Hydrodynamic and Rayleigh-Plateau instabilities of Q-strings

As analogues of compact objects, solitons have attracted significant attention. We reveal that cylindrical Q-strings exhibit a dynamical instability to perturbations with wavelengths exceeding a threshold $\lambda>\lambda_{c}$. This instability can destroy the invariance in the cylindrical direction, as a generation mechanism for Q-balls, similar to the formation of droplets. As the interface of Q-strings approaches a thin wall, this long-wavelength instability degenerates into the Rayleigh-Plateau instability with a threshold related only to the geometric radius $\lambda_{c}=2\pi R$. Such results indicate that Q-strings, like black strings, resemble low-viscosity fluids with surface tension.