|Speaker:||Jean-Philippe Uzan (IAP)|
|Title:||Testing the equivalence principle: the link between constants, gravitation and cosmology|
|Date (JST):||Thu, Nov 10, 2011, 13:30 - 15:00|
|Place:||Seminar Room A|
Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter, signaling a violation of the equivalence principle. Thus, it is of importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy.
In this seminar, I will first recall the relations between the constants, the tests of the local position invariance and of the universality of free fall. I will also sketch the main theoretical frameworks in which the low-energy constants may actually be varying, focusing on the unification mechanisms and the relations between the variation of different constants.
Many experimental and observational constraints have been obtained from atomic clocks, the Oklo phenomenon, solar system observations, meteorite dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. I will discuss the need for a cosmological model to compare these observations.
To finish, cosmology, and in particular the models of the early universe, allows to adress the question of understanding their numerical values. While very speculative, and probably out of reach of any experimental or observational check, this may be the only insight to understand the apparent fine-tuning that the constants seem to confront us with.
 J.-P. Uzan, Liv. Rev. Relat. 4, 2 (2011)
 J.-P. Uzan and B. Leclercq, De l'importance d'etre une constante (Dunos, 2005); translated in English by (Springer, 2009).
 P. Peter and J.-P. Uzan, Primordial cosmology (Oxford University Press, 2009)
 K.A. Olive, M. Peloso, and J.-P. Uzan, The wall of fundamental constants, Phys. Rev. D 83 (2011) 043509.