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Spontaneous symmetry breaking can persist at all temperatures in certain biconical $\mathrm{O}(N)\times \mathbb{Z}_2$ vector models when the underlying field theories are ultraviolet complete. So far, the existence of such theories has been established in fractional dimensions for local but nonunitary models or in 2+1 dimensions but for nonlocal models. Here, we study local models at zero and finite temperature directly in 2+1 dimensions employing functional methods. At zero temperature, we establish that our approach describes the quantum critical behaviour with high accuracy for all $N\geq 2$. We then exhibit the mechanism of discrete symmetry breaking from $\mathrm{O}(N)\times \mathbb{Z}_2\to \mathrm{O}(N)$ for increasing temperature near the biconical critical point when $N$ is finite but large. We calculate the corresponding finite-temperature phase diagram and further show that the Hohenberg-Mermin-Wagner theorem is fully respected within this approach, i.e., symmetry breaking only occurs in the $\mathbb{Z}_2$ sector. Finally, we determine the critical $N$ above which this phenomenon can be observed to be $N_c \approx 15$., Comment: 6 + 5 pages, 3 + 2 figures, comments welcome

We study dipole Chern-Simons theory with and without a cosmological constant in $2+1$ dimensions. We write the theory in a second order formulation and show that this leads to a fracton gauge theory coupled to Aristotelian geometry which can also be coupled to matter. This coupling exhibits the remarkable property of generalizing dipole gauge invariance to curved spacetimes, without placing any limitations on the possible geometries. We also use the second order formulation to construct a higher dimensional generalization of the action. Finally, for the $(2+1)$-dimensional Chern-Simons theory we find solutions and interpret these as electric monopoles, analyze their charges and argue that the asymptotic symmetries are infinite-dimensional., Comment: 25 pages, no figures

We investigate the most general gauging operations in 2+1 dimensional oriented field theories with finite symmetry groups, which correspond to gapped boundary conditions in 3+1 dimensional Dijkgraaf-Witten theory. The classification is achieved by enumerating 2+1 dimensional oriented topological quantum field theories that cancel the 't Hooft anomaly associated with the symmetry. This framework is rigorously formulated using twisted crossed extensions of modular fusion categories and projective 3-representations. Additionally, we explore the resulting fusion 2-category symmetries and argue that this framework captures all possible categorical symmetries in 2+1 dimensional oriented field theories., Comment: 22 pages, 7 figures, v2: minor revisions

In this article, we develop a systematic approach of the invariant subspace method combined with variable transformation to find the generalized separable exact solutions of the nonlinear two-component system of time-fractional PDEs (TFPDEs) in (2+1)-dimensions for the first time. Also, we explicitly explain how to construct various kinds of finite-dimensional invariant linear product spaces for the given system using the invariant subspace method combined with variable transformation. Additionally, we present how to use the obtained invariant linear product spaces to derive the generalized separable exact solutions of the discussed system. We also note that the discussed method will help to reduce the nonlinear two-component system of TFPDEs in (2+1)-dimensions into the nonlinear two-component system of TFPDEs in (1+1)-dimensions, which again reduces to a system of time-fractional ODEs through the obtained invariant linear product spaces. More specifically, the significance and efficacy of the systematic investigation of the discussed method have been investigated through the initial and boundary value problems of the generalized nonlinear two-component system of time-fractional reaction-diffusion equations (TFRDEs) in (2+1)-dimensions for finding the generalized separable exact solutions, which can be expressed in terms of the exponential, trigonometric, polynomial, Euler-Gamma and Mittag-Leffler functions. Also, 2D and 3D graphical representations of some of the obtained solutions are presented for different values of fractional orders.

