A Lambda CDM bounce scenario

We study a contracting universe composed of cold dark matter and radiation, and with a positive cosmological constant. As is well known from standard cosmological perturbation theory, under the assumption of initial quantum vacuum fluctuations the Fourier modes of the comoving curvature perturbation that exit the (sound) Hubble radius in such a contracting universe at a time of matter-domination will be nearly scale-invariant. Furthermore, the modes that exit the (sound) Hubble radius when the effective equation of state is slightly negative due to the cosmological constant will have a slight red tilt, in agreement with observations. We assume that loop quantum cosmology captures the correct high-curvature dynamics of the space-time, and this ensures that the big-bang singularity is resolved and is replaced by a bounce. We calculate the evolution of the perturbations through the bounce and find that they remain nearly scale-invariant. We also show that the amplitude of the scalar perturbations in this cosmology depends on a combination of the sound speed of cold dark matter, the Hubble rate in the contracting branch at the time of equality of the energy densities of cold dark matter and radiation, and the curvature scale that the loop quantum cosmology bounce occurs at. Finally, for a small sound speed of cold dark matter, this scenario predicts a small tensor-to-scalar ratio

Discrete Symmetries in Covariant LQG

We study time-reversal and parity ---on the physical manifold and in internal space--- in covariant loop gravity. We consider a minor modification of the Holst action which makes it transform coherently under such transformations. The classical theory is not affected but the quantum theory is slightly different. In particular, the simplicity constraints are slightly modified and this restricts orientation flips in a spinfoam to occur only across degenerate regions, thus reducing the sources of potential divergences.Comment: 8 pages, v2: Minor change

Addendum to "Relational Hamiltonian for group field theory"

In this addendum to E. Wilson-Ewing, [Phys. Rev. D 99, 086017 (2019)], we extend the construction of a Hamiltonian formalism to a new class of group field theory actions with a kinetic term that is local in the group variables and depends only on their derivatives; such a kinetic term will couple magnetic indices of opposite sign in the Peter-Weyl decomposition. The main results of that Wilson-Ewing paper for the resulting cosmology extend to this case

Qualitative study in Loop Quantum Cosmology

This work contains a detailed qualitative analysis, in General Relativity and in Loop Quantum Cosmology, of the dynamics in the associated phase space of a scalar field minimally coupled with gravity, whose potential mimics the dynamics of a perfect fluid with a linear Equation of State (EoS). Dealing with the orbits (solutions) of the system, we will see that there are analytic ones, which lead to the same dynamics as the perfect fluid, and our goal is to check their stability, depending on the value of the EoS parameter, i.e., to show whether the other orbits converge or diverge to these analytic solutions at early and late times.Comment: 12 pages, 7 figures. Version accepted for publication in CQ

Loop quantum cosmology of the Bianchi I model: complete quantization

We complete the canonical quantization of the vacuum Bianchi I model within the improved dynamics scheme of loop quantum cosmology, characterizing the Hilbert structure of the physical states and providing a complete set of observables acting on them. In order to achieve this task, it has been essential to determine the structure of the separable superselection sectors that arise owing to the polymeric quantization, and to prove that the initial value problem obtained when regarding the Hamiltonian constraint as an evolution equation, interpreting the volume as the evolution parameter, is well-posed.Comment: 4 pages, Proceedings of Loops'11, Madrid, to appear in Journal of Physics: Conference Series (JPCS

Lattice loop quantum cosmology: scalar perturbations

We study the scalar modes of linear perturbations in loop quantum cosmology. This is done on a lattice where each cell is taken to be homogeneous and isotropic and can be quantized via standard homogeneous loop quantum cosmology techniques. The appropriate interactions between nearby cells are included in the Hamiltonian in order to obtain the correct physics. It is shown that the quantum theory is anomaly-free: the scalar and diffeomorphism constraint operators weakly commute with the Hamiltonian. Finally, the effective theory encoding the leading order quantum gravity corrections is derived and is shown to give the same holonomy-corrected effective equations that have been obtained in previous studies.Comment: 32 pages, v2: Minor change

