Publications

Order by: publication date number of citations

• $\mathbb{Z}_4$ transitions in quantum loop models on a zig-zag ladder

  Bowy M. La Rivière, Natalia Chepiga

  SciPost Phys. 17, 144 (2024) · published 26 November 2024 | Toggle abstract · pdf

  We study the nature of quantum phase transitions out of $\mathbb{Z}_4$ ordered phases in quantum loop models on a zig-zag ladder. We report very rich critical behavior that includes a pair of Ising transitions, a multi-critical Ashkin-Teller point and a remarkably extended interval of a chiral transition. Although plaquette states turn out to be essential to realize chiral transitions, we demonstrate that critical regimes can be manipulated by deforming the model as to increase the presence of leg-dimerized states. This can be done to the point where the chiral transition turns into first order, we argue that this is associated with the emergence of a critical end point.

  2 citations

• Time-reversal symmetry breaking and emergence in driven-dissipative Ising models

  Daniel A. Paz, Mohammad F. Maghrebi

  SciPost Phys. 12, 066 (2022) · published 17 February 2022 | Toggle abstract · pdf

  Fluctuation-dissipation relations (FDRs) and time-reversal symmetry (TRS), two pillars of statistical mechanics, are both broken in generic driven-dissipative systems. These systems rather lead to non-equilibrium steady states far from thermal equilibrium. Driven-dissipative Ising-type models, however, are widely believed to exhibit effective thermal critical behavior near their phase transitions. Contrary to this picture, we show that both the FDR and TRS are broken even macroscopically at, or near, criticality. This is shown by inspecting different observables, both even and odd operators under time-reversal transformation, that overlap with the order parameter. Remarkably, however, a modified form of the FDR as well as TRS still holds, but with drastic consequences for the correlation and response functions as well as the Onsager reciprocity relations. Finally, we find that, at criticality, TRS remains broken even in the weakly-dissipative limit.

  2 citations

• Scattering from an external field in quantum chromodynamics at high energies: From foundations to interdisciplinary connections

  Athanasia-Konstantina Angelopoulou, Anh Dung Le, Stéphane Munier

  SciPost Phys. Lect. Notes 92 (2025) · published 12 March 2025 | Toggle abstract · pdf

  We review the factorization of the $S$-matrix elements in the context of particle scattering off an external field, which can serve as a model for the field of a large nucleus. The factorization takes the form of a convolution of light cone wave functions describing the physical incoming and outgoing states in terms of bare partons, and products of Wilson lines. The latter represent the interaction between the bare partons and the external field. Specializing to elastic scattering amplitudes of onia at very high energies, we introduce the color dipole model, which formulates the calculation of the modulus-squared of the wave functions in quantum chromodynamics with the help of a branching random walk, and the scattering amplitudes as observables on this classical stochastic process. Methods developed for general branching processes produce analytical formulas for the asymptotics of such observables, and thus enable one to derive exact large-rapidity expressions for onium-nucleus cross sections, from which electron-nucleus cross sections may be inferred.

  2 citations

• Dual applications of Chebyshev polynomials method: Efficiently finding thousands of central eigenvalues for many-spin systems

  Haoyu Guan, Wenxian Zhang

  SciPost Phys. 11, 103 (2021) · published 8 December 2021 | Toggle abstract · pdf

  Computation of a large group of interior eigenvalues at the middle spectrum is an important problem for quantum many-body systems, where the level statistics provides characteristic signatures of quantum chaos. We propose an exact numerical method, dual applications of Chebyshev polynomials (DACP), to simultaneously find thousands of central eigenvalues, where the level space decreases exponentially with the system size. To disentangle the near-degenerate problem, we employ twice the Chebyshev polynomials, to construct an exponential semicircle filter as a preconditioning step and to generate a large set of proper basis states in the desired subspace. Numerical calculations on Ising spin chain and spin glass shards confirm the correctness and efficiency of DACP. As numerical results demonstrate, DACP is $30$ times faster than the state-of-the-art shift-invert method for the Ising spin chain while $8$ times faster for the spin glass shards. In contrast to the shift-invert method, the computation time of DACP is only weakly influenced by the required number of eigenvalues, which renders it a powerful tool for large scale eigenvalues computations. Moreover, the consumed memory also remains a small constant (5.6 GB) for spin-$1/2$ systems consisting of up to $20$ spins, making it desirable for parallel computing.

