arXiv subjects

Antonio Palazzo

Publications and source records attributed to Antonio Palazzo.

At least 19 recordsLinked to original sources

arXiv2026

Effective Matter Flavor Conversion Mediated by Pseudo-Sterile States as the Possible Origin of Neutrino Oscillation Anomalies

Neutrino oscillation experiments present anomalous results across a vast range of baselines and energies. Here we show that a 3+1 scenario in which sterile neutrinos feel a novel matter potential $V_s$ proportional to background density of ordinary or (asymmetric) dark matter is able to explain several anomalies. At low-energies ($E\lesssim$ 1 TeV) the model behaves as an effective 3-flavor NSI-like scheme among active flavors and eliminates the tension between the two LBL experiments NOvA and T2K provided that the potential is negative and the two sterile mixing angles $θ_{14}$ and $θ_{24}$ are non-zero. A further indication in favor of a negative non-zero potential comes from the anomalous excess of $ν_e$-like events observed in Super-Kamiokande atmospheric neutrinos, which, in the new scenario is explained by a modification of the 3-flavor resonance at few GeV. A high energies ($E\gtrsim $ 1 TeV) the new framework reveals its 4-flavor nature and produces a resonant behavior at $E \simeq$ 10 TeV as hinted at by IceCube. We identify an irreducible 3-level dynamics generating a new resonance in the $(ν_e, ν_μ)$ sector intertwined with two conventional resonances in the $(ν_e, ν_s$) and $(ν_μ, ν_s)$ systems. The novel amplification mechanism manifests with the emergence of effective mixing angles in matter ($θ_{12}^m$ or $θ_{13}^m$) involving active neutrinos. The scenario requires values of $f = V_s/|V_{NC}| \sim -20 $, $Δm^2_{41} \sim 60 $ eV$^2$, $|U_{e4}|^2\simeq \sin^2θ_{14} \simeq 0.01-0.03$ and $|U_{\mu4}|^2 \simeq \sin^2θ_{24}\simeq 10^{-4}-10^{-3}$. Such a very small size of $|U_{\mu4}|^2$ eliminates the tension between IceCube and the other $ν_μ$ disappearance searches. The model can be directly probed by KATRIN, which is very sensitive to the electron-sterile neutrino admixture in the region of high $Δm^2_{41}$.

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arXiv2025

Updated bounds on the (1,2) neutrino oscillation parameters after first JUNO results

Within the standard $3ν$ framework, we discuss updated bounds on the leading oscillation parameters related to the $(ν_1,\,ν_2)$ states, namely, the squared mass difference $δm^2=m^2_2-m^2_1$ and the mixing parameter $\sin^2θ_{12}$. A previous global analysis of 2024 oscillation data estimated $δm^2$ and $\sin^2θ_{12}$ with fractional $1σ$ errors of about $2.3\%$ and $4.5\%$, respectively. First we update the analysis by applying the latest SNO+ constraints, that slightly shift the $(δm^2,\,\sin^2θ_{12})$ best fits. Then we apply the constraints placed by the first JUNO results, that significantly reduce the uncertainties of both parameters. Our updated global bounds (as of 2025) can be summarized as: $δm^2/10^{-5}{\rm eV}^2 = 7.48\pm 0.10$ and $\sin^2θ_{12}=0.3085\pm0.0073$ (with correlation $ρ=-0.20$), corresponding to $1σ$ uncertainties as small as $1.3\%$ and $2.4\%$, respectively. We also comment on minor physical and statistical effects that, in the future, may contribute to lift the current mass-ordering degeneracy of $(δm^2,\,θ_{12})$ estimates.

