A viable scenario for Inflationary Magnetogenesis

Dienstag, 10. Juli 2018, 14:00 - 15:00
Veranstaltungsort* Library
Magnetic elds have been observed in galaxy, galaxy clusters and even in voids.
A lower bound of strength 10?15 G on Mpc scales has been suggested by gamma
ray observation of Blazars. The precise mechanism for the origin of these large-
scale magnetic elds still does not have a satisfactory explanation. The gener-
ation of these elds is supposed to have happened by the ampli cation of seed
elds. In order to generate the observed elds with known ampli cation mech-
anisms, seed elds of sucient strength need to be produced suciently early.
Generation of these seed elds during inflation is one of the possible scenarios
suggested in the literature. One of the model of inflationary magnetogenesis is
f2FF type model (Ratra model) where f is a function of the inflaton eld.
This model, however, su ers from certain drawbacks such as strong coupling and
back-reaction. A possible scenario where these problems are avoided has been
suggested. In this scenario the coupling function (f) grows during inflation and
transits to a decaying phase post-inflation. By choosing a suitable evolution of
coupling function, it has been demonstrated that the above-mentioned dicul-
ties (arising from strong coupling and back-reaction) are avoided. However, to
avoid back-reaction post inflation, reheating has to be below  1:7  104 GeV.
The generated magnetic energy spectrum is blue and it satis es the gamma-
ray bounds. If we consider reheating at QCD (150 MeV) epoch, the estimated
present day magnetic eld strength and the corresponding correlation length
are 1:4  10?12 G and 6:1  10?4 Mpc, respectively.

: Ramkishor Sharma, University of Delhi