Séminaire / Seminar GReCO |
| « CMB temperature anisotropy at large scales induced by a causal primordial magnetic field » |
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C. Caprini |
| A possible explanation for the origin of the large scale magnetic fields observed in galaxies and clusters is that they have been generated in the primordial universe. A stochastic background of primordial magnetic fields generated in the early universe with a mean amplitude well below micro-Gauss level can leave imprints on the temperature anisotropy of the cosmic microwave background. In this talk I present an analytical derivation of the CMB temperature anisotropy induced at large scales from a primordial magnetic field. The magnetic field is assumed to be generated by a causal process, as for example a phase transition, which consistently sets the initial conditions. Einstein''s and conservation equations for the perturbations at large scales are then solved analytically including neutrinos, in order to derive the magnetic Sachs Wolfe effect. Indeed, the presence of a non-zero anisotropic stress in the primordial fluid after neutrino decoupling strongly affects the scale-dependence of the magnetic Sachs Wolfe spectrum: this analysis confirms that it increases quadratically in the angular scale, as found in the latest numerical analyses. |
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lundi 28 juin 2010 - 11:00 Salle des séminaires Évry Schatzman Institut d'Astrophysique de Paris |
| Pages web du séminaire / Seminar's webpage |