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arXiv2025

Neutrino masses and mixing: Entering the era of subpercent precision

We perform an updated global analysis of the known and unknown parameters of the standard $3ν$ framework as of 2025. The known oscillation parameters include three mixing angles $(θ_{12},\,θ_{23},\,θ_{13})$ and two squared mass gaps, chosen as $δm^2=m^2_2-m^2_1>0$ and $Δm^2=m^2_3-{\textstyle\frac{1}{2}}(m^2_1+m^2_2)$, where $α=\mathrm{sign}(Δm^2)$ distinguishes normal ordering (NO, $α=+1$) from inverted ordering (IO, $α=-1$). With respect to our previous 2021 update, the combination of oscillation data leads to appreciably reduced uncertainties for $θ_{23}$, $θ_{13}$ and $|Δm^2|$. In particular, $|Δm^2|$ is the first $3ν$ parameter to enter the domain of subpercent precision (0.8\% at $1σ$). We underline some issues about systematics, that might affect this error estimate. Concerning oscillation unknowns, we find a relatively weak preference for NO versus IO (at $2.2σ$), for CP violation versus conservation in NO (1.3$σ$) and for the first $θ_{23}$ octant versus the second in NO ($1.1σ$). We discuss the status and qualitative prospects of the mass ordering hint in the plane $(δm^2,\,Δm^2_{ee})$, where $Δm^2_{ee}=|Δm^2|+{\textstyle\frac{1}{2}}α(\cos^2θ_{12}-\sin^2θ_{12})δm^2$, to be measured by the JUNO experiment with subpercent precision. We also discuss upper bounds on nonoscillation observables. We report $m_β<0.50$~eV and $m_{ββ}<0.086$~eV ($2σ$). Concerning the sum of neutrino masses $Σ$, we discuss representative combinations of data, with or without augmenting the $Λ$CDM model with extra parameters accounting for possible systematics or new physics. The resulting $2σ$ upper limits are roughly spread around the bound $Σ< 0.2$~eV within a factor of three. [Abridged]

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arXiv2024

Status of tension between NO$ν$A and T2K after Neutrino 2024 and possible role of non-standard neutrino interactions

In a previous work we have shown that the data presented by the two long-baseline accelerator experiments NO$ν$A and T2K at the Neutrino 2020 conference displayed a tension, and that it could be alleviated by non-standard neutrino interactions (NSI) of the flavor changing type involving the $e-μ$ or the $e-τ$ sectors with couplings $|\varepsilon_{eμ}| \sim |\varepsilon_{eτ}|\sim 0.1$. As a consequence a hint in favor of NSI emerged. In the present paper we reassess the issue in light of the new data released by the two experiments at the Neutrino 2024 conference. We find that the tension in the determination of the standard CP-phase $δ_{\mathrm {CP}}$ extracted by the two experiments in the normal neutrino mass ordering persists and has a statistical significance of $\sim2σ$. Concerning the NSI, we find that including their effects in the fit, the two values of $δ_{\mathrm {CP}}$ preferred by NO$ν$A and T2K return in very good agreement. The current statistical significance of the hint of non zero NSI is $\sim1.8σ$. Further experimental data are needed in order to settle the issue.

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arXiv2022

Resolving the NO$ν$A and T2K tension in the presence of Neutrino Non-Standard interactions

The current data of the two long-baseline accelerator experiments NO$ν$A and T2K, shows a tension at more than 90$\%$ C.L. for 2 degrees of freedom, in the determination of the standard CP-phase $δ_{\mathrm {CP}}$ in case of neutrino normal ordering (NO). NO$ν$A measures the value close to $δ_{\mathrm {CP}} \sim 0.8 π$, while T2K prefers the value of $δ_{\mathrm {CP}} \sim 1.4 π$. We show that such a tension can be resolved if one hypothesizes the existence of neutral-current non-standard interactions (NSI) of neutrinos involving the flavor changing type $e-μ$ or the $e-τ$ sectors with couplings $|\varepsilon_{eμ}| \sim |\varepsilon_{eτ}|\sim 0.2$. Remarkably, our analyses show that in the presence of such NSI, both the experiments point towards the same common value of the standard CP-phase $δ_{\mathrm {CP}} \sim 3π/2$, thereby indicating towards the maximal CP-violation in the standard $3ν$ framework. We also show that the best fit values of the new CP-phases $ϕ_{eμ}$ or $ ϕ_{eτ}$ are close to $\sim 3π/2$, hence pointing towards the maximal CP-violation in the NSI sector.

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arXiv2021

The unfinished fabric of the three neutrino paradigm

In the current 3nu paradigm, flavor oscillations probe 3 mixing angles (theta_12, theta_23, theta_13), one CP phase delta, and two squared mass differences delta m^2>0 and Delta m^2, where sign(Delta m^2)=+ (-) for normal (inverted) ordering. Absolute nu masses can be probed by the effective m_beta in beta decay, by the total mass Sigma in cosmology and, if neutrinos are Majorana, by another effective m_{beta beta} in 0nu2beta decay. Within an updated global analysis of (non)oscillation data, we constrain these 3nu parameters, both separately and in selected pairs, and highlight the concordance or discordance among different constraints. Five oscillation parameters (delta m^2, Delta m^2, theta_12, theta_23, theta_13) are consistently measured, with an overall accuracy ranging from ~1% for Delta m^2 to ~6% for sin^2(theta_23) (due to its octant ambiguity). We find overall hints for normal ordering (at 2.5 sigma), as well as for theta_23<pi/4 and for sin(delta)<0 (both at 90% C.L.), and discuss some tensions among datasets. Concerning nonoscillation data, we include the recent KATRIN constraints on m_beta, and we combine the latest 76-Ge, 130-Te and 136-Xe bounds on m_{beta beta}, accounting for NME covariances. We also discuss some variants related to CMB anisotropy and lensing data, which may affect cosmological constraints on Sigma and hints on sign(Delta m^2). The default option, including all Planck results, irrespective of the lensing anomaly, sets upper bounds on Sigma at the level of ~10^-1 eV, and further favors normal ordering up to ~3 sigma. An alternative option, that includes recent ACT results + other independent results (from WMAP and selected Planck data) globally consistent with standard lensing, is insensitive to the ordering but prefers Sigma ~(few) x 10^-1 eV, with different implications for m_beta and m_{beta beta} searches. (Abridged)

