arXiv subjects

João Paulo Pinheiro

Publications and source records attributed to João Paulo Pinheiro.

At least 19 recordsLinked to original sources

arXiv2026

Improving the robustness of the $δ_{CP}$ determination with $ν$SCOPE

The determination of leptonic CP violation is a primary goal of future long-baseline neutrino experiments such as DUNE and T2HK. The extraction of $δ_{\mathrm{CP}}$ relies on the near-to-far extrapolation and on the assumed knowledge of the cross-section ratios $σ_{ν_e}/σ_{ν_μ}$ and $σ_{\barν_e}/σ_{\barν_μ}$, which are typically inferred under theoretical assumptions such as lepton universality and depend on nuclear modeling. In this work, we quantify how much of the sensitivity of DUNE and T2HK arises from these assumptions by performing a model-agnostic, data-driven estimation of systematic uncertainties in $ν_e$ and $\barν_e$ cross sections. We find that adopting such an agnostic approach can substantially degrade the CP-violation sensitivity, reducing it by nearly $3σ$ at maximal CP violation for DUNE, and $4σ$ for T2HK. We then assess the impact of the proposed $ν$SCOPE experiment, which, through a combination of neutrino tagging and the Narrow-Band Off-Axis technique, can provide percent-level measurements of $σ_{ν_μ}$ and $σ_{\barν_μ}$ and constrain the ratio $σ_{ν_e}/σ_{ν_μ}$ at the $\sim 2\%$ level. We show that including prospective $ν$SCOPE measurements largely restores the lost sensitivity, highlighting that precise external cross-section measurements may be essential for a fully robust determination of $δ_{\mathrm{CP}}$ and for breaking its degeneracy with nuclear mis-modeling or possible new physics affecting neutrino detection.

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arXiv2026

Defect-Mediated Conversion: Dark Matter from Cosmological Domain-Wall Scattering

We propose a new mechanism for dark matter genesis, \emph{Defect-Mediated Conversion} (DMC). Cosmological domain walls can host a scalar condensate in their core acting as a mixing portal between the Standard Model and a dark sector: thermal-bath fermions crossing the wall are partially and non-thermally converted into dark particles. The conversion probability is governed by a single dimensionless mixing area built from the wall profile, and the yield by the area density of the network. For a light dark particle the probability is independent of both the incident energy and the dark mass, and the relic abundance collapses onto a single mass--coupling relation running from the keV Lyman-$α$ floor to the wall-formation scale. For a heavy one, conversion turns the energy of a single incident fermion into the dark mass, populating dark sectors with masses exceeding both the bath temperature and the mediator mass. The same portal also sources ordinary freeze-in, but DMC, boosted by the coherent wall-area enhancement, dominates it by one to two orders of magnitude at fixed couplings and remains operative in the heavy regime, where freeze-in shuts off.

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arXiv2026

Earth rotation turns event timing into a geometric probe of UHE neutrino origin

It has been proposed that the ultra-high-energy (UHE) event $\rm KM3-230213A$ detected by KM3NeT could be explained by dark matter (DM) decay. Prima facie this seems unlikely because the arrival direction of the event is opposite to the Galactic Centre. We develop a per-event test statistic to quantitively assess this possibility and forecast the required future events to exclude the DM hypothesis in favour of an isotropic signal. For the single event observed, the DM decay hypothesis is disfavoured but not excluded ($p\text{-value}_{\rm DM}\simeq0.13$--$0.15$). We emphasise how including the time-averaged detector visibility helps discrimination despite reducing the proportion of visible sky, reducing the number of events for exclusion from $\sim33$--$43$ to $\sim22$--$27$. Moving beyond this, we perform a fully time-resolved forecast and find that the required number of events for exclusion reduces by $40\%$, $\sim14$--$16$. The time variation in the signal provides vital information allowing one to exclude or confirm the DM hypothesis with much fewer events. Our results are robust against DM decay channels and halo distributions and can readily be applied to other relics distributed similarly. Our framework allows one to turn event timing into a probe of signal geometry and is generic to any UHE equatorial neutrino telescopes.

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arXiv2026

Diagnosing Unmodeled Neutrino Physics via DUNE and T2HK Complementarity

Unmodeled beyond Standard Model (BSM) physics in neutrino propagation can masquerade as parameter degeneracies in future precision measurements. Because the upcoming DUNE and T2HK experiments will operate at substantially different baselines, interpreting their data under the standard three-flavor framework provides a powerful diagnostic tool: any propagation BSM effect can manifest as an artificial tension between their extracted parameters. We demonstrate this principle using the complex non-standard interactions (NSI) currently favored to resolve the $\sim2σ$ tension between NO$ν$A and T2K. If these NSI solutions are realized, the NSI-induced interference term $\propto\sin(δ_{\rm CP}+ϕ)$ systematically distorts the DUNE appearance rates, leading to a correlated misidentification of the atmospheric mixing octant and the CP phase $δ_{\rm CP}$. Specifically, for $\varepsilon_{eμ}$ ($\varepsilon_{eτ}$) NSI, the DUNE fit shifts toward CP-conserving values (the opposite CP half-plane) along with a preference for the wrong octant. In contrast, the shorter-baseline T2HK experiment remains largely insensitive to this effect. The resulting $\sim3σ$ incompatibility between the DUNE and T2HK standard-fit results (after 6 years of data collection for each experiment)can provide a powerful experimental diagnostic for propagation NSI, illustrating how baseline complementarity can be a valuable tool to uncover new physics in the precision era.

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arXiv2026

Disentangle RG Running Parameters with Medium-Baseline Reactor Experiments

We study how the renormalization group running beta functions of mixing angles and leptonic CP phases affect the slow and fast oscillation modes at JUNO. While the slow mode is modulated by the solar parameters, its amplitude can also be affected by the solar angle beta function $β_s$ and its phase by the Majorana CP phase counterpart $β_{\rm M1}$. On the other hand, the fast mode also receives corrections from the beta functions of the Dirac CP phase $δ_D$ and the Majorana CP phase $δ_{\rm M3}$. Since the fast mode is essentially the one measuring the neutrino mass ordering, the RG running effect can then interfere to deteriorate the sensitivity. Fortunately, the JUNO-TAO near detector can provide supplementary measurements of the RG running parameters to restore the mass ordering sensitivity. Since the rephasing phases $δ_{\rm M1}$ and $δ_{\rm M3}$ can be shifted by a vector-like rephasing for Dirac neutrinos, their running is physical only in the Majorana case. In consolidated, the mild preference for a nonzero $β_{\rm M1}$ by the current JUNO data thus hints the Majorana nature of neutrinos.

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arXiv2026

Coherent Elastic Neutrino-Nucleus Scattering at the Japan Proton Accelerator Research Complex

The Japan Proton Accelerator Research Complex (J-PARC) currently delivers a 1 MW, 3 GeV proton beam to the Materials and Life Science Experimental Facility (MLF). Power is expected to increase to 1.3 MW, driven by the needs of Hyper-Kamiokande. As a result, the MLF presently provides the highest neutron yield of any spallation source, while potentially holding the best current and foreseeable conditions for Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) experimentation. We explore this potential, using as examples detector technologies presently funded for construction and under development. We quantify their sensitivity to a rich variety of particle physics scenarios, finding that very-high-statistics CE$ν$NS measurements with significant sensitivity to relevant scenarios are feasible at this facility within the next few years.

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arXiv2026

Complementarity Between Neutrino Neutral and Charged Current Events in the Search for New Physics

At long-baseline neutrino experiments, neutral-current (NC) events accumulate in large numbers but are seldom exploited for new physics searches. We demonstrate their potential using non-standard neutrino interactions (NSI) with quarks as a case study. Charged-current (CC) analyses constrain NSI through matter effects on neutrino propagation, which probe almost exclusively the isoscalar combination of up- and down-quark couplings; the orthogonal isovector combination is suppressed by a factor of $\sim$100. Because NSI also modify NC cross sections in a flavor-dependent way, NC events become sensitive to oscillations: the far-to-near detector ratio acquires a dependence on the beam's flavor composition that probes both isoscalar and isovector couplings with comparable weight. Using existing NOvA data and DUNE projections, we derive the first bounded constraints on isovector NSI from a long-baseline experiment and show that combining CC and NC measurements resolves the individual quark couplings, breaking a degeneracy that persists in either analysis alone.

