Publications

Order by: publication date number of citations

• Investigation of role of antisite disorder in pristine cage compound FeGa$_3$

  C. Kaufmann Ribeiro , L. Mello , V. Martelli , D. Cornejo, M. B. Silva Neto , E. Fogh , H. M. Rønnow, J. Larrea Jiménez

  SciPost Phys. Proc. 11, 023 (2023) · published 5 September 2023 | Toggle abstract · pdf

  The role of controlled Fe antisite disorder in the narrow gap semiconductor FeGa$_3$ has been investigated. Polycrystalline samples were synthesized by the combination of arc-melting furnace and successive annealing processes. Deviations from occupation numbers of Fe and Ga sites expected in the pristine compound were obtained from X-ray data using Rietveld refinement analysis. Besides that, electrical transport and magnetization measurements reveal that hierarchy in Fe and Ga site disorder tunes the ground state of FeGa$_3$ from paramagnetic semiconductor to a magnetic metal. These findings are discussed inside the framework of Anderson localization in the vicinity of metal-semiconductor transitions and spin fluctuations.

  2 citations

• Feynman integrals for binary systems of black holes

  Philipp Alexander Kreer, Robert Runkel, Stefan Weinzierl

  SciPost Phys. Proc. 7, 023 (2022) · published 21 June 2022 | Toggle abstract · pdf

  The initial phase of the inspiral process of a binary black-hole system can be described by perturbation theory. At the third post-Minkowskian order a two-loop double box graph, known as H-graph, contributes. In this talk we report how all master integrals of the H-graph with equal masses can be expressed up to weight four in terms of multiple polylogarithms. We also discuss techniques for the unequal mass case. The essential complication (and the focus of the talk) is the occurrence of several square roots.

  2 citations

• Entanglement negativity and defect extremal surface

  Yilu Shao, Ma-Ke Yuan, Yang Zhou

  SciPost Phys. Core 7, 027 (2024) · published 8 May 2024 | Toggle abstract · pdf

  We study entanglement negativity for evaporating black hole based on the holographic model with defect brane. We introduce a defect extremal surface formula for entanglement negativity. Based on partial reduction, we show the equivalence between defect extremal surface formula and island formula for entanglement negativity in AdS$_3$/BCFT$_2$. Extending the study to the model of eternal black hole plus CFT bath, we find that black hole-black hole negativity decreases until vanishing, left black hole-left radiation negativity is always a constant, radiation-radiation negativity increases and then saturates at a time later than Page time. In all the time dependent cases, defect extremal surface formula agrees with island formula.

  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

• Traveling discontinuity at the quantum butterfly front

  Camille Aron, Éric Brunet, Aditi Mitra

  SciPost Phys. 15, 042 (2023) · published 2 August 2023 | Toggle abstract · pdf

  We formulate a kinetic theory of quantum information scrambling in the context of a paradigmatic model of interacting electrons in the vicinity of a superconducting phase transition. We carefully derive a set of coupled partial differential equations that effectively govern the dynamics of information spreading in generic dimensions. Their solutions show that scrambling propagates at the maximal speed set by the Fermi velocity. At early times, we find exponential growth at a rate set by the inelastic scattering. At late times, we find that scrambling is governed by shock-wave dynamics with traveling waves exhibiting a discontinuity at the boundary of the light cone. Notably, we find perfectly causal dynamics where the solutions do not spill outside of the light cone.

  2 citations

• One-form symmetries and the 3d $\mathcal{N}=2$ $A$-model: Topologically twisted indices and CS theories

  Cyril Closset, Elias Furrer, Osama Khlaif

  SciPost Phys. 18, 066 (2025) · published 24 February 2025 | Toggle abstract · pdf

  We study three-dimensional $\mathcal{N}=2$ supersymmetric Chern–Simons-matter gauge theories with a one-form symmetry in the $A$-model formalism on $\Sigma_g× S^1$. We explicitly compute expectation values of topological line operators that implement the one-form symmetry. This allows us to compute the topologically twisted index on the closed Riemann surface $\Sigma_g$ for any real compact gauge group $G$ as long as the ground states are all bosonic. All computations are carried out in the effective $A$-model on $\Sigma_g$, whose $S^1$ ground states are the so-called Bethe vacua. We discuss how the 3d one-form symmetry acts on the Bethe vacua, and also how its 't Hooft anomaly constrains the vacuum structure. In the special case of the $SU(N)_K$ $\mathcal{N}=2$ Chern–Simons theory, we obtain results for the $(SU(N)/\mathbb{Z}_r)^{\theta}_K$ $\mathcal{N}=2$ Chern–Simons theories, for all non-anomalous $\mathbb{Z}_r \subseteq \mathbb{Z}_N$ subgroups of the centre of the gauge group, and with a $\mathbb{Z}_r$ $\theta$-angle turned on. In the special cases with $N$ even, ${N\over r}$ odd and ${K\over r}$ even, we find a mixed 't Hooft anomaly between gravity and the $\mathbb{Z}_r^{(1)}$ one-form symmetry of the $SU(N)_K$ theory, and the infrared 3d TQFT after gauging is spin. In all cases, we count the Bethe states and the higher-genus states in terms of refinements of Jordan's totient function. This counting gives us the twisted indices if and only if the infrared 3d TQFT is bosonic. Our results lead to precise conjectures about integrality of indices, which appear to have a strong number-theoretic flavour. Note: this paper directly builds upon unpublished notes by Brian Willett from 2020.

