Publications

Order by: publication date number of citations

• Excitations and ergodicity of critical quantum spin chains from non-equilibrium classical dynamics

  Stéphane Vinet, Gabriel Longpré, William Witczak-Krempa

  SciPost Phys. Core 5, 035 (2022) · published 7 July 2022 | Toggle abstract · pdf

  We study a quantum spin-1/2 chain that is dual to the canonical problem of non-equilibrium Kawasaki dynamics of a classical Ising chain coupled to a thermal bath. The Hamiltonian is obtained for the general disordered case with non-uniform Ising couplings. The quantum spin chain (dubbed Ising-Kawasaki) is stoquastic, and depends on the Ising couplings normalized by the bath's temperature. We give its exact ground states. Proceeding with uniform couplings, we study the one- and two-magnon excitations. Solutions for the latter are derived via a Bethe Ansatz scheme. In the antiferromagnetic regime, the two-magnon branch states show intricate behavior, especially regarding their hybridization with the continuum. We find that that the gapless chain hosts multiple dynamics at low energy as seen through the presence of multiple dynamical critical exponents. Finally, we analyze the full energy level spacing distribution as a function of the Ising coupling. We conclude that the system is non-integrable for generic parameters, or equivalently, that the corresponding non-equilibrium classical dynamics are ergodic.

  1 citation

• Visions in quantum gravity

  Luca Buoninfante, Benjamin Knorr, K. Sravan Kumar, Alessia Platania, Damiano Anselmi, Ivano Basile, N. Emil J. Bjerrum-Bohr, Robert Brandenberger, Mariana Carrillo González, Anne-Christine Davis, Bianca Dittrich, Paolo Di Vecchia, John F. Donoghue, Fay Dowker, Gia Dvali, Astrid Eichhorn, Steven B. Giddings, Alessandra Gnecchi, Giulia Gubitosi, Lavinia Heisenberg, Renata Kallosh, Alexey S. Koshelev, Stefano Liberati, Renate Loll, Leonardo Modesto, Paulo Moniz, Daniele Oriti, Olga Papadoulaki, Jan M. Pawlowski, Roberto Percacci, Lesław Rachwał, Mairi Sakellariadou, Alberto Salvio, Kellogg Stelle, Sumati Surya, Arkady Tseytlin, Neil Turok, Thomas Van Riet, Richard P. Woodard

  SciPost Phys. Comm. Rep. 11 (2025) · published 25 August 2025 | Toggle abstract · pdf

  To deepen our understanding of Quantum Gravity and its connections with black holes and cosmology, building a common language and exchanging ideas across different approaches is crucial. The Nordita Program "Quantum Gravity: from gravitational effective field theories to ultraviolet complete approaches" created a platform for extensive discussions, aimed at pinpointing both common grounds and sources of disagreements, with the hope of generating ideas and driving progress in the field. This contribution summarizes the twelve topical discussions held during the program and collects individual thoughts of speakers and panelists on the future of the field in light of these discussions.

  1 citation

• Twisted gauging and topological sectors in (2+1)d Abelian lattice gauge theories

  Bram Vancraeynest-De Cuiper, Clement Delcamp

  SciPost Phys. 19, 054 (2025) · published 22 August 2025 | Toggle abstract · pdf

  Given a two-dimensional quantum lattice model with an Abelian gauge theory interpretation, we investigate a duality operation that amounts to gauging its invertible 1-form symmetry, followed by gauging the resulting 0-form symmetry in a twisted way via a choice of discrete torsion. Using tensor networks, we introduce explicit lattice realisations of the so-called condensation defects, which are obtained by gauging the 1-form symmetry along submanifolds of spacetime, and employ the same calculus to realise the duality operators. By leveraging these tensor network operators, we compute the non-trivial interplay between symmetry-twisted boundary conditions and charge sectors under the duality operation, enabling us to construct isometries relating the dual Hamiltonians. Whenever a lattice gauge theory is left invariant under the duality operation, we explore the possibility of promoting the self-duality to an internal symmetry. We argue that this results in a symmetry structure that encodes the 2-representations of a 2-group.

