Wilson Loops Research Articles

Flat equivariant gerbes: holonomies and dualities

We examine the role of global topological data associated to choices of holonomy for flat gauge fields in string compactification. Our study begins with perturbative string compactification on compact flat manifolds preserving 8 supercharges in 5 dimensions. By including non-trivial holonomy for Wilson lines in the heterotic string and for the B-field gerbe in the type II string we find worldsheet dualities that relate these backgrounds to other string compactifications. While our simple examples allow for explicit analysis, the concepts and some of the methods extend to a broader class of compactifications and have implications for string dualities, perturbative and otherwise.

Phases of Wilson Lines in Conformal Field Theories.

We study the low-energy limit of Wilson lines (charged impurities) in conformal gauge theories in 2+1 and 3+1 dimensions. As a function of the representation of the Wilson line, certain defect operators can become marginal, leading to interesting renormalization group flows and for sufficiently large representations to complete or partial screening by charged fields. This result is universal: in large enough representations, Wilson lines are screened by the charged matter fields. We observe that the onset of the screening instability is associated with fixed-point mergers. We study this phenomenon in a variety of applications. In some cases, the screening of the Wilson lines takes place by dimensional transmutation and the generation of an exponentially large scale. We identify the space of infrared conformal Wilson lines in weakly coupled gauge theories in 3+1 dimensions and determine the screening cloud due to bosons or fermions. We also study QED in 2+1 dimensions in the large N_{f} limit and identify the nontrivial conformal Wilson lines. We briefly discuss 't Hooft lines in 3+1-dimensional gauge theories and find that they are screened in weakly coupled gauge theories with simply connected gauge groups. In non-Abelian gauge theories with S duality, this together with our analysis of the Wilson lines gives a compelling picture for the screening of the line operators as a function of the coupling.

Wilson lines construction of [formula omitted] toroidal conformal blocks

We study W3 toroidal conformal blocks for degenerate primary fields in AdS/CFT context. In the large central charge limit W3 algebra reduces to sl3 algebra and sl3 blocks are defined as contributions to W3 blocks coming from the generators of sl3 subalgebra. We consider the construction of sl3 toroidal blocks in terms of Wilson lines operators of 3d Chern-Simons gravity in the thermal AdS3 space-time. According to the correspondence, degenerate primary fields are associated with Wilson lines operators acting in the corresponding finite-dimensional sl3 representations. We verify this dual construction for one-point toroidal block using sl3 tensor technique in the bulk theory and an algorithm based on AGT correspondence in the boundary CFT.

Holographic entanglement entropy in [formula omitted]-deformed AdS3

In this work, we study the holographic entanglement entropy in AdS3 gravity with the certain mixed boundary condition, which turns out to correspond to TT¯-deformed 2D CFTs. By employing the Chern-Simons formalism and Wilson line technique, the holographic entanglement entropy in TT¯-deformed BTZ black hole is obtained. We also get the same formula by calculating the RT surface. The holographic entanglement entropy agrees with the perturbation result derived from both TT¯-deformed CFTs and cutoff AdS3. Moreover, our result shows that the deformed entanglement entropy for large deformation parameter behaves like the entanglement entropy of CFT at zero temperature. We also consider the entanglement entropy of two intervals and study the effect of TT¯ deformation on phase transition.

Wilson loops for 5d and 3d conformal linear quivers

Within the electrostatic formulation of holographic duals to (balanced) conformal quivers in five and three dimensions, we study Wilson loops in antisymmetric representations. We derive general expressions for various quantities participating in the formalism (VEV of Wilson loops, representation, gauge-node) and apply these to examples, connecting some results present in the bibliography. In the case of three dimensional quivers, we present a relation between Wilson loops in an 'electric' and in the 'magnetic/mirror' descriptions. In a very detailed appendix, we relate the electrostatic and holomorphic description of the holographic duals to these SCFTS.