We address the question of whether holographic entropy inequalities obeyed in static states (by the RT formula) are always obeyed in time-dependent states (by the HRT formula), focusing on the case where the bulk spacetime is 2+1 dimensional. An affirmative answer to this question was previously claimed by Czech-Dong. We point out an error in their proof when the bulk is multiply connected. We nonetheless find strong support, of two kinds, for an affirmative answer in that case. We extend the Czech-Dong proof for simply-connected spacetimes to spacetimes with $\pi_1=\mathbb{Z}$ (i.e. 2-boundary, genus-0 wormholes). Specializing to vacuum solutions, we also numerically test thousands of distinct inequalities (including all known RT inequalities for up to 6 regions) on millions of randomly chosen configurations of regions and bulk spacetimes, including three different multiply-connected topologies; we find no counterexamples. In an appendix, we prove some (dimension-independent) facts about degenerate HRT surfaces and symmetry breaking., Comment: 30 pages. Watch a 4-minute video abstract: https://www.youtube.com/watch?v=ols92YU8rus

We consider families of invertible many-body quantum states in $d$ spatial dimensions that are parameterized over some parameter space $X$. The space of such families is expected to have topologically distinct sectors classified by the cohomology group $\mathrm{H}^{d+2}(X;\mathbb{Z})$. These topological sectors are distinguished by a topological invariant built from a generalization of the Berry phase, called the higher Berry phase. In the previous work, we introduced a generalized inner product for three one-dimensional many-body quantum states, (``triple inner product''). The higher Berry phase for one-dimensional invertible states can be introduced through the triple inner product and furthermore the topological invariant, which takes its value in $\mathrm{H}^{3}(X;\mathbb{Z})$, can be extracted. In this paper, we introduce an inner product of four two-dimensional invertible quantum many-body states. We use it to measure the topological nontriviality of parameterized families of 2d invertible states. In particular, we define a topological invariant of such families that takes values in $\mathrm{H}^{4}(X;\mathbb{Z})$. Our formalism uses projected entangled pair states (PEPS). We also construct a specific example of non-trivial parameterized families of 2d invertible states parameterized over $\mathbb{R}P^4$ and demonstrate the use of our formula. Applications for symmetry-protected topological phases are also discussed., Comment: 31pages, 10 figures

We extended the notion of Newton-Wigner localization, already constructed in the bi-dimensional de Sitter space, to the tri-dimensional case for both principal and complementary series. We identify the one-particle subspace, generated by the positive-energy modes solution of the Klein-Gordon equation, as an irreducible representation of the de Sitter group. The time-evolution of the Newton-Wigner operator was obtained explicitly, and for the complementary series the evolution is trivial, i.e., there are no dynamics. Also, we discussed heuristically the existing sign ambiguity when we do not require as a postulate that the Newton-Wigner functions must be proportional to their respective solutions in the representation of solutions of the Klein-Gordon equation., Comment: Preliminary version, comments are welcome

Conformal electrodynamics is a particularly interesting example of power Maxwell non-linear electrodynamics, designed to possess conformal symmetry in all dimensions. In this paper, we propose a regularized version of Conformal electrodynamics, minimally regularizing the field of a point charge at the origin by breaking the conformal invariance of the theory with a dimensionfull "Born-Infeld-like" parameter. In four dimensions the new theory reduces to the recently studied Regularized Maxwell electrodynamics, distinguished by its "Maxwell-like" solutions for accelerated and slowly rotating black hole spacetimes. Focusing on three dimensions, we show that the new theory shares many of the properties of its four-dimensional cousin, including the existence of the charged C-metric solution (currently unknown in the Maxwell theory)., Comment: 10 pages, 2 figures

We investigate the propagation of a scalar field in a $(2+1)$-dimensional accelerated black hole, recently revisited in \cite{Arenas_Henriquez_2022}. We briefly describe the minimally-coupled configuration as rendering a trivial scalar perturbation with a rescale of the field mass. On the contrary, the free scalar field propagation presents an intricate dynamic, whose equation may be reduced through the use of Israel junction conditions and a non-trivial ansatz. In this case, using two different methods we calculate the quasinormal modes of the solution also obtaining unstable field profiles delivered by the linear scalar perturbation to the background geometry. We scrutinize the parameter space of angular eigenvalue of the field and accelerations under which such instabilities happen., Comment: 12 pages, 2 figures, 4 tables

