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Register a new userThe Cosmological Moduli Problem and Preheating
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G.F. Giudice
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Many models of supersymmetry breaking, in the context of either supergravity or superstring theories, predict the presence of particles with Planck-suppressed couplings and masses around the weak scale. These particles are generically called moduli. The excessive production of moduli in the early Universe jeopardizes the successful predictions of nucleosynthesis. In this paper we show that the efficient generation of these dangerous relics is an unescapable consequence of a wide variety of inflationary models which have a preheating stage. Moduli are generated as coherent states in a novel way which differs from the usual production mechanism during parametric resonance. The corresponding limits on the reheating temperature are often very tight and more severe than the bound of 10^9 GeV coming from the production of moduli via thermal scatterings during reheating.
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This contribution to the proceedings collects new recent results on preheating after inflation. We discuss tachyonic preheating in the SUSY motivated hybrid inflation; development of equilibrium after preheating; theory of fermionic preheating and the problem of gravitino overproduction from preheating.
As a model-independent generic feature of string moduli, we find that their derivative interactions make them decay into (pseudo) Nambu-Goldstone bosons (NGBs) without suppression by the mass of decay products. Combining this feature with the fact that moduli decay well after spontaneous electroweak symmetry breaking, we show that the decay into the longitudinal weak gauge bosons is generally dominant, recovering the standard hot big bang universe. Further, interestingly, as a natural consequence of non-suppression of axionic decay modes, an observable amount of dark radiation is expected in any extension of the Standard Model that includes a cosmologically stable NGB such as the QCD axion. In such extensions, the fermionic superpartner of the NGB can also contribute to the dark matter as a feebly interacting massive particle.
Light fields with spatially varying backgrounds can modulate cosmic preheating, and imprint the nonlinear effects of preheating dynamics at tiny scales on large scale fluctuations. This provides us a unique probe into the preheating era which we dub the cosmic microscope. We identify a distinctive effect of preheating on scalar perturbations that turns the Gaussian primordial fluctuations of a light scalar field into square waves, like a diode. The effect manifests itself as local non-Gaussianity. We present a model, modulated partial preheating, where this nonlinear effect is consistent with current observations and can be reached by near future cosmic probes.
We investigate the effects of bosonic trilinear interactions in preheating after chaotic inflation. A trilinear interaction term allows for the complete decay of the massive inflaton particles, which is necessary for the transition to radiation domination. We found that typically the trilinear term is subdominant during early stages of preheating, but it actually amplifies parametric resonance driven by the four-legs interaction. In cases where the trilinear term does dominate during preheating, the process occurs through periodic tachyonic amplifications with resonance effects, which is so effective that preheating completes within a few inflaton oscillations. We develop an analytic theory of this process, which we call tachyonic resonance. We also study numerically the influence of trilinear interactions on the dynamics after preheating. The trilinear term eventually comes to dominate after preheating, leading to faster rescattering and thermalization than could occur without it. Finally, we investigate the role of non-renormalizable interaction terms during preheating. We find that if they are present they generally dominate (while still in a controllable regime) in chaotic inflation models. Preheating due to these terms proceeds through a modified form of tachyonic resonance.
Several mechanisms exist for generating a stochastic background of gravitational waves in the period following inflation. These mechanisms are generally classical in nature, with the gravitational waves being produced from inhomogeneities in the fields that populate the early universe and not quantum fluctuations. The resulting stochastic background could be accessible to next generation gravitational wave detectors. We develop a framework for computing such a background analytically and computationally. As an application of our framework, we consider the stochastic background of gravitational waves generated in a simple model of preheating.
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