  1 citation

• Unifying description of the damping regimes of a stochastic particle in a periodic potential

  Antonio Piscitelli, Massimo Pica Ciamarra

  SciPost Phys. 3, 018 (2017) · published 4 September 2017 | Toggle abstract · pdf

  We analyze the classical problem of the stochastic dynamics of a particle confined in a periodic potential, through the so called Il'in and Khasminskii model, with a novel semi-analytical approach. Our approach gives access to the transient and the asymptotic dynamics in all damping regimes, which are difficult to investigate in the usual Brownian model. We show that the crossover from the overdamped to the underdamped regime is associated with the loss of a typical time scale and of a typical length scale, as signaled by the divergence of the probability distribution of a certain dynamical event. In the underdamped regime, normal diffusion coexists with a non Gaussian displacement probability distribution for a long transient, as recently observed in a variety of different systems. We rationalize the microscopic physical processes leading to the non-Gaussian behavior, as well as the timescale to recover the Gaussian statistics. The theoretical results are supported by numerical calculations and are compared to those obtained for the Brownian model.

  1 citation

• Quasi-equilibrium polariton condensates in the non-linear regime and beyond

  Ned Goodman, Brendan C. Mulkerin, Jesper Levinsen, Meera M. Parish

  SciPost Phys. 15, 116 (2023) · published 26 September 2023 | Toggle abstract · pdf

  We investigate the many-body behavior of polaritons formed from electron-hole pairs strongly coupled to photons in a two-dimensional semiconductor microcavity. We use a microscopic mean-field BCS theory that describes polariton condensation in quasi-equilibrium across the full range of excitation densities. In the limit of vanishing density, we show that our theory recovers the exact single-particle properties of polaritons, while at low densities it captures non-linear polariton-polariton interactions within the Born approximation. For the case of highly screened contact interactions between charge carriers, we obtain analytic expressions for the equation of state of the many-body system. This allows us to show that there is a photon resonance at a chemical potential higher than the photon cavity energy, where the electron-hole pair correlations in the polariton condensate become universal and independent of the details of the carrier interactions. Comparing the effect of different ranged interactions between charge carriers, we find that the Rytova-Keldysh potential (relevant to transition metal dichalcogenides) offers the best prospect of reaching the BCS regime, where pairs strongly overlap and the minimum pairing gap occurs at finite momentum. Finally, going beyond thermal equilibrium, we argue that there are generically two polariton branches in the driven-dissipative system and we discuss the possibility of a density-driven exceptional point within our model.

  1 citation

• Exploring superconformal Yang-Mills theories through matrix Bessel kernels

  Zoltan Bajnok, Bercel Boldis, Gregory P. Korchemsky

  SciPost Phys. 19, 004 (2025) · published 2 July 2025 | Toggle abstract · pdf

  A broad class of observables in four-dimensional $\mathcal{N}=2$ and $\mathcal{N}=4$ superconformal Yang-Mills theories can be exactly computed in the planar limit for arbitrary 't Hooft coupling as Fredholm determinants of integrable Bessel operators. These observables admit a unifying description through a one-parameter generating function, which possesses a determinant representation involving a matrix generalization of the Bessel operator. We analyze this generating function over a wide range of parameter values and finite 't Hooft coupling. We demonstrate that it has a well-behaved weak-coupling expansion with a finite radius of convergence. In contrast, the strong-coupling expansion exhibits factorially growing coefficients, necessitating the inclusion of non-perturbative corrections that are exponentially suppressed at strong coupling. We compute these non-perturbative corrections and observe a striking resemblance between the resulting trans-series expansion of the generating function and the partition function of a strongly coupled theory expanded in powers of a mass gap.

