LERMA UMR8112

Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères



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Offres de Thèses

Offre de thèse du CNES

Appel à candidatures thèses/post-doctorats CNES
Avec les thèses et les post-doctorats du CNES : inventons l’espace du futur ! Chaque année, le CNES accorde une centaine d’allocations de recherche (...)

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Open PHD position in Astrophysics

(October 2017)
Subject : Sulphur-bearing molecules in star forming regions : Observational and laboratory investigations.
Supervisors : L.E. Kristensen (Niels Bohr Institute & Natural (...)

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Séminaires à venir

Vendredi 26 avril 2019, 14h00
Salle de l'atelier, Paris
The Effect of Gravitational Lensing on Cosmological Parameter Estimation
KAISER, Nick
ENS
résumé :
A long standing question in cosmology is whether gravitational
lensing by structure biases the apparent distance or the mean flux
density of sources. Interest in this has been rekindled by recent
calculations in 2nd order relativistic perturbation theory which
suggest significant implications for cosmological parameter
estimation from both supernovae and the microwave background. In
this talk I shall first review the somewhat confusing history of
the subject, going back to the early '60s and including both
Weinberg's 1976 argument that there should be no effect on grounds
of flux conservation and the general relativistic "focusing theorem"
of the '80s that seems to contradict this and which foreshadows the
more recent results. I then describe recent work with John Peacock
where we have shown how these conflicts are resolved. Regarding
Weinberg we show that there is a loophole in his argument, and
lensing does in fact bias the apparent distance, but it is a very
small effect. We show that the apparent intrinsic tendency for
structure to cause focusing of light rays that emerges from the
focusing theorem is a statistical rather than a physical effects.
 
Vendredi 21 juin 2019, 14h00
Salle de l'atelier, Paris
Accretion-driven turbulence and observational signatures
Pierre GUILLARD
IAP
 
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