Realistic Oscillon Interactions

TL;DR

The paper investigates how long-lived oscillon configurations interact with each other and their environment in a post-inflationary universe, using realistic oscillons extracted from simulations with a generalized monodromy potential. It advances a practical approach by boosting selected oscillons toward each other to study non-relativistic collisions in a fixed background, including background waves, while tracking phase dependence. The key findings show phase-controlled mergers and bounces for identical oscillons, and effectively stochastic outcomes for mismatched wild oscillons due to their distinct internal frequencies, with drag effects from background waves influencing trajectories. This framework enables quantitative exploration of oscillon dynamics in cosmology, with implications for oscillon-dominated eras, gravitational waves, and reheating after inflation.

Abstract

Oscillons are long-lived nonlinear pseudo-solitonic configurations of scalar fields and many plausible inflationary scenarios predict an oscillon-dominated phase in the early universe. Many possible aspects of this phase remain unexplored, particularly oscillon-oscillon interactions and interactions between oscillons and their environment. However the primary long range forces between oscillons are gravitational and thus slow-acting relative to the intrinsic timescales of the oscillons themselves. Given that simulations with local gravity are computationally expensive we explore these effects by extracting individual specimens from simulations and then engineering interactions. We find that oscillons experience friction when moving in an inhomogeneous background and, because oscillons in non-relativistic collisions bounce or merge as a function of their relative phases, the outcomes of interactions between ``wild'' oscillons depend on their specific trajectories.

Figures (11)

• Figure 1: The relative energy density, $\rho/\rho_\text{av}$, is plotted for $(\alpha,\beta)=(0.5,50)$ at $2.37$ e-folds into the simulation, showing a healthy population of oscillons.
• Figure 2: A slice showing the relative energy density $\rho/\rho_\text{av}$ from the plot in Figure \ref{['fig:universe']} with labeled oscillons. The 0th oscillon spans all corners of the grid due to the periodic boundary condition. The blue contour marks the $\rho/\rho_{\textrm{av}}=4$ threshold.
• Figure 3: (Top) A slice of through an oscillon from a simulation with $\alpha=0.05$, $\beta=25$ at 1.69 e-folds. The blue contour outlines the initial mask; the green contour shows the full extracted region. (Bottom) The same configuration on a $128^3$ grid with the fluctuations blurred.
• Figure 4: The center of energy speeds of oscillons that were given desired boosts of $v_x\sim0.02c$ and $v_y\sim v_x\sim0$. Each oscillon is extracted from different simulated universes and made to evolve in an empty and non-expanding universe.
• Figure 5: An isolated oscillon subject to an incoming planar wave $(\alpha,\beta)=(0.5,50)$. Top is a linear scale to see the oscillon in detail, while bottom is the same plot in a logarithmic scale to bring out the background radiation.