Publications

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Introduction to Monte Carlo for matrix models

Raghav G. Jha

SciPost Phys. Lect. Notes 46 (2022) · published 4 April 2022 | · pdf

We consider a wide range of matrix models and study them using the Monte Carlo technique in the large N limit. The results we obtain agree with exact analytic expres- sions and recent numerical bootstrap methods for models with one and two matrices. We then present new results for several unsolved multi-matrix models where no other tool is yet available. In order to encourage an exchange of ideas between different numerical approaches to matrix models, we provide programs in Python that can be easily modified to study potentials other than the ones discussed. These programs were tested on a laptop and took between a few minutes to several hours to finish depending on the model, N, and the required precision.

2 citations
Generalized Komar charges and Smarr formulas for black holes and boson stars

Romina Ballesteros, Tomás Ortín

SciPost Phys. Core 8, 038 (2025) · published 24 April 2025 | · pdf

The standard Komar charge is a $(d-2)$-form that can be defined in spacetimes admitting a Killing vector and which is closed when the vacuum Einstein equations are satisfied. Its integral at spatial infinity (the Komar integral) gives the conserved charge associated to the Killing vector, and, due to its on-shell closedness, the same value (expressed in terms of other physical variables) is obtained integrating over the event horizon (if any). This equality is the basis of the Smarr formula. This charge can be generalized so that it still is closed on-shell in presence of matter and its integrals give generalizations of the Smarr formula. We show how the Komar charge and other closed $(d-2)$-form charges can be used to prove non-existence theorems for gravitational solitons and boson stars. In particular, we show how one can deal with generalized symmetric fields (invariant under a combination of isometries and other global symmetries) and how the generalized symmetric Ansatz permits to evade the non-existence theorems.

2 citations
Incorporating non-local anyonic statistics into a graph decomposition

Matthias Mühlhauser, Viktor Kott, Kai Phillip Schmidt

SciPost Phys. Core 7, 031 (2024) · published 30 May 2024 | · pdf

In this work we describe how to systematically implement a full graph decomposition to set up a linked-cluster expansion for the topological phase of Kitaev's toric code in a field. This demands to include the non-local effects mediated by the mutual anyonic statistics of elementary charge and flux excitations. Technically, we describe how to consistently integrate such non-local effects into a hypergraph decomposition for single excitations. The approach is demonstrated for the ground-state energy and the elementary excitation energies of charges and fluxes in the perturbed topological phase.

2 citations
Frequency-independent optical spin injection in Weyl semimetals

Yang Gao, Chong Wang, Di Xiao

SciPost Phys. Core 7, 002 (2024) · published 22 January 2024 | · pdf

We demonstrate that in Weyl semimetals, the momentum-space helical spin texture can couple to the chirality of the Weyl node to generate a frequency-independent optical spin injection. This frequency-independence is rooted in the topology of the Weyl node. Since the helicity and the chirality are always locked for Weyl nodes, the injected spin from a pair of Weyl nodes always add up, implying no symmetry requirements for Weyl semimetals. Finally, we show that such frequency-independent spin injection is robust against multiband corrections and lattice-regularization effect and capable of realizing all-optical magnetization switching in the THz regime.

2 citations
Di-$\pi^0$ correlations in p+p, p+Al and p+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at STAR

Xiaoxuan Chu

SciPost Phys. Proc. 8, 043 (2022) · published 12 July 2022 | · pdf

The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-$\pi^0$ produced at forward pseudorapidity ($2.6<\eta<4.0$) in $p+$$p$, $p+$$\mathrm{Al}$ and $p+$$\mathrm{Au}$ collisions at a center-of-mass energy per nucleon-nucleon pair of 200 GeV. A clear suppression of the correlated away-side yields is observed in $p+$$\mathrm{Au}$ and for the first time in $p+$$\mathrm{Al}$ collisions, compared with the $p$$+$$p$ data. The enhanced suppression found in $p+$$\mathrm{Au}$ with respect to $p+$$\mathrm{Al}$ collisions exhibits the saturation scale ($Q_s^2$) dependence on the mass number~~$A$. The observed suppression of back-to-back pairs as a function of event activity and transverse momentum points to non-linear gluon dynamics arising at high parton densities.

