arXiv subjects

A. R. Vieira

Publications and source records attributed to A. R. Vieira.

At least 19 recordsLinked to original sources

arXiv2026

Soft Scale Symmetry Breaking with Laguerre Explicit Regulators

In this work, we search for explicit regulators that do not spuriously break scale invariance starting from conditions established by implicit regularization. There is a family of regulator functions that obeys the conditions and leads to soft breaking terms of the dilatation current. This family of functions is shown to be related to the Laguerre polynomials. We apply this approach by revisiting quadratic divergences in the context of the naturalness problem of the Standard Model and show that the quadratic dependence of the Higgs mass on the cutoff is not required by consistency of scale-symmetry breaking and can be removed within this class of regulators.

hep-ph↗

arXiv2025

Vacuum Cherenkov radiation for nonminimal dimension-5 Lorentz violation

Vacuum Cherenkov radiation is investigated in the Lorentz-violating Standard-Model Extension for isotropic dim-5 operators $\hat{m}$ and $\hat{a}^μ$ in the fermion sector. Both the kinematics and dynamics of this process are analyzed by analytical and numerical means, leading to its decay and radiated-energy rates as functions of the initial-fermion momentum. We adopt the point of view that vacuum Cherenkov radiation is actually a physical phenomenon expected to occur for a charged, massive fermion in the presence of Lorentz violation, when some additional requirements are satisfied. The absence of this effect in ultrahigh-energy cosmic rays detected on Earth allows us to infer stringent bounds on isotropic dim-5 Lorentz violation in protons, quarks, and electrons.

hep-ph↗

arXiv2025

Gauge symmetry and radiatively induced terms in dimension-5 non-minimal Lorentz-violating QED

In this work, we derive the conditions that assure gauge invariance of a non-minimal dimension-5 Lorentz-violating QED. The two and three point functions at one-loop are computed. The gauge Ward identities are checked and the conditions to assure gauge symmetry of this non-minimal framework is found to be the same of the usual QED. Induced terms are also investigated and it is shown that the non-minimal Lorentz-violating $a^{(5)}_F$-term of the fermion sector can induce radiatively a non-minimal Lorentz-violating term in the photon sector.

hep-th↗

arXiv2025

Do Anomalies Break Momentum Routing Invariance?

The diagrammatic computation of the chiral anomaly is associated with momentum-routing invariance breaking. This happens because the momentum routing in the internal lines of a loop diagram is chosen such that the gauge Ward identities hold and the chiral Ward identity is broken by the finite term measured in the pion decay into two photons. Since the latter is observable, it seems that there is a preferred momentum routing set by experiments. However, it is shown in this work that the chiral anomaly is momentum-routing invariant. This idea is specially important for situations in which there are no experiments yet to decide on the momentum routing, like in supersymmetric theories and in frameworks with CPT and Lorentz violation. Therefore, we resort to momentum-routing invariance to find out what symmetry is broken in a nonminimal CPT- and Lorentz-violating version of quantum electrodynamics.

hep-th↗

arXiv2025

Do anomalies break the momentum routing invariance?

The diagrammatic computation of anomalies is usually associated with the breaking of the momentum routing invariance. This is because the momentum routing is usually chosen to fulfill the desired Ward identity. In the case of the chiral anomaly, the momentum routing is chosen in order to fulfill the gauge Ward identity and break the chiral Ward identity. Although the chiral anomaly is physical because it is associated with the pion decay into two photons, this does not necessarily mean that the momentum routing invariance is broken because the momentum routing was chosen in the computation of the anomaly. The reciprocal is not true, {\it i. e.} anomalies do not imply in momentum routing invariance breaking. In this work, we show that if gauge invariance is assumed, the chiral and the scale anomalies are independent of the momentum routing chosen and as a result they are momentum routing invariant. This idea is applied to a QED with non-minimal CPT and Lorentz violation, where momentum routing invariance is used to find out what symmetry is broken in the Ward identities.

hep-th↗

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.

hep-th↗

arXiv2023

Scale anomaly in a Lorentz and CPT-violating Quantum Electrodynamics

We compute the classical and the quantum breaking of the dilatation current in the minimal Lorentz and CPT-violating quantum electrodynamics. At the classical level, scale symmetry is broken by the general mass term \barψMψand the Chern-Simons-like term. At the quantum level, it is broken by all expected observable fermion operators in the massless limit.

hep-th↗

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.

hep-th↗

arXiv2022

The unambiguous Lorentz-violating induced terms

In this work, we show that surface terms, which map dependence on regularization, can be fixed requiring momentum routing invariance of tadpoles or diagrams with more external legs. This condition makes the Lorentz-violating terms induced by quantum corrections determined and uniques.

hep-th↗

arXiv2021

Two-loop renormalisation of gauge theories in $4D$ Implicit Regularisation and connections to dimensional methods

