arXiv subjects

Pedro Pasquini

Publications and source records attributed to Pedro Pasquini.

At least 19 recordsLinked to original sources

arXiv2026

Disentangling Charged-Current Scalar NSI from the Solar Sector at JUNO

We constrain charged-current scalar non-standard interaction with reactor antineutrinos within a quantum field theory framework of neutrino oscillations. We derive an analytical expression up to $\mathcal{O}(\varepsilon^{4})$ for the electron antineutrino survival probability including scalar NSI contributions, and show that these effects induce spectral distortions that admit a large mixing angle solution for $\theta_{12}$. Using the 59.1-day and preliminary 207.2-day JUNO datasets, we obtain the first neutrino-oscillation determination of NSI parameters individually, rather than in a flavor-summed combination, from reactor experiments. Assuming one year of data taken, we show that the only solar sector analysis breaks the degeneracy with the solar mixing angle at $3\sigma$ of C.L.

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arXiv2026

RG Running of Multiple Neutrino Mixing Parameters at Oscillation Experiments

If the new physics scale is within the energy scale of neutrino oscillation experiments, it may lead to a renormalization group (RG) running effect between the production and detection processes as well as between different experiments. It is then possible to use multiple neutrino oscillation experiments to disentangle the multiple RG running parameters. We investigate this effect in a general model-independent sense for a variety of flavor structures in the context of upcoming experiments DUNE-ND, JUNO-TAO, and FASER$\nu$2 that span a large range in neutrino energies and many different flavor combinations. We find strong sensitivity to the running effects of new physics with combination of these experiments, especially the possibility of addressing the non-trivial degeneracies.

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arXiv2025

Alleviating the present tension between T2K and NO$ν$A with nonstandard neutrino interactions

Since neutrino oscillation was observed, several experiments have been built to measure its parameters. NO$ν$A and T2K are two long-baseline experiments dedicated to measuring mainly the mixing angle $θ_{23}$, the charge-parity conjugation phase $δ_{\rm CP}$, and the mass ordering. However, there is a tension in current data. The T2K allowed region is in conflict with the region allowed by NO$ν$A. We propose a nonstandard charged current interaction (CC-NSI) in neutrino production to relieve this tension. The CC-NSI is computed through quantum field theory (QFT) formalism, where we derive perturbative analytical formulae considering CC-NSI in the pion decay. Within this new approach, we can alleviate NO$ν$A and T2K tension for a CC-NSI complex parameters of order $10^{-3}$. We show the new phase has a degeneracy to the Dirac CP phase of the form $δ_{\rm CP} \pm ϕ= 1.5π$ being a possible source of violation of charge-parity symmetry.

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arXiv2025

Exploring Quantum Statistics for Dirac and Majorana Neutrinos using Spinor-Helicity techniques

Recently, there has been interest in the applicability of quantum statistics to distinguish Dirac from Majorana neutrinos in multi-neutrino final states. In particular, debate has arisen over the validity of the Dirac-Majorana confusion theorem in these processes, i.e. that any distinction between the Dirac and Majorana processes goes to zero as the neutrino mass goes to zero. Here we approach this problem equipped with spinor-helicity methods generalized for massive Dirac and Majorana fermions. We explicitly calculate all helicity amplitudes for the decay of a light scalar particle to two neutrinos and two oppositely charged leptons. This allows us to pinpoint the crucial steps which could lead to claims of a violation of the confusion theorem. We show that if the correct anti-symmetrization of Dirac to Majorana amplitudes is used, identification of which is clear in this framework, and all relevant contributions are appropriately summed, a scalar decay into two charged leptons and two neutrinos satisfies the Dirac-Majorana confusion theorem.

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arXiv2025

Testing the RG Running of the Leptonic Dirac CP Phase with Reactor Neutrinos

We propose the possibility of using the near detector at reactor neutrino experiments to probe the renormalization group (RG) running effect on the leptonic Dirac CP phase $δ_D$. Although the reactor neutrino oscillation cannot directly measure $δ_D$, it can probe the deviation $Δδ\equiv δ_D(Q^2_d) - δ_D(Q^2_p)$ caused by the RG running. Being a key element, the mismatched momentum transfers at neutrino production ($Q^2_p$) and detection ($Q^2_d$) processes can differ by two orders. We illustrate this concept with the upcoming Taishan Antineutrino Observatory (TAO, also known as JUNO-TAO) experiment and obtain the projected sensitivity to the CP RG running beta function $β_δ$.

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arXiv2024

Neutrino Mass Measurement with Cosmic Gravitational Focusing

We thoroughly explore the cosmic gravitational focusing of cosmic neutrino fluid (C$ν$F) by dark matter (DM) halo using both general relativity for a point source of gravitational potential and Boltzmann equations for continuous overdensities. Derived in the general way for both relativistic and non-relativistic neutrinos, our results show that the effect has fourth power dependence on the neutrino mass and temperature. With nonlinear mass dependence which is different from the cosmic microwave background (CMB) and large scale structure (LSS) observations, the cosmic gravitational focusing can provide an independent cosmological way of measuring the neutrino mass and ordering. We take DESI as an example to illustrate that the projected sensitivity as well as its synergy with existing terrestrial neutrino oscillation experiments and other cosmological observations can significantly improve the neutrino mass measurement.