We investigate quasitopological black holes in $(2+1)$ dimensions in the context of electromagnetic-generalized-quasitopological-gravities (EM-GQT). For three different families of geometries of quasitopological nature, we study the causal structure and their response to a probe scalar field. To linear order, we verify that the scalar field evolves stably, decaying in different towers of quasinormal modes. The studied black holes are either charged geometries (regular and singular) or a regular Ba\~nados-Teitelboim-Zanelli (BTZ)-like black hole, both coming from the EM-GQT theory characterized by nonminimal coupling parameters between gravity and a background scalar field. We calculate the quasinormal modes applying different numerical methods with convergent results between them. The oscillations demonstrate a very peculiar structure for charged black holes: in the intermediate and near extremal cases, a particular scaling arises, similar to that of the rotating BTZ geometry, with the modes being proportional to the distance between horizons. For the single horizon black hole solution, we identify the presence of different quasinormal families by analyzing the features of that spectrum. In all three considered geometries, no instabilities were found., Comment: 26 pages, 5 figures. References added

We study the Skyrmion of the $SO(2)$ gauged $O(3)$ sigma model in $2+1$ dimensions in the presence of a Skyrme--Chern-Simons (SCS) term, and compare its properties with the corresponding properties of the Skyrmion in the presence of the usual Chern-Simons (CS) term. We find that these properties are qualitatively largely similar in both cases, meaning that the SCS density can be employed as an alternative to the CS term also in higher dimensions, most importantly in even dimensions where no CS term is defined, $e.g.,$ in $3+1$ dimensions. The SCS density employed here is defined in terms of the pair of $SO(2)\times SO(2)$ gauge fields and an auxiliary $O(5)$ Skyrme scalar, which is contracted to an effective $O(3)$ Skyrme scalar. Technically, this study maps the methods to be applied in higher dimensional examples., Comment: 26 pages, 10 figures

General relativity becomes vastly simpler in three spacetime dimensions: all vacuum solutions have constant curvature, and the moduli space of solutions can be almost completely characterized. As a result, this lower dimensional setting becomes an ideal test bed for a wide range of approaches to quantum gravity, from reduced phase phase space quantization to covariant canonical quantization to path integral methods to asymptotic quantization of "edge states." Here I review a variety of classical descriptions of the moduli space of solutions and a broad range of quantizations, with special attention to implications for realistic quantum gravity in four spacetime dimensions., Comment: 27 pages; invited contribution to the 2nd edition of the Encyclopedia of Mathematical Physics

The (2+1)-dimensional analog self-dual gravity which is obtained via dimension reduction of the (3+1)-dimensional Holst action without reducing the internal gauge group is studied. A Chern-Simons formulation for this theory is constructed based on the gauge group $SL(2,\CC)_\RR\rcross \Rsix$ and maps the 3d complex self-dual dynamical variable and connection to $6d$ real variables which combines into a $12d$ Cartan connection. Quantization is given by the application of the combinatorial quantisation program of Chern-Simons theory. The Poisson structure for the moduli space of flat connections on $(SL(2,\CC)_\RR\rcross \Rsix)^{n+2g}$ which emerges in the combinatorial description of the phase space on $\RR \times \Sigma_{g,n},$ where $\Sigma_{g,n}$ is a genus $g$ surface with $n$ punctures is given in terms of the classical $r$-matrix for the quantum double $D(SL(2,\CC)_\RR)$ viewed as the double of a double $ D(SU(2)\dcross AN(2))$. This quantum double provides a feature for quantum symmetries of the quantum theory for the model., Comment: 26 pages

Two actions which are functionals of different variables but describing the same dynamical system can be shown to possess the same origin by constructing a master action which generates both of them. We first present the master action which produces an action depending on the fluid variables and a gauge theory action whose equations of motion are equivalent to the incompressible fluid Euler equations in $2+1$ dimensions. We then introduce the master action generating the actions which on shell provide the linearized shallow water equations. One of them is a functional of the variables of the shallow water and the other one is the Maxwell-Chern-Simons gauge theory action.The maps between gauge vector fields and fluid variables are obtained for both of the systems. We employ them to derive the corresponding gauge theory solutions of the Hopfion and the coastal Kelvin wave solutions., Comment: 8 pages

