Publications (107)309.43 Total impact
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ABSTRACT: In this paper, we discuss the gluon propagator in the linear covariant gauges in $D=2,3,4$ Euclidean dimensions. Nonperturbative effects are taken into account via the socalled Refined GribovZwanziger framework. We point out that, as in the Landau and maximal Abelian gauges, for $D=3,4$, the gluon propagator displays a massive (decoupling) behaviour, while for $D=2$, a scaling one emerges. All results are discussed in a setup that respects the BecchiRouetStoraTyutin (BRST) symmetry, through a recently introduced nonperturbative BRST transformation. We also propose a minimizing functional that could be used to construct a lattice version of our nonperturbative definition of the linear covariant gauge. 
Article: Confinement and dynamical chiral symmetry breaking in a nonperturbative renormalizable quark model
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ABSTRACT: Inspired by the construction of the GribovZwanziger action in the Landau gauge, we introduce a quark model exhibiting both confinement and chiral symmetry aspects. An important feature is the incorporation of spontaneous chiral symmetry breaking in a renormalizable fashion. The quark propagator in the condensed vacuum turns out to be of a confining type. Besides a real pole, it exhibits complex conjugate poles. The resulting spectral form is explicitly shown to violate positivity, indicative of its unphysical character. Moreover, the ensuing quark mass function fits well to existing lattice data. To further validate the physical nature of the model, we identify a massless pseudoscalar (i.e. a pion) in the chiral limit and present estimates for the rho meson mass and decay constant.  [Show abstract] [Hide abstract]
ABSTRACT: In this paper, we study the influence of an external magnetic field in holographic QCD models where the backreaction is modeled in via an appropriate choice of the background metric. We add a phenomenological soft wall dilaton to incorporate better IR behavior (confinement). Elaborating on previous studies conducted by [JHEP 1505 (2015) 121], we first discuss the HawkingPage transition, the dual of the deconfinement transition, as a function of the magnetic field. We confirm that the critical deconfinement temperature can drop with the magnetic field. Secondly, we study the quark condensate holographically as a function of the applied magnetic field and demonstrate that this model does not exhibit inverse magnetic catalysis at the level of the chiral transition. The quest for a holographic QCD model that qualitatively describes the inverse magnetic catalysis at finite temperature is thus still open. Throughout this work, we pay special attention to the different holographic parameters and we attempt to fix them by making the link to genuine QCD as close as possible. This leads to several unanticipated and so far overlooked complications (such as the importance of the AdS length L) that we discuss in detail.  [Show abstract] [Hide abstract]
ABSTRACT: In this short note, we come back to the recent proposal put forward by Kharzeev and Levin [PRL 114 (2015) 24, 242001], in which they phenomenologically couple the nonperturbative Veneziano ghost to the perturbative gluon, leading to a modified gluon propagator (the "glost") of the Gribov type, with complex poles. As such, a possible link was made between the QCD topological \thetavacuum (Veneziano ghost) and color confinement (no physically observable gluons). We discuss some subtleties concerning gauge (BRST) invariance of this proposal, related to the choice of Feynman gauge. We furthermore provide an example in the Landau gauge of a similar phenomenological vertex that also describes the necessary Veneziano ghost but does not affect the Landau gauge gluon propagator.  [Show abstract] [Hide abstract]
ABSTRACT: We point out a subtlety in choosing the radiation gauge (A(z)=0 combined with the Lorenz gauge) for gauge fields in AdS/QCD for black hole backgrounds. We then demonstrate the effect of this on the momentumdependence of the spectral functions of the J/psi vector meson, showing a spreading with momentum and a breaking of isotropy, in contrast to previous results in the literature. We also discuss the dependence on a background magnetic field, following our earlier proposed model. (C) 2015 The Authors. Published by Elsevier B.V.  [Show abstract] [Hide abstract]
ABSTRACT: We point out the existence of a nonperturbative exact nilpotent BRST symmetry for the GribovZwanziger action in the Landau gauge. We then put forward a manifestly BRST invariant resolution of the Gribov gauge fixing ambiguity in the linear covariant gauge. 
Article: Confinement interpretation in a YangMills + Higgs theory when considering Gribov's ambiguity
