Charge separation in Reheating after Cosmological Inflation (1108.0541v3)

Abstract: New aspects of parametrically resonant heating of a relativistic scalar O(2)-symmetric self-interacting field are presented. This process is a candidate for reheating at the end of the early-universe epoch of inflation. Although a model with a fully O(2)-symmetric ground state is used, transient, metastable spontaneous symmetry breaking can be observed. This manifests itself in the form of persistent regimes of opposite and, inside these, uniform charge overdensities separated by thin lines and walls similar to topological defects, in two and three spatial dimensions, respectively. The configuration is found to correspond to an attractive non-equilibrium fixed point of the underlying dynamic equations which prevents thermalisation over an extended period of time.

• The paper finds that a relativistic scalar field can form metastable charge overdensities segregated by walls during reheating, persisting through non-thermal fixed points.
• Leveraging classical field simulations and 2PI effective action theory, the research links wave turbulence to quasi-topological defects in scalar field dynamics before thermalization.
• Numerical simulations reveal charge separation correlates with non-thermal IR scaling ($\\kappa^{\\mathrm{IR}} = d+1$) and transitions to UV weak-wave turbulence scaling ($\\kappa \\simeq 1.5$ in d=3) before thermal equilibrium.

Charge Separation in Reheating After Cosmological Inflation

The paper "Charge Separation in Reheating After Cosmological Inflation" examines the intricate dynamics of a relativistic scalar $O(2)$-symmetric field, specifically in the context of its role in reheating the universe post-cosmological inflation. The authors, Gasenzer, Nowak, and Sexty, present a thorough exploration of the processes that pertain to parametrically resonant heating, leveraging both classical and quantum field theoretical frameworks to elucidate the interactions and transformations within the scalar field dynamics.

Summary of Findings

Metastable Charge States: The authors explore a scenario often posed in cosmological reheating where a self-interacting scalar field can, under specified conditions, lead to parametrically resonant amplification of fluctuations. This field, despite an overall symmetric ground state, can briefly exhibit spontaneous, metastable symmetry breaking. The research highlights that transient configurations emerge as charge overdensities which are stably segregated by thin lines or walls, reminiscent of topological defects in spatial dimensions two and three. This charge separation persists through non-thermal fixed points, which temper the system’s thermalization process.

Wave-Turbulence Connection: A significant contribution of this paper is linking the behavior of wave turbulence to quasi-topological defects during inflaton dynamics. The authors apply a formalism that combines classical field simulations with dynamic equations from two-particle irreducible (2PI) effective action theory, enabling them to navigate into the nonperturbative regime. This approach successfully delineates the metamorphosis from early amplification of modes to the gradual energy dispersion across the spectrum, capturing turbulent phases before eventual thermal relaxation.

Numerical Results

Through numerical lattice simulations, strong correlation between charge separation and both infrared and ultraviolet scaling exponents are observed. Specifically:

• IR Turbulence: The paper documents a dominant infrared scaling behavior with exponents $\kappa^\mathrm{IR} = d+1$, attributed to non-thermal fixed points.
• UV Behaviors: At larger wave numbers, the distribution transitions towards thermal equilibrium, with scaling reflecting weak-wave turbulence models. In $d = 3$ space, the simulations identify a UV weak-wave turbulence scaling exponent aligning with theoretical expectations, $\kappa \simeq 1.5$.

Theoretical and Practical Implications

The results outlined indicate significant implications for cosmic field configurations post-inflation, suggesting a temporary formation of charged domains in a universe where no symmetry breaking is apparent initially in the Lagrangian framework. This holds potential ramifications for understanding of early universe dynamics and might illuminate mechanisms akin to the Affleck-Dine baryogenesis, albeit under different symmetry and field configurations.

On a theoretical level, these findings encourage deeper exploration into non-thermal dynamic phenomena which parallel critical behaviors usually identified far from equilibrium. The manifestations of stable soliton-like structures within a QFT landscape necessitate new tools and strategies for handling similar complex dynamics in cosmological models that incorporate scalar fields.

Future Directions

The link between wave-turbulence phenomena and charge pattern formations posits intriguing questions for future investigation. Expanding this analysis to more complex frameworks, such as incorporating gauge symmetries or extending the model to realistic inflaton contexts, could unearth further transformative dynamics. Moreover, the insights provided could ultimately shape the understanding of particle creation and energy distribution post-inflation, influencing observational predictions relevant to cosmic microwave background radiation or big bang nucleosynthesis.

The paper delivers a comprehensive treatment of fields during reheating, paving pathways for more nuanced scrutiny into the non-equilibrium dynamics that influenced the universe's thermal history.