  2 citations

• Next-generation EDIpack: A Lanczos-based package for quantum impurity models featuring general broken-symmetry phases, flexible bath topologies and multi-platform interoperability

  Lorenzo Crippa, Igor Krivenko, Samuele Giuli, Gabriele Bellomia, Alexander Kowalski, Francesco Petocchi, Alberto Scazzola, Markus Wallerberger, Giacomo Mazza, Luca de Medici, Giorgio Sangiovanni, Massimo Capone, Adriano Amaricci

  SciPost Phys. Codebases 58 (2025) · published 24 September 2025 | Toggle abstract · pdf

  We present a next-generation version of EDIpack, a flexible, high-performance numerical library using Lanczos-based exact diagonalization to solve generic quantum impurity problems, such as those introduced in Dynamical Mean-Field Theory to describe extended strongly correlated materials. This new release efficiently solves impurity problems allowing for different broken-symmetry solutions, including superconductivity, featuring local spin-orbit coupling and/or electron-phonon coupling. It provides quick access to dynamical correlation functions on the entire complex frequency plane at zero and low-temperatures. The modular architecture of the software not only provides Fortran APIs but also includes bindings to C/C++, interfaces with Python and Julia or with TRIQS and w2dynamics research platforms, thus ensuring unprecedented level of inter-operability. The outlook includes further extensions to study quantum materials and cold atoms quantum simulators, as well as quantum information applications.

  2 citations

• A theory vade mecum for PSI experiments

  G. Colangelo, F. Hagelstein, A. Signer, P. Stoffer

  SciPost Phys. Proc. 5, 005 (2021) · published 6 September 2021 | Toggle abstract · pdf

  This article gives a compact introduction and overview of the theory underlying the experiments described in the rest of this review.

  2 citations

• GRIFFIN: A C++ library for electroweak radiative corrections in fermion scattering and decay processes

  Lisong Chen, Ayres Freitas

  SciPost Phys. Codebases 18 (2023) · published 10 October 2023 | Toggle abstract · pdf

  This paper describes a modular framework for the description of electroweak scattering and decay processes, including but not limited to Z-resonance physics. The framework consistently combines a complex-pole expansion near an s-channel resonance with a regular fixed-order perturbative description away from the resonance in a manifestly gauge-invariant scheme. Leading vertex correction contributions are encapsulated in form factors that can be predicted or treated as numerical fit parameters. This framework has been implemented in the publicly available object-oriented C++ library GRIFFIN. Version 1.0 of this library provides Standard Model predictions for the IR-subtracted matrix elements for the process $f\bar{f} \to f'\bar{f}'$ with full NNLO and leading higher-order contributions on the Z-resonance, and with NLO corrections off-resonance. The library can straightforwardly be extended to include higher-order corrections, should they become available, or predictions for new physics models. It can be interfaced with Monte-Carlo programs to account for QED and QCD initial-state and final-state radiation.

  2 citations

• On the unexpected fate of scientific ideas: An archeology of the Carroll group

  Jean-Marc Lévy-Leblond

  SciPost Phys. Proc. 14, 006 (2023) · published 23 November 2023 | Toggle abstract · pdf

  In 1965, I published a paper, exhibiting a hitherto unknown limit of the Lorentz group, which I christened "Carroll group" due to its seemingly paradoxical physical contents. Since I saw it as more curious than relevant, I published it in French in a journal somewhat afar from the mainstream of theoretical physics at that time. It was most gratifying to witness the quite unexpected favour this paper started to enjoy half a century later, so much that a so-called "Carrollian physics" is now developing, with applications in various domains of forefront theoretical physics, such as quantum gravitation, supersymmetry, string theory, etc. I offer this narrative as an example of the very diverse time scales with which scientific ideas may develop — or not.

  2 citations

• Cyclotron trap

  D. Gotta, L. M. Simons

  SciPost Phys. Proc. 5, 013 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The cyclotron trap was developed at SIN/PSI to increase the stopping density of nega- tively charged particle beams for the formation of exotic atoms in low pressure gases. A weak focusing magnetic field, produced by superconducting solenoids, is used. Particles are injected radially through the fringe field to a moderator, which decelerates them into orbits bound by the field. Further deceleration by moderators and/or low-pressure gases leads the particles to the center of the device, where they can be stopped or eventually extracted. Experiments became feasible with this technique, such as those dealing with pionic hydrogen/deuteriumat SIN/PSI.Muonic hydrogen laser experiments also became possible with the extraction of muons from the cyclotron trap. The formation of antipro- tonic hydrogen in low pressure targets led to successful experiments at LEAR/CERN.

  2 citations

• Impact parameter dependence of color charge correlations in the proton

  Adrian Dumitru, Heikki Mäntysaari, Risto Paatelainen

  SciPost Phys. Proc. 8, 058 (2022) · published 12 July 2022 | Toggle abstract · pdf

  The impact parameter dependence of color charge correlators in the proton is obtained from the light front formalism in light cone gauge. We include NLO corrections due to the $|qqqg\rangle$ Fock state via light-cone perturbation theory. Near the center of the proton, the $b$-dependence of the correlations is very different from a "transverse profile function". The resulting $t$-dependence of exclusive $J/\Psi$ photoproduction transitions from exponential to power law at $|t| \approx 1$ GeV$^2$. This prediction could be tested at upcoming DIS facilities or in nucleus-proton ultraperipheral collisions (UPCs).

  2 citations