Publications

Order by: publication date number of citations

• EFT matching from analyticity and unitarity

  Stefano De Angelis, Gauthier Durieux

  SciPost Phys. 16, 071 (2024) · published 12 March 2024 | Toggle abstract · pdf

  We present a new on-shell method for the matching of ultraviolet models featuring massive states onto their massless effective field theory. We employ a dispersion relation in the space of complex momentum dilations to capture, in a single variable, the relevant analytic structure of scattering amplitudes at any multiplicity. Multivariate complex analysis and crossing considerations are therefore avoided. Remarkably, no knowledge about the infrared effective field theory is required in dimensional regularisation. All matching information is extracted from the residues and iscontinuities of the ultraviolet scattering amplitudes, which unitarity expresses in terms of lower-point and lower-loop results, respectively. This decomposition into simpler building blocks could deliver new insight in the structure of the effective field theories obtained from classes of ultraviolet scenarios and facilitate computations at higher loop orders.

  10 citations

• Low temperature quantum bounds on simple models

  Silvia Pappalardi, Jorge Kurchan

  SciPost Phys. 13, 006 (2022) · published 22 July 2022 | Toggle abstract · pdf

  In the past few years, there has been considerable activity around a set of quantum bounds on transport coefficients (viscosity) and chaos (Lyapunov exponent), relevant at low temperatures. The interest comes from the fact that Black-Hole models seem to saturate all of them. The goal of this work is to gain physical intuition about the quantum mechanisms that enforce these bounds on simple models. To this aim, we consider classical and quantum free dynamics on curved manifolds. These systems exhibit chaos up to the lowest temperatures and - as we discuss - they violate the bounds in the classical limit. First of all, we show that the quantum dimensionless viscosity and the Lyapunov exponent only depend on the de Broglie length and a geometric length-scale, thus establishing the scale at which quantum effects become relevant. Then, we focus on the bound on the Lyapunov exponent and identify three different ways in which quantum effects arise in practice. We illustrate our findings on a toy model given by the surface of constant negative curvature - a paradigmatic model of quantum chaos - glued to a cylinder. By exact solution and numerical investigations, we show how the chaotic behaviour is limited by the quantum effects of the curvature itself. Interestingly, we find that at the lowest energies the bound to chaos is dominated by the longest length scales, and it is therefore a collective effect.

  10 citations

• Generalized charges, part II: Non-invertible symmetries and the symmetry TFT

  Lakshya Bhardwaj, Sakura Schäfer-Nameki

  SciPost Phys. 19, 098 (2025) · published 15 October 2025 | Toggle abstract · pdf

  Consider a $d$-dimensional quantum field theory (QFT) $\mathfrak{T}$, with a generalized symmetry $\mathcal{S}$, which may or may not be invertible. We study the action of $\mathcal{S}$ on generalized or $q$-charges, i.e. $q$-dimensional operators. The main result of this paper is that $q$-charges are characterized in terms of the topological defects of the Symmetry Topological Field Theory (SymTFT) of $\mathcal{S}$, also known as the "Sandwich Construction". The SymTFT is a $(d+1)$-dimensional topological field theory, which encodes the symmetry $\mathcal{S}$ and the physical theory in terms of its boundary conditions. Our proposal applies quite generally to any finite symmetry $\mathcal{S}$, including non-invertible, categorical symmetries. Mathematically, the topological defects of the SymTFT form the Drinfeld Center of the symmetry category $\mathcal{S}$. Applied to invertible symmetries, we recover the result of Part I of this series of papers. After providing general arguments for the identification of $q$-charges with the topological defects of the SymTFT, we develop this program in detail for QFTs in 2d (for general fusion category symmetries) and 3d (for fusion 2-category symmetries).

  10 citations

• Towards a data-driven model of hadronization using normalizing flows

  Christian Bierlich, Phil Ilten, Tony Menzo, Stephen Mrenna, Manuel Szewc, Michael K. Wilkinson, Ahmed Youssef, Jure Zupan

  SciPost Phys. 17, 045 (2024) · published 12 August 2024 | Toggle abstract · pdf

  We introduce a model of hadronization based on invertible neural networks that faithfully reproduces a simplified version of the Lund string model for meson hadronization. Additionally, we introduce a new training method for normalizing flows, termed MAGIC, that improves the agreement between simulated and experimental distributions of high-level (macroscopic) observables by adjusting single-emission (microscopic) dynamics. Our results constitute an important step toward realizing a machine-learning based model of hadronization that utilizes experimental data during training. Finally, we demonstrate how a Bayesian extension to this normalizing-flow architecture can be used to provide analysis of statistical and modeling uncertainties on the generated observable distributions.

  10 citations

• Exclusive emissions of rho-mesons and the unintegrated gluon distribution

  Andrèe Dafne Bolognino, Francesco Giovanni Celiberto, Dmitry Yu. Ivanov, Alessandro Papa

  SciPost Phys. Proc. 8, 089 (2022) · published 13 July 2022 | Toggle abstract · pdf

  Exclusive emissions of vector mesons in forward directions of rapidity offer us a faultless chance to probe the proton structure at small-$x$. A high-energy factorization formula is established within BFKL, given as the convolution of an impact factor depicting the forward-meson emission and of an unintegrated gluon distribution (UGD) driving the gluon evolution at small-$x$. As a nonperturbative quantity, the UGD is not well known and several models for it exist. We present recent progresses on the study of the exclusive forward $\rho$-meson leptoproduction at HERA and EIC energies, showing how osbervables sensitive to different polarization states of the $\rho$-particle act as discriminators for the existing UGD models.

