arXiv subjects

Julio Leite

Publications and source records attributed to Julio Leite.

18 recordsLinked to original sources

arXiv2026

Prompt Engineering Strategies for LLM-based Qualitative Coding of Psychological Safety in Software Engineering Communities: A Controlled Empirical Study

Qualitative analysis plays a pivotal role in understanding the human and social aspects of software engineering. However, it remains a demanding process shaped by the subjective interpretation of individual researchers and sensitive to methodological choices such as prompt design. Recent advancements in Large Language Models (LLMs) offer promising opportunities to support this type of analysis, although their reliability in reproducing human qualitative reasoning under varying prompting conditions remains largely untested. This study presents a controlled empirical evaluation of three LLMs -- Claude Haiku, DeepSeek-Chat, and Gemini 2.5 Flash -- across two prompt engineering strategies (zero-shot and multi-shot closed coding), using Cohen's kappa as the primary agreement metric over ten independent runs per configuration. Results suggest that multi-shot prompting significantly improves agreement for Claude Haiku (Delta kappa = +0.034, Wilcoxon p = 0.004) but not for DeepSeek-Chat or Gemini 2.5 Flash. Intra-model stability varies substantially -- DeepSeek-Chat and Claude Haiku exhibit the lowest variance (SD approx. 0.017), while Gemini 2.5 Flash is the least stable (SD = 0.038). A systematic over-prediction of "Sharing Negative Feedback" is identified across all models (bias ratios up to 5.25x), alongside consistent under-prediction of "Expressing Concerns." Collectively, these findings provide empirical evidence for prompt engineering guidelines in LLM-assisted qualitative coding for software engineering research.

cs.SE↗

arXiv2025

Scotogenic mechanism from an extended $\boldsymbol{SU(2)_1 \times SU(2)_2 \times U(1)_Y}$ electroweak symmetry

We propose an extension of the electroweak sector of the Standard Model in which the gauge group $SU(2)_L$ is promoted to $SU(2)_1 \times SU(2)_2$. This framework naturally includes a viable dark matter candidate and generates neutrino masses radiatively \`a la Scotogenic. Our scenario can be viewed as an ultraviolet extension of the Scotogenic mechanism, addressing some of its shortcomings. The resulting phenomenology may be probed through a range of experimental signatures, from precision electroweak measurements to searches for lepton flavor violation.

hep-ph↗

arXiv2025

Flavor-changing axions and Dirac neutrino masses

Implementing the axion concept in the context of 3-3-1 extensions of the Standard Model (SM) leads to richer properties than in the simpler axion setups, and related to the Dirac neutrino seesaw mechanism. In this way the smallness of neutrino masses, the strong CP problem, the nature of dark matter and the number of families all have a common origin. Besides having an enhanced coupling to photons, our revamped axion can also be distinguished from DFSZ and KSVZ axions through its couplings to fermions. The latter lead to interesting phenomenological consequences, including flavor-changing axion-emitting two-body K, B and D meson decays.

hep-ph↗

arXiv2024

QCD axion, colour-mediated neutrino masses, and $B^+\to K^+ + E_{\text{miss}}$ anomaly

Motivated by the recent Belle II result indicating a $2.7\,\sigma$ excess of $B^+\to K^+ + E_{\text{miss}}$ events compared to the Standard Model (SM) prediction for $B^+ \to K^+ \nu\bar{\nu}$, we explore an explanation to this anomaly based on a KSVZ-type QCD axion model featuring a Peccei-Quinn (PQ) symmetry breaking at high-scale, that can provide a solution to the strong CP problem with dark matter relic abundance. The model contains a PQ-charged scalar} leptoquark which can interact with the SM quarks only via mass-mixing of the latter with vector-like quarks. The mixing between SM and vector-like quarks is determined by the PQ mass scales and can explain the excess $B^+\to K^+ + E_{\text{miss}}$ events while respecting other flavour constraints. The same PQ-charged scalar leptoquarks and vector-like quarks also mediate the two-loop radiative neutrino masses.

hep-ph↗

arXiv2023

Dynamical scoto-seesaw mechanism with gauged $B-L$

We propose a dynamical scoto-seesaw mechanism using a gauged $B-L$ symmetry. Dark matter is reconciled with neutrino mass generation, in such a way that the atmospheric scale arises \textit{a la seesaw}, while the solar scale is \textit{scotogenic}, arising radiatively from the exchange of ``dark'' states. This way we ``explain'' the solar-to-atmospheric scale ratio. The TeV-scale seesaw mediator and the two dark fermions carry different $B-L$ charges. Dark matter stability follows from the residual matter parity that survives $B-L$ breaking. Besides having collider tests, the model implies sizeable charged lepton flavour violating (cLFV) phenomena, including Goldstone boson emission processes.

hep-ph↗

arXiv2022

Scale-invariant 3-3-1-1 model with $B-L$ symmetry

Motivated by a possible interplay between the mechanism of dynamical symmetry breaking and the seesaw mechanism for generating fermion masses, we present a scale-invariant model that extends the gauge symmetry of the Standard Model electroweak sector to SU(3)$_L\otimes$U(1)$_X\otimes$U(1)$_N$, with a built-in $B-L$ symmetry. The model is based on the symmetry structure of the known 3-3-1 models and, thus, it relates the number of the three observed fermion generations with the cancellation of gauge anomalies. Symmetry breaking is triggered via the Coleman-Weinberg mechanism taking into account a minimal set of scalar field multiplets. We establish the stability conditions for the tree-level scalar potential imposing the copositivity criteria and use the method of Gildener-Weinberg for computing the one-loop effective potential when one has multiple scalar fields. With the addition of vectorial fermions, getting their mass mainly through the vacuum expectation value of scalar singlets at $10^3$ TeV, the $B-L$ symmetry leads to textures for the fermion mass matrices, allowing seesaw mechanisms for neutrinos and quarks to take place. In particular, these mechanisms could partly explain the mass hierarchies of the quarks. Once the breakdown of the SU(3)$_L$ symmetry is supposed to occur around 10 TeV, the model also predicts new particles with TeV-scale masses, such as a neutral scalar, $H_{1}$, a charged scalar, $H^\pm$, and the gauge bosons $Z^{\prime}$, $W^{\prime\pm}$ and $Y^0$, that could be searched with the high-luminosity LHC.

hep-ph↗

arXiv2021

Axion-Neutrino Interplay in a Gauged Two-Higgs-Doublet Model

We propose a gauged two-Higgs-doublet model (2HDM) featuring an anomalous Peccei-Quinn symmetry, $U(1)_{PQ}$. Dangerous tree-level flavour-changing neutral currents, common in 2HDMs, are forbidden by the extra gauge symmetry, $U(1)_X$. In our construction, the solutions to the important issues of neutrino masses, dark matter and the strong CP problem are interrelated. Neutrino masses are generated via a Dirac seesaw mechanism and are suppressed by the ratio of the $U(1)_X$ and the $U(1)_{PQ}$ breaking scales. Naturally small neutrino masses suggest that the breaking of $U(1)_X$ occurs at a relatively low scale, which may lead to observable signals in near-future experiments. Interestingly, spontaneous symmetry breaking does not lead to mixing between the $U(1)_X$ gauge boson, $Z^\prime$, and the standard $Z$. For the expected large values of the $U(1)_{PQ}$ scale, the associated axion becomes "invisible", with DFSZ-like couplings, and may account for the observed abundance of cold dark matter. Moreover, a viable parameter space region, which falls within the expected sensitivities of forthcoming axion searches, is identified. We also observe that the flavour-violating process of kaon decaying into pion plus axion, $K^+ \to \pi^+ a$, is further suppressed by the $U(1)_X$ scale, providing a rather weak lower bound for the axion decay constant $f_a$.

hep-ph↗

arXiv2021

Phenomenology of fermion dark matter as neutrino mass mediator with gauged B-L

We analyze a model with unbroken B-L gauge symmetry where neutrino masses are generated at one loop, after spontaneous breaking of a global U(1) symmetry. These symmetries ensure dark matter stability and the Diracness of neutrinos. Within this context, we examine fermionic dark matter. Consistency between the required neutrino mass and the observed relic abundance indicates dark matter masses and couplings within the reach of direct detection experiments.

hep-ph↗

arXiv2020

Scotogenic neutrino masses and dark matter stability from residual gauge symmetry

