Constraints on field flows of quintessence dark energy

The quest for understanding the late-time acceleration is haunted by an immense freedom in the analysis of dynamical models for dark energy in extended parameter spaces. Oftentimes having no prior knowledge at our disposal, arbitrary choices are implemented to reduce the degeneracies between parameters. We also encounter this issue in the case of quintessence fields, where a scalar degree of freedom drives the late-time acceleration. In this study, we implement a more physical prescription, the flow condition, to fine-tune the quintessence evolution for several field potentials. We find that this prescription agrees well with the most recent catalogue of data, namely supernovae type Ia, baryon acoustic oscillations, cosmic clocks, and distance to the last scattering surface, and it enables us to infer the initial conditions for the field, both potential and cosmological parameters. At 2σ we find stricter bounds on the potential parameters f/mpl>0.26 and n<0.15 for the PNGB and IPL potentials, respectively, while constraints on cosmological parameters remain extremely consistent across all assumed potentials. By implementing information criteria to assess their ability to fit the data, we do not find any evidence against thawing models, which in fact are statistically equivalent to ΛCDM, and the freezing ones are moderately disfavored. Through our analysis we place upper bounds on the slope of quintessence potentials, consequently revealing a strong tension with the recently proposed swampland criterion, finding the 2σ upper bound of λ∼0.31 for the exponential potential. © 2019 American Physical Society

Augmenting photometric redshift estimates using spectroscopic nearest neighbours

As a consequence of galaxy clustering, close galaxies observed on the plane of the sky should be spatially correlated with a probability that is inversely proportional to their angular separation. In principle, this information can be used to improve photometric redshift estimates when spectroscopic redshifts are available for some of the neighbouring objects. Depending on the depth of the survey, however, this angular correlation is reduced by chance projections. In this work, we implement a deep-learning model to distinguish between apparent and real angular neighbours by solving a classification task. We adopted a graph neural network architecture to tie together photometry, spectroscopy, and the spatial information between neighbouring galaxies. We trained and validated the algorithm on the data of the VIPERS galaxy survey, for which photometric redshifts based on spectral energy distribution are also available. The model yields a confidence level for a pair of galaxies to be real angular neighbours, enabling us to disentangle chance superpositions in a probabilistic way. When objects for which no physical companion can be identified are excluded, all photometric redshift quality metrics improve significantly, confirming that their estimates were of lower quality. For our typical test configuration, the algorithm identifies a subset containing ~75% high-quality photometric redshifts, for which the dispersion is reduced by as much as 50% (from 0.08 to 0.04), while the fraction of outliers reduces from 3% to 0.8%. Moreover, we show that the spectroscopic redshift of the angular neighbour with the highest detection probability provides an excellent estimate of the redshift of the target galaxy, comparable to or even better than the corresponding template-fitting estimate.Comment: 9 pages, 12 figures, matching the accepted version. NezNet is available at https://github.com/tos-1/NezNe

Ripples in a pond: Do social work students need to learn about terrorism?

In the face of heightened awareness of terrorism, however it is defined, the challenges for social work are legion. Social work roles may include working with the military to ensure the well-being of service-men and women and their families when bereaved or injured, as well as being prepared to support the public within the emergency context of an overt act of terrorism. This paper reviews some of the literature concerning how social work responds to confl ict and terrorism before reporting a smallscale qualitative study examining the views of social work students, on a qualifying programme in the UK, of terrorism and the need for knowledge and understanding as part of their education