We study a massless real self-interacting scalar field $\varphi$ non-minimally coupled to Einstein gravity with torsion in (2+1) space-time dimensions in the presence of cosmological constant. The field equations with a self-interaction potential $V(\varphi)$ including $\varphi^{n}$ terms are derived by a variational principle. By numerically solving these field equations with the 4th Runge-Kutta method, the circularly symmetric rotating solutions for (2+1) dimensions Einstein gravity with torsion are obtained. Exact analytical solutions to the field equations are derived for the proposed metric in the absence of both torsion and angular momentum. We find that the self-interacting potential only exists for $n=6$. We also study the motion of massive and massless particles in (2+1) Einstein gravity with torsion coupled to a self-interacting scalar field. The effect of torsion on the behavior of the effective potentials of the particles is analyzed numerically., Comment: 17 pages, 25 figures

In this paper, we study thermodynamics and its applications to the static charged dilaton black hole in 2+1 dimensions. We chose the extended phase space where the pressure $P = -\frac{\Lambda}{ 8 \pi}$. There is a number $N$ for the black hole solutions which leads to a class of black holes where $ \frac{2}{3} \leq N < 2$. We noticed that thermodynamic behavior falls into two broad categories: For $\frac{2}{3} \leq N < 1$, the black hole is locally stable for all values of the horizon radius and does not go through phase transitions. For $ 1 \leq N < 2$, small black holes are locally stable and large black holes are not: there is a first order phase transition between small black holes and the thermal AdS space similar to Hawking-Page phase transition. In order to demonstrate the two broad categories, we have focused on $N =1, \frac{2}{3}$ and $N = \frac{6}{7}$ black holes in detail. We computed the first law and the Smarr relations for the black hole and introduced two new thermodynamical parameters in order to satisfy the first law. We computed specific heat capacities, internal energy and free energy for black holes and studied local and global stability of the black hole. We have also studied the Joule-Thomson expansion for the black hole. It is also noted that unlike the charged BTZ black hole, the charged dilaton black hole does not violate the Reverse Isoperimetric Inequality for certain values of parameters of the theory., Comment: 31 pages, 24 figures

We study the fermion pair creation phenomenon due to the time dependence of curves, where boundary conditions are imposed on a Dirac field in 2+1 dimensions. These conditions, which lead to non-trivial relations for the normal component of the fermionic current, depend on the value of a dimensionless parameter. We show that the pair creation effect is maximized for bag boundary conditions, obtained for a particular value of that parameter. The effect is studied in terms of the effective action to extract information on the probability of vacuum decay, using an expansion in powers of the deformation of the curves with respect to straight lines. We demonstrate that the first non-trivial contributions to this process can be obtained from the electromagnetic vacuum polarization tensor for a Dirac field coupled to static boundaries., Comment: 16 pages, LaTeX

In the present work we explore the interaction of a one-dimensional kink-like front of the sine-Gordon equation moving in 2-dimensional spatial domains. We develop an effective equation describing the kink motion, characterizing its center position dynamics as a function of the transverse variable. The relevant description is valid both in the Hamiltonian realm and in the non-conservative one bearing gain and loss. We subsequently examine a variety of different scenarios, without and with a spatially-dependent heterogeneity. The latter is considered both to be one-dimensional ($y$-independent) and genuinely two-dimensional. The spectral features and the dynamical interaction of the kink with the heterogeneity are considered and comparison with the effective quasi-one-dimensional description (characterizing the kink center as a function of the transverse variable) is also provided. Generally, good agreement is found between the analytical predictions and the computational findings in the different cases considered., Comment: 26 pages, 21 figures