Topological invariant and domain connectivity in moiré materials

Recently, a moir\'e material has been proposed in which multiple domains of different topological phases appear in the moir\'e unit cell due to a large moir\'e modulation. Topological properties of such moir\'e materials may differ from those of the original untwisted layered material. In this paper, we study how the topological properties are determined in moir\'e materials with multiple topological domains. We show a correspondence between the topological invariant of moir\'e materials at the Fermi level and the topology of the domain structure in real space. We also find a bulk-edge correspondence that is compatible with a continuous change in the truncation condition, which is specific to moir\'e materials. We demonstrate these correspondences in the twisted Bernevig-Hughes-Zhang model that describes general ${\mathbb{Z}}_{2}$-indicated topological insulator phases, by tuning its domain structure in the moir\'e unit cell. The obtained result can only be used to determine the topology at the Fermi level in the charge-neutral condition, but it can be combined with the traditional Wilson loop analysis to determine topologies of other gaps around. These results give a feasible method to evaluate a topological invariant for all occupied bands of a moir\'e material and contribute to the design of topological moir\'e materials and devices.

Topological invariants for interacting systems: From twisted boundary conditions to center-of-mass momentum

Beyond the well-known topological band theory for single-particle systems, it is a great challenge to characterize the topological nature of interacting multiparticle quantum systems. Here, we uncover the relation between topological invariants defined through the twisted boundary condition (TBC) and the center-of-mass (c.m.) momentum state in multiparticle systems. We find that the Berry phase defined through the TBC can be equivalently obtained from the multiparticle Wilson loop formulated by c.m. momentum states. As the Chern number can be written as the winding of the Berry phase, we consequently prove the equivalence of Chern numbers obtained via TBC and c.m. momentum state approaches. As a proof-of-principle example, we study topological properties of the Aubry-Andr\'e-Harper model. Our numerical results show that the TBC approach and c.m. approach are well consistent with each other for both the many-body case and the few-body case. Our work lays a concrete foundation and provides insights for exploring multiparticle topological states.

Tunable symmetry-protected higher-order topological states with fermionic atoms in bilayer optical lattices

Higher-order topological states that possess gapped bulk energy bands and exotic topologically protected boundary states with at least two dimension lower than the bulk have significantly opened a new perspective for understanding of topological quantum matters. Here, we propose to generate two-dimensional topological boundary states for implementing synthetic magnetic flux of ultracold atoms trapped in bilayer optical lattices, which includes Chern insulator, Dirac semimetals, and second-order topological phase (SOTP) by the interplay of the two-photon detuning and effective Zeeman shift. These observed topological phases can be well characterized by the energy gap of bulk, Wilson loop spectra, and the spin textures at the higher symmetric points of system. We show that the SOTP exhibits a pair of $0$D boundary states. While the phases of Dirac semimetals and Chern insulator support the conventional $1$D boundary states due to the principle of bulk-boundary correspondence. Strikingly, the emerged boundary states for Dirac semimetals and SOTP are topologically protected by $\cal P T$-symmetry and chiral-mirror symmetry ($\mathcal{\widetilde{M}}_{\alpha}$), respectively. In particular, the location of $0$D corner states for SOTP which are associated with existing $\mathcal{\widetilde{M}}_{\alpha}$-symmetry can be highly manipulated by tuning magnetic flux. Our scheme herein provides a platform for emerging exotic topological boundary states, which may facilitate the study of higher-order topological phases in ultracold atomic gases.

