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A. P. Baêta Scarpelli

Publications and source records attributed to A. P. Baêta Scarpelli.

At least 19 recordsLinked to original sources
arXiv2026

Classical investigations in a CPT-even Lorentz-violating model and their implications for the Compton effect

In this work, we investigate some aspects of the Maxwell electrodynamics with the additive Lorentz-violating (LV) CPT-even term. For this model, we derive the energy and momentum conservation laws, highlighting the modifications introduced by Lorentz violation. Furthermore, using the modified dispersion relations, we analyze the correction to Compton effect arising from the presence of the LV vector.

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arXiv2024

On the nonlinear electrodynamics in a Lorentz-breaking scenario

In this work, we study a model in nonlinear electrodynamics in the presence of a CPT-even term that violates Lorentz symmetry. The Lorentz-breaking vector, in addition to the usual background magnetic field, produces interesting effects in the dispersion relations. The consequences on the vacuum refractive index and the group velocity are studied. Vacuum birefringence is discussed in the case the nonlinear electrodynamics is a Euler-Heisenberg model.

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arXiv2023

The full Lorentz-violating vacuum polarization tensor: low and high energy limits

We compute the full vacuum polarization tensor in the fermion sector of Lorentz-violating QED. Even if we assume momentum routing invariance of the Feynman diagrams, it is not possible to fix all surface terms and find an unambiguity free vacuum polarization tensor. The high and low energy limits of this tensor is presented. In the high energy limit, only $c_{μν}$ coeffcients contribute. In the low energy limit, we fnd that Lorentz-violating induced terms depend only on $b_μ$, $c_{μν}$ and $g_{μνλ}$ coeffcients and they are suppressed by powers of $\frac{p^{2}}{m^{2}}$. This limit allows to obtain implications for condensed matter systems, explicitly, for the Hall effect in Weyl semimetals.

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arXiv2022

Advances towards the systematization of calculations with Implicit Regularization

There is currently a high demand for theoretical predictions for processes at next-to-next-to-leading order (NNLO) and beyond, mainly due to the large amount of data which has already been collected at LHC. This requires practical methods that meet the physical requirements of the models under study. We develop a new procedure for applying Constrained Implicit Regularization which simplifies the calculation of amplitudes, including finite parts. The algebraic identities to separate the divergent parts free from the external momenta are used after the Feynman parametrization. These algebraic identities establish a set of scale relations which are always the same and do not need to be calculated in each situation. This procedure unifies the calculations in massive and non-massive models in an unique procedure. We establish a systematization of the calculation of one-loop amplitudes and extend the procedure for higher-loop orders.

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arXiv2022

One-loop calculations in CPT-even Lorentz-breaking scalar QED

In this paper, we study a CPT-even Lorentz-breaking extension of the scalar QED. For this theory, we calculate the one-loop lower-order contributions in the Lorentz-violating parameters to the two-point functions of scalar and gauge fields. We found that the two background tensors, coming from the two sectors (scalar and gauge) are mixed in the one-loop corrections both in finite and divergent parts. This shows that these two Lorentz-breaking terms cannot be studied in an isolated form. Besides, the results in the gauge sector are confirmed to be transversal.

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arXiv2022

Residual gauge-invariance in a massive Lorentz-violating extension of QED

We reassess an alternative CPT-odd electrodynamics obtained from a Palatini-like procedure. Starting from a more general situation, we analyze the physical consistency of the model for different values of the parameter introduced in the mass tensor. We show that there is a residual gauge-invariance in the model if the local transformation is taken to vary only in the direction of the Lorentz-breaking vector. This residual gauge-invariance can be extended to all models whose only source of gauge symmetry breaking is such a mass term.

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arXiv2020

No radiative corrections to the Carroll-Field-Jackiw term beyond one-loop order

We demonstrate explicitly the absence of the quantum corrections to the Carroll-Field-Jackiw (CFJ) term beyond one-loop within the Lorentz-breaking CPT-odd extension of QED. The proof holds within two prescriptions of quantum calculations, with the axial vector in the fermion sector {}treated either as a perturbation or as a contribution in the exact propagator of the fermion field.

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arXiv2020

Higher-order one-loop renormalization in the spinor sector of minimal LV extended QED

We calculate contributions to the one-loop renormalization in the spinor sector of the minimal Lorentz-violating extended QED in the second order in Lorentz-breaking parameters. From the renormalizability viewpoint, we show that the inclusion of some of the Lorentz-breaking terms in the model is linked to the presence of others. We also demonstrate that the Ward identities are satisfied up to this order.

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arXiv2016

Tree-level equivalence between a Lorentz-violating extension of QED and its dual model in electron-electron scattering

S-matrix amplitudes for the electron-electron scattering are calculated in order to verify the quantum equivalence of dual models. We used an extended Quantum Electrodynamics with CPT-even Lorentz-violating kinetic and mass terms, which was used in a process of gauge embedding, known as Noether dualizationn method (NDM), in order to generate its gauge-invariant dual model. The physical equivalence was established at tree-level and the cross section was calculated to second order in the Lorentz-violating parameter.

