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On the effective string spectrum of the tridimensional Z2 gauge model
Get PDFWe study the Z_2 lattice gauge theory in three dimensions, and present high precision estimates for the first few energy levels of the string spectrum. These results are obtained from new numerical data for the two-point Polyakov loop correlation function, which is measured in the 3d Ising spin system using duality. This allows us to perform a stringent comparison with the predictions of effective string models. We find a remarkable agreement between the numerical estimates and the Nambu-Goto predictions for the energy gaps at intermediate and large distances. The precision of our data allows to distinguish clearly between the predictions of the full Nambu-Goto action and the simple free string model up to an interquark distance r ≈ 10/√σ. At the same time, our results also confirm the breakdown of the effective picture at short distances, supporting the hypothesis that terms which are not taken into account in the usual Nambu-Goto string formulation yield a non-trivial shift to the energy levels. Furthermore, we discuss the theoretical implications of these results
N=2 Supersymmetric Yang-Mills and the Quantum Hall Effect
Get PDFIt is argued that there are strong similarities between the infra-red physics of N=2 supersymmetric Yang-Mills and that of the quantum Hall effect, both systems exhibit a hierarchy of vacua with a sub-group of the modular group mapping between them. The β-function for pure SU(2) N = 2 supersymmetric Yang-Mills in 4-dimensions is re-examined and an earlier suggestion in the literature, that was singular at strong coupling, is modified to a form that is well behaved at both weak and strong coupling and describes the crossover in an analytic fashion. Similarities between the phase diagram and the flow of SUSY Yang-Mills and that of the quantum Hall effect are then described, with the Hall conductivity in the latter playing the role of the θ-parameter in the former. Hall plateaux, with odd denominator filling fractions, are analogous to fixed points at strong coupling in N=2 SUSY Yang-Mills, where the massless degrees of freedom carry an odd monopole charge
Large Systems of path-repellent Brownian motions in a trap at positive temperature
Get PDFWe study a model of N mutually repellent Brownian motions under confinement to stay in some bounded region of space. Our model is defined in terms of a transformed path measure under a trap Hamiltonian, which prevents the motions from escaping to infinity, and a pair-interaction Hamiltonian, which imposes a repellency of the N paths. In fact, this interaction is an N-dependent regularisation of the Brownian intersection local times, an object which is of independent interest in the theory of stochastic processes. The time horizon (interpreted as the inverse temperature) is kept fixed. We analyse the model for diverging number of Brownian motions in terms of a large deviation principle. The resulting variational formula is the positive-temperature analogue of the well-known Gross-Pitaevskii formula, which approximates the ground state of a certain dilute large quantum system; the kinetic energy term of that formula is replaced by a probabilistic energy functional. This study is a continuation of the analysis in [ABK04] where we considered the limit of diverging time (i.e., the zero-temperature limit) with fixed number of Brownian motions, followed by the limit for diverging number of motions
A numerical study of confinement in compact QED
Get PDFCompact U(1) lattice gauge theory in four dimensions is studied by means of an efficient algorithm which exploits the duality transformation properties of the model. We focus our attention onto the confining regime, considering the interquark potential and force, and the electric field induced by two infinitely heavy sources. We consider both the zero and finite temperature setting, and compare the theoretical predictions derived from the effective string model and the dual superconductor scenario to the numerical results
Meromorphic Scaling Flow of N = 2 Supersymmetric SU(2) Yang-Mills with Matter
Get PDFβ-functions are derived for the flow of N = 2 SUSY SU(2) Yang-Mills in 4-dimensions with massless matter multiplets in the fundamental representation of the gauge group. The β-functions represent the flow of the couplings as the VEV of the Higgs field is lowered and are modular forms of weight -2. They have the correct asymptotic behaviour at both the strong and weak coupling fixed points. Corrections to the massless β-functions when masses are turned on are discussed
QCD string from D0 branes
Get PDFWe report the results of a set of high precision simulations performed in the 3d gauge Ising model. We evaluated the interquark potential and the first few energy levels and compared them with the predictions obtained with the effective Nambu-Goto string and with the free bosonic string. The data are precise enough to unambiguously distinguish between the free string predictions and those obtained using the N-G effective string. At large distances we find a remarkable agreement between Monte Carlo data and N-G predictions for the first excited energy level, while the free string picture is definitely excluded. As the interquark distance is decreased (and/or the finite temperature becomes higher) the Monte Carlo results show larger and larger deviations both from the N-G and from the free string predictions. In order to better understand this behaviour we re-derived the effective Nambu-Goto theory result for the Polyakov loop correlator using a covariant quantization. We chose as boundary conditions those of an open string attached to two D0-branes at spatial distance R, in a target space with compact euclidean time. Obviously our treatment is fully consistent only in d = 26. The extension to generic d requires taking into account the Liouville mode of Polyakov’s formulation. The analogy with the standard light cone calculation suggests that the contribution due to the Liouville field can be neglected for large R. At shorter scales, the Liouville mode cannot be neglected and its contribution to the interquark potential might be the source of the discrepancies with respect to the effective N-G results that we observe in our Monte Carlo simulations
Zero-Field Hall Effect in (2+1)-Dimensional QED
Get PDFIn three-dimensional QED, a quantum Hall effect occurs in the absence of any magnetic field. We give a simple and transparent explanation. In solid-state physics, the Hall conductivity for rational magnetic flux is expected to be given by a Chern number. In our field-free situation, however, the conductivity is ±1/2 in natural units. We explain why the integrality of the conductivity breaks down and explain its quantization geometrically. For quasi-periodic boundary conditions, we calculate the finite size correction to the Hall conductivity. Our paper establishes an explicit connection between quantum field theory and solid-state physics