In the realm of lower-dimensional accelerating spacetimes, it is well-established that the presence of domain walls, which are co-dimension one topological defects, is a necessary condition for their construction. We expand the geometric framework by adding a conformally coupled scalar field. This endeavor leads to the identification of several new families of three-dimensional accelerating spacetimes with asymptotically locally anti-de Sitter (AdS) behavior. Notably, one of these solutions showcases a hairy generalization of the accelerating BTZ black hole. This solution is constructed at both slow and rapid phases of acceleration, and its connection with established vacuum spacetime models is explicitly elucidated. The inclusion of the scalar field imparts a non-constant Ricci curvature to the domain wall, thereby rendering these configurations particularly suitable for the construction of two-dimensional quantum black holes. To establish a well-posed variational principle in the presence of the domain wall, two essential steps are undertaken. First, we extend the conventional renormalized AdS$_3$ action to accommodate the presence of the scalar field. Second, to establish a well-posed variational principle, we extend the renormalized AdS$_3$ action to include the scalar field and incorporate the Gibbons--Hawking--York term for internal boundaries and domain wall tension. We engage in holographic computations, thereby determining the explicit form of the holographic stress tensor. In this context, the stress tensor can be expressed as that of a perfect fluid situated on a curved background. Additionally, it paves the road to ascertain the spacetime mass. Finally, we close by demonstrating the existence of three-dimensional accelerating spacetimes with asymptotically locally flat and asymptotically locally de Sitter geometries, particularly those embodying black holes., Comment: 45 pages, 17 figures, 3 tables. Published version

This paper studies the holographic description of $2+1-$dimensional accelerating black holes. We start by using an ADM decomposition of the coordinates suitable to identify boundary data. As a consequence, the holographic CFT lies in a fixed curved background which is described by the holographic stress tensor of a perfect fluid. We compute the Euclidean action ensuring that the variational principle is satisfied in the presence of the domain wall. This requires including the Gibbons--Hawking--York term associated with internal boundaries on top of the standard renormalised AdS$_{3}$ action. Finally, we compute the entanglement entropy by firstly mapping the solution to the Rindler--AdS spacetime in which the Ryu--Takayanagi surface is easily identifiable. We found that as the acceleration increases the accessible region of the conformal boundary decreases and also the entanglement entropy, indicating a loss of information in the dual theory due to acceleration., Comment: 15 pages, 7 figures, 1 table. V2: minor changes, references added, typos corrected, accepted for publication in JHEP

There is a surge of research devoted to the formalism and physical manifestations of non-Lorentzian kinematical symmetries, which focuses especially on the ones associated with the Galilei and Carroll relativistic limits (the speed of light taken to infinity or to zero, respectively). The investigations have also been extended to quantum deformations of the Carrollian and Galilean symmetries, in the sense of (quantum) Hopf algebras. The case of 2+1 dimensions is particularly worth to study due to both the mathematical nature of the corresponding (classical) theory of gravity, and the recently finalized classification of all quantum-deformed algebras of spacetime isometries. Consequently, the list of all quantum deformations of (anti-)de Sitter-Carroll algebra is immediately provided by its well-known isomorphism with either Poincar\'{e} or Euclidean algebra. Quantum contractions from the (anti-)de Sitter to (anti-)de Sitter-Carroll classification allow to almost completely recover the latter. One may therefore conjecture that the analogous contractions from the (anti-)de Sitter to (anti-)de Sitter-Galilei $r$-matrices provide (almost) all coboundary deformations of (anti-)de Sitter-Galilei algebra. This scheme is complemented by deriving (Carrollian and Galilean) quantum contractions of deformations of Poincar\'{e} algebra, leading to coboundary deformations of Carroll and Galilei algebras., Comment: 28 pages, 4 figures, 1 table v2 some results improved, details clarified, new Section 6, Introduction expanded, references added, 1 extra figure, 1 extra table v3 Introduction, Conclusions and Appendix expanded, minor corrections and clarifications elsewhere, figures updated, references added

It is known that the $2+1$d single Majorana fermion theory has an anomaly of the reflection, which is canceled out when 16 copies of the theory are combined. Therefore, it is expected that the reflection symmetric boundary condition is impossible for one Majorana fermion, but possible for 16 Majorana fermions. In this paper, we consider a reflection symmetric boundary condition that varies at a single point, and find that there is a problem with one Majorana fermion. The problem is the absence of a corresponding outgoing wave to a specific incoming wave into the boundary, which leads to the non-conservation of the energy. For 16 Majorana fermions, it is possible to connect every incoming wave to an outgoing wave without breaking the reflection symmetry. In addition, we discuss the connection with the fermion-monopole scattering in $3+1$ dimensions., Comment: 24 pages, 2 figures