Asymmetric transverse momentum broadening in an inhomogeneous medium

Gradient jet tomography in high-energy heavy-ion collisions utilizes the asymmetric transverse momentum broadening of a propagating parton in an inhomogeneous medium. Such broadening is studied within a path-integral description of the evolution of the Wigner distribution for a propagating parton in medium. Going beyond the eikonal approximation of multiple scattering, the evolution operator in the transverse direction can be expressed as the functional integration over all classical trajectories of a massive particle with the light-cone momentum $\ensuremath{\omega}$ as its mass. With a dipole approximation of the Wilson line correlation function, evolution with the light-cone time $t$ is determined by the jet transport coefficient $\stackrel{^}{q}$ that can vary with space and time. In a uniform medium with a constant ${\stackrel{^}{q}}_{0}$, the analytical solution to the Wigner distribution becomes a typical drifted Gaussian in both transverse momentum and coordinate with the diffusion width $\sqrt{{\stackrel{^}{q}}_{0}t}$ and $\sqrt{{\stackrel{^}{q}}_{0}{t}^{3}/3{\ensuremath{\omega}}^{2}}$, respectively. In the case of a simple Gaussian-like transverse inhomogeneity with a spatial width $\ensuremath{\sigma}$ on top of a uniform medium, the final asymmetrical momentum distribution can be calculated semianalytically. The transverse asymmetry defined for jet gradient tomography that characterizes the asymmetrical distribution is found to linearly correlate with the initial transverse position of the propagating parton within the domain of the inhomogeneity. It decreases with the parton energy $\ensuremath{\omega}$, increases with the propagation time initially and saturates when the diffusion distance is much larger than the size of the inhomogeneity or ${t}^{3}\ensuremath{\gg}3{\ensuremath{\omega}}^{2}{\ensuremath{\sigma}}^{2}/{\stackrel{^}{q}}_{0}$. The transverse momentum broadening due to the inhomogeneity also saturates at late times in contrast to the continued increase with time if the drifted diffusion in space is ignored.

Holographic imaginary potential of a quark antiquark pair in the presence of gluon condensation

For a moving heavy quark antiquark (QQ) in a quark gluon plasma (QGP), we use gauge/gravity duality to study both real and imaginary parts of the potential ( operatorname{Re}{V}_{Qoverline{Q}} and operatorname{Im}{V}_{Qoverline{Q}} respectively) in a gluon condensate (GC) theory. The complex potential is derived from the Wilson loop by considering the thermal fluctuations of the worldsheet of the Nambu-Goto holographic string. We calculate operatorname{Re}{V}_{Qoverline{Q}} and operatorname{Im}{V}_{Qoverline{Q}} in both cases where the axis of the moving Qoverline{Q} pair is transverse and parallel with respect to its direction of movement in the plasma. Using the renormalization scheme for the operatorname{Re}{V}_{Qoverline{Q}} , we find that the inclusion of GC increases the dissociation length while rapidity has the opposite effect. While for the operatorname{Im}{V}_{Qoverline{Q}} , we observe that by considering the effect of GC, the operatorname{Im}{V}_{Qoverline{Q}} is generated for larger distance thus decreasing quarkonium dissociation, while rapidity has opposite effect. In particular, as the value of GC decreases in the deconfined phase, the operatorname{Im}{V}_{Qoverline{Q}} is generated for smaller distance thus enhancing quarkonium dissociation, and at high temperatures it is nearly not modified by GC, consistent with previous findings of the entropic force.

Analogous quadrupole topology induced by non-Hermiticity

Non-Hermiticity can alter the topological phases of Hermitian lattices and induce gapped edge states and in-gap corner states for the topologically trivial structures in Hermitian cases. To date, however, the realizations of non-Hermiticity-induced higher-order topological phases have often needed intricate designs, where the non-Hermitian systems on a square lattice are comprised of 16 atoms per unit cell with staggered on-site non-Hermitian components at least. It is still necessary to further investigate their topological characteristics in both Hermitian and non-Hermitian systems. In this paper, we suggest an extended quadrupole topological insulator that contains eight atoms in each unit cell and whose topological phases in Hermitian cases are governed by the couplings between adjacent atoms. By introducing external losses into such a higher-order topological insulator, we show that therein the trivial lattices can also give rise to nontrivial quadrupole topology with higher-order corner states. Calculating the biorthogonal nested Wilson loop characterizes the topology for such a non-Hermitian system. Interestingly, the non-Hermitian system has four Wannier bands, with two near zero and two deviating from zero and distributing symmetrically in the negative and positive sections, implying a topology similar to the nontrivial phase in the Hermitian case. Furthermore, both the positive and negative Wannier bands exhibit a nontrivial polarization of 0.5 whereas the remain Wannier bands near zero carry a trivial polarization, indicating that the non-Hermitian system hosts a nontrivial quadrupole topology. We also propose a complete design with acoustic resonators to implement the homologous non-Hermitian topology in acoustic systems to validate our theory. The numerical results match the analytical solution perfectly. Our work introduces an alternative method for fabricating non-Hermitian-induced quadrupole topological insulators and paves the way for future research into the non-Hermitian higher-order topology.

