An introduction to quintessence

Institut d Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France riazuelo iap.fr 

There are two problems which appear when one considers the possibility of a small but non zero cosmological constant. The first one has to do with the 

1 See however Alain Blanchard s contribution for another point of view. 

Blanchard and M. Signore (eds.), Frontiers of Cosmology, 139-148. 2005 Springer. Printed in the Netherlands. 

The biggest mystery related to the cosmological constant lies there indeed, from very general quantum held theory considerations, any particle with momentum k should have a contribution E Tiuo to the total energy even in its lowest energy state, so that one expects that any species should contribute to the vacuum energy density according to 

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