Cosmic structure formation in Hybrid Inflation models

Abstract

A wide class of inflationary models, known as Hybrid Inflation models, may produce topological defects during a phase transition at the end of the inflationary epoch. We point out that, if the energy scale of these defects is close to that of Grand Unification, then their effect on cosmic structure formation and the generation of microwave background anisotropies cannot be ignored. Therefore, it is possible for structure to be seeded by a combination of the adiabatic perturbations produced during inflation and active isocurvature perturbations produced by defects. Since the two mechanisms are uncorrelated the power spectra can be computed by a weighted average of the individual contributions. We investigate the possible observational consequences of this with reference to general Hybrid Inflation models and also a specific model based on Supergravity. These mixed perturbation scenarios have some novel observational consequences and these are discussed qualitatively.

Figures (14)

• Figure 1: The effective spectral index as function of the comoving scale during inflation for $\kappa=0.08$ (solid line), $\kappa=0.1$ (dotted line), $\kappa=0.12$ (short dash line), $\kappa=0.13$ (long dash line) $\kappa=0.14$ (dot-short dash line) and $\kappa=0.15$ (dot-long dash line).
• Figure 2: On the left the angular power spectrum of CMB anisotropies and on the right the power spectrum of fluctuations in the CDM for the Linde-Riotto model without a string induced component, using the standard cosmological parameters and $\kappa=0.08$ (solid line), $\kappa=0.1$ (dotted line), $\kappa=0.12$ (short dash line), $\kappa=0.13$ (long dash line), $\kappa=0.14$ (dot-short dash line) and $\kappa=0.15$ (dot-long dash line). In both cases the current observational data points are also included to guide the eye. Notice that the CMB anisotropies for $\kappa=0.15$ are wildly at odds with the observations at all scales and that even the models with smaller values of $\kappa$ are clearly at odds with the amplitude and shape of the observed matter power spectrum.
• Figure 3: On the left the angular power spectrum of CMB anisotropies and on the right the power spectrum of fluctuations in the CDM for the standard scaling source (solid line) and the standard string model (dotted line). In both cases the standard cosmological parameters have been used. The current observational data points and the equivalent spectra for the standard CDM scenario (short dash line) are also included to guide the eye.
• Figure 4: On the left the angular power spectrum of CMB anisotropies and on the right the power spectrum of fluctuations in the CDM for the standard CDM scenario mixed with standard scaling source using a ratio of $\alpha=1.0$ (solid line), $\alpha=0.75$ (short dash line), $\alpha=0.5$ (long dash line), $\alpha=0.25$ (short dash-dotted line) and $\alpha=0.0$ (dotted line).
• Figure 5: On the left the angular power spectrum of CMB anisotropies and on the right the power spectrum of fluctuations in the CDM for the standard CDM scenario mixed with standard string source using a ratio of $\alpha=1.0$ (solid line), $\alpha=0.75$ (short dash line), $\alpha=0.5$ (long dash line), $\alpha=0.25$ (short dash-dotted line) and $\alpha=0.0$ (dotted line).