  2 citations

• Symmetries, conservation laws and entanglement in non-Hermitian fermionic lattices

  Rafael D. Soares, Youenn Le Gal, Chun Y. Leung, Dganit Meidan, Alessandro Romito, Marco Schirò

  SciPost Phys. 19, 094 (2025) · published 13 October 2025 | Toggle abstract · pdf

  Non-Hermitian quantum many-body systems feature steady-state entanglement transitions driven by the competition between unitary dynamics and dissipation. In this work, we reveal the fundamental role of conservation laws in shaping this competition. Focusing on translation-invariant non-interacting fermionic models with U(1) symmetry, we present a theoretical framework to understand the structure of the steady-state of these models and their entanglement content based on two ingredients: the nature of the spectrum of the non-Hermitian Hamiltonian and the constraints imposed on the steady-state single-particle occupation by the conserved quantities. These emerge from an interplay between Hamiltonian symmetries and initial state, due to the non-linearity of measurement back-action. For models with complex energy spectrum, we show that the steady state is obtained by filling single-particle right eigenstates with the largest imaginary part of the eigenvalue. As a result, one can have partially filled or fully filled bands in the steady-state, leading to an entanglement entropy undergoing a filling-driven transition between critical sub-volume scaling and area-law, similar to ground-state problems. Conversely, when the spectrum is fully real, we provide evidence that local observables can be captured using a diagonal ensemble, and the entanglement entropy exhibits a volume-law scaling independently on the initial state, akin to unitary dynamics. We illustrate these principles in the Hatano-Nelson model with periodic boundary conditions and the non-Hermitian Su-Schrieffer-Heeger model, uncovering a rich interplay between the single-particle spectrum and conservation laws in determining the steady-state structure and the entanglement transitions. These conclusions are supported by exact analytical calculations and numerical calculations relying on the Faber polynomial method.

  2 citations

• SOLAX: A Python solver for fermionic quantum systems with neural network support

  Louis Thirion, Philipp Hansmann, Pavlo Bilous

  SciPost Phys. Codebases 51 (2025) · published 20 February 2025 | Toggle abstract · pdf

  Numerical modeling of fermionic many-body quantum systems presents similar challenges across various research domains, necessitating universal tools, including state-of-the-art machine learning techniques. Here, we introduce SOLAX, a Python library designed to compute and analyze fermionic quantum systems using the formalism of second quantization. SOLAX provides a modular framework for constructing and manipulating basis sets, quantum states, and operators, facilitating the simulation of electronic structures and determining many-body quantum states in finite-size Hilbert spaces. The library integrates machine learning capabilities to mitigate the exponential growth of Hilbert space dimensions in large quantum clusters. The core low-level functionalities are implemented using the recently developed Python library JAX. Demonstrated through its application to the Single Impurity Anderson Model, SOLAX offers a flexible and powerful tool for researchers addressing the challenges of many-body quantum systems across a broad spectrum of fields, including atomic physics, quantum chemistry, and condensed matter physics.

  2 citations

• Looking forward to forward physics at the CERN's LHC

  Luis A. Anchordoqui

  SciPost Phys. Proc. 13, 042 (2023) · published 19 October 2023 | Toggle abstract · pdf

  For decades, new physics searches in collider experiments have focused on the high-$p_T$ region. However, it has recently become evident that the LHC physics potential has not been fully exploited. To be specific, forward collisions, which produce particles along the beamline with enormous rates, have been almost completely ignored. For all practical purposes, these collisions are a treasure trove of physics, containing the highest-energy neutrinos ever produced by humans, as well as possible evidence for dark matter, light and weakly-coupled particles, and new forces. In the upcoming LHC Run 3 the ForwArd Search ExpeRiment (FASER) and its cousin FASER$\nu$ will extend the LHC's physics potential. A continuation of this forward physics program for the HL-LHC aims at the Forward Physics Facility (FPF), with larger scale experiments. In this report, I give an overview of the physics motivations for FASER, FASER$\nu$, and the FPF experiments, including both Standard Model and beyond Standard Model physics.

  2 citations

• Coherent photoproduction of $J/\psi$ in nucleus-nucleus collisions \\in the color dipole approach- an update

  Agnieszka Łuszczak, Wolfgang Schäfer

  SciPost Phys. Proc. 8, 109 (2022) · published 13 July 2022 | Toggle abstract · pdf

  We discuss the role of $c \bar c g$-Fock states in the diffractive photoproduction of $J/\psi$-mesons. We build on our earlier description of the process in the color-dipole approach, where we took into account the rescattering of $c \bar c$ pairs using a Glauber-Gribov form of the dipole-nucleus amplitude. We compare the results of our calculations to recent data on the photoproduction of $J/\psi$ by the ALICE and LHCb collaborations.

  2 citations