Soft-collinear gravity with fermionic matter

We extend the effective field theory for soft and collinear gravitons to interactions with fermionic matter fields. The full theory features a local Lorentz symmetry in addition to the usual diffeomorphisms, which requires incorporating the former into the soft-collinear gravity framework. The local Lorentz symmetry gives rise to Wilson lines in the effective theory that strongly resemble those in SCET for non-abelian gauge interactions, whereas the diffeomorphisms can be treated in the same fashion as in the case of scalar matter. The basic structure of soft-collinear gravity, which features a homogeneous soft background field, giving rise to a covariant derivative and multipole-expanded covariant Riemann-tensor interactions, remains unaltered and generalises in a natural way to fermion fields.

Topological skyrmion phases of matter

We introduce topological phases of matter defined by skyrmions in the ground state spin—or pseudospin—expectation value textures in the Brillouin zone, the chiral and helical topological skyrmion phases of matter. These phases are protected by a symmetry present in centrosymmetric superconductors. We consider a tight-binding model for spin-triplet superconductivity in transition metal oxides and find it realizes each of these topological skyrmion phases. The chiral phase is furthermore realized for a parameter set characterizing Sr2RuO4 with spin-triplet superconductivity. We also find two types of topological phase transitions by which the skyrmion number can change. The second type occurs without the closing of energy gaps in a system described by a quadratic Hamiltonian without breaking the protecting symmetries when atomic spin–orbit coupling is non-negligible and there is a suitable additional degree of freedom. This contradicts the ‘flat band’ limit assumption important in use of entanglement spectrum and Wilson loops, and in construction of the ten-fold way classification scheme of topological phases of matter. We furthermore predict two kinds of bulk-boundary correspondence signatures—one for measurements which execute a partial trace over degrees of freedom other than spin, which yields quantized transport signatures—and a second resulting from skyrmions trapping defects with their own non-trivial topology that is discussed in a second work, which yields generalizations of unpaired Majorana zero-modes.

Bootstrap for lattice Yang-Mills theory

We study the $SU(\infty)$ lattice Yang-Mills theory at the dimensions $D=2,3,4$ via the numerical bootstrap method. It combines the Makeenko-Migdal loop equations, with a cut-off $L_{\mathrm{max}}$ on the maximal length of loops, and positivity conditions on certain matrices of Wilson loops. Our algorithm is inspired by the pioneering paper of P.Anderson and M.Kruczenski but it is significantly more efficient, as it takes into account the symmetries of the lattice theory and uses the relaxation procedure in line with our previous work on matrix bootstrap. We thus obtain rigorous upper and lower bounds on the plaquette average at various couplings and dimensions. For $D=4$, the lower bound data appear to be close to the MC data in the strong coupling phase and the upper bound data in the weak coupling phase reproduce well the 3-loop perturbation theory. Our results suggest that this bootstrap approach can provide a tangible alternative to the, so far uncontested, Monte Carlo approach.

Velocity Laws for Bound States in Asymptotically AdS Geometries

AbstractWe study the behavior of heavy quark bound states in moving plasmas that are dual to theories with generic non‐trivial renormalization group flows interpolating between an AdS geometry in the ultraviolet and infrared fixed points with broken symmetries. We investigate analytically the observables associated with the bound state and find their scaling exponents with respect to the Lorentz factor for ultrarelativistic motion. Despite having asymptotically an AdS geometry, the scaling is not universal and depends on geometric conditions of the Fefferman‐Graham expansion in the near boundary regime, or equivalently on the order of the asymptotic background expansion that provides the leading contributions to the Wilson loops. We finally discuss the qualitative implications on the dissociation of the bound states with respect to the relative angle of motion.

