Cosmological Acceleration Through Transition to Constant Scalar Curvature

As shown by Parker and Raval, quantum field theory in curved spacetime gives a possible mechanism for explaining the observed recent acceleration of the universe. This mechanism, which differs in its dynamics from quintessence models, causes the universe to make a transition to an accelerating expansion in which the scalar curvature, R, of spacetime remains constant. This transition occurs despite the fact that we set the renormalized cosmological constant to zero. We show that this model agrees very well with the current observed type-Ia supernova (SNe-Ia) data. There are no free parameters in this fit, as the relevant observables are determined independently by means of the current cosmic microwave background radiation (CMBR) data. We also give the predicted curves for number count tests and for the ratio, w(z), of the dark energy pressure to its density, as well as for dw(z)/dz versus w(z). These curves differ significantly from those obtained from a cosmological constant, and will be tested by planned future observations.Comment: 31 pages, 7 figures; to appear in ApJ. Corrected numerical results; described quantum basis of theory; 18 references added; 2 figures adde

A Screen for Genetic Modifiers of Protein Phosphatase 1 Function in Drosophila Collective Cell Cohesion and Migration

Cells can migrate collectively in tightly or loosely-associated groups during tissue and organ formation, during embryonic development, in tumor metastases, and in wound healing. Drosophilaborder cellsserve as an excellent genetic model of collective cell migration inside a developing tissue. During ovarian development, 6-8 cells form the border cell cluster and migrate together as a cohesive group to reach the large oocyte. Previous experiments have shown that Nuclear inhibitor of Protein Serine Threonine Phosphatase 1 (NiPP1) causes border cells to separate into single cells, rather than stay in a group, and limits their ability to migrate. NiPP1 inhibits the activity of the Protein Phosphatase 1 (PP1) enzyme. Therefore, overexpressing NiPP1, though a modifier screen, will allows us identify genes that work with PP1 to promote the adhesion and collective migration of border cells. To carry out this genetic screen, females expressing NiPP1 in border cells are crossed to a collection of mutant strains, called deficiencies, that remove a number of genes. Ovaries from the resulting progeny are assayed for cohesion and migration of the border cell cluster by fluorescent microscopy. In this project, larger deficiencies have been shown to suppress (“revert to wild type”), or enhance (“make worse”) the mutant phenotype. The goal is to identify the exact gene required for this suppression or enhancement, using smaller deficiency mutant strains that delete only a few genes. Such mutant deficiencies represent candidate NiPP1 modifying genes. The candidate genes will be knocked out by RNAi one by one to definitively determine the genes required for PP1 function in cell-to-cell adhesion and collective migration. Because many Drosophilagenes have human homologs, these studies of PP1 have implications for collective cell migration in humans

Sudden Gravitational Transition

We investigate the properties of a cosmological scenario which undergoes a gravitational phase transition at late times. In this scenario, the Universe evolves according to general relativity in the standard, hot big bang picture until a redshift z≲1. Nonperturbative phenomena associated with a minimally-coupled scalar field catalyzes a transition, whereby an order parameter consisting of curvature quantities such as R2, RabRab, RabcdRabcd acquires a constant expectation value. The ensuing cosmic acceleration appears driven by a dark-energy component with an equation-of-state w\u3c−1. We evaluate the constraints from type 1a supernovae, the cosmic microwave background, and other cosmological observations. We find that a range of models making a sharp transition to cosmic acceleration are consistent with observations

Deep Learning Algorithms Improve Automated Identification of Chagas Disease Vectors