In this paper we parallel the construction of Tong of a gauge theory for shallow water, by writing a gauge theory for the Euler fluid in 2+1 dimensions. We then extend it to an Euler fluid coupled to electromagnetic background. We argue that the gauge theory formulation provides a topological argument for the quantization of 2+1 dimensional Euler Hopfion solution. In the process, we find a (non-gauge) action for the Euler fluid that can be extended to any dimension, including the physical 3+1 dimensions. We discuss several aspects of the ABC flow., Comment: 20 pages, no figures; reference added, connection to previous Euler fluid action explained; references added

Quantum electrodynamics in $2+1$ dimensions (QED$_3$) has been proposed as a critical field theory describing the low-energy effective theory of a putative algebraic Dirac spin liquid or of quantum phase transitions in two-dimensional frustrated magnets. We provide compelling evidence that the intricate spectrum of excitations of the elementary but strongly frustrated $J_1$-$J_2$ Heisenberg model on the triangular lattice is in one-to-one correspondence to a zoo of excitations from QED$_3$, in the quantum spin liquid regime. This includes a large manifold of explicitly constructed monopole and bilinear excitations of QED$_3$, which is thus shown to serve as an organizing principle of phases of matter in triangular lattice antiferromagnets and their low-lying excitations. Moreover, we observe signatures of an emergent valence bond solid (VBS), which suggests a scenario where only the critical point of a transition from the $120^\circ$ N\'eel order to a VBS is described by QED$_3$. Our results are obtained by comparing ansatz wave functions from a parton construction to exact eigenstates obtained using large-scale exact diagonalization up to $N=48$ sites., Comment: 8 pages, 5 figures, including supplementary material

We apply the framework of Cauchy Slice Holography to the quantization of gravity on closed slices with $\Lambda>0$ (with a focus on $2+1$ dimensions for concreteness). We obtain solutions to the Wheeler-DeWitt equation in a basis of CPT-dual branches. Each branch is a $T^2$-deformed CFT partition function with imaginary central charge. We compute explicit solutions in $2+1$ dimensions in a minisuperspace toy model of pure gravity. This analysis gives us evidence to conjecture a connection between the choice of superposition of branches and the choice of class of geometries to sum over in the gravitational path integral. We further show that, in full quantum gravity on closed slices, bulk unitarity holds, despite the Euclidean holographic field theory not being reflection-positive. We conjecture about the (non)uniqueness of the quantum state of the Universe, in light of this analysis., Comment: 28 pages, 8 figures; added a few more clarifications and comments

We test the eigenstate thermalization hypothesis (ETH) for 2+1 dimensional SU(2) lattice gauge theory. By considering the theory on a chain of plaquettes and truncating basis states for link variables at $j=1/2$, we can map it onto a quantum spin chain with local interactions and numerically exactly diagonalize the Hamiltonian for reasonably large lattice sizes. We find energy level repulsion in momentum sectors with no remaining discrete symmetry. We study two local observables made up of Wilson loops and calculate their matrix elements in the energy eigenbasis, which are shown consistent with the ETH., Comment: 7+6 pages, 4+4 figures, v3: published version, minor change compared with v2

The dynamics of defect excitations in crystalline solids is necessary to understand the macroscopic low-energy properties of elastic media. We use fracton-elasticity duality to systematically study the defect dynamics and interactions in the linear isotropic medium. We derive the explicit expressions for the dual gauge potentials for moving dislocations and the resulting Jefimenko equations. We also compute stresses and strains. The paper includes two physical situations: when the vacancy number is fixed and when the number is fluctuating. If defects are present we show a constraint that needs to be satisfied by them when they climb perpendicularly to their Burgers vector. Next, we extend the classic result of Peach and Koehler for the force between two dislocations and show that, similarly, to moving charges in electrodynamics, it is non-reciprocal, when one dislocation is moving. We argue that our formalism can be extended beyond Cauchy's elasticity by exploiting the simplifications provided by the dual gauge formulation of elastic stresses., Comment: v2: 11 pages, minor corrections, updated material and references, accepted for publication in Physical Review B

