21 research outputs found
Renormalization of the Yang-Mills theory in the ambiguity-free gauge
The renormalization procedure for the Yang-Mills theory in the gauge free of
the Gribov ambiguity is constructed. It is shown that all the ultraviolet
infinities may be removed by renormalization of the parameters entering the
classical Lagrangian and the local redefinition of the fields.Comment: 20 pages. Some explanations extended, one reference added. Final
version published in the journa
Centre symmetric 3d effective actions for thermal SU(N) Yang-Mills from strong coupling series
We derive three-dimensional, Z(N)-symmetric effective actions in terms of
Polyakov loops by means of strong coupling expansions, starting from thermal
SU(N) Yang-Mills theory in four dimensions on the lattice. An earlier action in
the literature, corresponding to the (spatial) strong coupling limit, is thus
extended by several higher orders, as well as by additional interaction terms.
We provide analytic mappings between the couplings of the effective theory and
the parameters of the original thermal lattice theory, which can
be systematically improved. We then investigate the deconfinement transition
for the cases SU(2) and SU(3) by means of Monte Carlo simulations of the
effective theory. Our effective models correctly reproduce second order 3d
Ising and first order phase transitions, respectively. Furthermore, we
calculate the critical couplings and find agreement with
results from simulations of the 4d theory at the few percent level for
.Comment: 27 pages, 21 figures; final version published in JHEP; attached the
corresponding Erratum (ref. JHEP 1107:014,2011, DOI 10.1007/JHEP07(2011)014)
for ease of consultatio
On the massive gluon propagator, the PT-BFM scheme and the low-momentum behaviour of decoupling and scaling DSE solutions
We study the low-momentum behaviour of Yang-Mills propagators obtained from
Landau-gauge Dyson-Schwinger equations (DSE) in the PT-BFM scheme. We compare
the ghost propagator numerical results with the analytical ones obtained by
analyzing the low-momentum behaviour of the ghost propagator DSE in Landau
gauge, assuming for the truncation a constant ghost-gluon vertex and a simple
model for a massive gluon propagator. The asymptotic expression obtained for
the regular or decoupling ghost dressing function up to the order is proven to fit pretty well the numerical PT-BFM results.
Furthermore, when the size of the coupling renormalized at some scale
approaches some critical value, the numerical PT-BFM propagators tend to behave
as the scaling ones. We also show that the scaling solution, implying a
diverging ghost dressing function, cannot be a DSE solution in the PT-BFM
scheme but an unattainable limiting case.Comment: 16 pages, 2 figs., 2 tabs (updated version to be published in JHEP
On the gauge boson's properties in a candidate technicolor theory
The technicolor scenario replaces the Higgs sector of the standard model with
a strongly interacting sector. One candidate for a realization of such a sector
is two-technicolor Yang-Mills theory coupled to two degenerate flavors of
adjoint, massless techniquarks. Using lattice gauge theory the properties of
the technigluons in this scenario are investigated as a function of the
techniquark mass towards the massless limit. For that purpose the minimal
Landau gauge two-point and three-point correlation functions are determined,
including a detailed systematic error analysis. The results are, within the
relatively large systematic uncertainties, compatible with a behavior very
similar to QCD at finite techniquark mass. However, the limit of massless
techniquarks exhibits features which could be compatible with a
(quasi-)conformal behavior.Comment: 27 pages, 17 figures, 1 table; v2: persistent notational error
corrected, some minor modification
Solitary waves in the Nonlinear Dirac Equation
In the present work, we consider the existence, stability, and dynamics of
solitary waves in the nonlinear Dirac equation. We start by introducing the
Soler model of self-interacting spinors, and discuss its localized waveforms in
one, two, and three spatial dimensions and the equations they satisfy. We
present the associated explicit solutions in one dimension and numerically
obtain their analogues in higher dimensions. The stability is subsequently
discussed from a theoretical perspective and then complemented with numerical
computations. Finally, the dynamics of the solutions is explored and compared
to its non-relativistic analogue, which is the nonlinear Schr{\"o}dinger
equation. A few special topics are also explored, including the discrete
variant of the nonlinear Dirac equation and its solitary wave properties, as
well as the PT-symmetric variant of the model
Nonperturbative study of the four gluon vertex
In this paper we study the nonperturbative structure of the SU(3) four-gluon vertex in the Landau gauge, concentrating on contributions quadratic in the metric. We employ an approximation scheme where 'one-loop' diagrams are computed using fully dressed gluon and ghost propagators, and tree-level vertices. When a suitable kinematical configuration depending on a single momentum scale p is chosen, only two structures emerge: the tree-level four-gluon vertex, and a tensor orthogonal to it. A detailed numerical analysis reveals that the form factor associated with this latter tensor displays a change of sign (zero-crossing) in the deep infrared, and finally diverges logarithmically. The origin of this characteristic behavior is proven to be entirely due to the masslessness of the ghost propagators forming the corresponding ghost-loop diagram, in close analogy to a similar effect established for the three-gluon vertex. However, in the case at hand, and under the approximations employed, this particular divergence does not affect the form factor proportional to the tree-level tensor, which remains finite in the entire range of momenta, and deviates moderately from its naive tree-level value. It turns out that the kinematic configuration chosen is ideal for carrying out lattice simulations, because it eliminates from the connected Green's function all one-particle reducible contributions, projecting out the genuine one-particle irreducible vertex. Motivated by this possibility, we discuss in detail how a hypothetical lattice measurement of this quantity would compare to the results presented here, and the potential interference from an additional tensorial structure, allowed by Bose symmetry, but not encountered within our scheme
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe