arXiv subjects

Pedro A. N. Machado

Publications and source records attributed to Pedro A. N. Machado.

At least 19 recordsLinked to original sources

arXiv2026

Beyond $Δm^2$: Absolute Mass Sensitivity in Neutrino Oscillations

Conventional wisdom says that neutrino oscillations measure only mass-squared differences and not the absolute neutrino mass scale. This is true, however, only at leading order in the expansion parameters $m_i/E$, the ratios of the neutrino masses $m_i$ ($i=1,2,3$) to the neutrino energy $E$. At next-to-leading order, the oscillation phase includes terms proportional to $m_i^4-m_j^4 = Δm^2_{ij}(m_i^2+m_j^2)$, and is therefore sensitive to the absolute mass scale. In this paper, we derive the next-to-leading-order corrections using a wave-packet treatment and taking into account the neutrino-production kinematics. We then apply this result to reactor antineutrinos and find that the JUNO experiment is sensitive to neutrino masses of a few hundred keV. While not competitive with existing bounds from beta decay, electron capture, and cosmology, neutrino oscillations provide a novel, complementary probe of the neutrino mass scale, with sensitivity to a different combination of neutrino masses.

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arXiv2026

Widen the Resonance at Ultra-High Energies: Novel Probes of Neutrino Self-interactions in the High-Mass Regime

Neutrino self-interaction beyond the Standard Model is well motivated by the nonzero masses of neutrinos, which are the only known particles guaranteed to have new physics. Cosmic messengers, especially neutrinos, play a central role in probing new physics, as they provide experimental conditions far beyond the reach of laboratories and serve as the link between laboratory fundamental-physics discoveries and their roles in the Universe, where many new physics motivations originate. In this work, we propose a novel probe of neutrino self-interactions through ultra-high-energy neutrinos scattering off the cosmic neutrino background when the lightest neutrino species remains relativistic today. This allows us to ``Widen the Resonance'' of such scattering. Meanwhile, we also provide a semi-analytic framework for cosmogenic UHE neutrino production, avoiding computationally intensive simulations and yielding results precise enough for BSM studies. The widened resonance enables future ultrahigh-energy neutrino telescopes, in particular GRAND, to probe mediator masses from MeV to GeV, reaching couplings down to $g \sim 10^{-3}$ -- up to two orders of magnitude beyond current bounds. Our results enhance the discovery potential of $ν$SI in the high-mass regime, potentially offering crucial insights into the connections between the neutrino sector and dark sector.

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arXiv2026

Neutrino Dipole Moments and Radiative Signatures from Partial Compositeness

We investigate composite neutrino models where heavy neutrinos emerge as bound states from a near-conformal strongly coupled sector. Standard Model neutrinos mix with these composite singlets via an inverse seesaw mechanism, where the anomalous scaling dimensions of the composite-sector operators naturally suppress light neutrino masses to sub-eV scales. Matching the conformal dynamics onto low-energy theory yields enhanced electromagnetic transition dipole operators with couplings $d_{μN} \sim 10^{-6}$-$10^{-8}\,\mathrm{GeV}^{-1}$, parametrically larger than the loop-level predictions of minimal Dirac or Majorana models. We carry out a dedicated event-level simulation of the production-and-decay chain $νX \to \mathcal{U} X \to νγX$ and compute the resulting event rates at MiniBooNE and MINERvA within the model, accounting for the composite production cross section and decay kinematics in detail. We further present predictions for the photon energy, angular, and multiplicity distributions. For the benchmark scenarios accessible at these experiments the radiative signal is predominantly single-photon; the composite structure additionally permits fragmentation of the up-scattered state into multiple heavy neutrinos, each decaying as $N\toνγ$, with multi-photon final states emerging for lighter compositeness scales or higher beam energies as a qualitatively new probe of the composite dynamics.

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arXiv2026

Standard Candles for Supernova Neutrino Detection at DUNE

The Deep Underground Neutrino Experiment (DUNE) far detector is sensitive to $\mathcal{O}(10)$ MeV electron neutrinos through $ν_e$ charged-current reaction with argon. This capability is a unique window into the $ν_e$ component of a Galactic core-collapse supernova flux. Extracting the properties of the supernova spectrum is, however, limited by the poorly-known $ν_e$-Ar cross section. We propose a data-driven strategy that leverages $^8$B solar neutrinos and muon-decay-at-rest neutrinos as standard candles for this process. These calibration samples constrain both the low-energy and high-energy components of the cross section relevant for supernova detection. Our method reduces the reliance on nuclear models, which can bias the extraction of the spectral parameters by as much as 300$\%$.

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arXiv2026

Neutrino-Antineutrino Conversion from Ultralight Vector Dark Matter

We show that Majorana neutrinos convert into antineutrinos in a background of ultralight vector dark matter coupled to lepton number, such as the gauge boson of $\text{U}(1)_{B-L}$ or $\text{U}(1)_{L_i - L_j}$ with $i, j = e , μ, τ$. This effect is suppressed by the small neutrino mass, but the enhancement by long astrophysical baselines can enable future searches for solar and supernova neutrinos to explore uncharted parameter space. For instance, for $\text{U}(1)_{B-L}$ dark matter, the observation of a supernova neutrino burst at DUNE, Hyper-Kamiokande, and JUNO could probe gauge couplings as small as $e^\prime \sim 10^{-32} - 10^{-25}$ for dark matter masses of $m_{A^\prime} \sim 10^{-22} \ \text{eV} - 10^{-14} \ \text{eV}$, beyond the capability of other future probes.

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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

Improving Neutrino Oscillation Measurements through Event Classification

Precise neutrino energy reconstruction is essential for next-generation long-baseline oscillation experiments, yet current methods remain limited by large uncertainties in neutrino-nucleus interaction modeling. Even so, it is well established that different interaction channels produce systematically varying amounts of missing energy and therefore yield different reconstruction performance--information that standard calorimetric approaches do not exploit. We introduce a strategy that incorporates this structure by classifying events according to their underlying interaction type prior to energy reconstruction. Using supervised machine-learning techniques trained on labeled generator events, we leverage intrinsic kinematic differences among quasi-elastic scattering, meson-exchange current, resonance production, and deep-inelastic scattering processes. A cross-generator testing framework demonstrates that this classification approach is robust to microphysics mismodeling and, when applied to a simulated DUNE $ν_μ$ disappearance analysis, yields improved accuracy and sensitivity at the 10-20% level. These results highlight a practical path toward reducing reconstruction-driven systematics in future oscillation measurements.

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arXiv2026

Open system approach to neutrinos propagating in an ultralight scalar background

We examine decoherence in neutrino oscillations induced by an ultralight scalar field coupled to neutrinos. The scalar induces time- and position-dependent shifts in the neutrino mass matrix. Neutrinos sample different field configurations throughout an experimental data-taking period, which leads to damping effects in the oscillation pattern in the form of decoherence. By recasting the neutrino-scalar dynamics within the open quantum systems framework, we establish a mapping between a complete model and phenomenological decoherence approaches. We find that the parameter driving decoherence scales as $L^2/E^2$, where $L$ is the baseline and $E$ is the neutrino energy, as opposed to $L/E$ typically assumed in phenomenological studies of open system approaches to neutrino oscillations.

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arXiv2025

Mass Reconstruction of Heavy Neutral Leptons from Stopped Mesons

Heavy neutral leptons (HNLs), depending on their mass and mixing, can be efficiently produced in meson decays from the target or absorber in short- to medium-baseline accelerator neutrino experiments, leaving detectable signals through their decays inside the neutrino detectors. We show that the currently running ICARUS experiment at Fermilab can reconstruct the HNL mass and explore new HNL parameter space in the mass range of 70-190 MeV. The mass reconstruction is enabled by two ingredients: (i) simple two-body kinematics of HNL production from stopped kaon decays at the NuMI absorber, followed by HNL decay into a charged-lepton pair and neutrino at the detector, and (ii) high resolution of Liquid Argon Time Projection Chamber (LArTPC) detectors in reconstructing final state particles. Our mass reconstruction method is robust under realistic energy resolution and angular smearing of the charged leptons, and is applicable to any LArTPC detector. We also discuss the synergy between ICARUS and future facilities like DUNE near detector and PIP-II beam dump in probing the HNL parameter space.