The Hamiltonian limit of lattice gauge theories can be found by extrapolating the results of anisotropic lattice computations, i.e., computations using lattice actions with different temporal and spatial lattice spacings ($a_t\neq a_s$), to the limit of $a_t\to 0$. In this work, we present a study of this Hamiltonian limit for a Euclidean $U(1)$ gauge theory in 2+1 dimensions (QED3), regularized on a toroidal lattice. The limit is found using the renormalized anisotropy $\xi_R=a_t/a_s$, by sending $\xi_R \to 0$ while keeping the spatial lattice spacing constant. We compute $\xi_R$ in $3$ different ways: using both the ``normal'' and the ``sideways'' static quark potential, as well as the gradient flow evolution of gauge fields. The latter approach will be particularly relevant for future investigations of combining quantum computations with classical Monte Carlo computations, which requires the matching of lattice results obtained in the Hamiltonian and Lagrangian formalisms.

This note presents a new proof of the well-known Strichartz estimates for the Schr\"odinger equation in $2+1$ dimensions, building on ideas from our recent work \cite{MO}., Comment: Additional remarks and corrections from the referees were implemented

We investigate the Gross-Neveu model in $2+1$ dimensions in a constant and homogeneous magnetic field using one reducible flavor of overlap fermions. Our lattice simulations suggest that the magnetic catalysis phenomenon, i.e., an increase of the chiral condensate with the magnetic field, is present for all temperatures below the chiral phase transition, in accordance with predictions from mean-field and beyond-mean-field calculations., Comment: 7 pages, 4 figures; talk given at the 39th International Symposium on Lattice Field theory (LATTICE 2022) in Bonn; August 8-13 2022

In this work, inhomogeneous chiral phases are studied in a variety of Four-Fermion and Yukawa models in $2+1$ dimensions at zero and non-zero temperature and chemical potentials. Employing the mean-field approximation, we do not find indications for an inhomogeneous phase in any of the studied models. We show that the homogeneous phases are stable against inhomogeneous perturbations. At zero temperature, full analytic results are presented., Comment: 10 pages, 1 figure, contains ancillary files with plot data; talk given at the 39th International Symposium on Lattice Field theory (LATTICE 2022) in Bonn; August 8-13 2022

We show that infinite families of non-relativistic spin-$3$ symmetries in $2+1$ dimensions, which include higher-spin extensions of the Bargmann, Newton-Hooke, non-relativistic Maxwell, and non-relativistic AdS-Lorentz algebras, can be obtained as Lie algebra expansions of two different spin-$3$ extensions of the Nappi-Witten symmetry. These higher-spin Nappi-Witten algebras, in turn, are obtained by means of In\"on\"u-Wigner contractions applied to suitable direct product extensions of $\mathfrak{sl}(3,\mathbb{R})$. Conversely, we show that the same result can be obtained by considering contractions of expanded $\mathfrak{sl}(3,\mathbb{R})$ algebras. The method can be used to define non-relativistic higher-spin Chern-Simon gravity theories in $2+1$ dimensions in a systematic way., Comment: 44 pages, typos corrected, references added

Rank-2 toric code (R2TC), a prototypical archetype of the discrete rank-2 symmetric gauge theory, has properties that differ from those of the standard toric code. Specifically, it features a blending of UV and IR in its ground state, restricted mobility of its quasiparticles, and variations in the braiding statistics of its quasiparticles based on their position. In this paper, we investigate various aspects of $\mathbb{Z}_N$ rank-2 gauge theory in ${(2+1)}$-dimensional spacetime. Firstly, we demonstrate that $U(1)$ rank-2 gauge theory can arise from ${U(1)\times U(1)}$ rank-1 gauge theory after condensing the gauge charges in a specific way. This construction scheme of $U(1)$ rank-2 gauge theory carries over to the $\mathbb{Z}_N$ case simply by Higgsing $U(1)$ to $\mathbb{Z}_N$, after which the resulting rank-2 gauge theory can be tuned to the R2TC. The holonomy operators of R2TC are readily identified using this scheme and are given clear physical interpretation as the pair creation/annihilation of various monopoles and dipoles. Explicit tensor network construction of the ground states of R2TC are given as two copies of the ground states of Kitaev's toric code that are `sewn together' according to the condensation scheme. In addition, through a similar anyon condensation protocol, we present a double semion version of rank-2 toric code whose flux excitations exhibit restricted mobility and semionic statistics. Finally, we identify the generalized discrete symmetries of the R2TC, which are much more complex than typical 1-form symmetries. They include conventional and unconventional 1-form symmetries, such as framed 1-form symmetries and what we call sublattice 1-form symmetries. Using these, we interpret the R2TC's unique properties (UV/IR mixing, position-dependent braiding, etc.) from the modern perspective of generalized spontaneous symmetry breaking and 't Hooft anomalies., Comment: 26 pages, 14 figures, one append section

