arXiv subjects

Ivan Martinez-Soler

Publications and source records attributed to Ivan Martinez-Soler.

At least 19 recordsLinked to original sources

arXiv2026

Probing Scalar Non-Standard Neutrino Interactions using High-Energy Astrophysical Neutrinos

Scalar non-standard interaction (SNSI) of neutrinos contributes as modifications to the neutrino mass matrix in the oscillation Hamiltonian and can induce a small active-sterile mass splitting due to the matter effect induced by the relic neutrino background via a Majorana-type interaction. This framework leads to pseudo-Dirac behavior of neutrinos, introducing rich phenomenology in neutrino oscillations, particularly for high-energy astrophysical neutrinos. We show that these hyperfine active-sterile splittings imprint themselves in two complementary ways on high-energy astrophysical neutrino flux, namely, in modifying the flavor composition and energy distribution. In this work, we perform both flavor and spectral analyses of the high-energy astrophysical neutrino flux to probe SNSI. We confront the predicted flavor ratios with current IceCube measurements and with the projected reach of next-generation detectors such as IceCube-Gen2. For the spectral analysis, we use the diffuse-flux ESTES (tracks) and cascade data sets, together with point-source spectral shape analysis based on a recent catalog of neutrino-bright sources. The regions excluded by the combined flavor and spectral analyses are translated into limits on the underlying SNSI parameters, namely, Yukawa couplings and scalar mass, providing new sensitivities on the SNSI parameter space for ultra-light mediators.

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arXiv2026

Charged Lepton Flavor Violation at Neutrino Telescopes

Any observation of charged lepton flavor violation (CLFV) would be a clear signal of beyond-the-Standard-Model physics. Here, we propose a novel CLFV search using neutrino telescopes with their large cosmic-ray muon samples. Specifically, we use a recent IceCube cosmic-ray muon dataset and propose a new search for muon-to-tau conversion inside the IceCube detector. We illustrate our idea with CLFV interactions described by model-independent Effective Field Theory (EFT) operators and present the IceCube sensitivity on the relevant EFT scale. We also consider a specific realization of the EFT operator in terms of an axial-vector $Z'$ interaction and show sensitivities in the $Z'$ mass-coupling plane. We compare our sensitivities with those from low-energy CLFV searches, as well as from current and future collider experiments. We also show projections from next-generation neutrino telescopes, such as IceCube-Gen2 and HUNT, and demonstrate how neutrino telescopes can provide a powerful complementary probe of CLFV.

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arXiv2026

When CPT Violation Hides in Plain Sight: How CP Measurements Are Compromised and How to Fix Them

The extraction of the leptonic charge-parity (CP)-violating phase $δ_{\rm CP}$ from long-baseline neutrino oscillation experiments rests on the assumption of charge-parity-time (CPT) conservation. We show that CPT violation, parametrized as an asymmetry $δΔm^2_{31} \equiv Δ\bar{m}^2_{31} - Δm^2_{31}$ between neutrino and antineutrino mass splittings, induces an effective, energy-dependent phase shift $ϕ_{\rm eff}(E)$ that is functionally degenerate with $δ_{\rm CP}$ in the appearance asymmetry $\langleΔP\rangle$. This has a profound implication for long-baseline experiments, where the tension between T2K and NO$ν$A CPT-conserving best-fit $δ_{\rm CP}$ values can be significantly alleviated by a CPT-violating truth; and a CPT-conserving fit can miss the true CP phase entirely for $|δΔm^2_{31}|\gtrsim 0.3\times10^{-3}~\text{eV}^2$ for DUNE. We then demonstrate that atmospheric neutrino telescopes provide the natural tool to resolve this degeneracy: using existing data from IceCube-DeepCore (7.74 yr) and KM3NeT/ORCA-6 (433 kt-yr), we derive a world-leading constraint on CPT-violation at $| δΔm^2_{31}|\leq 0.57\times10^{-3}~\text{eV}^2$ at 90% CL. With the IceCube Upgrade and full ORCA detector, we can reach a $1σ$ constraint at $10^{-4}~\text{eV}^2$ within a decade, providing the independent CPT constraint needed to ensure that DUNE's $δ_{\rm CP}$ measurement is unambiguous.

