New Constraints on Inflation from the WMAP data
1er juillet 2006
Current theories of the early universe include a period of inflation, just after the Big Bang, where the characteristic scale of the universe increases by 60 orders of magnitude in less than one second. Recently, an international team including researchers from Paris Observatory, has proposed to interprete inflation models by considering them in the framework of superconductivity, critical phenomena and phase transitions. In this new approach, the precise form of the inflationary potential is constructed from the WMAP data, and predictions are made for the inflation model which best fits the present data.
Inflation has been proposed more than 25yrs ago to solve the problem of flatness and the horizon, problem, among others ; i.e. to explain why regions in the sky much more distant than a light path from the Big-Bang (the horizon size) are observed with exactly the same radiation temperature. These regions apparently should not be connected, and paradoxically they are homogeneous. Inflation assumes they come from the same causally connected region, which has been inflated considerably. What produces inflation ? The hypothesis of Grand Unification Theory (GUT) accounts for that. GUT unifies the strong interaction with the weak and electromagnetic interaction. This unification should occur at temperatures of T= 1029K, only available in the early universe. Above and around this temperature, particles are submitted only to the unified force, and when the universe cools down below this, the symmetry between the forces is broken, producing a phase transition, which releases a gigantic energy. This formidable energy would drive the inflation. Inflation provides a generic mechanism for generating scalar (density) and tensor (gravitational wave) perturbations. A characteristic aspect of inflationary perturbations is that these are generated by quantum fluctuations. After their wavelength becomes larger than the Hubble radius (the horizon), these fluctuations are amplified and grow, becoming classical and decoupling from causal microphysical processes. Upon re-entering the horizon during the matter era, these classical perturbations seed the inhomogeneities which generate the cosmological structures upon gravitational collapse. Inflation predicts fairly generic features : a gaussian and nearly scale invariant spectrum of (mostly) adiabatic scalar and tensor primordial fluctuations. This spectrum is perfectly compatible with the highly precise wealth of data provided by the Wilkinson Microwave Anisotropy Probe (WMAP). Simple inflation is described by a scalar field (the inflaton) which drives the dynamics of the scale factor of the expanding universe, plus small quantum fluctuations. In WMAP data, departures from scale invariance and gaussianity are determined by the departures from flatness of the potential, which can be measured by its derivatives. These derivatives can be combined into a hierarchy of dimensionless slow varying parameters. Figure 1 : Predictions for r (the ratio of gravitational waves to density perturbations) as a function of the spectral scalar index ns for different values of the asymmetry |h| of the potential. A maximun value of ns is found : nsmax = 0.961528 and the corresponding r is r max = 0.114769. The absolute maximun value of r is r absolute-max = 0.16 and corresponds to a purely quadratic potential. For ns = 0.95 (present central observed value), 0.03 < r
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http://www.obspm.fr/cgi-bin/whereis?=sanchez+N] (Observatoire de Paris, LERMA, et CNRS)
Dernière modification le 4 mars 2013