The construction of Quasi-topological gravities in three-dimensions requires coupling a scalar field to the metric. As shown in arXiv:2104.10172, the resulting "Electromagnetic" Quasi-topological (EQT) theories admit charged black hole solutions characterized by a single-function for the metric, $-g_{tt}=g^{-1}_{rr}\equiv f(r)$, and a simple azimuthal form for the scalar. Such black holes, whose metric can be determined fully analytically, generalize the BTZ solution in various ways, including singularity-free black holes without any fine-tuning of couplings or parameters. In this paper we extend the family of EQT theories to general curvature orders. We show that, beyond linear order, $f(r)$ satisfies a second-order differential equation rather than an algebraic one, making the corresponding theories belong to the Electromagnetic Generalized Quasi-topological (EGQT) class. We prove that at each curvature order, the most general EGQT density is given by a single term which contributes nontrivially to the equation of $f(r)$ plus densities which do not contribute at all to such equation. The proof relies on the counting of the exact number of independent order-$n$ densities of the form $\mathcal{L}(R_{ab},\partial_a \phi)$, which we carry out. We study some general aspects of the new families of EGQT black-hole solutions, including their thermodynamic properties and the fulfillment of the first law, and explicitly construct a few of them numerically., Comment: 30 pages, 1 figure. v2: some new references added

We present a theory of hydrodynamics for a vector U(1) charge in 2+1 dimensions, whose rotational symmetry is broken to the point group of an equilateral triangle. We show that it is possible for this U(1) to have a chiral anomaly. The hydrodynamic consequence of this anomaly is the introduction of a ballistic contribution to the dispersion relation for the hydrodynamic modes. We simulate classical Markov chains and find compelling numerical evidence for the anomalous hydrodynamic universality class. Generalizations of our theory to other symmetry groups are also discussed.

This paper investigates a new class of regular black hole solutions in (2 + 1)-dimensions by introducing a generalization of the quasi-localized matter model proposed by Estrada and Tello-Ortiz. Initially, we try to physically interpret the matter source encoded in the energy-momentum tensor as originating from nonlinear electrodynamics. We show, however, that the required conditions for the quasi-locality of the energy density are incompatible with the expected behavior of nonlinear electrodynamics, which must tend to Maxwell's theory on the asymptotic limit. Despite this, we propose a generalization for the quasi-localized energy density that encompasses the existing models in the literature and allows us to obtain a class of regular black hole solutions exhibiting remarkable features on the event horizons and their thermodynamic properties. Furthermore, since the usual version of the first law of thermodynamics, due to the presence of the matter fields, leads to incorrect values of entropy and thermodynamics volume for regular black holes, we propose a new version of the first law for regular black holes., Comment: 17 pages, 4 figures, improved version, author added, published in Phys. Lett. B

We extend the concept of dual unitary quantum gates to quantum lattice models in $2 + 1$ dimensions, by introducing and studying ternary unitary four-particle gates, which are unitary in time and both spatial dimensions. When used as building blocks of lattice models with periodic boundary conditions in time and space (corresponding to infinite temperature states), dynamical correlation functions exhibit a light-ray structure. We also generalize solvable MPS to two spatial dimensions with cylindrical boundary conditions, by showing that the analogous solvable PEPS can be identified with matrix product unitaries. In the resulting tensor network for evaluating equal-time correlation functions, the bulk ternary unitary gates cancel out. We delineate and implement a numerical algorithm for computing such correlations by contracting the remaining tensors., Comment: 16 pages, 6 figures