2 citations
Information flow in non-unitary quantum cellular automata

Elisabeth Wagner, Ramil Nigmatullin, Alexei Gilchrist, Gavin K. Brennen

SciPost Phys. 16, 014 (2024) · published 17 January 2024 | · pdf

The information flow in a quantum system is a fundamental feature of its dynamics. An important class of dynamics are quantum cellular automata (QCA), systems with discrete updates invariant in time and space, for which an index theory has been proposed for the quantification of the net flow of quantum information across a boundary. While the index is rigid in the sense of begin invariant under finite-depth local circuits, it is not defined when the system is coupled to an environment, i.e.for non-unitary time evolution of open quantum systems. We propose a new measure of information flow for non-unitary QCA denoted the information current which is not rigid, but can be computed locally based on the matrix-product operator representation of the map.

2 citations
Codebase release 0.1 for MatsubaraFunctions.jl

Dominik Kiese, Anxiang Ge, Nepomuk Ritz, Jan von Delft, Nils Wentzell

SciPost Phys. Codebases 24-r0.1 (2024) · published 11 January 2024 | · src

The Matsubara Green's function formalism stands as a powerful technique for computing the thermodynamic characteristics of interacting quantum many-particle systems at finite temperatures. In this manuscript, our focus centers on introducing MatsubaraFunctions.jl, a Julia library that implements data structures for generalized n-point Green's functions on Matsubara frequency grids. The package's architecture prioritizes user-friendliness without compromising the development of efficient solvers for quantum field theories in equilibrium. Following a comprehensive introduction of the fundamental types, we delve into a thorough examination of key facets of the interface. This encompasses avenues for accessing Green's functions, techniques for extrapolation and interpolation, as well as the incorporation of symmetries and a variety of parallelization strategies. Examples of increasing complexity serve to demonstrate the practical utility of the library, supplemented by discussions on strategies for sidestepping impediments to optimal performance.

2 citations
Modified rational six vertex model on the rectangular lattice

Samuel Belliard, Rodrigo Alves Pimenta, Nikita A. Slavnov

SciPost Phys. 16, 009 (2024) · published 9 January 2024 | · pdf

We consider a rational six vertex model on a rectangular lattice with boundary conditions that generalize the usual domain wall type. We find that the partition function of the inhomogeneous version of this model is given by a modified Izergin determinant. The proofs are based on the quantum inverse scattering method and its representation theory together with elementary linear algebra.

2 citations
Wegner's Ising gauge spins versus Kitaev's Majorana partons: Mapping and application to anisotropic confinement in spin-orbital liquids

Urban F. P. Seifert, Sergej Moroz

SciPost Phys. 16, 147 (2024) · published 5 June 2024 | · pdf

Emergent gauge theories take a prominent role in the description of quantum matter, supporting deconfined phases with topological order and fractionalized excitations. A common construction of $\mathbb{Z}_2$ lattice gauge theories, first introduced by Wegner, involves Ising gauge spins placed on links and subject to a discrete $\mathbb{Z}_2$ Gauss law constraint. As shown by Kitaev, $\mathbb{Z}_2$ lattice gauge theories also emerge in the exact solution of certain spin systems with bond-dependent interactions. In this context, the $\mathbb{Z}_2$ gauge field is constructed from Majorana fermions, with gauge constraints given by the parity of Majorana fermions on each site. In this work, we provide an explicit Jordan-Wigner transformation that maps between these two formulations on the square lattice, where the Kitaev-type gauge theory emerges as the exact solution of a spin-orbital (Kugel-Khomskii) Hamiltonian. We then apply our mapping to study local perturbations to the spin-orbital Hamiltonian, which correspond to anisotropic interactions between electric-field variables in the $\mathbb{Z}_2$ gauge theory. These are shown to induce anisotropic confinement that is characterized by emergence of weakly-coupled one-dimensional spin chains. We study the nature of these phases and corresponding confinement transitions in both absence and presence of itinerant fermionic matter degrees of freedom. Finally, we discuss how our mapping can be applied to the Kitaev spin-1/2 model on the honeycomb lattice.

2 citations
Extremality as a consistency condition on subregion duality

Ronak M. Soni

SciPost Phys. 17, 133 (2024) · published 13 November 2024 | · pdf

In JT gravity coupled to a CFT, I argue without using the path integral that the entanglement wedge of a boundary region is bounded by a quantum extremal surface (QES). For any candidate not bounded by a QES, a unitary in the complement can make reconstruction within the candidate inconsistent with boundary causality. The case without islands is a direct consequence of subregion duality, and the case with islands can also be dealt with with a stronger assumption.

2 citations

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