Anisotropic evolution of D-dimensional FRW spacetime

We examine the time evolution of the D=d+4 dimensional Einstein field equations subjected to a flat Robertson-Walker metric where the 3D and higher-dimensional scale factors are allowed to evolve at different rates. We find the exact solution to these equations for a single fluid component, which yields two limiting regimes offering the 3D scale factor as a function of the time. The fluid regime solution closely mimics that described by 4D FRW cosmology, offering a late-time behavior for the 3D scale factor after becoming valid in the early universe, and can give rise to a late-time accelerated expansion driven by vacuum energy. This is shown to be preceded by an earlier volume regime solution, which offers a very early-time epoch of accelerated expansion for a radiation-dominated universe for d=1. The time scales describing these phenomena, including the transition from volume to fluid regime, are shown to fall within a small fraction of the first second when the fundamental constants of the theory are aligned with the Planck time. This model potentially offers a higher-dimensional alternative to scalar-field inflationary theory and a consistent cosmological theory, yielding a unified description of early- and late-time accelerated expansions via a 5D spacetime scenario.Comment: Title changed from "A possible higher-dimensional alternative to scalar-field inflationary theory". Several new results have been added including a predicted lower- and upper-bound on the time scales marking the end of an early-time inflationary epoch and the beginning of an FRW epoch for d=

Anisotropic evolution of 5D Friedmann-Robertson-Walker spacetime

We examine the time evolution of the five-dimensional Einstein field equations subjected to a flat, anisotropic Robertson-Walker metric, where the 3D and higher-dimensional scale factors are allowed to dynamically evolve at different rates. By adopting equations of state relating the 3D and higher-dimensional pressures to the density, we obtain an exact expression relating the higher-dimensional scale factor to a function of the 3D scale factor. This relation allows us to write the Friedmann-Robertson-Walker field equations exclusively in terms of the 3D scale factor, thus yielding a set of 4D effective Friedmann-Robertson-Walker field equations. We examine the effective field equations in the general case and obtain an exact expression relating a function of the 3D scale factor to the time. This expression involves a hypergeometric function and cannot, in general, be inverted to yield an analytical expression for the 3D scale factor as a function of time. When the hypergeometric function is expanded for small and large arguments, we obtain a generalized treatment of the dynamical compactification scenario of Mohammedi [Phys.Rev.D 65, 104018 (2002)] and the 5D vacuum solution of Chodos and Detweiler [Phys.Rev.D 21, 2167 (1980)], respectively. By expanding the hypergeometric function near a branch point, we obtain the perturbative solution for the 3D scale factor in the small time regime. This solution exhibits accelerated expansion, which, remarkably, is independent of the value of the 4D equation of state parameter w. This early-time epoch of accelerated expansion arises naturally out of the anisotropic evolution of 5D spacetime when the pressure in the extra dimension is negative and offers a possible alternative to scalar field inflationary theory.Comment: 20 pages, 4 figures, paper format streamlined with main results emphasized and details pushed to appendixes, current version matches that of published versio

Solutions of Higher Dimensional Gauss-Bonnet FRW Cosmology

We examine the effect on cosmological evolution of adding a Gauss-Bonnet term to the standard Einstein-Hilbert action for a (1 + 3)+ d dimensional Friedman-Robertson-Walker (FRW) metric. By assuming that the additional dimensions compactify as a power law as the usual 3 spatial dimensions expand, we solve the resulting dynamical equations and find that the solution may be of either de Sitter or Kasner form depending upon whether the Gauss-Bonnet term or the Einstein term dominates.Comment: 10 pages, references added/corrected, accepted for publication in General Relativity and Gravitatio

Australasian randomised trial to evaluate the role of maternal intramuscular dexamethasone versus betamethasone prior to preterm birth to increase survival free of childhood neurosensory disability (A*STEROID): Study protocol

BACKGROUND Both dexamethasone and betamethasone, given to women at risk of preterm birth, substantially improve short-term neonatal health, increase the chance of the baby being discharged home alive, and reduce childhood neurosensory disability, remaining safe into adulthood. However, it is unclear which corticosteroid is of greater benefit to mother and child. This study aims to determine whether giving dexamethasone to women at risk of preterm birth at less than 34 weeks’ gestation increases the chance of their children surviving free of neurosensory disability at two years’ corrected age, compared with betamethasone. METHODS/DESIGN Design randomised, multicentre, placebo controlled trial. Inclusion criteria women at risk of preterm birth at less than 34 weeks’ gestation with a singleton or twin pregnancy and no contraindications to the use of antenatal corticosteroids and who give informed consent. Trial entry & randomisation at telephone randomisation eligible women will be randomly allocated to either the dexamethasone group or the betamethasone group, allocated a study number and corresponding treatment pack. Study groups women in the dexamethasone group will be administered two syringes of 12 mg dexamethasone (dexamethasone sodium phosphate) and women in the betamethasone group will be administered two syringes of 11.4 mg betamethasone (Celestone Chronodose). Both study groups consist of intramuscular treatments 24 hours apart. Primary study outcome death or any neurosensory disability measured in children at two years’ corrected age. Sample size a sample size of 1449 children is required to detect either a decrease in death or any neurosensory disability from 27.0% to 20.1% with dexamethasone compared with betamethasone, or an increase from 27.0% to 34.5% (two-sided alpha 0.05, 80% power, 5% loss to follow up, design effect 1.2). DISCUSSION This study will provide high-level evidence of direct relevance for clinical practice. If one drug clearly results in significantly fewer deaths and fewer disabled children then it should be used consistently in women at risk of preterm birth and would be of great importance to women at risk of preterm birth, their children, health services and communities. TRIAL REGISTRATION Trial registration number: ACTRN12608000631303Caroline A Crowther, Jane E Harding, Philippa F Middleton, Chad C Andersen, Pat Ashwood, Jeffrey S Robinso

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level