We compute the two-loop $β$-function of scalar and spinorial quantum electrodynamics as well as pure Yang-Mills and quantum chromodynamics using the background field method in a fully quadridimensional setup using Implicit Regularization (IREG). Moreover, a thorough comparison with dimensional approaches such as conventional dimensional regularization (CDR) and dimensional reduction (DRED) is presented. Subtleties related to Lorentz algebra contractions/symmetric integrations inside divergent integrals as well as renormalisation schemes are carefully discussed within IREG where the renormalisation constants are fully defined as basic divergent integrals to arbitrary loop order. Moreover, we confirm the hypothesis that momentum routing invariance in the loops of Feynman diagrams implemented via setting well-defined surface terms to zero deliver non-abelian gauge invariant amplitudes within IREG just as it has been proven for abelian theories.

hep-ph↗

arXiv2021

On plane wave solutions in Lorentz-violating extensions of gravity

In this paper, we obtain dispersion relations corresponding to plane wave solutions in various Lorentz-breaking extensions of gravity with dimensions 3, 4, 5 and 6. We demonstrate that these dispersion relations display an usual Lorentz-invariant mode when the corresponding additive term involves higher derivatives.

gr-qc↗

arXiv2020

Lorentz and CPT Violation in Partons

A framework is presented for the factorization of high-energy hadronic processes in the presence of Lorentz and CPT violation. The comprehensive effective field theory describing Lorentz and CPT violation, the Standard-Model Extension, is used to demonstrate factorization of the hadronic tensor at leading order in electroweak interactions for deep inelastic scattering and for the Drell-Yan process. Effects controlled by both minimal and nonminimal coefficients for Lorentz violation are explored, and the equivalent parton-model description is derived. The methodology is illustrated by determining cross sections and studying estimated attainable sensitivities to Lorentz violation using real data collected at the Hadronen-Elektronen Ring Anlage and the Large Hadron Collider and simulated data for the future US-based electron-ion collider.

hep-ph↗

arXiv2020

Pair approximation for the noisy threshold $q$-voter model

In the standard $q$-voter model, a given agent can change its opinion only if there is a full consensus of the opposite opinion within a group of influence of size $q$. A more realistic extension is the threshold $q$-voter, where a minimal agreement (at least $0<q_0\le q$ opposite opinions) is sufficient to flip the central agent's opinion, including also the possibility of independent (non conformist) choices. Variants of this model including non-conformist behavior have been previously studied in fully connected networks (mean-field limit). Here we investigate its dynamics in random networks. Particularly, while in the mean-field case it is irrelevant whether repetitions in the influence group are allowed, we show that this is not the case in networks, and we study the impact of both cases, with or without repetition. Furthermore, the results of computer simulations are compared with the predictions of the pair approximation derived for uncorrelated networks of arbitrary degree distributions.

physics.soc-ph↗

arXiv2019

Lorentz-Violating Running of Coupling Constants

We compute the full vacuum polarization tensor in the minimal QED extension. We find that its low-energy limit is dominated by the radiatively induced Chern-Simons-like term and the high-energy limit is dominated by the c-type coefficients. We investigate the implications of the high-energy limit for the QED and QCD running couplings. In particular, the QCD running offers the possibility to study Lorentz-violating effects on the parton distribution functions and observables such as the hadronic R ratio.

hep-ph↗

arXiv2018

On the Bose symmetry and the left- and right-chiral anomalies

It is generally assumed that in order to preserve Bose symmetry in the left- (or right-chiral) current it is necessary to equally distribute the chiral anomaly between the vectorial and the axial Ward identities, requiring the use of counterterms to restore consistency. In this work, we show how to calculate the quantum breaking of the left- and right-chiral currents in a way that allows to preserve Bose symmetry independently of the chiral anomaly, using the Implicit Regularization method.

hep-th↗

arXiv2017

Lorentz violation and deep inelastic scattering

The effects of quark-sector Lorentz violation on deep inelastic electron-proton scattering are studied. We show that existing data can be used to establish first constraints on numerous coefficients for Lorentz violation in the quark sector at an estimated sensitivity of parts in a million.

hep-ph↗

arXiv2016

Lorentz-Violating QCD Corrections to Deep Inelastic Scattering

In this work, we present CPT- and Lorentz-violating corrections to observable quantities in electron-proton scattering. We also show how the theoretical prediction can be used together with data to establish bounds on a coefficient for CPT and Lorentz violation in the QCD sector.

hep-ph↗

arXiv2016

$γ_{5}$ algebra ambiguities in Feynman amplitudes: momentum routing invariance and anomalies in $D=4$ and $D=2$

We address the subject of chiral anomalies in two and four dimensional theories. Ambiguities associated with the $γ_5$ algebra within divergent integrals are identified, even though the physical dimension is not altered in the process of regularization. We present a minimal prescription that leads to unique results and apply it to a series of examples. For the particular case of abelian theories with effective chiral vertices, we show: 1- Its implication on the way to display the anomalies democratically in the Ward identities. 2- The possibility to fix an arbitrary surface term in such a way that a momentum routing independent result emerges. This leads to a reinterpretation of the role of momentum routing in the process of choosing the Ward identity to be satisfied in an anomalous process. 3- Momentum Routing Invariance (MRI) is a necessary and sufficient condition to assure vectorial gauge invariance of effective chiral Abelian gauge theories. We also briefly discuss the case of complete chiral theories, using the Chiral Schwinger Model as an example.

hep-th↗