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arXiv2026

Testing the three massive neutrino paradigm: Constraints on Neutrino Properties and Interactions from Recent Experimental Data

Neutrino physics offers unique insights into phenomena beyond the Standard Model (BSM). This thesis presents phenomenological investigations organized around three pillars: consolidation of the three-flavor oscillation paradigm, exploration of new physics viability, and precise determination of solar neutrino fluxes. The theoretical framework introduces massive neutrinos, leptonic mixing, and flavor transitions, followed by experimental results emphasizing Borexino and NOvA data analyses. The first pillar establishes the three-flavor framework through global analysis of solar, atmospheric, reactor, and accelerator data, providing updated determinations of mixing angles ($θ_{12}$, $θ_{13}$, $θ_{23}$) and mass-squared differences ($Δm^2_{21}$, $Δm^2_{31}$), while quantifying ambiguities in mass ordering and $θ_{23}$ octant. The second pillar investigates Non-Standard Interactions (NSI) with electrons and quarks, combining Borexino data with COHERENT's CE$ν$NS measurements to establish bounds on propagation and detection couplings, excluding viable NSI parameter regions including potential LMA-D solutions. The third pillar advances solar neutrino physics through precision flux determinations, integrating pp-chain and CNO-cycle measurements. Results show preference for high-metallicity Standard Solar Models and incompatibility between $3+1$ mixing parameters favored by Gallium experiments and solar observations. This synthesis guides future experiments toward resolving mass ordering, CP violation, and dark sector interactions.

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arXiv2026

Neutrino backgrounds in matter-wave interferometry: implications for dark matter searches and beyond-Standard Model physics

We present a comprehensive theoretical analysis of neutrino-induced decoherence in macroscopic matter-wave interferometry experiments designed to search for dark matter and beyond-Standard Model physics. Our calculation includes contributions from the cosmic neutrino background (C$ν$B), solar neutrinos, and reactor antineutrinos, accounting for coherent scattering processes across nuclear, atomic, and macroscopic length scales. Within the Standard Model, we find negligible decoherence rates for planned experiments such as MAQRO ($s/σ_s \sim 10^{-27}$) and terrestrial interferometers like Pino ($s/σ_s \sim 10^{-22}$). However, these experiments achieve competitive sensitivity to beyond-Standard Model physics through light vector mediator interactions, with C$ν$B constraining coupling products to $g_νg_n \lesssim 10^{-17}$ for $Z'$ masses below 1 eV. Our results provide a theoretical framework for interpreting matter-wave interferometry measurements in terms of neutrino interaction physics and for deriving constraints on BSM models from experimental data.

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arXiv2025

Three decades of FCNC studies in 3-3-1 model with right-handed neutrinos: from $Z^\prime$-dominance to the alignment limit

Flavor-changing neutral current (FCNC) processes play a prominent role in the search for physics beyond the Standard Model (SM) due to their sensitivity to new physics at the TeV scale. Meson-antimeson transitions and rare meson decays provide stringent constraints on new physics through precision measurements of observables such as mass differences, CP asymmetries, and branching ratios. Extensions of the SM based on the $\text{SU}(3)_C \times \text{SU}(3)_L \times \text{U}(1)_N$ gauge group offer a compelling framework for flavor physics, as FCNC processes emerge inexorably at tree level due to the non-universal transformations of the quark families. Among its various realizations, the version incorporating right-handed neutrinos (331RHN) is the most phenomenologically viable. This review synthesizes three decades of theoretical developments in FCNC phenomenology within the 331RHN model, from early $Z^\prime$-dominated studies to the recent recognition of the decisive role played by the SM-like Higgs boson and the identification of the alignment limit. We demonstrate that viable parameter space spans orders of magnitude, from $m_{Z^\prime} \sim$ a few hundred GeV to $\sim 100$ TeV, depending critically on quark mixing parametrizations and scalar alignment configurations, with significant implications for experimental searches at current and future colliders.

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arXiv2025

Neutrinoless Double Beta Decay in Light of JUNO First Data

The first results from the JUNO reactor neutrino oscillation experiment improve our knowledge of neutrino masses and mixing parameters, especially the solar angle $θ_s \equiv θ_{12}$ and the solar mass squared difference $Δm^2_s \equiv Δm^2_{21}$. We discuss the implications of these results on neutrinoless double beta decay by itself and in combination with the global fit of neutrino oscillation experiments, the JUNO first data, and cosmological constraints on the neutrino mass sum. For the effective mass $\langle m_{ee} \rangle$, the uncertainties in its lower limits for both mass orderings and upper limits for the normal ordering are largely reduced. Since the cosmological CMB and DESI BAO data put a stringent constraint on the neutrino mass scale, we also show how the probability distribution of both the real and imaginary parts of the effective mass $\langle m_{ee} \rangle$ on the complex plane is affected. Especially, the funnel region with $|\langle m_{ee} \rangle| \lesssim 1$\,meV receives larger chance to happen. Correspondingly, the chance of determining the two Majorana CP phases simultaneously in this region also increases with reduced uncertainty.

