## SCL Online Seminar by Andrea Richaud

You are cordially invited to the SCL online seminar of the Center for the Study of Complex Systems, which will be held on Thursday, 30 November 2023 at 14:00 on Zoom (the link is given below). The talk entitled

will be given by Dr. Andrea Richaud (Department of Physics, Polytechnic University of Catalunya, Barcelona, Spain). The abstract of the talk:

In quantum matter, vortices are topological excitations characterized by quantized circulation of the velocity field. They are often modeled as funnel-like holes around which the quantum fluid exhibits a swirling ﬂow. In this perspective, vortex cores are nothing more than empty regions where the superfluid density goes to zero. In the last few years, this simple view has been challenged and it is now increasingly clear that, in many real systems, vortex cores are not that empty. In these cases, the hole in the superfluid is filled by particles or excitations which thus dress the vortices and provide them with an effective inertial mass.

In this talk, we will discuss the dynamics of two-dimensional point vortices of one species that have small cores of a different species. We will show how to derive the relevant Lagrangian itself, based on the time-dependent variational method with a two-component Gross-Pitaevskii trial function. The resulting Lagrangian resembles that of charged particles in a static electromagnetic field, where the canonical momentum includes an electromagnetic term. We will also show some interesting dynamical regimes. The simplest example is a single vortex within a rigid circular boundary, where a massless vortex can only precess uniformly. In contrast, the presence of a small core mass can lead to small radial oscillations, which are, in turn, clear signatures of the associated inertial effect. Eventually, we will show that the non-zero effective mass of the vortex core can give place to two-vortex collisions leading to vortex/antivortex annihilation processes or to the stabilization of doubly charged vortices.

[1] A. Richaud, V. Penna, R. Mayol, and M. Guilleumas, Phys. Rev. A 101, 013630 (2020).

[2] A. Richaud, V. Penna, and A. L. Fetter, Phys. Rev. A 103, 023311 (2021).

[3] A. Richaud, G. Lamporesi, M. Capone, and A. Recati, Phys. Rev. A 107, 053317 (2023).

**Massive vortices in superfluids**will be given by Dr. Andrea Richaud (Department of Physics, Polytechnic University of Catalunya, Barcelona, Spain). The abstract of the talk:

In quantum matter, vortices are topological excitations characterized by quantized circulation of the velocity field. They are often modeled as funnel-like holes around which the quantum fluid exhibits a swirling ﬂow. In this perspective, vortex cores are nothing more than empty regions where the superfluid density goes to zero. In the last few years, this simple view has been challenged and it is now increasingly clear that, in many real systems, vortex cores are not that empty. In these cases, the hole in the superfluid is filled by particles or excitations which thus dress the vortices and provide them with an effective inertial mass.

In this talk, we will discuss the dynamics of two-dimensional point vortices of one species that have small cores of a different species. We will show how to derive the relevant Lagrangian itself, based on the time-dependent variational method with a two-component Gross-Pitaevskii trial function. The resulting Lagrangian resembles that of charged particles in a static electromagnetic field, where the canonical momentum includes an electromagnetic term. We will also show some interesting dynamical regimes. The simplest example is a single vortex within a rigid circular boundary, where a massless vortex can only precess uniformly. In contrast, the presence of a small core mass can lead to small radial oscillations, which are, in turn, clear signatures of the associated inertial effect. Eventually, we will show that the non-zero effective mass of the vortex core can give place to two-vortex collisions leading to vortex/antivortex annihilation processes or to the stabilization of doubly charged vortices.

[1] A. Richaud, V. Penna, R. Mayol, and M. Guilleumas, Phys. Rev. A 101, 013630 (2020).

[2] A. Richaud, V. Penna, and A. L. Fetter, Phys. Rev. A 103, 023311 (2021).

[3] A. Richaud, G. Lamporesi, M. Capone, and A. Recati, Phys. Rev. A 107, 053317 (2023).