Publications

Order by: publication date number of citations

• Engaging with the State. Illegalized migrants, welfare institutions and the law in French-Speaking Belgium

  Sophie Andreetta

  Mig. Pol. 1, 001 (2022) · published 21 March 2022 | Toggle abstract · pdf

  By highlighting informal strategies and solidarities on the one hand, and protests on the other, current studies of citizenship and illegalized migration describe two main forms of political subjectivities among illegalized migrants: ‘without’ the state or ‘against’ it. In contrast, this article unpacks how migrants make use of state laws and institutions, voice expectations, and pursue their claims using official venues – in short, how they act ‘with’ the state. It builds on ethnographic fieldwork on illegalized migrants’ welfare requests in French-speaking Belgium and the various sets of actors involved in assessing or furthering their cases. Migrants’ discourses and expectations of the welfare office provide insights into their understandings of the state, highlight the crucial role of immigration lawyers in brokering cases, and ultimately allow for a more nuanced reading of the idea that welfare dependency leads to deportability. On a theoretical level, this article contributes to ongoing debates both in the study of statehood and in migration studies, showing how procedural fairness can be a central aspect of – in this case – migrants’ relationship to and expectations of the state, and how migrants’ strategies and practices of inclusion can also be formal ones, based on existing state laws and institutions.

  3 citations

• Replica method for eigenvalues of real Wishart product matrices

  Jacob A. Zavatone-Veth, Cengiz Pehlevan

  SciPost Phys. Core 6, 026 (2023) · published 5 April 2023 | Toggle abstract · pdf

  We show how the replica method can be used to compute the asymptotic eigenvalue spectrum of a real Wishart product matrix. For unstructured factors, this provides a compact, elementary derivation of a polynomial condition on the Stieltjes transform first proved by Müller [IEEE Trans. Inf. Theory. 48, 2086-2091 (2002)]. We then show how this computation can be extended to ensembles where the factors are drawn from matrix Gaussian distributions with general correlation structure. For both unstructured and structured ensembles, we derive polynomial conditions on the average values of the minimum and maximum eigenvalues, which in the unstructured case match the results obtained by Akemann, Ipsen, and Kieburg [Phys. Rev. E 88, 052118 (2013)] for the complex Wishart product ensemble.

  3 citations

• Rapidity distribution within the defocusing non-linear Schrödinger equation model

  Yasser Bezzaz, Léa Dubois, Isabelle Bouchoule

  SciPost Phys. Core 6, 064 (2023) · published 26 September 2023 | Toggle abstract · pdf

  We consider the classical field integrable system whose evolution equation is the nonlinear Schrödinger equation with defocusing non-linearities, which is the classical limit of the quantum Lieb-Liniger model. We propose a simple derivation of the relation between two sets of conserved quantities: on the one hand the trace of the monodromy matrix, parameterized by the spectral parameter and introduced in the inverse-scattering framework, and on the other hand the rapidity distribution, a concept imported from the Lieb-Liniger model. To do so we use the definition of the rapidity distribution as the asymptotic momentum distribution after a very large expansion. We propose two different ways to derive the result, each one using a thought experiment that implements an expansion.

  3 citations

• Mulan: a part-per-million measurement of the muon lifetime and determination of the Fermi constant

  R. Carey, T. Gorringe, D.W. Hertzog

  SciPost Phys. Proc. 5, 016 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The part-per-million measurement of the positive muon lifetime and determination of the Fermi constant by the MuLan experiment at the Paul Scherrer Institute is reviewed. The experiment used an innovative, time-structured, surface muon beam and a near-4π, finely-segmented, plastic scintillator positron detector. Two in-vacuum muon stopping targets were used: a ferromagnetic foil with a large internal magnetic field, and a quartz crystal in a moderate external magnetic field. The experiment acquired a dataset of 1.6e12 positive muon decays and obtained a muon lifetime τ_µ = 2 196 980.3(2.2) ps (1.0 ppm) and Fermi constant G_F = 1.166 378 7(6) × 10−5 GeV^−2 (0.5 ppm). The thirty fold improvement in τ_µ has proven valuable for precision measurements in nuclear muon capture and the commensurate improvement in G_F has proven valuable for precision tests of the standard model.

  3 citations

• Photoemission "experiments" on holographic lattices

  Filip Herček, Vladan Gecin, Mihailo Čubrović

  SciPost Phys. Core 6, 027 (2023) · published 6 April 2023 | Toggle abstract · pdf

  We construct a 2D holographic ionic lattice with hyperscaling-violating infrared geometry and study single-electron spectral functions ("ARPES photoemission curves") on this background. The spectra typically show a three-peak structure, where the central peak undergoes a crossover from a sharp but not Fermi-liquid-like quasiparticle to a wide incoherent maximum, and the broad side peaks resemble the Hubbard bands. These findings are partially explained by a perturbative near-horizon analysis of the bulk Dirac equation. Comparing the holographic Green functions in imaginary frequency with the Green functions of the Hubbard model obtained from quantum Monte Carlo, we find that the holographic model provides a very good fit to the Hubbard Green function. However, the information loss when transposing the holographic Green functions to imaginary frequencies implies that a deeper connection to Hubbard-like models remains questionable.