This is a pre-copyedited, author-produced version of an article accepted for publication in Journal of Medical Entomology following peer review. The version of record is available online at: https;//doi.org/https://doi.org/10.1093/jme/tjz065Vector-borne Chagas disease is endemic to the Americas and imposes significant economic and social burdens on public health. In a previous contribution, we presented an automated identification system that was able to discriminate among 12 Mexican and 39 Brazilian triatomine (Hemiptera: Reduviidae) species from digital images. To explore the same data more deeply using machine-learning approaches, hoping for improvements in classification, we employed TensorFlow, an open-source software platform for a deep learning algorithm. We trained the algorithm based on 405 images for Mexican triatomine species and 1,584 images for Brazilian triatomine species. Our system achieved 83.0 and 86.7% correct identification rates across all Mexican and Brazilian species, respectively, an improvement over comparable rates from statistical classifiers (80.3 and 83.9%, respectively). Incorporating distributional information to reduce numbers of species in analyses improved identification rates to 95.8% for Mexican species and 98.9% for Brazilian species. Given the ‘taxonomic impediment’ and difficulties in providing entomological expertise necessary to control such diseases, automating the identification process offers a potential partial solution to crucial challenges

A Sudden Gravitational Transition

We investigate the properties of a cosmological scenario which undergoes a gravitational phase transition at late times. In this scenario, the Universe evolves according to general relativity in the standard, hot Big Bang picture until a redshift z \lesssim 1. Non-perturbative phenomena associated with a minimally-coupled scalar field catalyzes a transition, whereby an order parameter consisting of curvature quantities such as R^2, R_{ab}R^{ab}, R_{abcd}R^{abcd} acquires a constant expectation value. The ensuing cosmic acceleration appears driven by a dark-energy component with an equation-of-state w < -1. We evaluate the constraints from type 1a supernovae, the cosmic microwave background, and other cosmological observations. We find that a range of models making a sharp transition to cosmic acceleration are consistent with observations.Comment: 8 pages, 8 figures; added reference

The present universe in the Einstein frame, metric-affine R+1/R gravity

We study the present, flat isotropic universe in 1/R-modified gravity. We use the Palatini (metric-affine) variational principle and the Einstein (metric-compatible connected) conformal frame. We show that the energy density scaling deviates from the usual scaling for nonrelativistic matter, and the largest deviation occurs in the present epoch. We find that the current deceleration parameter derived from the apparent matter density parameter is consistent with observations. There is also a small overlap between the predicted and observed values for the redshift derivative of the deceleration parameter. The predicted redshift of the deceleration-to-acceleration transition agrees with that in the \Lambda-CDM model but it is larger than the value estimated from SNIa observations.Comment: 11 pages; published versio

Acceleration of the universe in the Einstein frame of a metric-affine f(R) gravity

We show that inflation and current cosmic acceleration can be generated by a metric-affine f(R) gravity formulated in the Einstein conformal frame, if the gravitational Lagrangian L(R) contains both positive and negative powers of the curvature scalar R. In this frame, we give the equations for the expansion of the homogeneous and isotropic matter-dominated universe in the case L(R)=R+{R^3}/{\beta^2}-{\alpha^2}/{3R}, where \alpha and \beta are constants. We also show that gravitational effects of matter in such a universe at very late stages of its expansion are weakened by a factor that tends to 3/4, and the energy density of matter \epsilon scales the same way as in the \Lambda-CDM model only when \kappa*\epsilon<<\alpha.Comment: 12 pages; published versio

The cosmic snap parameter in f(R) gravity

We derive the expression for the snap parameter in f(R) gravity. We use the Palatini variational principle to obtain the field equations and regard the Einstein conformal frame as physical. We predict the present-day value of the snap parameter for the particular case f(R)=R-const/R, which is the simplest f(R) model explaining the current acceleration of the universe.Comment: 9 pages; published versio

Consistent modified gravity: dark energy, acceleration and the absence of cosmic doomsday

We discuss the modified gravity which includes negative and positive powers of the curvature and which provides the gravitational dark energy. It is shown that in GR plus the term containing negative power of the curvature the cosmic speed-up may be achieved, while the effective phantom phase (with $w$ less than -1) follows when such term contains the fractional positive power of the curvature. The minimal coupling with matter makes the situation more interesting: even 1/R theory coupled with the usual ideal fliud may describe the (effective phantom) dark energy. The account of $R^2$ term (consistent modified gravity) may help to escape of cosmic doomsday.Comment: LaTeX file, 9 pages, based on the talk given by S.D. Odintsov (Int. Conference Mathematical Methods in Physics, Rio de Janeiro, Augest, 2004), to appear in CQG, Letter