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ABSTRACT: This work presents concisely the results obtained from the analysis of the twopoint function of the gauge field in the $SU(2)$ and $SU(2)\times U(1)$ gauge theories, in the Landau gauge, coupled to a scalar Higgs field in the fundamental or adjoint representation. Nonperturbative effects are considered by taking into account the Gribov ambiguity. In general, in both YangMills models the gluon propagator has nontrivial contributions of physical and nonphysical modes, which clearly depends on the group representation of the Higgs field. These results were presented during the Fourth Winter Workshop on Nonperturbative Quantum Field Theory, which took place in SophiaAntipolis  France.  [Show abstract] [Hide abstract]
ABSTRACT: We consider finite temperature SU(2) gauge theory in the continuum formulation, which necessitates the choice of a gauge fixing. Choosing the Landau gauge, the existing gauge copies are taken into account by means of the GribovZwanziger (GZ) quantization scheme, which entails the introduction of a dynamical mass scale (Gribov mass) directly influencing the Green functions of the theory. Here, we determine simultaneously the Polyakov loop (vacuum expectation value) and Gribov mass in terms of temperature, by minimizing the vacuum energy w.r.t. the Polyakov loop parameter and solving the Gribov gap equation. Inspired by the Casimir energystyle of computation, we illustrate the usage of Zeta function regularization in finite temperature calculations. Our main result is that the Gribov mass directly feels the deconfinement transition, visible from a cusp occurring at the same temperature where the Polyakov loop becomes nonzero. In this exploratory work we mainly restrict ourselves to the original GribovZwanziger quantization procedure in order to illustrate the approach and the potential direct link between the vacuum structure of the theory (dynamical mass scales) and (de)confinement. We also present a first look at the critical temperature obtained from the Refined GribovZwanziger approach. Finally, a particular problem for the pressure at low temperatures is reported.  [Show abstract] [Hide abstract]
ABSTRACT: In this note, we consider the Landau gauge in the continuum formulation. Our purposes are twofold. Firstly, we try to work out the consequences of the recently derived CucchieriMendes bounds on the inverse FaddeevPopov operator at the level of the path integral quantization. Secondly, we give an explicit renormalizable prescription to implement the socalled Landau Bgauges as introduced by Maas.  [Show abstract] [Hide abstract]
ABSTRACT: We discuss a method to extract the K\"all\'enLehmann spectral density of a particle (be it elementary or bound state) propagator and apply it to compute gluon spectral densities from lattice data. Furthermore, we also consider the interpretation of the Landaugauge gluon propagator at finite temperature as a massivetype bosonic propagator.  [Show abstract] [Hide abstract]
ABSTRACT: In this note, we consider the Landau gauge in the continuum formulation. Our purposes are twofold. Firstly, we try to work out the consequences of the recently derived CucchieriMendes bounds on the inverse FaddeevPopov operator at the level of the path integral quantization. Secondly, we give an explicit renormalizable prescription to implement the socalled Landau Bgauges as introduced by Maas.  [Show abstract] [Hide abstract]
ABSTRACT: By evaluating the socalled Boseghost propagator, we present the first numerical evidence of BRSTsymmetry breaking for YangMills theory in minimal Landau gauge, i.e. due to the restriction of the functional integration to the first Gribov region in the GribovZwanziger approach. Our data are well described by a simple fitting function, which can be related to a massive gluon propagator in combination with an infraredfree (FaddeevPopov) ghost propagator. As a consequence, the Boseghost propagator, which has been proposed as a carrier of the confining force in minimal Landau gauge, displays a 1/p^4 singularity in the infrared limit.  [Show abstract] [Hide abstract]
ABSTRACT: We study the influence of a background magnetic field on the melting of the J/psi vector meson by introducing a BornInfeld modification of the softwall model. Out of the three polarizations of the massive vector meson, we find that the longitudinal one (parallel to the applied magnetic field) melts only at an even higher temperature than the deconfinement temperature, whereas the two transverse polarizations melt at a lower temperature than in the absence of a magnetic field. We also conduct a preliminary investigation of the effect of the magnetic field on the heavy quark diffusion coefficient, showing an increased diffusion constant for the longitudinal polarization with respect to the transverse polarizations.  [Show abstract] [Hide abstract]
ABSTRACT: The Boseghost propagator has been proposed as a carrier of the confining force in YangMills theories in minimal Landau gauge. We present the first numerical evaluation of this propagator, using lattice simulations for the SU(2) gauge group in the scaling region. Our data are well described by a simple fitting function, which is compatible with an infraredenhanced Boseghost propagator. This function can also be related to a massive gluon propagator in combination with an infraredfree (FaddeevPopov) ghost propagator. Since the Boseghost propagator can be written as the vacuum expectation value of a BRSTexact quantity and should therefore vanish in a BRSTinvariant theory, our results provide the first numerical manifestation of BRSTsymmetry breaking due to restriction of gaugeconfiguration space to the Gribov region.  [Show abstract] [Hide abstract]