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arXiv2026

Boomerang mechanism explaining the excess radio background

We propose a boomerang mechanism for the explanation of the excess radio background detected by ARCADE 2. In an early stage of the Universe, at a temperature $T$ in the range $\sim 0.1\,{\rm keV}$--$1\,{\rm MeV}$, a fraction of relic neutrinos is resonantly converted into dark neutrinos by mixing induced by a pre-existing lepton asymmetry. Dark neutrinos decay much later into a dark-standard photon state and a dark fermion, with a lifetime longer than the age of the Universe, as required by a solution to the excess radio background. This scenario circumvents the upper bound on the neutrino magnetic moment but still implies a testable lower bound.

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arXiv2026

Lessons from the first JUNO results

First results from the JUNO reactor neutrino experiment already determine with world-leading precision the small neutrino squared-mass splitting $Δm^2_{21}$ and the mixing angle $θ_{12}$. In this article we perform an exploratory study beyond these, taking advantage of the first JUNO data release to discuss its sensitivity to the large squared-mass splitting, $Δm^2_{3\ell}$. When combined with constraints from global oscillation data, this may already contain some information on the neutrino mass ordering. Indeed, we find that the combination of the complementary $Δm^2_{3\ell}$-determinations gives a slight preference for Normal Ordering, with a p-value for Inverted Ordering of 2%-2.6% ($2.2σ$-$2.3σ$). We study the robustness of this result with respect to potential systematic uncertainties and statistical fluctuations. Taken at face value, a full global analysis of oscillation data including the publicly available JUNO information and data leads to a preference for Normal Ordering with $Δχ^2 = 4.6$ and 9.4 without and with Super-K and IceCube-24 atmospheric neutrino data, respectively.

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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

Updated Constraints on Large Extra Dimensions from Reactor Antineutrino Experiments

We investigate constraints on large extra dimensions (LED) using the latest results from reactor antineutrino experiments. Specifically, we analyze the full data sets from Daya Bay, RENO, KamLAND, NEOS, and STEREO to derive updated bounds. For the case of one extra dimension, we find constrains on its radius $a$ of $a \lesssim 0.58~{\rm μm}$ ($a \lesssim 0.12~{\rm μm}$) at the $99\%$ confidence level for normal (inverted) ordering, an improvement of approximately $\sim 20\%$ ($\sim 25\%$) with respect to previous bounds, assuming a massless lightest active neutrino. Furthermore, we present new limits on $4+d$ LED scenarios, with $d = 2, 3, 4$ denoting the number of extra dimensions, based on the same reactor data and assuming equal radii for all extra dimensions. We find that the constraints become increasingly stringent with a larger number of extra dimensions. In particular, $d = 4$ with a massless lightest active neutrino, we obtain limits of $a \lesssim 0.28~{\rm μm}$ for normal and $a \lesssim 0.05~{\rm μm}$ for inverted orderings at the $99\%$ confidence level.

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arXiv2025

Probing the Cosmic Neutrino Background and New Physics with TeV-Scale Astrophysical Neutrinos

We use recent evidence of TeV neutrino events from the most significant astrophysical sources detected by IceCube -- NGC 1068, TXS 0506+056, PKS 1424+240 -- to constrain the local and global overdensity of relic neutrinos and to explore potential new neutrino self-interactions. Assuming a relic neutrino overdensity, such high-energy neutrinos have travelled considerable distances through a sea of relic neutrinos and could have undergone scattering, altering their observed flux on Earth. Considering only Standard Model interactions, we constrain the relic overdensity to $η\leq 2 \times 10^{14}$ at the 90$\%$ confidence level, assuming the sum of neutrino masses saturates the cosmological bound, $\sum_i m_i = 0.13$ eV. We demonstrate that this limit improves for larger neutrino masses and study how it depends on the scale of the overdensity region. Considering new interactions between TeV-scale neutrinos and relic neutrinos, mediated by a light boson, we probe couplings of approximately $g \sim 10^{-2}$ with current data for a boson mass around the MeV scale. We demonstrate that this limit improves with larger neutrino masses and the scale of the overdensity region.

