Quasi-Single Field Inflation with Large Mass (1205.0160v2)

Abstract: We study the effect of massive isocurvaton on density perturbations in quasi-single field inflation models, when the mass of the isocurvaton M becomes larger than the order of the Hubble parameter H. We analytically compute the correction to the power spectrum, leading order in coupling but exact for all values of mass. This verifies the previous numerical results for the range 0<M<3H/2 and shows that, in the large mass limit, the correction is of order H^2/M^2.

Overview of Quasi-Single Field Inflation with Large Mass

The paper under review investigates quasi-single field inflation characterized by massive fields, specifically isocurvatons, whose masses exceed the Hubble parameter during inflation ($M > H$). This work operates within the framework of effective field theory where the inflaton moves through a complex field landscape, incorporating the dynamical effects of isocurvatons orthogonal to the inflaton trajectory. By meticulously examining these massive isocurvatons' influence on inflation, the authors provide an analytical computation of corrections to the power spectrum, establishing a relation of order $H^2/M^2$ in the large mass limit.

In the context of string theory and supergravity models, massive fields naturally emerge during inflation. The paper attempts to elucidate how these fields, particularly when their mass is significantly greater than the Hubble parameter, effectively decouple from the inflationary dynamics, an aspect addressed by previous numerical studies only for masses $0 < M < 3H/2$. Here, the authors extend this analysis by providing exact results valid for all mass values, confirmed through analytical methods for the specified model.

Key Findings

• The paper derives two main contributions to the power spectrum correction: both contributions are analyzed using the in-in formalism.
• The authors compare the analytical results for $M/H < 3/2$ with existing numerical findings, demonstrating consistency while deriving results beyond this range.
• In the large mass limit, a power-law suppression dominates, specifically $H^2/(4M^2)$, deviating from the intuitive exponential suppression akin to thermal field theory predictions.
• The authors differentiate between contributions with and without time-ordering and their respective impacts on the power spectrum, discovering the interplay between Boltzmann-like and power-law suppressed terms.

Implications and Further Directions

By closing the gap between semi-classical approximations and precise analytical results, this work offers detailed insights into the decoupling mechanism of massive fields during inflation. These findings have profound implications for understanding corrections to primordial density fluctuations and open avenues for explaining observations from cosmic microwave background studies and large-scale structures.

Future research could focus on extending this framework to more complex multi-field scenarios or incorporating varying mass scales and coupling constants to further understand their phenomenological impacts, especially in non-static or dynamically evolving inflationary models. Additionally, exploring the interplay between massive isocurvatons and non-Gaussianities could offer deeper insights into the early universe's perturbation structures.

Such comprehensive analytical approaches form essential building blocks in cosmology, supporting theoretical predictions with rigorous proof and contributing to the broader understanding of field dynamics during inflation. As researchers integrate these analytical tools into more advanced models, they can anticipate numerous fruitful explorations within theoretical and observational cosmology.