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arXiv2024

Neutrino CP Measurement in the Presence of RG Running with Mismatched Momentum Transfers

The neutrino mixing parameters are expected to have RG running effect in the presence of new physics. If the momentum transfers at production and detection mismatch with each other, the oscillation probabilities are generally modified and become dependent on not just the neutrino energy but also the momentum transfer. Even in the limit of vanishing baseline, the transition probability for the appearance channel is interestingly not zero. This would significantly affect the sensitivity of the genuine leptonic Dirac CP phase. We further explore the possibility of combing the long- and short-baseline neutrino experiments to constrain such RG running effect for the purpose of guaranteeing the CP measurement. To simulate the double dependence on the neutrino energy and momentum transfer, we extend the usual GLoBES simulation of fixed baseline experiments and use a two-dimensional $χ^2$ analysis to obtain sensitivities.

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arXiv2023

Disentangle Neutrino Electromagnetic Properties with Atomic Radiative Pair Emission

We elaborate the possibility of using the atomic radiative emission of neutrino pair (RENP) to probe the neutrino electromagnetic properties, including magnetic and electric dipole moments, charge radius, and anapole. With the typical O(eV) momentum transfer, the atomic RENP is sensitive to not just the tiny neutrino masses but also very light mediators to which the massless photon belongs. The neutrino EM properties introduce extra contribution besides the SM one induced by the heavy W/Z gauge bosons. Since the associated photon spectrum is divided into several sections whose boundaries are determined by the final-state neutrino masses, it is possible to identify the individual neutrino EM form factor elements. Most importantly, scanning the photon spectrum inside the particular section with deviation from the SM prediction once observed allows identification of the neutrino EM form factor type. The RENP provides an ultimate way of disentangling the neutrino EM properties to go beyond the current experimental searches or observations.

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arXiv2023

Unique Probe of Neutrino Electromagnetic Moments with Radiative Pair Emission

The neutrino magnetic and electric moments are zero at tree level but can arise in radiative corrections. Any deviation from the Standard Model prediction would provide another indication of neutrino-related new physics in addition to the neutrino oscillation and masses. Especially, Dirac and Majorana neutrinos have quite different structures in their electromagnetic moments. Nevertheless, the recoil measurements and astrophysical stellar cooling can only constrain combinations of neutrino magnetic and electric moments with the limitation of not seeing their detailed structures. We propose using the atomic radiative emission of neutrino pair to serve as a unique probe of the neutrino electromagnetic moments with the advantage of not just separating the magnetic and electric moments but also identifying their individual elements. Both searching strategy and projected sensitivities are illustrated in this letter.

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arXiv2022

Improving CP Measurement with THEIA and Muon Decay at Rest

We explore the possibility of using the recently proposed THEIA detector to measure the $\bar ν_μ\rightarrow \bar ν_e$ oscillation with neutrinos from a muon decay at rest ($μ$DAR) source to improve the leptonic CP phase measurement. Due to its intrinsic low-energy beam, this $μ$THEIA configuration ($μ$DAR neutrinos at THEIA) is only sensitive to the genuine leptonic CP phase $δ_D$ and not contaminated by the matter effect. With detailed study of neutrino energy reconstruction and backgrounds at the THEIA detector, we find that the combination with the high-energy DUNE can significantly reduce the CP uncertainty, especially around the maximal CP violation cases $δ_D = \pm 90^\circ$. Both the $μ$THEIA-25 with 17kt and $μ$THEIA-100 with 70kt fiducial volumes are considered. For DUNE + $μ$THEIA-100, the CP uncertainty can be better than $8^\circ$.

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arXiv2022

Solar Active-Sterile Neutrino Conversion with Atomic Effects at Dark Matter Direct Detection Experiments

The recent XENON1T excess can be explained by the solar active-sterile neutrino conversion with bound electrons via light mediator. Nevertheless, the atomic effects are usually omitted in the solar neutrino explanations. We systematically establish a second quantization formalism for both bound and ionized electrons to account for the atomic effects. This formalism is of great generality to incorporate various interactions for both neutrino and dark matter scatterings. Our calculation shows that the change in the cross section due to atomic effects can have important impact on the differential cross section. It is necessary to include atomic effects in the low-energy electron recoil signal at dark matter direct detection experiments even for energetic solar neutrinos. With the best-fit values to the XENON1T data, we also project the event rate at PandaX-4T, XENONnT, and LZ experiments.

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arXiv2022

Non-minimal Lorentz invariance violation in light of muon anomalous magnetic moment and long-baseline neutrino oscillation data

In light of the increasing hints of new physics at the muon $g-2$ and neutrino oscillation experiments, we consider the recently observed tension in the long-baseline neutrino oscillation experiments as a potential indication of Lorentz invariance violation. For this purpose, the latest data from T2K and NO$ν$A is analysed in presence of non-minimal Lorentz invariance violation. Indeed, we find that isotropic violation in dimensions $D =$ 4, 5 and 6 can alleviate the tension in neutrino oscillation data by 0.4$-$2.4$σ$ CL significance, with the isotropic coefficient $γ^{(5)}_{ττ} =$ 3.58$\times$10$^{-32}$GeV$^{-1}$ yielding the best fit. At the same time, the anomalous muon $g-2$ result can be reproduced with an additional non-isotropic violation of $d^{zt} =$ -1.7$\times$10$^{-25}$. The analysis highlights the possibility of simultaneous relaxation of experimental tensions with Lorentz invariance violation of mixed nature.

