Interacting Dark Energy -- constraints and degeneracies

In standard cosmologies, dark energy interacts only gravitationally with dark matter. There could be a non-gravitational interaction in the dark sector, leading to changes in the effective DE equation of state, in the redshift dependence of the DM density and in structure formation. We use CMB, BAO and SNIa data to constrain a model where the energy transfer in the dark sector is proportional to the DE density. There are two subclasses, defined by the vanishing of momentum transfer either in the DM or the DE frame. We conduct a Markov-Chain Monte-Carlo analysis to obtain best-fit parameters. The background evolution allows large interaction strengths, and the constraints from CMB anisotropies are weak. The growth of DM density perturbations is much more sensitive to the interaction, and can deviate strongly from the standard case. However, the deviations are degenerate with galaxy bias and thus more difficult to constrain. Interestingly, the ISW signature is suppressed since the non-standard background evolution can compensate for high growth rates. We also discuss the partial degeneracy between interacting DE and modified gravity, and how this can be broken.Comment: 12 pages, 18 figures. Clarification on instabilities. Accepted by PR

Late-time acceleration : interacting dark energy and modified gravity

In 1998 astronomical observations of distant stars exploding at the ends of their lives led to the discovery that the expansion of the Universe is accelerating. This is likely to be caused by an intrinsic part of Einstein’s General Theory of Relativity known as the cosmological constant, but naturalness issues and the need to improve observational tests have motivated the study of alternative models of the Universe. The research in this thesis is part of ongoing efforts to pin down the cause of late-time acceleration by better understanding these alternatives and their signatures in cosmological observations. One such alternative is known as interacting dark energy and would be caused by additional matter in the Universe, as yet unknown to particle physics. This would interact with another unknown particle called dark matter that has been part of the standard model of cosmology since the 1970’s. The first part of this thesis contains a review of works on interacting dark energy and investigates a particular version of the model which had not been studied in detail before, placing recent observational constraints on its parameters. Another alternative to the cosmological constant is known as modified gravity, where General Relativity is extended by the addition of new degrees of freedom. Theories of modified gravity are mathematically related to some models of interacting dark energy and can appear very similar in cosmological observations. The second part of this thesis investigates the extent to which the two can be distinguished using current observational data.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Observational constraints on thawing quintessence models

We use a dynamical systems approach to study thawing quintessence models, using a multi-parameter extension of the exponential potential which can approximate the form of typical thawing potentials. We impose observational constraints using a compilation of current data, and forecast the tightening of constraints expected from future dark energy surveys, as well as discussing the relation of our results to analytical constraints already in the literature.Comment: 6 pages MNRAS style with 8 figures included. Minor updates to match MNRAS accepted versio

The Distinguishability of Interacting Dark Energy from Modified Gravity

We study the observational viability of coupled quintessence models with their expansion and growth histories matched to modified gravity cosmologies. We find that for a Dvali-Gabadadze-Porrati model which has been fitted to observations, the matched interacting dark energy models are observationally disfavoured. We also study the distinguishability of interacting dark energy models matched to scalar-tensor theory cosmologies and show that it is not always possible to find a physical interacting dark energy model which shares their expansion and growth histories.Comment: 8 pages, 5 figure

Sunbeam Program Reduces Rate of Falls in Long-Term Care Residents With Mild to Moderate Cognitive Impairment or Dementia: Subgroup Analysis of a Cluster Randomized Controlled Trial

Objectives: The Sunbeam trial significantly reduced falls in long-term aged care (LTC) residents. The current study\u27s primary objective was to undertake subgroup analysis of the Sunbeam trial, to determine whether the intervention was effective for reducing falls in LTC residents with mild-moderate cognitive impairment/dementia. Secondary objectives were to determine intervention effects on cognitive and physical function. Design: Subgroup analysis of a cluster randomized controlled trial (RCT). Setting and Participants: Permanent residents of LTC in Australia who participated in the Sunbeam trial with Addenbrooke\u27s Cognitive Examination-Revised (ACE-R) scores \u3c83 (Mini-Mental State Examination \u3e14 = main trial inclusion criteria). Methods: Of 221 participants, 148 had an ACE-R \u3c83 and were included in this study. Sixteen LTC residences (clusters) were randomized to receive either the Sunbeam program or usual care. The Sunbeam program involved two 1-hour sessions/week of tailored and progressive resistance and balance training for 25 weeks followed by a maintenance program (two 30-min sessions/week of nonprogressive exercise for 6 months). Assessments were conducted at baseline, 6 months, and 12 months. Falls were recorded using routinely collected data from the LTC incident management systems. Results: Rate of falls (50%) and risk of falls (31%), multiple falls (40%), and injurious falls (44%) were reduced in the intervention group. The intervention group had significantly better balance (static and dynamic) and sit-to-stand ability when compared with the control group at 6 months and significantly better dynamic balance at 12 months. There were no serious adverse events. Conclusions and Implications: The Sunbeam Program significantly reduced falls and improved physical performance in cognitively impaired LTC residents. This is a novel and important finding, as many previous studies have excluded people with cognitive impairment/dementia and inconsistent findings have been reported when this population has been studied. Our findings suggest that progressive resistance and balance exercise is a safe and effective fall prevention intervention in LTC residents with mild-moderate cognitive impairment/dementia

Management of Falls in Community-Dwelling Older Adults: Clinical Guidance Statement From the Academy of Geriatric Physical Therapy of the American Physical Therapy Association

BACKGROUND: Falls in older adults are a major public health concern due to high prevalence, impact on health outcomes and quality of life, and treatment costs. Physical therapists can play a major role in reducing fall risk for older adults; however, existing clinical practice guidelines (CPGs) related to fall prevention and management are not targeted to physical therapists. OBJECTIVE: The purpose of this clinical guidance statement (CGS) is to provide recommendations to physical therapists to help improve outcomes in the identification and management of fall risk in community-dwelling older adults. DESIGN AND METHODS: The Subcommittee on Evidence-Based Documents of the Practice Committee of the Academy of Geriatric Physical Therapy developed this CGS. Existing CPGs were identified by systematic search and critically appraised using the Appraisal of Guidelines, Research, and Evaluation in Europe II (AGREE II) tool. Through this process, 3 CPGs were recommended for inclusion in the CGS and were synthesized and summarized. RESULTS: Screening recommendations include asking all older adults in contact with a health care provider whether they have fallen in the previous year or have concerns about balance or walking. Follow-up should include screening for balance and mobility impairments. Older adults who screen positive should have a targeted multifactorial assessment and targeted intervention. The components of this assessment and intervention are reviewed in this CGS, and barriers and issues related to implementation are discussed. LIMITATIONS: A gap analysis supports the need for the development of a physical therapy–specific CPG to provide more precise recommendations for screening and assessment measures, exercise parameters, and delivery models. CONCLUSION: This CGS provides recommendations to assist physical therapists in the identification and management of fall risk in older community-dwelling adults