arXiv subjects

Pablo Fernández-Menéndez

Publications and source records attributed to Pablo Fernández-Menéndez.

3 recordsLinked to original sources

arXiv2026

Evidence for Normal Neutrino Ordering with Combined Atmospheric Neutrino Experiments

We present a combined analysis of the latest publicly available atmospheric neutrino data from Super-Kamiokande including all data-taking stages previous to the gadolinium phase, IceCube-DeepCore, and the six-detection-unit configuration of KM3NeT/ORCA. Our fit uses all event samples simultaneously and treats the systematic uncertainties shared among experiments as fully correlated, while detector-response uncertainties are modeled independently for each experiment. %We measure The combined data constrain the atmospheric oscillation parameters to $Δm^2_{31} = 2.44^{+0.06}_{-0.04} \times 10^{-3}\,\mathrm{eV}^2$ and $\sin^2θ_{23} = 0.52^{+0.03}_{-0.04}$, with a precision of $2.2\%$ and $6.1\%$, respectively, which is competitive with current accelerator-based measurements, and independently constrain the $CP$-violating phase to $δ_{CP} = 1.30^{+0.24}_{-0.28}~π$. Finally, comparing the orderings of the neutrino mass spectrum, we find a preference for the normal ordering with $Δχ^2 = 11.0$; further calibrated with pseudoexperiments, we exclude the inverted ordering at $99.95\%$ confidence level ($3.3σ$).

hep-ex↗

arXiv2026

CHIC: Caley-Hamilton, Invariants and Constants for Neutrino Oscillation Probabilities and Gradients

We use the Caley-Hamilton theorem to derive analytical solutions for the three-flavor neutrino propagation amplitude in a constant-density medium and their derivatives with respect to the mixing parameters. This approach avoids the diagonalization of the Hamiltonian and exploits precomputed matrix invariants to separate the dependence of oscillation probabilities on neutrino energy and propagation baseline. The results are implemented in the CHIC software, which provides simple, fast and efficient computation of oscillation probabilities and their derivatives. Finally, we demonstrate the value of probability gradients for neutrino data analyses and introduce a complementary visualization, the oscillograds, to probe underlying features of neutrino mixing.

hep-ph↗

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.

hep-ph↗