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arXiv2022

Probing Light Mediators in the Radiative Emission of Neutrino Pair

We propose a new possibility of using the coherently enhanced neutrino pair emission to probe light-mediator interactions between electron and neutrinos. With typical momentum transfer at the atomic $\mathcal O(1$\,eV) scale, this process is extremely sensitive for the mediator mass range $\mathcal O(10^{-3} \sim 10^4$) eV. The sensitivity on the product of couplings with electron ($g^e$ or $y^e$) and neutrinos ($g^ν$ or $y^ν$) can touch down to $|y^e y^ν| < 10^{-9} \sim 10^{-19}$ for a scalar mediator and $|g^e g^ν| < 10^{-15} \sim 10^{-26}$ for a vector one, with orders of improvement from the existing constraints.

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arXiv2021

Probing the Dark Axion Portal with Muon Anomalous Magnetic Moment

We propose a new scenario of using the dark axion portal at one-loop level to explain the recently observed muon anomalous magnetic moment by the Fermilab Muon g-2 experiment. Both axion/axion-like particle (ALP) and dark photon are involved in the same vertex with photon. Although ALP or dark photon alone cannot explain muon $g-2$, since the former provides only negative contribution while the latter has very much constrained parameter space, dark axion portal can save the situation and significantly extend the allowed parameter space. The observed muon anomalous magnetic moment provides a robust probe of the dark axion portal scenario.

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arXiv2021

Searching for non-unitary neutrino oscillations in the present T2K and NO$ν$A data

The mixing of three active neutrino flavors is parameterized by the unitary PMNS matrix. If there are more than three neutrino flavors and if the extra generations are heavy isosinglets, the effective $3\times 3$ mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and \nova data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NO$ν$A data slightly (at $\sim 1\, σ$ C.L.) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the \nova best-fit point in the $\sin^2θ_{23}-δ_{CP}$ plane closer to the T2K best-fit point. The 2019 T2K data, on the other hand, cannot rule out any of the two mixing schemes. A combined analysis of the NO$ν$A and T2K 2019 data prefers the non-unitary mixing at $1\, σ$ C.L.. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NO$ν$A and T2K data. These constraints are weaker than previously found. The latest 2020 data from both the experiments prefer non-unitarity over unitary mixing at $1\, σ$ C.L. The combined analysis preferes non-unitarity at $2\, σ$ C.L. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis.

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arXiv2020

CP-violating Higgs Di-tau Decays: Baryogenesis and Higgs Factories

We demonstrate how probes of CP-violating observables in Higgs di-tau decays at prospective future lepton colliders could provide a test of weak scale baryogenesis with significant discovery potential. Measurements at the Circular Electron Positron Collider, for example, could exclude a CP phase larger than $2.9^\circ$ ($5.6^\circ$) at 68% (95%) C.L. assuming the Standard Model value for magnitude of the tau lepton Yukawa coupling. Conversely, this sensitivity would allow for a $5\,σ$ discovery for 82% of the CP phase range $[0,2π)$. The reaches of the Future Circular Collider - ee and International Linear Collider are comparable. As a consequence, future lepton colliders could establish the presence of CP violation required by lepton flavored electroweak baryogenesis with at least $3\,σ$ sensitivity. Our results illustrate that Higgs factories are not just precision machines but can also make $\mathcal O(1)$ measurement of the new physics beyond the Standard Model.

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arXiv2020

Parity Violation and Chiral Oscillation of Cosmological Relic Neutrinos

The conventional derivation of neutrino oscillation treats neutrino mass eigenstate as plane wave with an overall evolution phase. Nevertheless, due to the intrinsic parity-violating nature of weak interactions, only the left-chiral neutrino can be produced as initial condition. On the other hand, the neutrino mass term connects the left-chiral component to the right-chiral one and unavoidably leads to generation of the later through oscillation. This chiral oscillation has significant consequences on the detection of the cosmological relic neutrinos. The event rate is reduced by a factor of 2 than the conventional prediction.

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arXiv2020

Solar Neutrino Scattering with Electron into Massive Sterile Neutrino

The recent Xenon1T excess can be explained by solar neutrino scattering with electron via a light mediator, either scalar or vector, in addition to many other explanations from the dark sector. Since only the recoil electron is observable, a keV sterile neutrino instead of an active neutrino can appear in the final state. The sterile neutrino allows pseudoscalar mediator to explain the Xenon1T excess which was thought impossible. In addition, nonzero recoil energy lower bound arises from the sterile neutrino mass, which can be used to testify if the sterile neutrino is massive or not. We also briefly discuss the case of a sterile neutrino final state with light $Z'$ mediator.

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