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arXiv2025

Improving Neutrino Energy Reconstruction with Machine Learning

Faithful energy reconstruction is foundational for precision neutrino experiments like DUNE, but is hindered by uncertainties in our understanding of neutrino--nucleus interactions. Here, we demonstrate that dense neural networks are very effective in overcoming these uncertainties by estimating inaccessible kinematic variables based on the observable part of the final state. We find improvements in the energy resolution by up to a factor of two compared to conventional reconstruction algorithms, which translates into an improved physics performance equivalent to a 10-30% increase in the exposure.

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arXiv2025

Sterile-active resonance: A global qualitative picture

In the $ν$SM extended by adding an eV-scale sterile state, the $(3+1)$ model, the sterile-active level crossing entails the MSW resonance, here referred as the sterile-active (SA) resonance. In this paper, we construct an effective theory of SA resonance which involves only the sterile-active mixing angles and $Δm^2_{41}$, thanks to the given environment of high matter potential which freezes the $ν$SM oscillations. We give our first attempt at an analytic treatment of the effective theory to illuminate the global picture of the SA resonance at a glance. We formulate a perturbative framework in which the structure of ``texture zeros'' of the $S$ matrix in the flavor space and the suppression by the small parameters $\sin θ_{j 4}$ ($j=1,2,3$) allows us to reveal the flavor$-$event-type hierarchy of the resonance-effect strength in the probabilities. We have shown that the cascade events dominantly comes from the three paths through $P(ν_{e} \rightarrow ν_{e})$, $P(\barν_{e} \rightarrow \barν_{e})$, and $P(\barν_μ \rightarrow \barν_τ)$, and a three-component fit is suggested to disentangle the SA resonance generation mechanisms.

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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

Resonant Neutrino Flavor Conversion in the Atmosphere

Neutrinos produced in the atmosphere traverse a column density of air before being detected at neutrino observatories like IceCube or KM3NeT. In this work, we extend the neutrino flavor evolution in the {nuSQuIDS} code accounting for the varying height of neutrino production and the variable air density in the atmosphere. These effects can lead to sizeable spectral distortions in standard neutrino oscillations and are crucial to accurately describe some new physics scenarios. As an example, we study a model of quasi-sterile neutrinos that induce resonant flavor conversions at neutrino energies of ${O}(300)\text{ MeV}$ in matter densities of $1 \text{ g/cm}^3$. In atmospheric air densities, the same resonance is then realized at neutrino energies of ${O}(300- 700)$~GeV. We find that the new resonance can deplete the $ν_μ+ \overlineν_μ$ flux at the IceCube Neutrino Observatory by as much as $10\%$ in the direction of the horizon.

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arXiv2023

IceCube and the origin of ANITA-IV events

Recently, the ANITA collaboration announced the detection of new, unsettling upgoing Ultra-High-Energy (UHE) events. Understanding their origin is pressing to ensure success of the incoming UHE neutrino program. In this work, we study their internal consistency and the implications of the lack of similar events in IceCube. We introduce a generic, simple parametrization to study the compatibility between these two observatories in Standard Model-like and Beyond Standard Model scenarios: an incoming flux of particles that interact with Earth nucleons with cross section $σ$, producing particle showers along with long-lived particles that decay with lifetime $τ$ and generate a shower that explains ANITA observations. We find that the ANITA angular distribution imposes significant constraints, and when including null observations from IceCube only $τ\sim 10^{-3}$ - $10^{-2} \,\mathrm{s}$ and $σ\sim 10^{-33}$ - $10^{-32}\,\mathrm{cm^2}$ can explain the data. This hypothesis is testable with future IceCube data. Finally, we discuss a specific model that can realize this scenario. Our analysis highlights the importance of simultaneous observations by high-energy optical neutrino telescopes and new UHE radio detectors to uncover cosmogenic neutrinos or discover new physics.

