We study the importance of gravitational lensing in modelling the number counts of galaxies for the first time in spectroscopic surveys. We confirm previous results for photometric surveys, showing that lensing cannot be neglected in a survey like LSST since it would infer a significant shift of standard cosmological parameters. For a spectroscopic survey like SKA2, we find that neglecting lensing in the monopole, quadrupole and hexadecapole of the correlation function can also induce an important shift of cosmological parameters. For ΛCDM parameters, the shift is moderate, of the order of 0.6σ or less. However, for a model-independent analysis, that measures the growth rate of structure in each redshift bins, neglecting lensing introduces a shift of up to 2.3σ at high redshift. Since the growth rate is directly used to test the theory of gravity, such a strong shift would wrongly be interpreted as the breakdown of General Relativity. This shows the importance of including lensing in the analysis of future surveys. For a survey like DESI, we find on the other hand that lensing is not important, mainly due to the value of the magnification bias parameter of DESI, s(z), which strongly reduces the lensing contribution at high redshift. This result relies on our theoretical modelling of s(z) in DESI and should therefore be confirmed with measurements of s(z) in simulations. We also propose a way of improving the analysis of spectroscopic surveys, by including the cross-correlations between different redshift bins (which is neglected in spectroscopic surveys) from the spectroscopic survey or from a different photometric sample. We show that including the cross-correlations in the SKA2 analysis does not improve the constraints. On the other hand replacing the cross-correlations from SKA2 by cross-correlations measured with LSST improves the constraints by 10% to 20%. The marginal improvement is mainly due to the density correlations between nearby bins and, therefore, does not strongly depend on our knowledge of the magnification bias. Interestingly, for standard cosmological parameter estimation, the photometric survey LSST in its 12 redshift bin configuration and the spectroscopic SKA2 survey are highly complementary, since they are affected by different degeneracies between parameters: LSST yields the tightest constraints on Ωcdm, h and n s, while SKA2 better constrains Ωbaryon, A s and the bias.

Abstract We present a numerical weak-lensing analysis that is fully relativistic and non-perturbative for the scalar part of the gravitational potential and first-order in the vector part, frame dragging. Integrating the photon geodesics backwards from the observer to the emitters, we solve the Sachs optical equations and study in detail the weak-lensing convergence, ellipticity and rotation. For the first time, we apply such an analysis to a high-resolution relativistic N-body simulation, which consistently includes the leading-order corrections due to general relativity on both large and small scales. These are related to the question of gauge choice and to post-Newtonian corrections, respectively. We present the angular power spectra and one-point probability distribution functions for the weak-lensing variables, which we find are broadly in agreement with comparable Newtonian simulations. Our geometric approach, however, is more robust and flexible, and can therefore be applied consistently to non-standard cosmologies and modified theories of gravity.

Clustering of a perfect fluid does not lead to the generation of vorticity. It is the collisionless nature of dark matter, inducing velocity dispersion and shell crossing, which is at the origin of cosmological vorticity generation. In this paper we investigate the generation of vorticity during the formation of cosmological large scale structure using the public relativistic N-body code gevolution. We test several methods to compute the vorticity power spectrum and we study its convergence with respect to the mass and grid resolution of our simulations. We determine the power spectrum, the spectral index on large-scales, the amplitude of the peak position and their time evolution. We also compare the vorticity extracted from our simulations with the vector perturbations of the metric. Our results are accompanied by resolution studies and compared with previous studies in the literature.

We study the impact of neglecting lensing magnification in galaxy clustering analyses for future galaxy surveys, considering the ΛCDM model and two extensions: massive neutrinos and modifications of General Relativity. Our study focuses on the biases on the constraints and on the estimation of the cosmological parameters. We perform a comprehensive investigation of these two effects for the upcoming photometric and spectroscopic galaxy surveys Euclid and SKA for different redshift binning configurations. We also provide a fitting formula for the magnification bias of SKA. Our results show that the information present in the lensing contribution does improve the constraints on the modified gravity parameters whereas the lensing constraining power is negligible for the ΛCDM parameters. For photometric surveys the estimation is biased for all the parameters if lensing is not taken into account. This effect is particularly significant for the modified gravity parameters. Conversely for spectroscopic surveys the bias is below one sigma for all the parameters. Our findings show the importance of including lensing in galaxy clustering analyses for testing General Relativity and to constrain the parameters which describe its modifications. 1

We investigate the future perspectives of the detection of the relativistic dipole by cross-correlating the 21 cm emission in Intensity Mapping (IM) and galaxy surveys at low redshift. We model the neutral hydrogen (HI) and the galaxy population by means of the halo model to relate the parameters that affect the dipole signal such as the biases of the two tracers and the Poissonian noise. We investigate the behavior of the signal-to-noise as a function of the galaxy and magnification biases, for two fixed models of the neutral hydrogen. In both cases we found that the signal-to-noise does not grow by increasing the difference between the biases of the two tracers, due to the larger shot-noise yields by highly biased tracers. We also study and provide an optimal luminosity-threshold galaxy catalogue to enhance the signal-to-noise ratio of the relativistic dipole. Interestingly, we show that the maximum magnitude provided by the survey does not lead to the maximum signal-to-noise for detecting relativistic effects and we predict the optimal value for the limiting magnitude. Our work suggests that an optimal analysis could increase the signal-to-noise ratio up to a factor five compared to a standard one.

In this paper we present for the first time the angular power spectra C ℓ(z,z') for number counts from relativistic N-body simulations. We use the relativistic N-body code gevolution with its exact integration of lightlike geodesics which include all relativistic scalar contributions to the number counts. We compare our non-perturbative numerical results with the results from class using the hmcode approximation for the non-linear matter power spectrum. We find that this simple description is excellent for both, the density and the convergence. On the other hand, the current implementation of redshift-space distortions in Boltzmann codes is not accurate. We also find that the largest contribution to the unequal-redshift power spectra is the cross-correlation of the density and the lensing contribution to the number counts, especially for redshift bins that are far apart. Correlating the number counts with the convergence map we find that the signal is dominated by the lensing-lensing term when the convergence field redshift is not higher than the number counts one, while it is dominated by the density-lensing term in the opposite case. In the present study, the issue of galaxy bias is deliberately left aside by considering only unbiased samples of matter particles from the simulations.

Purpose – Narrative therapy uses psychological thinking to help people reconnect with important aspects of their lives that have become subjugated by a dominant problem story. Collective narrative practices (CNPs) such as the tree of life (ToL) metaphor apply these principles to communities. Limited research suggests that ToL groups benefit service users and staff in inpatient settings. The purpose of this paper is to explore the utility of a pilot ToL group, run in an inpatient treatment ward. Design/methodology/approach – Nine participants attended a seven-week ToL group. Eight service users and two facilitators contributed to the evaluation. Qualitative data were derived from interviews and questionnaires and analysed from a social constructionist perspective using inductive thematic analysis. Findings – Three themes were generated: first, a sense of community – service user and staff relationships developed both inside and outside of the group, through sharing personal experiences. Second, rediscovering identity – participants reconnected with important aspects of their lives, which helped them to plan their recovery. Third, usefulness of the metaphor – service users and staff reflected on useful aspects of the ToL metaphor and how groups could be improved in the future. Data collection methods were key limitations of the study. Further groups should be conducted, whilst considering means of developing CNPs and their evaluation in this setting. Originality/value – Few evaluations of ToL groups have been conducted in inpatient settings. This research outlines considerations for setting up and evaluating ToL groups and highlights their value for service users and staff.

No abstract