In the context of the $\mathrm{SU(3)_c \otimes SU(3)_L \otimes U(1)_X \otimes U(1)_{N}}$ (3-3-1-1) extension of the standard model, we show how the spontaneous breaking of the gauge symmetry gives rise to a residual symmetry which accounts for dark matter stability and small neutrino masses in a scotogenic fashion. As a special feature, the gauge structure implies that one of the light neutrinos is massless and, as a result, there is a lower bound for the $0\nu\beta\beta$ decay rate.

hep-ph↗

arXiv2020

Reloading the Axion in a 3-3-1 setup

We generalize the idea of the axion to an extended electroweak gauge symmetry setup. We propose a minimal axion extension of the Singer-Valle-Schechter (SVS) theory, in which the standard model fits in $\mathrm{SU(3)_L\otimes U(1)_X}$, the number of families results from anomaly cancellation, and the Peccei-Quinn (PQ) solution to the strong-CP problem is implemented. Neutrino masses arise from a type-I Dirac seesaw mechanism, suppressed by the ratio of SVS and PQ scales, suggesting the existence of new physics at a moderate SVS scale. Novel features include an enhanced axion coupling to photons when compared to the DFSZ axion, as well as flavour-changing axion couplings to quarks.

hep-ph↗

arXiv2020

Dark matter stability from Dirac neutrinos in scotogenic 3-3-1-1 theory

We propose the simplest TeV-scale scotogenic extension of the original 3-3-1 theory, where dark matter stability is linked to the Dirac nature of neutrinos, which results from an unbroken $B-L$ gauge symmetry. The new gauge bosons get masses through the interplay of spontaneous symmetry breaking \`a la Higgs and the Stueckelberg mechanism.

hep-ph↗

arXiv2020

Dynamical Symmetry Breaking and Fermion Mass Hierarchy in the Scale-Invariant 3-3-1 Model

We propose an extension of the Standard Model (SM) based on the $SU(3)_C\otimes SU(3)_L\otimes U(1)_X$ (3-3-1) gauge symmetry and scale invariance. Maintaining the main features of the so-called 3-3-1 models, such as the cancellation of gauge anomalies related to the number of chiral fermion generations, this model exhibits a very compact scalar sector. Only two scalar triplets and one singlet are necessary and sufficient to break the symmetries dynamically via the Coleman-Weinberg mechanism. With the introduction of an Abelian discrete symmetry and assuming a natural hierarchy among the vacuum expectation values of the neutral scalar fields, we show that all particles in the model can get phenomenologically consistent masses. In particular, most of the standard fermion masses are generated via a seesaw mechanism involving some extra heavy fermions introduced for consistency. This mechanism provides a partial solution for the fermion mass hierarchy problem in the SM. Furthermore, the simplicity of the scalar sector allows us to analytically find the conditions for the potential stability up to one-loop level and show how they can be easily satisfied. Some of the new particles, such as the scalars $H$, $H^\pm$ and all the non-SM vector bosons, are predicted to get masses around the TeV scale and, therefore, could be produced at the high-luminosity LHC. Finally, we show that the model features a residual symmetry which leads to the stability of a heavy neutral particle; the latter is expected to show up in experiments as missing energy.

hep-ph↗

arXiv2020

Scotogenic dark matter and Dirac neutrinos from unbroken gauged $B-L$ symmetry

We propose a simple extension of the standard model where neutrinos get naturally small "scotogenic" Dirac masses from an unbroken gauged $B-L$ symmetry, ensuring dark matter stability. The associated gauge boson gets mass through the Stueckelberg mechanism. Two scenarios are identified, and the resulting phenomenology briefly sketched.

hep-ph↗

arXiv2019

A theory for scotogenic dark matter stabilised by residual gauge symmetry

Dark matter stability can result from a residual matter-parity symmetry, following naturally from the spontaneous breaking of the gauge symmetry. Here we explore this idea in the context of the $\mathrm{SU(3)_c \otimes SU(3)_L \otimes U(1)_X \otimes U(1)_{N}}$ electroweak extension of the standard model. The key feature of our new scotogenic dark matter theory is the use of a triplet scalar boson with anti-symmetric Yukawa couplings. This naturally implies that one of the light neutrinos is massless and, as a result, there is a lower bound for the $\rm 0\nu\beta\beta$ decay rate.