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arXiv2023

Probing Pseudo-Dirac Neutrinos with Astrophysical Sources at IceCube

The recent observation of NGC 1068 by the IceCube Neutrino Observatory has opened a new window to neutrino physics with astrophysical baselines. In this Letter, we propose a new method to probe the nature of neutrino masses using these observations. In particular, our method enables searching for signatures of pseudo-Dirac neutrinos with mass-squared differences that reach down to $δm^2 \gtrsim 10^{-21}~\text{eV}^2$, improving the reach of terrestrial experiments by more than a billion. Finally, we discuss how the discovery of a constellation of neutrino sources can further increase the sensitivity and cover a wider range of $δm^2$ values.

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arXiv2022

Heavy Neutrino searches through Double-Bang Events at Super-Kamiokande, DUNE, and Hyper-Kamiokande

A variety of new physics scenarios allow for neutrinos to up-scatter into a heavy neutral lepton state. For a range of couplings and neutrino energies, the heavy neutrino may travel some distance before decaying to visible final states. When both the up-scattering and decay occur within the detector volume, these "double bang" events produce distinctive phenomenology with very low background. In this work, we first consider the current sensitivity at Super-Kamiokande via the atmospheric neutrino flux, and find current data may already provide new constraints. We then examine projected future sensitivity at DUNE and Hyper-Kamiokande, including both atmospheric and beam flux contributions to double-bang signals.

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arXiv2022

Tau Neutrinos in the Next Decade: from GeV to EeV

Tau neutrinos are the least studied particle in the Standard Model. This whitepaper discusses the current and expected upcoming status of tau neutrino physics with attention to the broad experimental and theoretical landscape spanning long-baseline, beam-dump, collider, and astrophysical experiments. This whitepaper was prepared as a part of the NuTau2021 Workshop.

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arXiv2022

SN1987A still shining: A Quest for Pseudo-Dirac Neutrinos

Ever since the discovery of neutrinos, we have wondered if neutrinos are their own antiparticles. One remarkable possibility is that neutrinos have a pseudo-Dirac nature, predicting a tiny mass difference between active and sterile states. We analyze the neutrino data from SN1987A in the light of active-sterile oscillations and find a mild preference ($Δχ^2\approx 3$) for $δm^2=6.31\times 10^{-20}{\rm eV}^2$. Notably, the same data is able to exclude $δm^2\sim[2.55,3.01]\times 10^{-20}{\rm eV}^2$ with $Δχ^2> 9$, the tiniest mass differences constrained so far. We further consider the next-generation of experiments and demonstrate their sensitivity exploring the nature of the neutrino mass.

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arXiv2022

The diffuse supernova neutrino background as a probe of late-time neutrino mass generation

The relic neutrinos from old supernova explosions are among the most ancient neutrino fluxes within experimental reach. Thus, the diffuse supernova neutrino background (DSNB) could teach us if neutrino masses were different in the past (redshifts $z\lesssim 5$). Oscillations inside the supernova depend strongly on the neutrino mass-squared differences and the values of the mixing angles, rendering the DSNB energy spectrum sensitive to variations of these parameters. Considering a purely phenomenological parameterization of the neutrino masses as a function of redshift, we compute the expected local DSNB spectrum here on Earth. Given the current knowledge of neutrino oscillation parameters, specially the fact that $|U_{e3}|^2$ is small, we find that the $ν_e$ spectrum could be significantly different from standard expectations if neutrinos were effectively massless at $z\gtrsim1$ as long as the neutrino mass ordering is normal. On the other hand, the $\overlineν_e$ flux is not expected to be significantly impacted. Hence, a measurement of both the neutrino and antineutrino components of the DSNB should allow one to test the possibility of recent neutrino mass generation.

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