Preinflationary primordial perturbations

Primordial perturbations from inflation

I review the standard analysis of adiabatic scalar and tensor perturbations produced by slow-roll inflation driven by a single scalar field, before going on to discuss recent work on the role of non-adiabatic modes during and after inflation. Isocurvature perturbations correlated with adiabatic modes may be produced during multi-field inflation and would give valuable information about the phys...

Classicality of the primordial perturbations

The promotion of cosmology from an area of speculation to an area of observation and measurement is one of the most remarkable developments in the history of human knowledge. Starting at an ‘initial’ temperature of a few MeV, the observable Universe is understood in considerable detail (we are setting ~ = c = kB = 1). At the initial epoch the expanding Universe is an almost isotropic and homoge...

Primordial magnetic fields from metric perturbations

We study the amplification of electromagnetic vacuum fluctuations induced by the evolution of scalar metric perturbations at the end of inflation. Such perturbations break the conformal invariance of Maxwell equations in Friedmann-Robertson-Walker backgrounds and allow the growth of magnetic fields on super-Hubble scales. We relate the strength of the fields generated by this mechanism with the...

A natural origin of primordial density perturbations

We suggest here a mechanism for the seeding of the primordial density fluctuations. We point out that a process like reheating at the end of inflation will inevitably generate perturbations, even on superhorizon scales, by the local diffusion of energy. Provided that the reheating temperature is of order the GUT scale, the density contrast δR for spheres of radius R will be of order 10 −5 at ho...

Lecture XXXVIII: Primordial perturbations: tensor sector