Influence of heavy modes on perturbations in multiple field inflation

Abstract

Abstract.We investigate linear cosmological perturbations in multiple field inflationary models where some of the directions are light while others are heavy (with respect to the Hubble parameter). By integrating out the massive degrees of freedom, we determine the multi-dimensional effective theory for the light degrees of freedom and give explicitly the propagation matrix that replaces the effective sound speed of the one-dimensional case. We then examine in detail the consequences of a sudden turn along the inflationary trajectory, in particular the possible breakdown of the low energy effective theory in case the heavy modes are excited. Resorting to a new basis in field space, instead of the usual adiabatic/entropic basis, we study the evolution of the perturbations during the turn. In particular, we compute the power spectrum and compare with the result obtained from the low energy effective theory.

Effective field theory during inflation. II. Stochastic dynamics and power spectrum suppression

“…Furthermore, there is no natural choice of the initial density matrices for the system or environmental fields, therefore to exhibit the main physical consequences of tracing over the environmental degrees of freedom in the simplest setting we choose 31) namely both fields are in their respective Bunch-Davies vacua. This condition can be generalized straightforwardly.…”

“…[28][29][30][31][32], however we emphasize that to next to leading order in 1/µ there emerge dissipative effects described by F D in (4.20) which are not captured by the treatments in these references since this term emerges from the time evolution of the density matrix and is not available from the simple path integral formulation in refs. [28][29][30][31][32].…”

Searching for primordial localized features with CMB and LSS spectra

“…This motivates a search for such kind of features produced by inflationary scenarios beyond canonical single field. 1 Several mechanisms that produce oscillatory features have been realized, such as a transient reduction in the speed of sound [4][5][6], step inflaton potential , different initial vacuum states [28][29][30][31], multifield dynamics [32][33][34][35][36][37], or phenomenological superimposed oscillations in the primordial power spectrum [38][39][40][41][42][43][44][45][46]. In this work we focus on searching for oscillatory features in the scenario of a transient reduction in the speed of sound.…”

Multi-field inflation and cosmological perturbations

“…Thus, regarding heaviness (or lightness) of the relevant degrees of freedom, it is most convenient to adopt another set of basis in which the mass matrix V IJ becomes diagonal. We may call this as the "mass basis" [29]. Then the two eigenvalues of the mass basis correspond to the light and heavy masses along the trajectory respectively.…”