1,721,100 research outputs found
theta dependence of SU(N) gauge theories
No full textWe study the theta dependence of four-dimensional SU(N) gauge theories, for N greater than or equal to 3 and in the large-N limit. We use numerical simulations of the Wilson lattice formulation of gauge theories to compute the first few terms of the expansion of the ground-state energy F(theta) around theta = 0, F(theta) - F(0) = A(2)theta(2) (1 + b(2)theta(2) + ...). Our results support Witten's conjecture: F(theta) - F(0) = Atheta(2) + O(1/N) for sufficiently small values of theta, theta < π. Indeed we verify that the topological susceptibility has a non-zero large-N limit χ(&INFIN;) = 2A with corrections of O(1/N-2), in substantial agreement with the Witten-Veneziano formula which relates χ(&INFIN;) to the η' mass. Furthermore, higher order terms in θ are suppressed; in particular, the O(θ(4)) term b(2) (related to η' - η' the elastic scattering amplitude) turns out to be quite small: b(2) = 0.023(7) for N = 3, and its absolute value decreases with increasing N, consistently with the expectation b(2) = O(1/N-2)
Topological susceptibility of SU(N) gauge theories at finite temperature
No full textWe investigate the large-N behavior of the topological susceptibility X in four-dimensional SU(N) gauge theories at finite temperature, and in particular across the finite-temperature transition at T-c. For this purpose, we consider the lattice formulation of the SU(N) gauge theories and perform Monte Carlo simulations for N = 4,6. The results indicate that X has a nonvanishing large-N limit for T T-c
Confining strings in representations with common n-ality
No full textWe study the spectrum of confining strings in SU(3) pure gauge theory, by means of lattice Monte Carlo simulations, using torelon operators in different representations of the gauge group. Our results provide direct evidence that the string spectrum is according to predictions based on n-ality. Torelon correlations in the rank-2 symmetric channel appear to be well reproduced by a two-exponential picture, in which the lowest state is given by the fundamental string sigma(1) = sigma, the heavier string state is such that the ratio sigma(2)/sigma(1) is approximately given by the Casimir ratio C-sym/C-f = 5/2, and the torelon has a much smaller overlap with the lighter fundamental string state
A model for string-breaking in QCD
Full text linkWe present a model for string breaking based on the existence of chromoelectric flux tubes. We predict the form of the long-range potential, and obtain an estimate of the string breaking length. A prediction is also obtained for the behaviour with temperature of the string breaking length near the deconfinement phase transition. We plan to use this model as a guide for a program of study of string breaking on the lattice
Spectrum of confining strings in SU(N) gauge theories
No full textWe study the spectrum of the confining strings in four-dimensional SU(N) gauge theories. We compute, for the SU(4) and SU(6) gauge theories formulated on a lattice, the string tensions sigma(k) related to sources with Z(N) charge k, using Monte Carlo simulations. Our results are consistent with the sine formula sigma(k)/sigma = sin k pi/N/sin pi/N for the ratio between sigma(k) and the standard string tension sigma. For the SU(4) and SU(6) cases the accuracy is approximately 1% and 2%, respectively. The sine formula is known to emerge in various realizations of supersymmetric SU(N) gauge theories. On the other hand, our results show deviations from Casimir scaling. We also discuss an analogous behavior exhibited by two-dimensional SU(N) x SU(N) chiral models
DETECTING DUAL SUPERCONDUCTIVITY IN THE GROUND-STATE OF GAUGE-THEORY
No full textWe explicitly construct a monopole creation operator: its vacuum expectation value is a disorder parameter for dual superconductivity, in that it signals a spontaneous breaking of the U(1) symmetry corresponding to monopole charge conservation. This operator is tested by numerical simulations in compact U(1) gauge theory. Our construction provides a general recipe for detection of the condensation of any topological soliton. In particular our operator can be used to detect dual superconductivity of the QCD vacuum
Spectral reconstruction in SU(4) gauge theory with fermions in multiple representations
No full textThe naturalness problem in the Higgs sector finds a popular solution in composite Higgs models. In such theories the Higgs boson emerges as the pseudo-Nambu-Goldstone boson associated with the breaking of a global symmetry realised in a new, strongly interacting sector. We address a model arising in this context, a SU(4) gauge theory with fermions in two distinct representations. We present a novel lattice study of this theory, in which we address the non-perturbative reconstruction of spectral densities from lattice correlators
Critical slowing down of topological modes
Full text linkWe investigate the critical slowing down of the topological modes using local
updating algorithms in lattice 2-d CP^(N-1) models. We show that the
topological modes experience a critical slowing down that is much more severe
than the one of the quasi-Gaussian modes relevant to the magnetic
susceptibility, which is characterized by with
. We argue that this may be a general feature of Monte Carlo
simulations of lattice theories with non-trivial topological properties, such
as QCD, as also suggested by recent Monte Carlo simulations of 4-d SU(N)
lattice gauge theories
Stability of lattice QCD simulations and the thermodynamic limit
Full text linkWe study the spectral gap of the Wilson--Dirac operator in two-flavour lattice QCD as a function of the lattice spacing , the space-time volume and the current-quark mass . It turns out that the median of the probability distribution of the gap scales proportionally to and that its width is practically equal to . In particular, numerical simulations are safe from accidental zero modes in the large-volume regime of QCD.We study the spectral gap of the Wilson--Dirac operator in two-flavour lattice QCD as a function of the lattice spacing , the space-time volume and the current-quark mass . It turns out that the median of the probability distribution of the gap scales proportionally to and that its width is practically equal to . In particular, numerical simulations are safe from accidental zero modes in the large-volume regime of QCD
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