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arXiv2025

Investigating DUNE oscillations sensitivity to sterile Pseudo-Dirac Neutrinos

We explore the sensitivity of the Deep Underground Neutrino Experiment (DUNE) to sterile neutrino oscillations within a $3+$(pseudo-Dirac pair) framework. We first consider a pair of two sterile neutrinos forming a pseudo-Dirac pair, then we consider a low-scale seesaw realization, that we name ``Linear-Inverse Seesaw" model. This scenario features two nearly degenerate sterile neutrino states at the keV scale, characterized by a small mass splitting arising from a small amount of lepton number violation. In this scenario, the oscillation behavior can be described in three distinct regimes depending on the sterile-sterile mass-squared difference : low ($< 1\,\mathrm{eV}^2$), resonant ($1$--$100\,\mathrm{eV}^2$), and high ($> 100\,\mathrm{eV}^2$) regimes, recovering in both low- and high-mass regimes an effective non-unitarity of the leptonic mixing matrix. A distinctive feature of this framework is that observable effects persist even in the low-mass limit, unlike the case of standard $3+1$ scenarios, due to rapid oscillation averaging from larger keV-scale splittings. We leverage the complementarity of both near and far detectors to explore the sensitivity for $ν_e$ and $ν_μ$ disappearance and $ν_e$ and $ν_τ$ appearance oscillation probabilities. Our analysis reveals that DUNE can achieve significant improvements over current experimental constraints, especially in neutrino appearance modes. Additionally, we show that new CP-violating phases associated with the sterile sector can dramatically alter the sensitivity, with destructive interference potentially suppressing signals by orders of magnitude.

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arXiv2025

CP Prediction from Residual $\mathbb Z_2^s$ and $\overline{\mathbb Z}_2^s$ Symmetries with JUNO First Data

The JUNO first data and the recent neutrino global fit results are implemented in the sum rule from the residual $\mathbb Z^s_2$ and $\overline{\mathbb Z}^s_2$ symmetries to make prediction of the leptonic Dirac CP phase $δ_D$. Without involving model parameters, the probability distribution of $δ_D$ can be readily obtained from the experimental measurements of the three mixing angles. We then confront the theoretical predictions with the global fit results for the CP phase as well as the T2K and NOvA joint analysis for their CP measurement to give the data preference of the two residual symmetries with Bayes factor for both normal and inverted orderings. We further extend our analysis to a two-dimensional probability distribution to fully explore the correlation between the CP phase $δ_D$ and the atmospheric angle $θ_a \equiv θ_{23}$.

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arXiv2025

NuFit-6.0: Updated global analysis of three-flavor neutrino oscillations

We present an updated global analysis of neutrino oscillation data as of September 2024. The parameters $θ_{12}$, $θ_{13}$, $Δm^2_{21}$, and $|Δm^2_{3\ell}|$ ($\ell = 1,2$) are well-determined with relative precision at $3σ$ of about 13\%, 8\%, 15\%, and 6\%, respectively. The third mixing angle $θ_{23}$ still suffers from the octant ambiguity, with no clear indication of whether it is larger or smaller than $45^\circ$. The determination of the leptonic CP phase $δ_{CP}$ depends on the neutrino mass ordering: for normal ordering the global fit is consistent with CP conservation within $1σ$, whereas for inverted ordering CP-violating values of $δ_{CP}$ around $270^\circ$ are favored against CP conservation at more than $3.6σ$. While the present data has in principle $2.5$--$3σ$ sensitivity to the neutrino mass ordering, there are different tendencies in the global data that reduce the discrimination power: T2K and NOvA appearance data individually favor normal ordering, but they are more consistent with each other for inverted ordering. Conversely, the joint determination of $|Δm^2_{3\ell}|$ from global disappearance data prefers normal ordering. Altogether, the global fit including long-baseline, reactor and IceCube atmospheric data results into an almost equally good fit for both orderings. Only when the $χ^2$ table for atmospheric neutrino data from Super-Kamiokande is added to our $χ^2$, the global fit prefers normal ordering with $Δχ^2 = 6.1$. We provide also updated ranges and correlations for the effective parameters sensitive to the absolute neutrino mass from $β$-decay, neutrinoless double-beta decay, and cosmology.

