arXiv subjects

Henri Verschelde

Publications and source records attributed to Henri Verschelde.

51 records · Page 3Linked to original sources

arXiv2011

A two-component picture of the condensate with instantons

We study the interplay between the condensate and instantons in non-Abelian gauge theory. Therefore we use the formalism of Local Composite Operators, with which the vacuum expectation value of this condensate can be analytically computed. We first use the dilute gas approximation and partially solve the infrared problem of instanton physics. In order to find quantitative results, however, we turn to an instanton liquid model, where we find how the different contributions to the condensate add up.

hep-th↗

arXiv2010

Analytic approach to the study of the electric-magnetic asymmetry of the dimension 2 condensate

Recent work by Chernodub and Ilgenfritz has uncovered non-trivial temperature dependence in the electric-magnetic asymmetry in the dimension 2 condensate. This asymmetry measures the difference between the spatial and the temporal components of the condensate. Lattice computations have shown very interesting phenomena. The asymmetry shows a jump at the deconfinement phase transition, beyond which it approaches its perturbative value. At temperatures lower than the critical temperature, it shows an exponential behavior with in the exponent a mass smaller than the lowest glueball mass. In this talk we present research done on this asymmetry, using a generalization of analytical methods developed to study . The purpose is to shed more insight on the findings of Chernodub and Ilgenfritz.

hep-th↗

arXiv2010

The asymmetry of the dimension two condensate

I present recent analytical work concerning the electric-magnetic asymmetry in the dimension two condensate in pure Yang-Mills theory. We reproduce qualitatively the lattice results previously found by Chernodub and Ilgenfritz.

hep-th↗

arXiv2010

Two-component liquid model for the quark-gluon plasma

We consider a two-component-liquid model, a la Landau, for the quark-gluon plasma. Qualitatively, the model fits well some crucial observations concerning the plasma properties. Dynamically, the model assumes the existence of an effective scalar field which is condensed. The existence of such a condensate is supported by lattice data. We indicate a possible crucial test of the model by lattice simulations.

hep-ph↗

arXiv2009

A renormalization group invariant scalar glueball operator in the (Refined) Gribov-Zwanziger framework

This paper presents a complete algebraic analysis of the renormalizability of the $d=4$ operator $F^2_{μν}$ in the Gribov-Zwanziger (GZ) formalism as well as in the Refined Gribov-Zwanziger (RGZ) version. The GZ formalism offers a way to deal with gauge copies in the Landau gauge. We explicitly show that $F^2_{μν}$ mixes with other $d=4$ gauge variant operators, and we determine the mixing matrix $Z$ to all orders, thereby only using algebraic arguments. The mixing matrix allows us to uncover a renormalization group invariant including the operator $F^2_{μν}$. With this renormalization group invariant, we have paved the way for the study of the lightest scalar glueball in the GZ formalism. We discuss how the soft breaking of the BRST symmetry of the GZ action can influence the glueball correlation function. We expect non-trivial mass scales, inherent to the GZ approach, to enter the pole structure of this correlation function.

hep-th↗

arXiv2008

A refinement of the Gribov-Zwanziger approach in the Landau gauge: infrared propagators in harmony with the lattice results

Recent lattice data have reported an infrared suppressed, positivity violating gluon propagator which is nonvanishing at zero momentum and a ghost propagator which is no longer enhanced. This paper discusses how to obtain analytical results which are in qualitative agreement with these lattice data within the Gribov-Zwanziger framework. This framework allows one to take into account effects related to the existence of gauge copies, by restricting the domain of integration in the path integral to the Gribov region. We elaborate to great extent on a previous short paper by presenting additional results, also confirmed by the numerical simulations. A detailed discussion on the soft breaking of the BRST symmetry arising in the Gribov-Zwanziger approach is provided.

hep-th↗

arXiv2007

Resolving the instability of the Savvidy vacuum by dynamical gluon mass

In this paper we apply the formalism of local composite operators as developed by Verschelde et al. in combination with a constant chromomagnetic field as considered in the seventies by Savvidy and others. We find that a nonzero minimizes the vacuum energy, as in the case with no chromomagnetic field, and that the chromomagnetic field itself is near-to zero. The Nielsen-Olesen instability, caused by the imaginary part in the action, also vanishes. We further investigate the effect of an external chromomagnetic field on the value of , finding that this condensate is destroyed by sufficiently strong fields. The inverse scenario, where is considered as external, results in analogous findings: when this condensate is sufficiently large, the induced chromomagnetic field is lowered to a perturbative value slightly below the applied .