  10 citations

• Hall anomaly and moving vortex charge in layered superconductors

  Assa Auerbach, Daniel P. Arovas

  SciPost Phys. 8, 061 (2020) · published 17 April 2020 | Toggle abstract · pdf

  Magnetotransport theory of layered superconductors in the flux flow steady state is revisited. Longstanding controversies concerning observed Hall sign reversals are resolved. The conductivity separates into a Bardeen-Stephen vortex core contribution, and a Hall conductivity due to moving vortex charge. This charge, which is responsible for Hall anomaly, diverges logarithmically at weak magnetic field. Its values can be extracted from magetoresistivity data by extrapolation of vortex core Hall angle from the normal phase. Hall anomalies in YBCO, BSCCO, and NCCO data are consistent with theoretical estimates based on doping dependence of London penetration depths. In the appendices, we derive the Streda formula for the hydrodynamical Hall conductivity, and refute previously assumed relevance of Galilean symmetry to Hall anomalies.

  10 citations

• Generalized Lindblad master equation for measurement-induced phase transition

  Yi-Neng Zhou

  SciPost Phys. Core 6, 023 (2023) · published 30 March 2023 | Toggle abstract · pdf

  The measurement-induced phase transition (MIPT) occurs when the system is evolving under unitary evolution together with local measurements followed by post-selection. We propose a generalized version of the Lindblad master equation as a continuous equation, to describe the dynamics of the second Rényi entropy in the MIPT. This generalized Lindblad equation explicitly takes into account the post-selection in the MIPT, which is realized as the Einstein-Podolsky-Rosen (EPR) state projection in the equation. Also, this generalized Lindblad equation preserves the Hermitian, unit trace, and positive definiteness of the density matrix. We further use the hard-core Bose-Hubbard model as a concrete example to numerically confirm that our generalized Lindblad equation is applicable to describing the MIPT.

  10 citations

• Particle fluctuations and the failure of simple effective models for many-body localized phases

  Maximilian Kiefer-Emmanouilidis, Razmik Unanyan, Michael Fleischhauer, Jesko Sirker

  SciPost Phys. 12, 034 (2022) · published 21 January 2022 | Toggle abstract · pdf

  We investigate and compare the particle number fluctuations in the putative many-body localized (MBL) phase of a spinless fermion model with potential disorder and nearest-neighbor interactions with those in the non-interacting case (Anderson localization) and in effective models where only interaction terms diagonal in the Anderson basis are kept. We demonstrate that these types of simple effective models cannot account for the particle number fluctuations observed in the MBL phase of the microscopic model. This implies that assisted and pair hopping terms---generated when transforming the microscopic Hamiltonian into the Anderson basis---cannot be neglected even at strong disorder and weak interactions. As a consequence, it appears questionable if the microscopic model possesses an exponential number of exactly conserved {\it local} charges. If such a set of conserved local charges does not exist, then particles are expected to ultimately delocalize for any finite disorder strength.

  10 citations

• Mobility control as state-making in civil war: Forcing exit, selective return and strategic laissez-faire

  Christiane Fröhlich, Lea Müller-Funk

  Mig. Pol. 2, 001 (2023) · published 27 March 2023 | Toggle abstract · pdf

  This paper addresses the question of how different actors attempt to control mobility during civil war, and how mobility control and processes of state-making interact in such settings. Mobility in civil wars is often considered a political act by the various actors involved: Leaving the country can be perceived as an act of opposition, as can moving between territories which are controlled by different, opposing factions. Drawing on literature on strategic displacement and migration politics and combining this with empirical insights from the ongoing wars in Libya and Syria, the paper identifies three mechanisms of mobility control in civil war settings: forcing exit, selective return as a form of expulsion, and strategic laissez-faire as the intentional absence of regulation regarding displacement and return. The analysis reveals that all three mechanisms are employed by state actor(s), rebels, and militias, and can be understood as elements of a new (post)war order that includes some citizens while excluding others depending on perceptions of political threats. We interpret the three mechanisms as ways in which actors in civil war settings attempt to manipulate a country’s demography in their own favour in a process of state-making. The paper is based on fieldwork conducted between 2018 and 2021 in Syria, Lebanon, Libya, and Tunisia.

  10 citations

• Resolving the nonequilibrium Kondo singlet in energy- and position-space using quantum measurements

  Andre Erpenbeck, Guy Cohen

  SciPost Phys. 10, 142 (2021) · published 11 June 2021 | Toggle abstract · pdf

  The Kondo effect, a hallmark of strong correlation physics, is characterized by the formation of an extended cloud of singlet states around magnetic impurities at low temperatures. While many implications of the Kondo cloud's existence have been verified, the existence of the singlet cloud itself has not been directly demonstrated. We suggest a route for such a demonstration by considering an observable that has no classical analog, but is still experimentally measurable: ``singlet weights'', or projections onto particular entangled two-particle states. Using approximate theoretical arguments, we show that it is possible to construct highly specific energy- and position-resolved probes of Kondo correlations. Furthermore, we consider a quantum transport setup that can be driven away from equilibrium by a bias voltage. There, we show that singlet weights are enhanced by voltage even as the Kondo effect is weakened by it. This exposes a patently nonequilibrium mechanism for the generation of Kondo-like entanglement that is inherently different from its equilibrium counterpart.

  10 citations