing food security for their households and communities. The gendered aspects of food security are visible along the four pillars of food security: availability, access, utilization and stability but one cause reported to hamper ineffectiveness is overlooking gender dynamics. Therefore this study aims to explore the gendered arguments towards food security by using different methodological tools while focusing on the food security criteria and the three sustainable development criteria (economic, social and environmental aspects). The specific objectives were to analyse differences between scientist and farmer perspectives in relation to the three upgrading strategies namely rainwater harvesting (RWH), improved processing, and household nutrition education and kitchen gardening) and to find out the difference in results when triangulating the tools on target group in order to set preferences in local contexts which helps to anticipate what measures would be needed to improve food security. The study used diverse assessment approaches namely a) a participatory stakeholder approach using the FoPIA tool (Framework for Participatory Impact Assessment) b) a scientific expert based approach using ScalA-FS (scaling up assessment-Food security tool), and c). Gender Analysis Matrix (GAM). Focus group discussions, key informant interviews and household survey were the main methods of data collection. The study found that female and male participants scored the criteria differently. Men considered social relations in the community and in the household more important for food security than women did. Women scored several production-related aspects as more important than men. Gender-based inequalities along the food value chain ‘from farm to plate’ that impede the attainment of food and nutritional security must therefore be addressed through effective gender responsive policies and programs. Keywords: impact assessment; gender; upgrading strategies; food value chain; Tanzania; participatory researc

Methodological Decisions in Context: The dilemmas and challenges of novice African scholars

This paper emerges out of a panel discussion during a PhD week and subsequent 8th International Environmental Education Invitation Seminar held at Rhodes University in 2004 and 2005 respectively. It illuminates some insights into our struggles (as novice African researchers) in trying to respond to contextual realities as we research education and social change in African contexts, seeking insight into what counts as legitimate research in this context. The paper considers our struggles at conceptual, methodological, analytical and data generation levels, and in a politics of research. This is done by means of examples drawn from five current doctoral research projects being undertaken in east and southern African regions, using a review framework that represents fairly common dimensions of PhD research. We conclude that research, when defined rigidly within research disciplines/paradigms (as have been defined in some – primarily Western – research trajectories) may fail to take into account African social and contextual realities when applied uncritically. We argue that there is need for researchers in Africa to consider a multiplicity of approaches if research is to be meaningful in, and responsive to, social and contextual realities. In particular, we argue for taking account of socio historical and socio-cultural contexts in creating African epistemology in and through research