A Possible solution to the Lithium problem?

Big Bang Nucleosynthesis (BBN) is an admirable achievement of the standard cosmological model as it very precisely predicts the amount of the most abundant elements, in particular hydrogen and helium. On close inspection the picture is marred by a long standing and annoying problem. Though its abundance is extremely small, the standard predicted amount of lithium is  about a factor 3 larger than what observed in some metal-poor stars believed to trace the primordial abundance. Tweaking the theory of BBN to correct the lithium abundance affects that of the hydrogen or helium to an extent that this is ruled out by the Cosmic Microwave Background (CMB).

In a very recent paper, Pasquale D. Serpico and Vivian Poulin (LAPTh, CNRS) have shown that a loophole in the calculation  of the electromagnetic cascades re-opens the possibility of finding an easy way out to the old problem of the lithium abundance.

Lire la suite : A Possible solution to the Lithium problem?

A course on cosmology by Wessel Valkenburg

Starting Monday 20 January Wessel Valkenburg (Lorentz Institute, Leiden Univ., NL) will give a series of 5 lectures on cosmology. The lectures require no prior knowledge of the subject and is addressed to both theorists and experimentalists, physics PhD students and researchers alike.

The 5 lectures Introduction to Cosmology cover
 
1) The universe today: overview of current understanding, based on Planck, WMAP, SDSS, an many more.
2) Cosmic microwave background as the Planck satellite sees it: from radio signals to spectra of perturbations (and back), and the importance of spectra.
3)  Large scale structure from BOSS, CFHTLens, LSST, Euclid: from angles and redshifts to spectra of perturbations (and back), and a bit on the importance of spectra.
4)  Inflation: probing high-energy physics with BICEP2, Planck, and others.
5) What are the most important pitfalls for cosmologists? Confirmation bias, believe vs pragmatic testing, etc. Where is the Nobel prize hiding?
 
For more information see the LAPTh indico : https://indico.in2p3.fr/category/365/

The  (6) videos of the lectures can be found on the LAPTh Youtube Channel

Habemus Logo

A new logo is born !

LAPTh has now a new logo! Putting 5 letters in a square was no easy job. Among a hundred of designs and a lot of discussions in the LAPTh patio, restaurant, sometimes heated but always jovial, this was the final choice. The logo comes now in a couple of versions. 

New Planck results, another one bites the dust

After four years of operation of the Planck satellite of the European Space Agency (ESA), the Planck Collaboration has build up an exquisitely precise map of the sky in both temperature and now of polarisation. These maps furnish a detailed picture of how the universe evolved. Among the numerous results provided by the Planck satellite over the last year, there is an assessment of the polarised dust emission at intermediate and high Galactic latitudes  (http://arxiv.org/abs/1409.5738). This is a crucial foreground in the searches for primordial B-mode polarisation patterns, possibly imprinted in the Cosmic Microwave Background by gravitational waves of  inflationary origin, also known as tensor modes. Thanks to this measurement, older estimates of this contribution have  been revisited and, in a joint effort by the BICEP2/Keck Array and Planck Data collaborations (http://arxiv.org/abs/1502.00612),  no statistically significant evidence for tensor modes has been found in a reanalysis of the BICEP 2 observations, which  in 2014 had been interpreted as a possible primordial B-mode detection  (http://arxiv.org/abs/1403.3985), an interpretation that made big waves in the media then... undeservedly. We will need to wait and be more careful about gravity waves.