A comprehensive collection of chicken cDNAs

AbstractBirds have played a central role in many biological disciplines, particularly ecology, evolution, and behavior. The chicken, as a model vertebrate, also represents an important experimental system for developmental biologists, immunologists, cell biologists, and geneticists. However, genomic resources for the chicken have lagged behind those for other model organisms, with only 1845 nonredundant full-length chicken cDNA sequences currently deposited in the EMBL databank. We describe a large-scale expressed-sequence-tag (EST) project aimed at gene discovery in chickens (http://www.chick.umist.ac.uk). In total, 339,314 ESTs have been sequenced from 64 cDNA libraries generated from 21 different embryonic and adult tissues. These were clustered and assembled into 85,486 contiguous sequences (contigs). We find that a minimum of 38% of the contigs have orthologs in other organisms and define an upper limit of 13,000 new chicken genes. The remaining contigs may include novel avian specific or rapidly evolving genes. Comparison of the contigs with known chicken genes and orthologs indicates that 30% include cDNAs that contain the start codon and 20% of the contigs represent full-length cDNA sequences. Using this dataset, we estimate that chickens have approximately 35,000 genes in total, suggesting that this number may be a characteristic feature of vertebrates

Strategies designed to help healthcare professionals to recruit participants to research studies.

BACKGROUND: Identifying and approaching eligible participants for recruitment to research studies usually relies on healthcare professionals. This process is sometimes hampered by deliberate or inadvertent gatekeeping that can introduce bias into patient selection. OBJECTIVES: Our primary objective was to identify and assess the effect of strategies designed to help healthcare professionals to recruit participants to research studies. SEARCH METHODS: We performed searches on 5 January 2015 in the following electronic databases: Cochrane Methodology Register, CENTRAL, MEDLINE, EMBASE, CINAHL, British Nursing Index, PsycINFO, ASSIA and Web of Science (SSCI, SCI-EXPANDED) from 1985 onwards. We checked the reference lists of all included studies and relevant review articles and did citation tracking through Web of Science for all included studies. SELECTION CRITERIA: We selected all studies that evaluated a strategy to identify and recruit participants for research via healthcare professionals and provided pre-post comparison data on recruitment rates. DATA COLLECTION AND ANALYSIS: Two review authors independently screened search results for potential eligibility, read full papers, applied the selection criteria and extracted data. We calculated risk ratios for each study to indicate the effect of each strategy. MAIN RESULTS: Eleven studies met our eligibility criteria and all were at medium or high risk of bias. Only five studies gave the total number of participants (totalling 7372 participants). Three studies used a randomised design, with the others using pre-post comparisons. Several different strategies were investigated. Four studies examined the impact of additional visits or information for the study site, with no increases in recruitment demonstrated. Increased recruitment rates were reported in two studies that used a dedicated clinical recruiter, and five studies that introduced an automated alert system for identifying eligible participants. The studies were embedded into trials evaluating care in oncology mainly but also in emergency departments, diabetes and lower back pain. AUTHORS' CONCLUSIONS: There is no strong evidence for any single strategy to help healthcare professionals to recruit participants in research studies. Additional visits or information did not appear to increase recruitment by healthcare professionals. The most promising strategies appear to be those with a dedicated resource (e.g. a clinical recruiter or automated alert system) for identifying suitable participants that reduced the demand on healthcare professionals, but these were assessed in studies at high risk of bias.We would like to acknowledge the support of the Methodology theme of theCancer ExperiencesCollaborative (CECo), who have supported this review.This is the final published version. It first appeared at http://onlinelibrary.wiley.com/doi/10.1002/14651858.MR000036.pub2/abstract

Numerical loop quantum cosmology: an overview

A brief review of various numerical techniques used in loop quantum cosmology and results is presented. These include the way extensive numerical simulations shed insights on the resolution of classical singularities, resulting in the key prediction of the bounce at the Planck scale in different models, and the numerical methods used to analyze the properties of the quantum difference operator and the von Neumann stability issues. Using the quantization of a massless scalar field in an isotropic spacetime as a template, an attempt is made to highlight the complementarity of different methods to gain understanding of the new physics emerging from the quantum theory. Open directions which need to be explored with more refined numerical methods are discussed.Comment: 33 Pages, 4 figures. Invited contribution to appear in Classical and Quantum Gravity special issue on Non-Astrophysical Numerical Relativit

Radio Astronomy

Contains reports on five research projects.National Aeronautics and Space Administration (Grant NsG-419)National Science Foundation (Grant GP-7046)National Aeronautics and Space Administration (Contract NSR-22-009-120)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U, S. Air Force, under Contract DA 28-043-AMC-02536(E)U. S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-000