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arXiv2021

Primordial Black Hole Dark Matter evaporating on the Neutrino Floor

Primordial black holes (PBHs) hypothetically generated in the first instants of life of the Universe are potential dark matter (DM) candidates. Focusing on PBHs masses in the range $[5 \times10^{14} - 5 \times 10^{15}]$g, we point out that the neutrinos emitted by PBHs evaporation can interact through the coherent elastic neutrino nucleus scattering (CE$ν$NS) producing an observable signal in multi-ton DM direct detection experiments. We show that with the high exposures envisaged for the next-generation facilities, it will be possible to set bounds on the fraction of DM composed by PBHs improving the existing neutrino limits obtained with Super-Kamiokande. We also quantify to what extent a signal originating from a small fraction of DM in the form of PBHs would modify the so-called "neutrino floor", the well-known barrier towards detection of weakly interacting massive particles (WIMPs) as the dominant DM component.

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arXiv2021

Interpretation of NO$ν$A and T2K data in the presence of a light sterile neutrino

We study in detail the impact of a light sterile neutrino in the interpretation of the latest data of the long baseline experiments NO$ν$A and T2K, assessing the robustness/fragility of the estimates of the standard 3-flavor parameters with respect to the perturbations induced in the 3+1 scheme. We find that all the basic features of the 3-flavor analysis, including the weak indication ($\sim$1.4$σ$) in favor of the inverted neutrino mass ordering, the preference for values of the CP-phase $δ_{13} \sim 1.2π$, and the substantial degeneracy of the two octants of $θ_{23}$, all remain basically unaltered in the 4-flavor scheme. Our analysis also demonstrates that it is possible to attain some constraints on the new CP-phase $δ_{14}$. Finally, we point out that, differently from non-standard neutrino interactions, light sterile neutrinos are not capable to alleviate the tension recently emerged between NO$ν$A and T2K in the appearance channel.

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arXiv2021

Non-standard neutrino interactions as a solution to the NO$ν$A and T2K discrepancy

The latest data of the two long-baseline accelerator experiments NO$ν$A and T2K, interpreted in the standard 3-flavor scenario, display a discrepancy. A mismatch in the determination of the standard CP-phase $δ_{\mathrm {CP}}$ extracted by the two experiments is evident in the normal neutrino mass ordering. While NO$ν$A prefers values close to $δ_{\mathrm {CP}} \sim 0.8 π$, T2K identifies values of $δ_{\mathrm {CP}} \sim 1.4 π$. Such two estimates are in disagreement at more than 90$\%$ C.L. for 2 degrees of freedom. We show that such a tension can be resolved if one hypothesizes the existence of complex neutral-current non-standard interactions (NSI) of the flavor changing type involving the $e-μ$ or the $e-τ$ sectors with couplings $|\varepsilon_{eμ}| \sim |\varepsilon_{eτ}|\sim 0.2$. Remarkably, in the presence of such NSI, both experiments point towards the same common value of the standard CP-phase $δ_{\mathrm {CP}} \sim 3π/2$. Our analysis also highlights an intriguing preference for maximal CP-violation in the non-standard sector with the NSI CP-phases having best fit close to $ϕ_{eμ} \sim ϕ_{eτ}\sim 3π/2$, hence pointing towards imaginary NSI couplings.

