# Quasiparticle disintegration in fermionic superfluids

### Submission summary

 As Contributors: Senne Van Loon Arxiv Link: https://arxiv.org/abs/2111.04692v2 (pdf) Code repository: https://github.com/hkurkjian/CodeArXiv_2111_04692 Date accepted: 2022-02-14 Date submitted: 2022-01-20 15:43 Submitted by: Van Loon, Senne Submitted to: SciPost Physics Academic field: Physics Specialties: Atomic, Molecular and Optical Physics - Theory Approach: Theoretical

### Abstract

We study the fermionic quasiparticle spectrum in a zero-temperature superfluid Fermi gas, and in particular how it is modified by different disintegration processes. On top of the disintegration by emission of a collective boson ($1\to2$, subject of a previous study, PRL 124, 073404), we consider here disintegration events where three quasiparticles are emitted ($1\to3$). We show that both disintegration processes are described by a $t$-matrix self-energy (as well as some highly off-resonant vacuum processes), and we characterize the associated disintegration continua. At strong coupling, we show that the quasiparticle spectrum is heavily distorted near the $1\to3$ disintegration threshold. Near the dispersion minimum, where the quasiparticles remain well-defined, the main effect of the off-shell disintegration processes is to shift the location of the minimum by a value that corresponds to the Hartree shift in the BCS limit. With our approximation of the self-energy, the correction to the energy gap with respect to the mean-field result however remains small, in contrast with experimental measurements.

Published as SciPost Phys. 12, 108 (2022)

### List of changes

*Added a discussion on the equation of state and how to relate $\mu/\Delta$ to the coupling $1/k_F a$.
*Added a discussion on possible higher-order processes contributing to the quasiparticle spectrum .
*Clarified that all numerical results make use of the full self-energy, valid for all couplings.
*Clarified why we expect to find a reduction of the corrected gap in the BCS limit, and how to include corrections similar to those predicted by Gor'kov and Melik-Barkhudarov.
*Rewrote the conclusion to reflect the fact that our predictions are experimentally verifiable, and to clarify the connection with superconductors.

### Submission & Refereeing History

#### Published as SciPost Phys. 12, 108 (2022)

Resubmission 2111.04692v2 on 20 January 2022
Submission 2111.04692v1 on 9 November 2021

## Reports on this Submission

### Report

The authors have addressed satisfactorily my remarks; I now fully support publication of the present manuscript on SciPost.

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### Report

The authors modified the manuscript, replying in a very satisfactory way to my remarks in my original referee report. It is therefore my pleasure to recommend the manuscript for publication in SciPost.

• validity: -
• significance: -
• originality: -
• clarity: -
• formatting: -
• grammar: -