arXiv subjects

Mauricio N. Ferreira

Publications and source records attributed to Mauricio N. Ferreira.

5 recordsLinked to original sources

arXiv2025

Pion physics with dressed quark-gluon vertices

Recently, a theoretical framework was set up in [1], which allows for the symmetry-preserving inclusion of full quark-gluon vertices in the description of the meson dynamics. In the present work, we develop a special truncation within this approach, which leads to a tractable set of functional equations that satisfy the fundamental chiral Ward-Takahashi identities. Specifically, the truncation allows us to simplify considerably the quark-gluon Schwinger-Dyson equation, without significant loss of quantitative accuracy. Importantly, this implies a substantial reduction of complexity of the renormalized Bethe-Salpeter equation: it is composed by a pair of one-loop diagrams that contain the full quark-gluon vertex, and a single two-loop diagram that is instrumental for the masslessness of the pion in the chiral limit. A detailed numerical analysis reveals that the incorporation of the aforementioned two-loop diagram is instrumental for the corresponding eigenvalue to reach unity. The key relation between the quark mass function and the pion wave function is shown to be satisfied to within the numerical precision of the loop integrals, which is at the level of about one percent or better. The field-theoretic ingredients required for the extension of this analysis beyond the chiral limit are briefly discussed.

hep-ph↗

arXiv2025

Physics of the gluon mass gap

It has long been known that the gluon propagator in Landau-gauge QCD exhibits a mass gap; and its emergence has been ascribed to the action of the Schwinger mechanism in the gauge sector of QCD. In the present work, we relate this property to the physical mass gap of QCD by considering two observables associated with confinement and chiral symmetry breaking, namely the confinement-deconfinement transition temperature and the pion decay constant, respectively. It turns out that the first observable is linearly proportional to the gluon mass gap, a fact that allows us to assign a direct physical meaning to this scale. Moreover, we identify three distinct momentum regimes in the gluon propagator, ultraviolet, intermediate, and deep infrared, and assess their impact on the aforementioned observables. Both observables are sensitive to the first two regions of momenta, where functional approaches essentially coincide, but are insensitive to the third, deep infrared, regime. The combined information is used for a simple fit for the gluon propagator, all of whose parameters admit a clear physical interpretation. Finally, we discuss how this fit can help us access the intertwined dynamics of confinement and chiral symmetry breaking in QCD-type theories.

hep-ph↗

arXiv2023

Computation of the Kugo-Ojima function from lattice simulations

In addition to its connection with a standard confinement criterion, the Kugo-Ojima function constitutes an indispensable component in a multitude of applications in the gauge sector of QCD. In the present work we report on preliminary results of an ongoing large-volume lattice simulation of this special function. In particular, the volume-dependence of the data is studied in detail, and a comparison with results obtained from Schwinger-Dyson equations is carried out.

hep-lat↗

arXiv2023

Causality violations in simulations of large and small heavy-ion collisions

Heavy-ion collisions, such as Pb-Pb or p-Pb, produce extreme conditions in temperature and density that make the hadronic matter transition to a new state, called quark-gluon plasma (QGP). Simulations of heavy-ion collisions provide a way to improve our understanding of the QGP's properties. These simulations are composed of a hybrid description that results in final observables in agreement with accelerators like LHC and RHIC. However, recent works pointed out that these hydrodynamic simulations can display acausal behavior during the evolution in certain regions, indicating a deviation from a faithful representation of the underlying QCD dynamics. To pursue a better understanding of this problem and its consequences, this work simulated two different collision systems, Pb-Pb and p-Pb at $\sqrt{s_{NN}} = 5.02$ TeV. In this context, our results show that causality violation, even though always present, typically occurs on a small part of the system, quantified by the total energy fraction residing in the acausal region. In addition, the acausal behavior can be reduced with changes in the pre-hydrodynamic factors and the definition of the bulk-viscous relaxation time. Since these aspects are fairly arbitrary in current simulation models, without solid guidance from the underlying theory, it is reasonable to use the disturbing presence of acausal behavior in current simulations to guide improvements towards more realistic modeling. While this work does not solve the acausality problem, it sheds more light on this issue and also proposes a way to solve this problem in simulations of heavy-ion collisions.

nucl-th↗

arXiv2022

General kinematics of the three-gluon vertex from quenched lattice QCD

We present new results for the transversely projected three-gluon vertex from quenched lattice QCD simulations using standard Wilson action. While previous works focused in some particular kinematics such as the symmetric $(q^2 = r^2 = p^2)$ and soft-gluon $(p = 0)$ cases, here we will present a detailed analysis of the bisectoral case $(r^2 = q^2 \ne p^2)$ where the transversely projected vertex can be cast in terms of three independent tensors. The lattice data show a clear dominance of the form-factor corresponding to the tree-level tensor, whose dependence on the momenta can be almost entirely expressed in terms of the symmetric combination of the momenta $s^2=(q^2+r^2+p^2)/2$.

hep-lat↗