Oscillons are mathematical curiosities: they are waves, but waves that “jog on the spot” rather than travelling through a medium. They only exist in materials that respond nonlinearly to stretching (and with a specific kind of nonlinearity) but it turns out that many proposed models of the very early universe have just the properties needed for oscillons to form. Consequently, during the first trillionth of a second after the Big Bang the universe may pass through a phase in which most of the material within it consists of oscillons.
Not only that, gravitational forces would cause oscillons to fall towards each other, forming clouds of oscillons millions of times smaller and much heavier than present-day atoms. This is hypothetical (nobody has shown it will definitely happen, but it is a strong possibility) but oscillons in these clouds may interact with one another.
However, interactions between “wild” oscillons have never been studied in detail – that is, between oscillons that might actually form in the early universe, rather than idealised and highly symmetrical configurations. Not only that, previous studies have mostly looked at oscillons moving at a large fraction of the speed of light but actual collisions are likely to happen at much lower speeds.
So, in this paper we take a first look at realistic (or at least semi-realistic!) oscillon interactions. Existing studies tell us that interacting oscillons will merge or bounce, depending on whether they are “in-step” or “out-of-step” when they meet. However, because each oscillon jogs at its own speed they change from being being in step and out of step as they move, so these interactions have a rich range of possible outcomes.
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.
- Xue, Chen, Verzyde, Hayman and Easther
- Realistic Oscillon Interactions
- ArXiV:2510.01597
Simulations
You can see oscillon interactions in the simulations below; we are showing 2D slices through a 3D simulation – the vertical direction corresponds to the value of a fundamental field (the “inflaton”) in the early universe. Because we are interested in realistic interactions the oscillons move slowly relative to their internal frequency.
The video below shows a merger, followed by a “ringdown” (see Figure 9 in paper). Waves emitted during the ringdown carry energy away from the combined oscillon,allowing it to settle into a more symmetrical configuration.
Conversely, this video shows a bounce (see Figure 10 in paper). The two oscillons are the same as in the video above but they approach each other at a slightly different speed, leading to the opposite outcome.