Theory and Numerics of Gravitational Waves from Preheating after Inflation (0707.0875v2)

Abstract: Preheating after inflation involves large, time-dependent field inhomogeneities, which act as a classical source of gravitational radiation. The resulting spectrum might be probed by direct detection experiments if inflation occurs at a low enough energy scale. In this paper, we develop a theory and algorithm to calculate, analytically and numerically, the spectrum of energy density in gravitational waves produced from an inhomogeneous background of stochastic scalar fields in an expanding universe. We derive some generic analytical results for the emission of gravity waves by stochastic media of random fields, which can test the validity/accuracy of numerical calculations. We contrast our method with other numerical methods in the literature, and then we apply it to preheating after chaotic inflation. In this case, we are able to check analytically our numerical results, which differ significantly from previous works. We discuss how the gravity wave spectrum builds up with time and find that the amplitude and the frequency of its peak depend in a relatively simple way on the characteristic spatial scale amplified during preheating. We then estimate the peak frequency and amplitude of the spectrum produced in two models of preheating after hybrid inflation, which for some parameters may be relevant for gravity wave interferometric experiments.

• The paper introduces a novel analytical and numerical framework for calculating the gravitational wave spectrum from preheating after inflation.
• It reveals that the amplitude and frequency of the spectrum peak are sensitive to the scale enhancements during the bubbly stage of scalar field dynamics.
• The refined method challenges previous estimates and holds practical implications for gravitational wave experiments like LIGO/VIRGO in low-energy inflation scenarios.

Analysis of Gravitational Wave Production from Preheating after Inflation

The paper by Dufaux et al. addresses the production of gravitational waves (GWs) during the preheating phase following cosmological inflation. Preheating is characterized by complex, time-dependent field inhomogeneities that act as a source of gravitational radiation. This work introduces a theoretical framework and numerical algorithm for assessing the spectrum of gravitational waves arising from these inhomogeneities within an expanding universe.

The authors develop a method to calculate gravitational wave energy density both analytically and numerically. They contrast their approach with existing numerical methods, highlighting significant differences in the results, particularly in the context of chaotic inflation scenarios. The amplitude and frequency of the gravitational wave spectrum’s peak are found to depend on the characteristics of the spatial scales enhanced during preheating.

The paper makes several key contributions to the paper of gravitational waves from preheating:

1. Analytical and Numerical Framework: The authors derive general analytical results for gravitational wave emission from stochastic fields and propose a new numerical method. They point out discrepancies with previous literature, emphasizing the rigorous checks against analytical predictions.
2. Practical Implications: The gravitational wave spectrum peaks calculated in this paper could hold significance for interferometric gravitational wave experiments like LIGO/VIRGO, provided inflation occurs at sufficiently low energy scales.
3. Comparison with Previous Methods: Unlike prior studies that may overestimate gravitational wave production due to methodological limitations, this paper ensures that calculations cover the entire evolution of gravitational waves. This comprehensive approach offers a more precise determination of gravitational wave characteristics.
4. Parameter Dependence and Models: The paper explores different parametrizations in chaotic and hybrid inflation models, demonstrating varying gravitational wave spectrum shapes. This reflects the sensitivity of gravitational wave characteristics to inflationary model parameters.
5. Role of Stages in Scalar Field Dynamics: The authors investigate the contributions of different stages in scalar field dynamics to gravitational wave production, highlighting the significant increase in gravitational wave energy density during the "bubbly" stage of preheating.

In contemplating future developments, the paper suggests improved sensitivity and range of gravitational wave detectors could enable experimental validation of gravitational wave spectra predicted by such inflationary scenarios. Enhanced computational modeling may also refine predictions and address more complex scenarios, including multifield and gauge field interactions. These advancements anticipate a broader understanding of the early universe and the role of gravitational waves as a probe into high-energy physics occurring during and after inflation.

In conclusion, this research provides a comprehensive analysis of gravitational wave production during preheating, offering a robust framework that challenges and refines prior methods. It extends the potential for direct detection of these phenomena and deepens our theoretical grasp of early universe cosmology.