We explore preheating in multi-field models of inflation in which the field-space metric is a highly curved hyperbolic manifold. One broad family of such models is called alpha-attractors, whose... Show moreWe explore preheating in multi-field models of inflation in which the field-space metric is a highly curved hyperbolic manifold. One broad family of such models is called alpha-attractors, whose single-field regimes have been extensively studied in the context of inflation and supergravity. We focus on a simple two-field generalization of the T-model, which has received renewed attention in the literature. Krajewski et al. concluded, using lattice simulations, that multi-field effects can dramatically speed-up preheating. We recover their results and further demonstrate that significant analytical progress can be made for preheating in these models using the WKB approximation and Floquet analysis. We find a simple scaling behavior of the Floquet exponents for large values of the field-space curvature, that enables a quick estimation of the T-model reheating efficiency for any large value of the field-space curvature. In this regime we further observe and explain universal preheating features that arise for different values of the potential steepness. In general preheating is faster for larger negative values of the field-space curvature and steeper potentials. For very highly curved field-space manifolds preheating is essentially instantaneous. Show less
SU(2) gauge fields can generate large gravitational waves during inflation, if they are coupled to an axion which can be either the inflaton or a spectator field. The shape of the produced tensor... Show moreSU(2) gauge fields can generate large gravitational waves during inflation, if they are coupled to an axion which can be either the inflaton or a spectator field. The shape of the produced tensor power spectrum h depends on the form of the axion potential. We derive analytic expressions and provide general templates for h for various types of the spectator axion potential. Furthermore, we explore the detectability of the oscillatory feature, which is present in h in the case of an axion monodromy model, by possible future CMB B-mode polarization observations. Show less
Benevento, G.; Raveri, M.; Lazanu, A.; Bartolo, N.; Liguori, M.; Brax, P.; Valageas, P. 2019