hep-th↗

arXiv2007

Unitarity analysis of a non-Abelian gauge invariant action with a mass

In previous work done by us and coworkers, we have been able to construct a local, non-Abelian gauge invariant action with a mass parameter, based on the nonlocal gauge invariant mass dimension two operator F1/D^2F. The renormalizability of the resulting action was proven to all orders of perturbation theory, in the class of linear covariant gauges. We also discussed the perturbative equivalence of the model with ordinary massless Yang-Mills gauge theories when the mass is identically zero. Furthermore, we pointed out the existence of a BRST symmetry with corresponding nilpotent charge. In this paper, we study the issue of unitarity of this massive gauge model. Firstly, we provide a short review how to discuss the unitarity making use of the BRST charge. Afterwards we make a detailed study of the most general version of our action, and we come to the conclusion that the model is not unitary, as we are unable to remove all the negative norm states from the physical spectrum in a consistent way.

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arXiv2003

On the fidelity of mixed states of two qubits

We consider a single copy of a mixed state of two qubits and show how its fidelity or maximal singlet fraction is related to the entanglement measures concurrence and negativity. We characterize the extreme points of the convex set of states with constant fidelity, and use this to prove tight lower and upper bounds on the fidelity for a given amount of entanglement.

quant-ph↗

arXiv2003

On quantum channels

One of the most challenging open problems in quantum information theory is to clarify and quantify how entanglement behaves when part of an entangled state is sent through a quantum channel. Of central importance in the description of a quantum channel or completely positive map (CP-map) is the dual state associated to it. The present paper is a collection of well-known, less known and new results on quantum channels, presented in a unified way. We will show how this dual state induces nice characterizations of the extremal maps of the convex set of CP-maps, and how normal forms for states defined on a Hilbert space with a tensor product structure lead to interesting parameterizations of quantum channels.

quant-ph↗

arXiv2003

On ghost condensation, mass generation and Abelian dominance in the Maximal Abelian Gauge

Recent work claimed that the off-diagonal gluons (and ghosts) in pure Yang-Mills theories, with Maximal Abelian gauge fixing (MAG), attain a dynamical mass through an off-diagonal ghost condensate. This condensation takes place due to a quartic ghost interaction, unavoidably present in MAG for renormalizability purposes. The off-diagonal mass can be seen as evidence for Abelian dominance. We discuss why ghost condensation of the type discussed in those works cannot be the reason for the off-diagonal mass and Abelian dominance, since it results in a tachyonic mass. We also point out what the full mechanism behind the generation of a real mass might look like.

hep-th↗

arXiv2002

The mass gap and vacuum energy of the Gross-Neveu model via the 2PPI expansion

We introduce the 2PPI (2-point-particle-irreducible) expansion, which sums bubble graphs to all orders. We prove the renormalizibility of this summation. We use it on the Gross-Neveu model to calculate the mass gap and vacuum energy. After an optimization of the expansion, the final results are qualitatively good.

hep-th↗

arXiv2000

Summation and renormalization of bubble graphs to all orders

We introduce the 2PPI expansion which sums the bubble graphs to all orders. We show that this expansion can be renormalised with the usual counterterms in a mass independent scheme. We discuss its application to the O(N) linear sigma model.

hep-th↗

arXiv1995

A Technique for generating Feynman Diagrams

We present a simple technique that allows to generate Feynman diagrams for vector models with interactions of order $2n$ and similar models (Gross-Neveu, Thirring model), using a bootstrap equation that uses only the free field value of the energy as an input. The method allows to find the diagrams to, in principle, arbitrarily high order and applies to both energy and correlation functions. It automatically generates the correct symmetry factor (as a function of the number of components of the field) and the correct sign for any diagram in the case of fermion loops. We briefly discuss the possibility of treating QED as a Thirring model with non-local interaction.

hep-th↗

arXiv1994

Large N limit of O(N) vector models

Using a simple identity between various partial derivatives of the energy of the vector model in 0+0 dimensions, we derive explicit results for the coefficients of the large N expansion of the model. These coefficients are functions in a variable $ρ^2$, which is the expectation value of the two point function in the limit $N=\infty$. These functions are analytic and have only one (multiple) pole in $ρ^2$. We show to all orders that these expressions obey a given general formula. Using this formula it is possible to derive the double scaling limit in an alternative way. All the results obtained for the double scaling limit agree with earlier calculations. (to be published in Physics Letters B)

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