Speaker
Description
Self-bound quantum droplets appear in various physical contexts, ranging from cold atomic gases to QCD matter such as those found in neutron stars. In this presentation, we discuss a universal effective field theory that describes the low-energy dynamics of small-amplitude surface oscillations in such diverse quantum droplets, independent of their microscopic binding mechanisms [1].
Focusing specifically on superfluid droplets, we perform our analysis by explicitly coupling the degrees of freedom of internal bulk gapless phonons to surface deformations under a fixed particle-number constraint. By deriving the effective action, we determine the normal-mode eigenfrequencies $\omega_\ell$ for each angular momentum quantum number $\ell$. We demonstrate that these frequencies depend on a single dimensionless parameter measuring the ratio of surface tension to bulk compressibility energy. Furthermore, we identify a critical value of this parameter at which the breathing mode ($\ell = 0$) becomes mechanically unstable, and we discuss the canonical quantization of these surface modes into ripplons in the low-energy regime.
A key advantage of this framework is its universality. The resulting description applies to the surface dynamics of generic nonrelativistic superfluids with a free interface, without relying on specific microscopic details. Consequently, this universal theory provides a robust theoretical foundation that is highly applicable to self-bound systems of dense QCD matter.
Refference
1. J. Mitsuhashi, K. Fujii, and M. Hongo, Effective theory of surface oscillations in self-bound superfluid droplets, Phys. Rev. A 114, 013303 (2026).