  3 citations

• Supersymmetric ground states of 3d $\mathcal{N}=4$ SUSY gauge theories and Heisenberg algebras

  Andrea E. V. Ferrari

  SciPost Phys. 14, 063 (2023) · published 6 April 2023 | Toggle abstract · pdf

  We consider 3d $\mathcal{N}=4$ theories on the geometry $\Sigma \times \mathbb{R}$, where $\Sigma$ is a closed and connected Riemann surface, from the point of view of a quantum mechanics on $\mathbb{R}$. Focussing on the elementary mirror pair in the presence of real deformation parameters, namely SQED with one hypermultiplet (SQED[1]) and the free hypermulitplet, we study the algebras of local operators in the respective quantum mechanics as well as their action on the vector space of supersymmetric ground states. We demonstrate that the algebras can be described in terms of Heisenberg algebras, and that they act in a way reminiscent of Segal-Bargmann (B-twist of the free hypermultiplet) and Nakajima (A-twist of SQED[1]) operators.

  3 citations

• Phonon pumping by modulating the ultrastrong vacuum

  Fabrizio Minganti, Alberto Mercurio, Fabio Mauceri, Marco Scigliuzzo, Salvatore Savasta, Vincenzo Savona

  SciPost Phys. 17, 027 (2024) · published 30 July 2024 | Toggle abstract · pdf

  The vacuum (i.e., the ground state) of a system in ultrastrong light-matter coupling contains particles that cannot be emitted without any dynamical perturbation and is thus called virtual. We propose a protocol for inducing and observing real mechanical excitations of a mirror enabled by the virtual photons in the ground state of a tripartite system, where a resonant optical cavity is ultrastrongly coupled to a two-level system (qubit) and, at the same time, optomechanically coupled to a mechanical resonator. Real phonons are coherently emitted when the frequency of the two-level system is modulated at a frequency comparable to that of the mechanical resonator and, therefore much lower than the optical frequency. We demonstrate that this hybrid effect is a direct consequence of the virtual photon population in the ground state. Within a classical physics analogy, attaching a weight to a spring only changes its resting position, whereas dynamically modulating the weight makes the system oscillate. In our case, however, the weight is the vacuum itself. We propose and accurately characterize a hybrid superconducting-optomechanical setup based on available state-of-the-art technology, where this effect can be experimentally observed.

  3 citations

• Unfolding $E_{11}$

  Nicolas Boulanger, Paul P. Cook, Josh A. O'Connor, Peter West

  SciPost Phys. 18, 149 (2025) · published 6 May 2025 | Toggle abstract · pdf

  We work out the unfolded formulation of the fields in the non-linear realisation of $E_{11}$. Using the connections in this formalism, we propose, at the linearised level, an infinite number of first-order duality relations between the dual fields in $E_{11}$. In this way, we introduce extra fields that do not belong to $E_{11}$ and we investigate their origin. The equations of motion of the fields are obtained by taking derivatives and higher traces of the duality relations.

  3 citations

• Coulomb branch surgery: Holonomy saddles, S-folds and discrete symmetry gaugings

  Elias Furrer, Horia Magureanu

  SciPost Phys. 17, 073 (2024) · published 5 September 2024 | Toggle abstract · pdf

  Symmetries of Seiberg–Witten (SW) geometries capture intricate physical aspects of the underlying 4d $\mathcal{N} = 2$ field theories. For rank-one theories, these geometries are rational elliptic surfaces whose automorphism group is a semi-direct product between the Coulomb branch (CB) symmetries and the Mordell-Weil group. We study quotients of the SW geometry by subgroups of its automorphism group, which most naturally become gaugings of discrete 0- and 1-form symmetries. Yet, new interpretations of these surgeries become evident when considering 5d $\mathcal{N}=1$ superconformal field theories. There, certain CB symmetries are related to symmetries of the corresponding $(p,q)$-brane web and, as a result, CB surgeries can give rise to (fractional) S-folds. Another novel interpretation of these quotients is the folding across dimensions: circle compactifications of the 5d $E_{2N_f + 1}$ Seiberg theories lead in the infrared to two copies of locally indistinguishable 4d SU(2) SQCD theories with $N_f$ fundamental flavours. This extends earlier results on holonomy saddles, while also reproducing detailed computations of 5d BPS spectra and predicting new 5d and 6d BPS quivers. Finally, we argue that the semi-direct product structure of the automorphism group of the SW geometry includes mixed 't Hooft anomalies between the 0- and 1-form symmetries, and we also present some new results on non-cyclic CB symmetries.

  3 citations

• Classical Lie bialgebras for AdS/CFT integrability by contraction and reduction

  Niklas Beisert, Egor Im

  SciPost Phys. 14, 157 (2023) · published 15 June 2023 | Toggle abstract · pdf

  Integrability of the one-dimensional Hubbard model and of the factorised scattering problem encountered on the worldsheet of AdS strings can be expressed in terms of a peculiar quantum algebra. In this article, we derive the classical limit of these algebraic integrable structures based on established results for the exceptional simple Lie superalgebra $\mathfrak{d}(2,1;\epsilon)$ along with standard $\mathfrak{sl}(2)$ which form supersymmetric isometries on 3D AdS space. The two major steps in this construction consist in the contraction to a 3D Poincaré superalgebra and a certain reduction to a deformation of the $\mathfrak{u}(2|2)$ superalgebra. We apply these steps to the integrable structure and obtain the desired Lie bialgebras with suitable classical r-matrices of rational and trigonometric kind. We illustrate our findings in terms of representations for on-shell fields on AdS and flat space.

  3 citations