Events of the Week

Soliton gases are infinite random ensembles of interacting solitons whose large-scale dynamics are governed by the elementary two-soliton collisions. By applying the spectral theory of soliton gases to the focusing nonlinear Schrödinger equation (fNLSE), we can describe the statistically stationary and spatially homogeneous integrable turbulence that emerges at large times from the spontaneous (noise-induced) modulational instability of the plane-wave and the elliptic “dn” solutions.

I will show that a special, critically dense soliton gas—the bound-state soliton condensate—provides an accurate model for the asymptotic state of both plane-wave and elliptic integrable turbulence. Moreover, certain statistical moments of the resulting turbulence can be computed analytically, allowing us to assess deviations from Gaussianity. These analytical predictions demonstrate excellent agreement with direct numerical simulations of the fNLSE.

The talk is based on the recent works:

“Statistics of Extreme Events in Integrable Turbulence”, T. Congy, G. A. El, G. Roberti, A. Tovbis, S. Randoux, and P. Suret, Phys. Rev. Lett. 132, 207201 (2024).

“Spontaneous modulational instability of elliptic periodic waves: The soliton condensate model”, D. S. Agafontsev, T. Congy, G. A. El, S. Randoux, G. Roberti, and P. Suret, Physica D 134956 (2025).

A permanent of a square matrix is exactly its determinant with all minus signs becoming plus. Despite the similarities, the computation of a determinant can be done in polynomial time, while that of a permanent is an NP-hard problem. In 2002, Laubenbacher and Swanson defined P_t(X) to be the ideal generated by all t-by-t subpermanents of X, and called it a permanental ideal. This is a counterpart of determinantal ideals, the center of many areas in Algebra and Geometry. We will discuss properties of P_2(X), including their Frobenius singularities over a field of prime characteristic, and related open questions.

The concept of integrable turbulence, introduced by Zakharov in 2009, provides a framework for describing random nonlinear dispersive waves governed by integrable equations, such as the Korteweg–de Vries (KdV) and the focusing nonlinear Schrödinger (fNLS) equations.

Within this framework, we focus on a specialized class of integrable turbulence dominated by solitons, known as a soliton gas, first introduced by Zakharov in 1971.

In recent years, there has been rapidly growing interest in soliton gas theory and its applications, as soliton gas dynamics have been shown to underpin a wide range of fundamental nonlinear wave phenomena, including modulational instability and the formation of rogue waves.

In this talk, we present recent results on one-dimensional soliton gases, with particular emphasis on the collision of monochromatic soliton gases, as well as recent extensions of the theory to two-dimensional soliton gases.

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