25,846 research outputs found
Chiral symmetry breaking revisited: the gap equation with lattice ingredients
We study chiral symmetry breaking in QCD, using as ingredients in the quark
gap equation recent lattice results for the gluon and ghost propagators. The
Ansatz employed for the quark-gluon vertex is purely non-Abelian, introducing a
crucial dependence on the ghost dressing function and the quark-ghost
scattering amplitude. The numerical impact of these quantities is considerable:
the need to invoke confinement explicitly is avoided, and the dynamical quark
masses generated are of the order of 300 MeV. In addition, the pion decay
constant and the quark condensate are computed, and are found to be in good
agreement with phenomenology.Comment: 3 pages, 5 figures. Talk presented at the Quark Confinement and the
Hadron Spectrum - Madrid 2010, August 30th - September 3rd 2010, Madrid,
Spai
New insights on non-perturbative Yang-Mills
In this talk we review some recent results on the infrared properties of the
gluon and ghost propagators in pure Yang-Mills theories. These results are
obtained from the corresponding Schwinger-Dyson equation formulated in a
special truncation scheme, which preserves gauge invariance. The presence of
massless poles in the three gluon vertex triggers the generation of a dynamical
gluon mass (Schwinger mechanism in d=4), which gives rise to an infrared finite
gluon propagator and ghost dressing function. As a byproduct of this analysis
we calculate the Kugo-Ojima function, required for the definition of the
non-perturbative QCD effective charge within the pinch technique framework. We
show that the numerical solutions of these non-perturbative equations are in
very good agreement with the results of SU(3) lattice simulations.Comment: Invited talk at XI Hadron Physics, Maresias, S\~ao Paulo, Brazil,
21-26 March, 201
Non-perturbative Green's functions and the QCD effective charge
Using as ingredients the non-perturbative solutions of various QCD Green's
function obtained from Schwinger-Dyson equations (SDEs), we study two versions
of the QCD effective charge. The first one obtained from the pinch technique
gluon self-energy, and the second from the ghost-gluon vertex. Despite the
distinct nature of their buildings blocks, the two effectives charges are
almost identical in the entire range of momenta, due to a fundamental identity
relating the ghost dressing function with the two form factors of Green's
function, which is of central importance in the PT-BFM formalism. In this talk,
we outline how to derive this crucial identity from the SDEs of the
aforementioned Green's functions. The renormalization procedure that preserves
the validity of this identity is discussed in detail. Most importantly, we show
that due to the infrared finiteness of the gluon propagator, the QCD charge
obtained with either definition freezes in the deep infrared, in agreement with
theoretical and phenomenological expectations.Comment: 12 pages, 8 figures. Talk presented at the International Workshop on
QCD Green's Functions, Confinement, and Phenomenology - QCD-TNT09, September
07 - 11 2009, ECT* Trento, Ital
On dynamical gluon mass generation
The effective gluon propagator constructed with the pinch technique is
governed by a Schwinger-Dyson equation with special structure and gauge
properties, that can be deduced from the correspondence with the background
field method. Most importantly the non-perturbative gluon self-energy is
transverse order-by-order in the dressed loop expansion, and separately for
gluonic and ghost contributions, a property which allows for a meanigfull
truncation. A linearized version of the truncated Schwinger-Dyson equation is
derived, using a vertex that satisfies the required Ward identity and contains
massless poles. The resulting integral equation, subject to a properly
regularized constraint, is solved numerically, and the main features of the
solutions are briefly discussed.Comment: Special Article - QNP2006: 4th International Conference on Quarks and
Nuclear Physics, Madrid, Spain, 5-10 June 200
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