  1 citation

• A $C^\ast$-algebraic view on the interaction of real- and reciprocal space topology in skyrmion crystals

  Pascal Prass, Fabian R. Lux, Emil Prodan, Duco van Straten, Yuriy Mokrousov

  SciPost Phys. Core 7, 080 (2024) · published 4 December 2024 | Toggle abstract · pdf

  Understanding the interaction of real- and reciprocal space topology in skyrmion crystals is an open problem. We approach it from the viewpoint of $C^\ast$-algebras and calculate all admissible Chern numbers of a strongly coupled tight-binding skyrmion system on a triangular lattice as a function of Fermi energy and texture parameters. Our analysis reveals the topological complexity of electronic states coupled to spin textures, and the failure of the adiabatic picture to account for it in terms of emergent electromagnetism. On the contrary, we explain the discontinuous jumps in the real-space winding number in terms of collective evolution in real-, reciprocal, and mixed space Chern numbers. Our work sets the stage for further research on topological dynamics in complex dynamic spin textures coupled to external fields.

  1 citation

• Local density of states correlations in the Lévy-Rosenzweig-Porter random matrix ensemble

  Aleksey Lunkin, Konstantin Tikhonov

  SciPost Phys. 19, 015 (2025) · published 16 July 2025 | Toggle abstract · pdf

  We present an analytical calculation of the local density of states correlation function $ \beta(\omega) $ in the Lévy-Rosenzweig-Porter random matrix ensemble at energy scales larger than the level spacing but smaller than the bandwidth. The only relevant energy scale in this limit is the typical level width $\Gamma_0$. We show that $\beta(\omega \ll \Gamma_0) \sim W/\Gamma_0$ (here $W$ is width of the band) whereas $\beta(\omega \gg \Gamma_0) \sim (W/\Gamma_0) (\omega/\Gamma_0)^{-\mu} $ where $\mu$ is an index characterising the distribution of the matrix elements. We also provide an expression for the average return probability at long times: $\ln [R(t\gg\Gamma_0^{-1})] \sim -(\Gamma_0 t)^{\mu/2}$. Numerical results based on the pool method and exact diagonalization are also provided and are in agreement with the analytical theory.

  1 citation

• Codebase release r1.1 for SmoQyDEAC.jl

  James Neuhaus, Nathan S. Nichols, Debshikha Banerjee, Benjamin Cohen-Stead, Thomas A. Maier, Adrian Del Maestro, Steven Johnston

  SciPost Phys. Codebases 39-r1.1 (2024) · published 12 November 2024 | Toggle abstract · src

  We introduce the SmoQyDEAC.jl package, a Julia implementation of the Differential Evolution Analytic Continuation (DEAC) algorithm [N. S. Nichols et al., Phys. Rev. E 106, 025312 (2022)] for analytically continuing noisy imaginary time correlation functions to the real frequency axis. Our implementation supports fermionic and bosonic correlation functions on either the imaginary time or Matsubara frequency axes, and treatment of the covariance error in the input data. This paper presents an overview of the DEAC algorithm and the features implemented in the SmoQyDEAC.jl package. It also provides detailed benchmarks of the package's output against the popular maximum entropy and stochastic analytic continuation methods. The code for this package can be downloaded from our GitHub repository at https://github.com/SmoQySuite/SmoQyDEAC.jl or installed using the Julia package manager. The online documentation, including examples, can be accessed at https://smoqysuite.github.io/SmoQyDEAC.jl/stable/.

  1 citation

• Lightcone Hamiltonian for Ising field theory I: $T < T_c$

  Andrew Liam Fitzpatrick, Emanuel Katz, Yuan Xin

  SciPost Phys. 18, 179 (2025) · published 5 June 2025 | Toggle abstract · pdf

  We study 2d Ising Field Theory (IFT) in the low-temperature phase in lightcone quantization, and show that integrating out zero modes generates a very compact form for the effective lightcone interaction that depends on the finite volume vacuum expectation value of the $\sigma$ operator. This form is most naturally understood in a conformal basis for the lightcone Hilbert space. We further verify that this simple form reproduces to high accuracy results for the spectra, the $c$-function, and the form-factors from integrability methods for the magnetic deformation of IFT. For generic non-integrable values of parameters we also compute the above observables and compare our numeric results to those of equal-time truncation. In particular, we report on new measurements of various bound-state form-factors as well as the stress-tensor spectral density. We find that the stress tensor spectral density provides additional evidence that certain resonances of IFT are surprisingly narrow, even at generic strong coupling. Explicit example code for constructing the effective Hamiltonian is included in an appendix.

  1 citation