The Statefinder hierarchy: An extended null diagnostic for concordance cosmology

We show how higher derivatives of the expansion factor can be developed into a null diagnostic for concordance cosmology (LCDM). It is well known that the Statefinder -- the third derivative of the expansion factor written in dimensionless form, a^{(3)}/aH^3, equals unity for LCDM. We generalize this result to higher derivatives of the expansion factor and demonstrate that the hierarchy, a^{(n)}/aH^n, can be converted to a form that stays pegged at unity in concordance cosmology. This remarkable property of the Statefinder hierarchy enables it to be used as an extended null diagnostic for the cosmological constant. The Statefinder hierarchy combined with the growth rate of matter perturbations defines a composite null diagnostic which can distinguish evolving dark energy from LCDM.Comment: 6 pages, 6 figures; to appear in Phys. Rev.

Possible use of self-calibration to reduce systematic uncertainties in determining distance-redshift relation via gravitational radiation from merging binaries

By observing mergers of compact objects, future gravity wave experiments would measure the luminosity distance to a large number of sources to a high precision but not their redshifts. Given the directional sensitivity of an experiment, a fraction of such sources (gold plated -- GP) can be identified optically as single objects in the direction of the source. We show that if an approximate distance-redshift relation is known then it is possible to statistically resolve those sources that have multiple galaxies in the beam. We study the feasibility of using gold plated sources to iteratively resolve the unresolved sources, obtain the self-calibrated best possible distance-redshift relation and provide an analytical expression for the accuracy achievable. We derive lower limit on the total number of sources that is needed to achieve this accuracy through self-calibration. We show that this limit depends exponentially on the beam width and give estimates for various experimental parameters representative of future gravitational wave experiments DECIGO and BBO.Comment: 6 pages, 2 figures, accepted for publication in PR

The Role of Patient and Physician in Establishing Patient-Physician Communication in the In-Patient Environment

Communication in the in-patient environment is crucial, and the relationship between a patient and physician can enhance patient health and improve overall wellness. Patients need to feel confident with their abilities in order to feel comfortable conversing with physicians, which would thus improve health and treat symptoms more effectively. This communication has decreased over time, hence patients are often are unable to obtain medical information from their healthcare providers. Are there psychological factors involved in a patient’s inability to communicate with a physician? What is the relationship between self-esteem and quality of patient-physician communication? In addition, what can physicians do to ensure increased patient comfort in the medical environment? Various factors can affect the patient’s comfort with the physician, and when addressed, these factors can help improve patient-physician communication. For this paper, articles were analyzed that explored the effects of language barriers on patient-physician communication, and these articles showed that the patient can feel intimidated and later inadequate when forced to be dependent on others to voice his concerns. Articles that showed the role of social support in the medical environment were also analyzed and these showed that a sense of belonging in one’s family or community help a patient find the encouragement needed to help cope with his medical concerns. Lastly, articles were analyzed that connect the role of increased time online to communication. While the patient can be increasingly independent because of the Internet, a large use of such technology decreases patient-physician communication. This also puts the patient at risk of misinformation as he may expose himself to false information and incorrectly treat symptoms. All of these aspects lead to a disparity in self-esteem that decreases the patient’s comfort with the physician. As the patient feels unable to voice his concerns properly to the healthcare provider, the physician needs to take more responsibility in this situation as he has the ability to create a comforting environment for the patient. Physicians need to take a more active role in patients’ lives and provide more resources to communicate their concerns effectively. This will help patients feel a sense of security and comfort in the medical environment, and this change will thus enable patients to work alongside their physicians in managing their health to allow improvement of communication as well as overall patient health

General analytic formulae for attractor solutions of scalar-field dark energy models and their multi-field generalizations

We study general properties of attractors for scalar-field dark energy scenarios which possess cosmological scaling solutions. In all such models there exists a scalar-field dominant solution with an energy fraction \Omega_{\phi}=1 together with a scaling solution. A general analytic formula is given to derive fixed points relevant to dark energy coupled to dark matter. We investigate the stability of fixed points without specifying the models of dark energy in the presence of non-relativistic dark matter and provide a general proof that a non-phantom scalar-field dominant solution is unstable when a stable scaling solution exists in the region \Omega_{\phi}<1. A phantom scalar-field dominant fixed point is found to be classically stable. We also generalize the analysis to the case of multiple scalar fields and show that for a non-phantom scalar field assisted acceleration always occurs for all scalar-field models which have scaling solutions. For a phantom field the equation of state approaches that of cosmological constant as we add more scalar fields.Comment: 11 pages, no figures, version to appear in Physical Review

New Vistas in Braneworld Cosmology

Traditionally, higher-dimensional cosmological models have sought to provide a description of the fundamental forces in terms of a unifying geometrical construction. In this essay we discuss how, in their present incarnation, higher-dimensional `braneworld' models might provide answers to a number of cosmological puzzles including the issue of dark energy and the nature of the big-bang singularity.Comment: Honorable mention in the 2002 Essay Competition of the Gravity Research Foundation. 10 pages, 2 figure