Deciphering colour building blocks of massive multiparton amplitudes at 4-loops and beyond

The soft function in non-abelian gauge theories exponentiate, and their logarithms can be organised in terms of the collections of Feynman diagrams called Cwebs. The colour factors that appear in the logarithm are controlled by the web mixing matrices. Direct construction of the diagonal blocks of Cwebs using the new concepts of Normal ordering, basis Cweb and Fused-Web was recently carried out in [1]. In this article we establish correspondence between the boomerang webs introduced in [2] and non-boomerang Cwebs. We use this correspondence together with Uniqueness theorem and Fused web formalism introduced in [1] to obtain the diagonal blocks of four general classes of Cwebs to all orders in perturbation theory which also cover all the four loop Boomerang Cwebs connecting four Wilson lines. We also fully construct the mixing matrix of a special Cweb to all orders in perturbation theory.

Constructing static quark-antiquark creation operators from Laplacian eigenmodes

We investigate static quark-antiquark operators based on trial states formed from eigenvectors of the covariant three-dimensional lattice Laplace operator. We test the method by computing the static quark-antiquark potential and comparing results to standard Wilson loop measurements. The new method is efficient not only for on-axis, but also for many off-axis quark-antiquark separations when a fine spatial resolution is required. We further improve the ground-state overlap by using multiple eigenvector pairs, weighted with Gaussian profile functions of the eigenvalues, providing a variational basis. The method presented here can be applied to potential functions for all possible excitations of a gluonic string with fixed ends, hybrid or tetraquark potentials, as well as static-light systems and allows visualization of the spatial distribution of the Laplace trial states.

Glueball spectroscopy in lattice QCD using gradient flow

Removing ultraviolet noise from the gauge fields is necessary for glueball spectroscopy in lattice QCD. It is known that the Yang-Mills gradient flow method is an alternative approach instead of link smearing or link fuzzing in various aspects. In this work we study the application of the gradient flow technique to the construction of the extended glueball operators. We examine a simple application of the gradient flow method, which has some problems in glueball mass calculations at large flow time because of its nature of diffusion in space-time. To avoid this problem, the spatial links are evolved by the ``spatial gradient flow'', that is defined to restrict the diffusion to spatial directions only. We test the spatial gradient flow in calculations of glueball two-point functions and Wilson loops as a new smearing method, and then discuss its efficiency in comparison with the original gradient flow method and the conventional method. Furthermore, to demonstrate the feasibility of our proposed method, we determine the masses of the three lowest-lying glueball states, corresponding to the $0^{++}$, $2^{++}$ and $0^{-+}$ glueballs, in the continuum limit in the pure Yang-Mills theory.

A dispersion relation for defect CFT

We present a dispersion relation for defect CFT that reconstructs two-point functions in the presence of a defect as an integral of a single discontinuity. The main virtue of this formula is that it streamlines explicit bootstrap calculations, bypassing the resummation of conformal blocks. As applications we reproduce known results for monodromy defects in the epsilon-expansion, and present new results for the supersymmetric Wilson line at strong coupling in mathcal{N} = 4 SYM. In particular, we derive a new analytic formula for the highest R-symmetry channel of single-trace operators of arbitrary length.

Hadronic structure on the light front. II. QCD strings, Wilson lines, and potentials

This is the second paper on hadronic wave functions in the light-front formulation. We first consider only confinement effects, using the classical Nambu-Gotto string with massive end points in the light-cone gauge. We derive the light-front Hamiltonian and show how to solve it, using an expansion in suitable basis functions. We next discuss the correlators of Wilson lines on the light front, leading to an effective Hamiltonian that includes spin effects. At the end, we consider a separate problem of instanton-induced interactions, at the origin of the pion as a massless Goldstone mode on the light front.