LARENA Julien
Position : Enseignantchercheur
Organism : UM2
Maître de Conférences
Team: LUPM/Particules, Astroparticules, Cosmologie : Théorie
julien.larena
umontpellier.fr
0467143770
Room: 11, Floor: 4, Build.: 21
Research Activities: 
Je m'intéresse aux effets relativistes en cosmologie, et plus particulièrement dans la formation et l'observation des grandes structures. Plus récemment, une partie importante de mon activité s'articule autour de la compréhension et de la modélisation des phénomènes de lentillage fort dans l'univers inhomogène. 
Research Topics:  sdu/sdu.astr/sdu.astr.co
 phys/phys.grqc

Scientific productions :


Measuring lineofsight shear with Einstein rings: a proof of concept
Author(s): Hogg Natalie b., Fleury Pierre, Larena J., Martinelli Matteo
(Article) Published:
Monthly Notices Of The Royal Astronomical Society, vol. p.5982–6000 (2023)
Links openAccess full text :
Ref Arxiv: 2210.07210
DOI: 10.1093/mnras/stad512
Ref. & Cit.: NASA ADS
Abstract: Lineofsight effects in strong gravitational lensing have long been treated as a nuisance. However, it was recently proposed that the lineofsight shear could be a cosmological observable in its own right, if it is not degenerate with lens model parameters. Using the formalism introduced by Fleury et al. (2021a), we firstly demonstrate that the lineofsight shear can be accurately measured from a simple simulated strong lensing image with percent precision. We then extend our analysis to more complex simulated images and stress test the recovery of the lineofsight shear when using deficient fitting models, finding that it escapes from degeneracies with lens model parameters, albeit at the expense of the precision. Lastly, we check the validity of the tidal approximation by simulating and fitting an image generated in the presence of many lineofsight dark matter haloes, finding that an explicit violation of the tidal approximation does not necessarily prevent one from measuring the lineofsight shear.
Comments: 16 + 3 pages, 14 figures, prepared for submission to MNRAS



Constraining spatial curvature with largescale structure
Author(s): Bel Julien, Larena J., Maartens Roy, Marinoni Christian, Perenon Louis
(Article) Published:
Journal Of Cosmology And Astroparticle Physics, vol. p.076 (2022)
Links openAccess full text :
Ref Arxiv: 2206.03059
DOI: 10.1088/14757516/2022/09/076
Ref. & Cit.: NASA ADS
Abstract: We analyse the clustering of matter on large scales in an extension of the concordance model that allows for spatial curvature. We develop a consistent approach to curvature and wideangle effects on the galaxy 2point correlation function in redshift space. In particular we derive the AlcockPaczynski distortion of $f\sigma_{8}$, which differs significantly from empirical models in the literature. A key innovation is the use of the `Clustering Ratio', which probes clustering in a different way to redshiftspace distortions, so that their combination delivers more powerful cosmological constraints. We use this combination to constrain cosmological parameters, without CMB information. In a curved Universe, we find that $\Omega_{{\rm m}, 0}=0.26\pm 0.04$ (68\% CL). When the clustering probes are combined with lowredshift background probes  BAO and SNIa  we obtain a CMBindependent constraint on curvature: $\Omega_{K,0} = 0.0041\,_{0.0504}^{+0.0500}$. We find no Bayesian evidence that the flat concordance model can be rejected. In addition we show that the sound horizon at decoupling is $r_{\rm d} = 144.57 \pm 2.34 \; {\rm Mpc}$, in agreement with its measurement from CMB anisotropies. As a consequence, the latetime Universe is compatible with flat $\Lambda$CDM and a standard sound horizon, leading to a small value of $H_{0}$, {\em without} assuming any CMB information. Clustering Ratio measurements produce the only lowredshift clustering data set that is not in disagreement with the CMB, and combining the two data sets we obtain $\Omega_{K,0}= 0.023 \pm 0.010$.
Comments: 40 pages; 13 figures; Version accepted by JCAP.
Réf Journal: JCAP09(2022)076
