Résumé / Abstract Seminaire_GReCO
SÉMINAIRE DU GRECO

"The cosmological constant problem and renormalization group"

I.L. Shapiro

The talk starts with an elementary introduction to the Cosmological Constant
(CC) problem. There are actually several distinct problems, one of them is
that many people apply the cut-off regularization in a very naive way and
misinterpret the results as a fundamental difficulty. From the other side
there is a real and very difficult CC problem, which results from the existence
of many independent contributions to the same small quantity, that is the CC,
or, equivalently, energy density of vacuum. The real CC problem consists in
the enormous precision of the requested fine-tuning for one of these
contributions. The CC problem can be seen as mainly a Quantum Field Theory
hierarchy-type problem, which comes from the "conflict" between the particle
physics scale where we evaluate the mentioned contributions and the tiny cosmic
scale where we observe their sum. The development and improvement of the
methods of Quantum Field Theory in curved space-time is necessary for better
understanding of the CC problem, in both early and late universe cases. In
particular, there is a possibility of variable CC due to the quantum effects
of matter fields, which can be described by the renormalization group running
of CC in the far IR. Since our present-day knowledge of the Appelquist and
Carazzone decoupling theorem in gravity is restricted, the possibility of
such a running can not be theoretically proved or ruled out at the present-day
state of art in the field, and this opens the door for some interesting
phenomenological applications in cosmology and astrophysics.

lundi 19 janvier 2015 - 11:00
Salle des séminaires Évry Schatzman,
Institut d'Astrophysique de Paris

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