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arXiv2016

Remarks on a Lorentz-breaking 4D chiral gauge theory

We investigate a Lorentz-violating chiral model composed by two fermions, a complex scalar field and a gauge field. We show that by convenientely adjusting the parameters of the model, it is possible to generate an unambiguous Carroll-Field-Jackiw term and, at the same time, provide the cancelation of the chiral anomaly. The renormalizability of the model is investigated and it is shown that the same counterterms needed in the symmetric phase also renormalize the model with broken symmetry.

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arXiv2016

Subtleties in the beta function calculation of N=1 supersymmetric gauge theories

We investigate some peculiarities in the calculation of the two-loop beta-function of $N=1$ supersymmetric models which are intimately related to the so-called "Anomaly Puzzle". There is an apparent paradox when the computation is performed in the framework of the covariant derivative background field method. In this formalism, it is obtained a finite two-loop effective action, although a non-null coefficient for the beta-function is achieved by means of the renormalized two-point function in the background field. We show that if the standard background field method is used, this two-point function has a divergent part which allows for the calculation of the beta-function via the renormalization constants, as usual. Therefore, we conjecture that this paradox has its origin in the covariant supergraph formalism itself, possibly being an artifact of the rescaling anomaly.

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arXiv2014

Guises and Disguises of Quadratic Divergences

In this contribution, we present a new perspective on the control of quadratic divergences in quantum field theory, in general, and in the Higgs naturalness problem, in particular. Our discussion is essentially based on an approach where UV divergences are parameterized, after being reduced to basic divergent integrals (BDI) in one internal momentum, as functions of a cutoff and a renormalization group scale $λ$. We illustrate our proposal with well-known examples, such as the gluon vacuum self energy of QCD and the Higgs decay in two photons within this approach. We also discuss frameworks in effective low-energy QCD models, where quadratic divergences are indeed fundamental.

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arXiv2014

Dual embedding of extended models with a Lorentz-breaking mass term

In this paper, we investigate a CPT-even model with a Lorentz-violating mass term. Such kind of models may present very interesting features like superluminal modes of propagation or even instantaneous long-range interactions. The mass term we investigate can be induced at classical or quantum level in a scenario with spontaneous gauge symmetry breaking in a gauge-Higgs model without Lorentz symmetry. We analyze the physical consistency of the model by studying the poles of the propagator. By using the Noether Dualization Method (NDM), we obtain a gauge invariant dual theory for this model. The physical equivalence between the two models is investigated and a general relation between the two propagators is obtained.

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arXiv2014

Arbitrariness in the gravitational Chern-Simons-like term induced radiatively

Lorentz violation through a radiatively induced Chern-Simons-like term in a fermionic theory embedded in linearized quantum gravity with a Lorentz- and CPT-violating axial-vector term in the fermionic sector proportional to a constant field $b_μ$ has been recently studied. In a similar fashion as for the extended-QED model of Carroll-Field-Jackiw, we explicitly show that neither gauge invariance nor the more stringent momentum routing invariance condition on underlying Feynman diagrams fix the arbitrariness inherent to such induced term at one loop order. We present the calculation in a nonperturbative expansion in $b_μ$ and within a framework which besides operating in the physical dimension (and thus avoiding $γ_5$ matrix Clifford algebra ambiguities), judiciously parametrizes regularization dependent arbitrary parameters usually fixed by symmetries.

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arXiv2013

Aspects of Quantum Corrections in a Lorentz-violating Extension of the Abelian Higgs Model

We investigate new aspects related to the abelian gauge-Higgs model with the addition of the Carroll-Field-Jackiw term. We focus on one-loop quantum corrections to the photon and Higgs sectors due to spontaneous breaking of gauge symmetry and show that new finite and definite Lorentz-breaking terms are induced. Specifically in the gauge sector, a CPT-even aether term is induced. Besides, aspects of the one-loop renormalization of the background vector dependent terms are discussed.

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arXiv2012

QED with minimal and nonminimal couplings: on the quantum generation of Lorentz violating terms in the pure photon sector

We consider an effective model formed by usual QED (minimal coupling) with the addition of a nonminimal Lorentz violating interaction (proportional to a fixed 4-vector $b_μ$) which may radiatively generate both CPT even and odd terms in the pure gauge sector. We show that gauge invariance from usual QED, considered as a limit of the model for $b_μ\rightarrow 0$, plays an important role in the discussion of the radiatively induced Lorentz violating terms at one-loop order. Moreover, despite the nonrenormalizability of the (effective) model preventing us from readily extending our discussion to higher orders, it is still possible to display the general form of the breaking terms of the photon sector in the on shell limit organized in powers of $b_μ$ which in turn can be considered as a small expansion parameter.

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