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arXiv2025

Tau Tridents at Accelerator Neutrino Facilities

We present the first detailed study of Standard Model neutrino tridents involving tau leptons at the near detectors of accelerator neutrino facilities. The rates of these processes were previously thought to be negligible, even at future facilities. Our full $2\to 4$ calculation, including both coherent and incoherent scatterings, reveals that the DUNE near detector could observe a considerable number of tau tridents, which is an important background to new physics searches. We identify promising kinematic features that may allow distinction of tau tridents from the usual neutrino charged-current background at DUNE, and thus establish the observation of tau tridents for the first time. We also comment on the detection prospects at other accelerator and collider neutrino experiments.

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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

Towards a Robust Exclusion of the Sterile-Neutrino Explanation of Short-Baseline Anomalies

The sterile neutrino interpretation of the LSND and MiniBooNE neutrino anomalies is currently being tested at three Liquid Argon detectors: MicroBooNE, SBND, and ICARUS. It has been argued that a degeneracy between $ν_μ\to ν_e$ and $ν_e \to ν_e$ oscillations significantly degrades their sensitivity to sterile neutrinos. Through an independent study, we show two methods to eliminate this concern. First, we resolve this degeneracy by including external constraints on $ν_e$ disappearance from the PROSPECT reactor experiment. Second, by properly analyzing the full three-dimensional parameter space, we demonstrate that the stronger-than-sensitivity exclusion from MicroBooNE alone already covers the entire 2$σ$ preferred regions of MiniBooNE at the level of $2-3σ$. We show that upcoming searches at SBND and ICARUS can improve on this beyond the $4σ$ level, thereby providing a rigorous test of short-baseline anomalies.

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arXiv2025

Neutrino-Nucleus Cross Section Impacts on Neutrino Oscillation Measurements

The challenges in neutrino-nucleus cross section modeling and its impact on neutrino oscillation experiments are widely recognized. However, a comprehensive and theoretically robust estimation of cross section uncertainties has been lacking, and few studies have quantitatively examined their impact on oscillation measurements. In this work, we evaluate the effect of cross section uncertainties on oscillation parameters using setups inspired by NOvA and DUNE. To characterize these uncertainties, we adopt multiple neutrino-nucleus event generators and simulate a realistic experimental procedure that incorporates near-detector data and near-to-far-detector extrapolation. Our results confirm that cross section uncertainties cannot significantly bias oscillation results in current statistics-dominated experiments like NOvA. However, they could lead to substantial bias for future systematics-dominated experiments like DUNE, even when near-detector data are employed to mitigate uncertainties. These findings underscore the need for further studies on the quantitative impacts of cross section modeling, improved strategies to utilize near-detector data and the PRISM concept, and more robust cross section models to optimize the success of future experiments.

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arXiv2025

Pseudo-Dirac Neutrinos and Relic Neutrino Matter Effect on the High-energy Neutrino Flavor Composition

We show that if neutrinos are pseudo-Dirac, they can potentially affect the flavor ratio predictions for the high-energy astrophysical neutrino flux observed by IceCube. In this context, we point out a novel matter effect induced by the cosmic neutrino background (C$ν$B) on the flavor ratio composition. Specifically, the active-sterile neutrino oscillations over the astrophysical baseline lead to an energy-dependent flavor ratio at Earth due to the C$ν$B matter effect, which is in principle distinguishable from the vacuum oscillation effect, provided there is an asymmetry between the neutrino and antineutrino number densities, as well as a local C$ν$B overdensity. Considering the projected precision of the 3-neutrino oscillation parameter measurements and improved flavor triangle measurements, we show that the next-generation neutrino telescopes, such as KM3NeT and IceCube-Gen2, can in principle probe the pseudo-Dirac neutrino hypothesis and the C$ν$B matter effect.

