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Arxiv New Filter | Bookmarks & clubs | Arxiv ref/author:

Evolving dark energy from GRBs
 
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David Parkinson



Joined: 19 Jan 2005
Posts: 21
Affiliation: KASI

PostPosted: January 12 2006  Reply with quote

Is anybody at the AAS meeting and saw the talk by Bradley Schaefer, which claims to have detected evolution in the dark energy using Gamma Ray Bursts as standard candles? There is a webpage with the abstract and some plots here www.phys.lsu.edu/GRBHD.

What do people think about his claim? It is only 2.5 sigma, so it is not conlcusive. They plot w0 against w'(=dw/dz), but will that parameterisation work at redshifts up to z~6? And what about other effects? Like SN-Ia, the mechanism for GRBs is unknown, so we don't know what kind of evolutions could take place between redshift 6 and 0.
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David Seery



Joined: 25 Jan 2005
Posts: 9
Affiliation: University of Sussex

PostPosted: January 13 2006  Reply with quote

I don't know if this is detailed enough to be any use, but there are some comments on this over at Cosmic Variance, viz. http://cosmicvariance.com/2006/01/11/evolving-dark-energy/, and some pointers to reaction.
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Ben Gold



Joined: 25 Sep 2004
Posts: 97
Affiliation: University of Minnesota

PostPosted: January 14 2006  Reply with quote

The sharpest criticism I've heard is that he doesn't appear to have properly marginalized over the overall magnitude offset. This basically amounts to claiming to know both the Hubble constant and the intrinsic GRB luminosity to perfect precision. Visually, if you look at the data: http://www.phys.lsu.edu/GRBHD/images/diagram1.jpg wouldn't the black line fit a whole lot better if you were allowed to move all the points upward a small amount (or equivalently, move the black line down)? If so, then that's what you should be comparing to the green "best-fit" line. Normally you account for all this by treating the offset as a free parameter and marginalizing over it; if this were done I suspect the claimed 2.5 σ exclusion of a c.c. would become far less significant.

Anyway, there's no paper yet describing what he did, so who knows?
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