André Lehum

Good news at the lights out of 2021! We have published two articles in the journal Physical Review D, both with the participation of the student Huan Souza, who is doing his master's under my supervision. In the paper entitled "Gravitational Corrections to two-loop beta function in quantum electrodynamics" we use the framework of effective field theory to couple Einstein's gravity to quantum electrodynamics (QED) and determine the gravitational corrections to the two-loop beta function of the electric charge in arbitrary electrodynamics (Lorentz-like) and arbitrary (de Donder like) gravitational gauges. Our results indicate that gravitational corrections do not alter the running behavior of the electric charge; on the contrary, we observe that it gives a positive contribution to the beta function, making the electric charge grow even faster. This work was carried out in collaboration with researchers L. Beviláqua (UFRN), M. Dias and C. Senise (UNIFESP), A. J. da Silva (USP) and H. Souza (UFPA).

In the second one, entitled "Universality of the gauge coupling constant in the Einstein-QED system", we discuss the universality of the renormalization of the gauge coupling constant in the quantum electrodynamics coupled to the Einstein's gravity in the framework of effective field theory in an arbitrary gauge, discussing how we can define the renormalization of the electric charge in a way  independent of process. We observe that the renormalization of the three-point functions with different particles receive different contributions from the gravitational sector. Despite that, the universality of the gauge coupling constants is guaranteed by the Ward identity that makes the renormalized electric charge receive no contribution from the gravitational sector at one-loop order. This work outlines the collaboration of researchers L. Beviláqua (UFRN) and H. Souza (UFPA).

To learn more, visit the article links on the PRD server or on the ArXiv preprints site:

1. Gravitational corrections for the two-loop beta function in quantum electrodynamics (PRD, ArXiv);

2. Universality of the gauge coupling constant in the Einstein-QED system (PRD, ArXiv).

In the paper "Soft supersymmetry breaking in the nonlinear sigma model" , recently published in Physics Letters B, we discuss the dynamical generation of mass in a deformed supersymmetric nonlinear sigma model in a two-dimensional space–time. We introduce the deformation by imposing a constraint that softly breaks supersymmetry. Through the tadpole method, we compute the effective potential at leading order in 1/N expansion showing that the model exhibit a dynamical generation of mass to the matter fields. Supersymmetry is recovered in the limit of the deformation parameter going to zero. Read more at https://doi.org/10.1016/j.physletb.2018.12.022. This work was done in collaboration with Leandro Beviláqua (UFRN) and Adilson José da Silva (USP).

In the recently published paper in the journal Europhysics Letters, entitled "CP(N−1) model in aether-superspace", we discuss the dynamical generation of mass in the Lorentz-violating CP(N−1) model defined in two- and three-dimensional aether-superspace. We show that even though the model presents a phase structure similar to the usual Lorentz-invariant case, the mass dynamically generated by quantum corrections has a dependence on the Lorentz-violating background properties, except for space-like LV vector parameter. This is to be contrasted with the behavior of the quantum electrodynamics in the two-dimensional aether-superspace, where the dynamical generation of mass was shown to exhibit an explicit dependence on the aether parameters in every possible case. This paper was made in collaboration with Prof. Dr. Alysson Ferrari (UFABC).