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arXiv2020

Neutrino mass ordering obfuscated by the NSI

Determination of the neutrino mass ordering (NMO) is one of the biggest priorities in the intensity frontier of high energy particle physics. To accomplish that goal a lot of efforts are being put together with the atmospheric, solar, reactor, and accelerator neutrinos. In the standard 3-flavor framework, NMO is defined to be normal if $m_1<m_2<m_3$, and inverted if $m_3<m_1<m_2$, where $m_1$, $m_2$, and $m_3$ are the masses of the three neutrino mass eigenstates $ν_1$, $ν_2$, and $ν_3$ respectively. Interestingly, two long-baseline experiments T2K and NO$ν$A are playing a leading role in this direction and provide a $\sim2.4σ$ indication in favor of normal ordering (NO) which we find in this work. In addition, we examine how the situation looks like in presence of non-standard interactions (NSI) of neutrinos with a special focus on the non-diagonal flavor changing type $\varepsilon_{eτ}$ and $\varepsilon_{eμ}$. We find that the present indication of NO in the standard 3-flavor framework gets completely vanished in the presence of NSI of the flavor changing type involving the $e-τ$ flavors.

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arXiv2020

Addendum to: Global constraints on absolute neutrino masses and their ordering

We revisit our previous work [Phys. Rev. D 95, 096014 (2017)] where neutrino oscillation and nonoscillation data were analyzed in the standard framework with three neutrino families, in order to constrain their absolute masses and to probe their ordering (either normal, NO, or inverted, IO). We include updated oscillation results to discuss best fits and allowed ranges for the two squared mass differences $δm^2$ and $Δm^2$, the three mixing angles $θ_{12}$, $θ_{23}$ and $θ_{13}$, as well as constraints on the CP-violating phase $δ$, plus significant indications in favor of NO vs IO at the level of $Δχ^2=10.0$. We then consider nonoscillation data from beta decay, from neutrinoless double beta decay (if neutrinos are Majorana), and from various cosmological input variants (in the data or the model) leading to results dubbed as default, aggressive, and conservative. In the default option, we obtain from nonoscillation data an extra contribution $Δχ^2 = 2.2$ in favor of NO, and an upper bound on the sum of neutrino masses $Σ< 0.15$ eV at $2σ$; both results - dominated by cosmology - can be strengthened or weakened by using more aggressive or conservative options, respectively. Taking into account such variations, we find that the combination of all (oscillation and nonoscillation) neutrino data favors NO at the level of $3.2-3.7σ$, and that $Σ$ is constrained at the $2σ$ level within $Σ< 0.12-0.69$ eV. The upper edge of this allowed range corresponds to an effective $β$-decay neutrino mass $m_β= Σ/3 = 0.23$ eV, at the sensitivity frontier of the KATRIN experiment.

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arXiv2020

Neutrino mass ordering obscured by non-standard interactions

One of the major open questions in particle physics is the issue of the neutrino mass ordering (NMO). The current data of the two long-baseline experiments NO$ν$A and T2K, interpreted in the standard 3-flavor scenario, provide a $\sim2.4σ$ indication in favor of the normal neutrino mass ordering. We show that such an indication is completely washed out if one assumes the existence of neutral-current non-standard interactions (NSI) of the flavor changing type involving the $e-τ$ flavors. This implies that the claim for a discovery of the NMO will require a careful consideration of the impact of hypothetical NSI.

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arXiv2019

Physics Potential of ESS$ν$SB in the presence of a Light Sterile Neutrino

ESS$ν$SB is a proposed neutrino super-beam project at the ESS facility. We study the performance of this setup in the presence of a light eV-scale sterile neutrino, considering 540 km baseline with 2 years (8 years) of $ν$ ($\barν$) run-plan. This baseline offers the possibility to work around the second oscillation maximum, providing high sensitivity towards CP-violation (CPV). We explore in detail its capability in resolving CPV generated by the standard CP phase $δ_{13}$, the new CP phase $δ_{14}$, and the octant of $θ_{23}$. We find that the sensitivity to CPV induced by $δ_{13}$ deteriorates noticeably when going from $3ν$ to 4$ν$ case. The two phases $δ_{13}$ and $δ_{14}$ can be reconstructed with a 1$σ$ uncertainty of $\sim15^0$ and $ \sim35^0$ respectively. Concerning the octant of $θ_{23}$, we find poor sensitivity in both $3ν$ and $4ν$ schemes. Our results show that a setup like ESS$ν$SB working around the second oscillation maximum with a baseline of 540 km, performs quite well to explore CPV in 3$ν$ scheme, but it is not optimal for studying CP properties in 3+1 scheme.

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arXiv2018

Signatures of a Light Sterile Neutrino in T2HK

We investigate the performance of T2HK in the presence of a light eV scale sterile neutrino. We study in detail its influence in resolving fundamental issues like mass hierarchy, CP-violation (CPV) induced by the standard CP-phase $δ_{13}$ and new CP-phase $δ_{14}$, and the octant ambiguity of $θ_{23}$. We show for the first time in detail that due to the impressive energy reconstruction capabilities of T2HK, the available spectral information plays an important role to enhance the mass hierarchy discovery reach of this experiment in 3$ν$ framework and also to keep it almost intact even in $4ν$ scheme. This feature is also of the utmost importance in establishing the CPV due to $δ_{14}$. As far as the sensitivity to CPV due to $δ_{13}$ is concerned, it does not change much going from $3ν$ to 4$ν$ case. We also examine the reconstruction capability of the two phases $δ_{13}$ and $δ_{14}$, and find that the typical 1$σ$ uncertainty on $δ_{13}$ ($δ_{14}$) in T2HK is $\sim15^0$ ($30^0$). While determining the octant of $θ_{23}$, we face a complete loss of sensitivity for unfavorable combinations of unknown $δ_{13}$ and $δ_{14}$.

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arXiv2017

Short- and long-baseline sterile neutrino phenomenology

Several anomalies observed in short-baseline neutrino experiments indicate that the standard 3-flavor framework may be incomplete and point towards the existence of light sterile neutrinos. Here, we present a concise review of the status of the neutrino oscillations within the 3+1 scheme, which is a minimal extension of the standard 3-flavor framework with one sterile neutrino species. We emphasize the potential role of LBL experiments in the searches of CP violation connected to sterile neutrinos and their complementarity with the SBL experiments.

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arXiv2017

Can we measure $θ_{23}$ octant in 3+1 scheme?

Current 3$ν$ global fits predict two degenerate solutions for $θ_{23}$: one lies in lower octant ($θ_{23} <π/4$), and the other belongs to higher octant ($θ_{23} >π/4$). Here, we study how the measurement of $θ_{23}$ octant would be affected in the upcoming Deep Underground Neutrino Experiment (DUNE) if there exist a light eV-scale sterile neutrino. We show that in 3+1 scheme, a new interference term in $ν_μ\to ν_e$ oscillation probability can spoil the chances of measuring $θ_{23}$ octant completely.

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arXiv2017

Global constraints on absolute neutrino masses and their ordering

Within the standard three-neutrino framework, the absolute neutrino masses and their ordering (either normal, NO, or inverted, IO) are currently unknown. However, the combination of current data coming from oscillation experiments, neutrinoless double beta decay searches, and cosmological surveys, can provide interesting constraints for such unknowns in the sub-eV mass range, down to O(0.1) eV in some cases. We discuss current limits on absolute neutrino mass observables by performing a global data analysis, that includes the latest results from oscillation experiments, neutrinoless double beta decay bounds from the KamLAND-Zen experiment, and constraints from representative combinations of Planck measurements and other cosmological data sets. In general, NO appears to be somewhat favored with respect to IO at the level of ~2 sigma, mainly by neutrino oscillation data (especially atmospheric), corroborated by cosmological data in some cases. Detailed constraints are obtained via the chi^2 method, by expanding the parameter space either around separate minima in NO and IO, or around the absolute minimum in any ordering. Implications for upcoming oscillation and non-oscillation neutrino experiments, including beta-decay searches, are also discussed.

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arXiv2017

Joint short- and long-baseline constraints on light sterile neutrinos

Recent studies have evidenced that long-baseline (LBL) experiments are sensitive to the extra CP-phases involved with light sterile neutrinos, whose existence is suggested by several anomalous short-baseline (SBL) results. We show that, within the 3+1 scheme, the combination of the existing SBL data with the LBL results coming from the two currently running experiments NO$ν$A and T2K, enables us to simultaneously constrain two active-sterile mixing angles $θ_{14}$ and $θ_{24}$ and two CP-phases $δ_{13} \equiv δ$ and $δ_{14}$, albeit the information on the second CP-phase is still weak at the moment. The two mixing angles are basically determined by the SBL data, while the two CP-phases are constrained by the LBL experiments, once the information coming from the SBL setups is taken into account. We also assess the robustness/fragility of the estimates of the standard 3-flavor parameters in the more general 3+1 scheme. To this regard we find that: i) the indication of CP-violation found in the 3-flavor analyses persists also in the 3+1 scheme, with $δ_{13} \equiv δ$ having still its best fit value around $-π/2$; ii) the 3-flavor weak hint in favor of the normal hierarchy becomes even less significant when sterile neutrinos come into play; iii) the weak indication of non-maximal $θ_{23}$ (driven by NO$ν$A disappearance data) persists in the 3+1 scheme, where maximal mixing is disfavored at almost the 90\% C.L. in both normal and inverted mass hierarchy; iv) the preference in favor of one of the two octants of $θ_{23}$ found in the 3-flavor framework (higher octant for inverted mass hierarchy) is completely washed out in the 3+1 scheme.

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