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arXiv2024

Measuring the weak mixing angle at SBND

The weak mixing angle provides a sensitive test of the Standard Model. We study SBND's sensitivity to the weak mixing angle using neutrino-electron scattering events. We perform a detailed simulation, paying particular attention to background rejection and estimating the detector response. We find that SBND can provide a reasonable constraint on the weak mixing angle, achieving 8% precision for $10^{21}$ protons on target, assuming an overall flux normalization uncertainty of 10%. This result is superior to those of current neutrino experiments and is relatively competitive with other low-energy measurements.

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arXiv2024

Could SBND-PRISM probe Lepton Flavor Violation?

We investigate the possibility of using the Short-Baseline Near Detector (SBND) at Fermilab to constrain lepton flavor violating decays of pions and kaons. We study how to leverage SBND-PRISM, the use of the neutrino beam angular spread to mitigate systematic uncertainties, to enhance this analysis. We show that SBND-PRISM can put stringent limits on the flavor violating branching ratios $\rm{BR}(π^+ \to μ^+ ν_e) = 8.9 \times 10^{-4}$, $\rm{BR}(K^+ \to μ^+ ν_e) = 3.2 \times 10^{-3}$, improving previous constraints by factors 9 and 1.25, respectively. We also estimate the SBND-PRISM sensitivity to lepton number violating decays, $\rm{BR}(π^+ \to μ^+ \overlineν_e)= 2.1 \times 10^{-3}$ and $\rm{BR}(K^+ \to μ^+ \overlineν_e) = 7.4 \times 10^{-3}$, though not reaching previous BEBC limits. Last, we identify several ways how the SBND collaboration could improve this analysis.

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arXiv2024

Shedding light on the MiniBoone Excess with Searches at the LHC

The origin of the excess of low-energy events observed by the MiniBooNE experiment remains a mystery, despite exhaustive investigations of backgrounds and a series of null measurements from complementary experiments. One intriguing explanation is the production of beyond-the-Standard-Model particles that could mimic the experimental signature of additional $ν_e$ appearance seen in MiniBooNE. In one proposed mechanism, muon neutrinos up-scatter to produce a new ``dark neutrino'' state that decays by emitting highly-collimated electron-positron pairs. We propose high-energy neutrinos produced from $W$ boson decays at the Large Hadron Collider as an ideal laboratory to study such models. Simple searches for a low-mass, boosted di-lepton resonance produced in association with a high-$p_\text{T}$ muon from the $W$ decay with Run 2 data would already provide unique sensitivity to a range of dark neutrino scenarios, with prompt and displaced searches providing complementarity. Looking farther ahead, we show how the unprecedented sample of $W$ boson decays anticipated at the HL-LHC, together with improved lepton acceptance would explore much of the parameter space most compatible with the MiniBooNE excess.

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arXiv2024

Dark fluxes from electromagnetic cascades

We study dark sector production in electromagnetic (EM) cascades. This problem requires accurate simulations of Standard Model (SM) and dark sector processes, both of which impact angular and energy distributions of emitted particles that ultimately determine flux predictions in a downstream detector. We describe the minimal set of QED processes which must be included to faithfully reproduce a SM cascade, and identify a universal algorithm to generate a dark sector flux given a Monte-Carlo simulation of a SM shower. We provide a new tool, $\texttt{PETITE}$, which simulates EM cascades with associated dark vector production, and compare it against existing literature and "off the shelf" tools. The signal predictions at downstream detectors can strongly depend on the nontrivial interplay (and modelling) of SM and dark sector processes, in particular multiple Coulomb scattering and positron annihilation. We comment on potential impacts of these effects for realistic experimental setups.

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