ABSTRACT: A Pad\'e approximation approach, rooted in an infrared moment technique, is employed to provide mass estimates for various glueball states in pure gauge theories. The main input in this analysis are theoretically wellmotivated fits to lattice gluon propagator data, which are by now available for both SU(2) and SU(3) in 3 and 4 spacetime dimensions. We construct appropriate gauge invariant and Lorentz covariant operators in the (pseudo)scalar and (pseudo)tensor sector. Our estimates compare reasonably well with a variety of lattice sources directly aimed at extracting glueball masses.  [Show abstract] [Hide abstract]
ABSTRACT: The Boseghost propagator has been proposed as a carrier of the confining force in YangMills theories in minimal Landau gauge. We present the first numerical evaluation of this propagator, using lattice simulations for the SU(2) gauge group in the scaling region. Our data are well described by a simple fitting function, which is compatible with an infraredenhanced Boseghost propagator. This function can also be related to a massive gluon propagator in combination with an infraredfree (FaddeevPopov) ghost propagator. Since the Boseghost propagator can be written as the vacuum expectation value of a BRSTexact quantity and should therefore vanish in a BRSTinvariant theory, our results provide the first numerical manifestation of BRSTsymmetry breaking due to restriction of gaugeconfiguration space to the Gribov region.  [Show abstract] [Hide abstract]
ABSTRACT: We address several aspects of gluon propagation at zero and finite temperature. In particular, we study the violation of spectral positivity, we discuss a method to extract the K\"all\'{e}nLehmann spectral density of a particle (be it elementary or bound state) propagator and apply it to compute gluon spectral densities from lattice data. Furthermore, we also consider the interpretation of the Landau gauge gluon propagator at finite temperature as a massive type bosonic propagator.  [Show abstract] [Hide abstract]
ABSTRACT: We consider the problem of "measuring" the K\"all\'enLehmann spectral density of a particle (be it elementary or bound state) propagator by means of 4d lattice data. As the latter are obtained from operations at (Euclidean momentum squared) p^2>=0, we are facing the generically illposed problem of converting a limited data set over the positive real axis to an integral representation, extending over the whole complex p^2plane. We employ a linear regularization strategy, commonly known as the Tikhonov method with Morozov discrepancy principle, with suitable adaptations to realistic data, e.g. with unknown threshold. An important virtue over the (standard) maximum entropy method is the possibility to also probe unphysical spectral densities, as, for example, of a confined gluon. We apply our proposal here to "physical" mock spectral data as a litmus test and then to the lattice SU(3) Landau gauge gluon at zero temperature.  [Show abstract] [Hide abstract]
ABSTRACT: An infrared moment technique, recently developed by some of us, is employed to provide mass estimates for various glueball states in pure gauge theories. The main input in this analysis are theoretically wellmotivated fits to lattice gluon propagator data, which are by now available for both SU(2) and SU(3) in 3 and 4 spacetime dimensions. We construct appropriate gauge invariant and Lorentz covariant operators in the (pseudo)scalar and (pseudo)tensor sector. Our final numbers compare reasonably well with a variety of lattice sources directly aimed at extracting glueball masses.  [Show abstract] [Hide abstract]
ABSTRACT: In this followup paper of 1105.2217 we further discuss the occurrence of a magnetically induced tachyonic instability of the rho meson in the twoflavour SakaiSugimoto model, uplifting two remaining approximations in the previous paper. That is, firstly, the magnetically induced splitting of the branes is now taken into account, evaluating without approximations the symmetrized trace which enters in the nonAbelian DiracBornInfeld (DBI) action. This leads to an extra mass generating effect for the charged heavylight rho meson through a holographic Higgs mechanism. Secondly, we compare the results in the approximation to second order in the field strength to the results using the full DBIaction. Both improvements cause an increase of the critical magnetic field for the onset of rho meson condensation. In addition, the stability in the scalar sector in the presence of the magnetic field is discussed.
Publication Stats
2k  Citations  
309.43  Total Impact Points  
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Institutions

19702015

Ghent University
 Department of Physics and Astronomy
Gand, Flanders, Belgium


2013

University of Coimbra
 Center for Computational Physics
Coímbra, Coimbra, Portugal


20082009

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, Massachusetts, United States