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arXiv2025

Meson Mixing Bounds on $Z^{\prime}$ Mass in the Alignment Limit: Establishing the Phenomenological Viability of the 331 Model

We perform a systematic study of flavor-changing neutral currents (FCNCs) in the 331 model with right-handed neutrinos (331RHNs), analyzing constraints on the $Z^\prime$ boson mass from $K$-, $D$-, $B_d$-, and $B_s$-meson oscillations. By explicitly incorporating scalar sector dynamics and quark rotation ambiguities ($V_L^{u,d}$), we demonstrate that $Z^\prime$ mass limits depend critically on the parametrization of Cabibbo-Kobayashi-Maskawa (CKM) matrix factors. Three scenarios are explored: (i) $V_L^u = V_\text{CKM}^\dagger$ (FCNCs restricted to $D$-mesons), (ii) $V_L^d = V_\text{CKM}$ (dominant $B_s$ constraints), and (iii) a hybrid mixing pattern. Strikingly, scenario (i) reduces the $Z^\prime$ mass bound to $M_{Z^\prime} \gtrsim 600\;\text{GeV}$-two orders of magnitude below literature values-by leveraging large experimental uncertainties in $D$-$\bar{D}$ oscillations. Conversely, scenario (ii) requires $M_{Z^\prime} \gtrsim 165\;\text{TeV}$ due to stringent $B_s$ data. We further establish the alignment limit $\cos(ϕ+φ) = 0$ for the SM-like Higgs, showing its viability depends on $V_L^{u,d}$ configurations, with $B_s$ systems enforcing $|\cos(ϕ+φ)| < 0.01$ in down-sector FCNC scenarios. Our analysis reveals that strategic choices of quark mixing matrices can suppress FCNC visibility, reconciling the 331 framework with flavor data without ultra-heavy $Z^\prime$ bosons. This work provides the first unified treatment of SM-like Higgs- and $Z^\prime$-mediated FCNCs in 331 models, identifying viable parameter spaces for collider phenomenology.

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arXiv2025

Constraining non-standard neutrino interactions with neutral current events at long-baseline oscillation experiments

We explore, for the first time, {\textit{neutral-current}} events at long-baseline experiments to constrain vector and axial-vector neutrino non-standard interactions (NSI) with quarks. We leverage the flavor dependence of NSIs to perform an oscillation analysis in the neutral-current channel. We first introduce a framework to parametrize the effect of NSI on the cross section. Then, as an example, we analyze NOvA neutral-current data which provides significantly improved constraints on the axial-vector NSI parameters $\varepsilon_{μμ}^A,~\varepsilon_{ττ}^A$ and $\varepsilon_{eμ}^A$. This is highly complementary to constraints from SNO data, which, differently from long-baseline neutral current data, is not sensitive to isospin conserving NSIs $\varepsilon^A_u=\varepsilon^A_d$. Additionally, we disfavor large values of the diagonal vectorial NSI $\varepsilon_{μμ}^V$ and \varepsilon_{ττ}^V$ which originate from the LMA-Dark solution. We also highlight the complementarity between NSI searches at oscillation experiments using charged current and neutral current channels.

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arXiv2025

Neutrino Theory in the Precision Era

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. \textbf{A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology.} Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, \textbf{we propose to establish a CERN Neutrino Physics Centre.} Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

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arXiv2025

Solar Model Independent Constraints on the Sterile Neutrino Interpretation of the Gallium Anomaly

We perform a global analysis of most up-to-date solar neutrino data and KamLAND reactor antineutrino data in the framework of the 3+1 sterile neutrino mixing scenario (invoked to explain the results of the Gallium source experiments) with the aim of quantifying the dependence of the (in)compatibility of the required mixing with assumptions on the initial fluxes. The analysis of solar data is performed in two alternative ways: using the flux predicted by the latest standard solar models, and in a model independent approach where the solar fluxes are also determined by the fit. The dependence on the normalization of the capture rate in the solar Gallium experiments is also quantified. Similarly, in the KamLAND analysis we consider both the case where the reactor flux normalization is assumed to be known a priori, as well as a normalization free case which relies solely on available neutrino data. Using a parameter goodness of fit test, we find that in most cases the compatibility between Gallium and solar+KamLAND data only occur at the $3σ$ level or higher. We also discuss the implications of enforcing better compatibility by tweaking the mechanism for the energy production in the Sun.

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