hep-ph↗

arXiv2019

Natural quark mixing and inverse seesaw in a left-right model with an axion

We consider a minimal left-right model with a Peccei-Quinn symmetry, where generalised charge conjugation plays the role of the left-right symmetry. We show how the spontaneous breaking of the Peccei-Quinn symmetry by a scalar singlet can provide us with solutions not only to the strong CP and dark matter problems but can also help to generate naturally suppressed off-diagonal CKM elements and small neutrino masses via the inverse seesaw mechanism. For this, we make use of an economical scalar sector composed of a bi-doublet, two doublets and a singlet only. As a result of the new gauge bosons and neutrinos, the neutrinoless double beta decay, as well as lepton flavour violating processes, receives new contributions which can, in principle, become relevant due to the low-scale nature of the inverse seesaw mechanism. The model can easily accommodate all the current data on fermion masses and mixing even if the left-right scale is only high enough to evade the current experimental constraints.

hep-ph↗

arXiv2016

Aspects of fermion dynamics from Lorentz symmetry violation

In this thesis we are interested in understanding how Lorentz symmetry violation can affect some features of fermion dynamics and, perhaps, help to solve some well-known problems in particle physics, such as the origin of neutrino masses and oscillations. Firstly, we consider two Lorentz-Invariance-Violating (LIV) models and investigate the possibility of generating masses and oscillations dynamically for both Dirac and Majorana neutrinos, using non-perturbative methods, such as the Schwinger-Dyson and the effective potential approaches. In our studies, Lorentz symmetric models are extended by the inclusion of higher-order LIV operators, which improve the convergence of loop integrals and introduce a natural mass scale to the theories. We then present how Lorentz invariance can be recovered, for both models, after quantisation, in such a way that the dynamical masses and mixing are the only quantum effects that remain finite. Additionally, we study how matter fields, especially fermions, behave when coupled to two modified gravity models. Such modified gravity models break the 4-dimensional diffeomorphism invariance and, consequently, induce local Lorentz violation. In particular, we consider Horava-Lifshitz gravity, which presents an improved ultraviolet behaviour when compared to General Relativity (GR), and thus addresses a fundamental problem in physics: the non-(perturbative-)renormalisability of the theory of GR. We calculate the LIV one-loop corrections to the matter sector dispersion relations, after integration over graviton components, and show that, by imposing reasonable constraints on the energy scales of our gravity models, our results are consistent with the current bounds on Lorentz symmetry violation.

hep-ph↗

arXiv2014

Quasi-relativistic fermions and dynamical flavour oscillations

We introduce new Lorentz-symmetry violating kinematics for a four-fermion interaction model, where dynamical mass generation is allowed, irrespectively of the strength of the coupling. In addition, these kinematics lead to a quasi-relativistic dispersion relation, in the sense that it is relativistic in both the infrared and the ultraviolet, but not in an intermediate regime, characterized by the mass $M$. For two fermions, we show that a flavour-mixing mass matrix is generated dynamically, and the Lorentz symmetric limit $M\to\infty$ leads to two free relativistic fermions, with flavour oscillations. This model, valid for either Dirac or Majorana fermions, can describe any set of phenomenological values for the eigen masses and the mixing angle.

hep-th↗

arXiv2013

Lorentz-Violating Regulator Gauge Fields as the Origin of Dynamical Flavour Oscillations

We show how a mass mixing matrix can be generated dynamically, for two massless fermion flavours coupled to a Lorentz invariance violating (LIV) gauge field. The LIV features play the role of a regulator for the gap equations, and the non-analytic dependence of the dynamical masses, as functions of the gauge coupling, allows to consider the limit where the LIV gauge field eventually decouples from the fermions. Lorentz invariance is then recovered, to describe the oscillation between two free fermion flavours, and we check that the finite dynamical masses are the only effects of the original LIV theory. We also discuss briefly a connection of our results with the case of Majorana neutrinos in both, the standard model, where only left-handed (active) neutrinos are considered, and extensions thereof, with sterile right-handed neutrinos.

hep-ph↗