University of Portsmouth

About: University of Portsmouth is a education organization based out in Portsmouth, Portsmouth, United Kingdom. It is known for research contribution in the topics: Population & Galaxy. The organization has 5452 authors who have published 14256 publications receiving 424346 citations. The organization is also known as: Portsmouth and Gosport School of Science and Art & Portsmouth and Gosport School of Science and the Arts.

Cosmology in generalized Proca theories

Abstract: We consider a massive vector field with derivative interactions that propagates only the 3 desired polarizations (besides two tensor polarizations from gravity) with second-order equations of motion in curved space-time. The cosmological implications of such generalized Proca theories are investigated for both the background and the linear perturbation by taking into account the Lagrangian up to quintic order. In the presence of a matter fluid with a temporal component of the vector field, we derive the background equations of motion and show the existence of de Sitter solutions relevant to the late-time cosmic acceleration. We also obtain conditions for the absence of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations in the small-scale limit. Our results are applied to concrete examples of the general functions in the theory, which encompass vector Galileons as a specific case. In such examples, we show that the de Sitter fixed point is always a stable attractor and study viable parameter spaces in which the no-ghost and stability conditions are satisfied during the cosmic expansion history.

Non-Gaussianities from ekpyrotic collapse with multiple fields

Abstract: We compute the non-Gaussianity of the curvature perturbation generated by ekpyrotic collapse with multiple fields. The transition from the multi-field scaling solution to a single-field dominated regime converts initial isocurvature field perturbations to an almost scale invariant comoving curvature perturbation. In the specific model of two fields, 1 and 2, with exponential potentials, −Viexp(−cii), we calculate the bispectrum of the resulting curvature perturbation. We find that the non-Gaussianity is dominated by non-linear evolution on super-Hubble scales and hence is of the local form. The non-linear parameter of the curvature perturbation is given by fNL = 5cj2/12, where cj is the exponent of the potential for the field which becomes subdominant at late times. Since cj2 must be large, in order to generate an almost scale invariant spectrum, the non-Gaussianity is inevitably large. Thus, the model is strongly constrained by observational bounds on the spectral index and non-Gaussianity.

LIGO Detector Characterization in the Second and Third Observing Runs

Abstract: The characterization of the Advanced LIGO detectors in the second and third observing runs has increased the sensitivity of the instruments, allowing for a higher number of detectable gravitational-wave signals, and provided confirmation of all observed gravitational-wave events. In this work, we present the methods used to characterize the LIGO detectors and curate the publicly available datasets, including the LIGO strain data and data quality products. We describe the essential role of these datasets in LIGO–Virgo Collaboration analyses of gravitational-waves from both transient and persistent sources and include details on the provenance of these datasets in order to support analyses of LIGO data by the broader community. Finally, we explain anticipated changes in the role of detector characterization and current efforts to prepare for the high rate of gravitational-wave alerts and events in future observing runs.

Will the truth come out? the effect of deception, age, status, coaching, and social skills on CBCA scores.

Abstract: The impact of Veracity, Age, Status (witness or suspect), Coaching (informed or uninformed regarding CBCA), and Social Skills (social anxiety, social adroitness, and self-monitoring) on Criteria-Based Content Analysis scores was examined. Participants (aged 5–6, 10–11, 14–15, and undergraduates) participated in a “rubbing the blackboard” event. In a subsequent interview they told the truth or lied about the event. They were accused of having rubbed the blackboard themselves (suspect condition) or were thought to have witnessed the event (witness condition), and were or were not taught some CBCA criteria prior to the interview. CBCA scores discriminated between liars and truth tellers in children, adults, witnesses, and suspects. However, truth tellers obtained higher CBCA scores than liars only when the liars were uninformed about CBCA. CBCA scores were correlated with social skills. It is argued that these findings should caution those who believe that the validity of CBCA has been conclusively demonstrated.

An empirical calibration of the completeness of the SDSS quasar survey

Abstract: Spectra of nearly 20,000 pointlike objects to a Galactic reddening–corrected magnitude of i = 19.1 have been obtained to test the completeness of the Sloan Digital Sky Survey (SDSS) quasar survey. We focus on spatially unresolved quasars, which comprise 94% of all SDSS quasars to the main survey magnitude limit. The objects were selected from all regions of color space, sparsely sampled from within a 278 deg2 area (effective area 233 deg2) of sky covered by this study. Only 10 quasars were identified that were not targeted as candidates by the SDSS quasar survey (including both color and radio source selection). The inferred density of unresolved quasars on the sky that are missed by the SDSS algorithm is 0.44 deg-2, compared with 8.28 deg-2 for the selected quasar density, giving a completeness of 94.9% to the limiting magnitude. Omitting radio selection reduces the color-only selection completeness by about 1%. Of the 10 newly identified quasars, three have detected broad absorption line systems, six are significantly redder than other quasars at the same redshift, and four have redshifts between 2.7 and 3.0 (the redshift range where the SDSS colors of quasars intersect the stellar locus). The fraction of quasars (and other unresolved sources) missed because of image defects and blends, independent of the selection algorithm, is ≈4%, but this number varies by a few percent with magnitude. Quasars with extended images comprise about 6% of the SDSS sample, and the completeness of the selection algorithm for extended quasars is approximately 81%, based on the SDSS galaxy survey. The combined end-to-end completeness for the SDSS quasar survey is ≈89%. The total corrected density of quasars on the sky to i = 19.1 is estimated to be 10.2 deg-2. The SDSS completeness restricted to z 3 quasars is expected to be considerably lower and is a strong function of redshift. The determination of the global completeness is required for the statistical properties of quasars to i = 19.1 derived from the SDSS data set, such as the luminosity function and correlation function, to be accurately determined.