40 research outputs found

### Neutrino oscillation probabilities through the looking glass

In this paper we review different expansions for neutrino oscillation
probabilities in matter in the context of long-baseline neutrino experiments.
We examine the accuracy and computational efficiency of different exact and
approximate expressions. We find that many of the expressions used in the
literature are not precise enough for the next generation of long-baseline
experiments, but several of them are while maintaining comparable simplicity.
The results of this paper can be used as guidance to both phenomenologists and
experimentalists when implementing the various oscillation expressions into
their analysis tools.Comment: 32 pages, 6 figure

### CPT and CP, an entangled couple

Even though it is undoubtedly very appealing to interpret the latest T2K
results as evidence of CP violation, this claim assumes CPT conservation in the
neutrino sector to an extent that has not been tested yet. As we will show, T2K
results are not robust against a CPT-violating explanation. On the contrary, a
CPT-violating CP-conserving scenario is in perfect agreement with current
neutrino oscillation data. Therefore, to elucidate whether T2K results imply CP
or CPT violation is of utter importance. We show that, even after combining
with data from NO$\nu$A and from reactor experiments, no claims about CP
violation can be made. Finally, we update the bounds on CPT violation in the
neutrino sector.Comment: 8 pages, 6 figure

### Neutrino oscillation phenomenology in the standard model and beyond

Over the last 20 years measurements of neutrino oscillation parameters have become very precise. In the standard neutrino oscillation picture most of the parameters are measured at the percent level. In this thesis we study neutrino oscillations in the standard picture and beyond. We analyze data from all types of neutrino oscillation experiments to obtain a global picture of neutrino oscillations. The remaining unknowns in the standard picture are the value of the CP-violating phase $\delta$, the octant of the atmospheric angle $\theta_{23}$ and the neutrino mass ordering. We discuss the current status of these unknowns and also comment on how well future experiments will do in measuring these quantities, where we discuss new facilities which will observe accelerator, atmossperic and reactor neutrinos. Using oscillation data it is possible to bound a possible violation of the CPT symmetry in the neutrino sector. This is done by performing a fit to neutrino and antineutrino oscillation data separately. We also address the capability of the future experiment DUNE to this scenario. We show that DUNE could improve some of the current bounds considerably. We discuss the sensitivity of DUNE together with the next generation reactor neutrino experiment JUNO to measure quasi-Dirac neutrino oscillations. We find that the future experiments will be able to bound the important quantities, mostly unbounded by current data. Finally, we discuss atmospheric neutrinos at the next generation neutrino telescope ORCA. We show that ORCA will put the best bounds on the invisible neutrino decay of $\nu_3$, coming from neutrino oscillation experiments. We also find that, a scenario like this would not affect the standard measurements of ORCA, namely the determination of the atmospheric neutrino oscillation parameters and the measurement of the neutrino mass ordering

### Combined analysis of neutrino decoherence at reactor experiments

Reactor experiments are well suited to probe the possible loss of coherence
of neutrino oscillations due to wave-packets separation. We combine data from
the short-baseline experiments Daya Bay and the Reactor Experiment for Neutrino
Oscillation (RENO) and from the long baseline reactor experiment KamLAND to
obtain the best current limit on the reactor antineutrino wave-packet width,
$\sigma > 2.1 \times 10^{-4}$ nm at 90% CL. We also find that the determination
of standard oscillation parameters is robust, i.e., it is mostly insensitive to
the presence of hypothetical decoherence effects once one combines the results
of the different reactor neutrino experiments.Comment: 8 pages, 4 figures. Version matches the one published in JHE

### Non-standard neutrino oscillations: perspective from unitarity triangles

We formulate an alternative approach based on unitarity triangles to describe
neutrino oscillations in presence of non-standard interactions (NSI). Using
perturbation theory, we derive the expression for the oscillation probability
in case of NSI and cast it in terms of the three independent parameters of the
leptonic unitarity triangle (LUT). The form invariance of the probability
expression (even in presence of new physics scenario as long as the mixing
matrix is unitary) facilitates a neat geometric view of neutrino oscillations
in terms of LUT. We examine the regime of validity of perturbative expansions
in the NSI case and make comparisons with approximate expressions existing in
literature. We uncover some interesting dependencies on NSI terms while
studying the evolution of LUT parameters and the Jarlskog invariant.
Interestingly, the geometric approach based on LUT allows us to express the
oscillation probabilities for a given pair of neutrino flavours in terms of
only three (and not four) degrees of freedom which are related to the geometric
properties (sides and angles) of the triangle. Moreover, the LUT parameters are
invariant under rephasing transformations and independent of the
parameterization adopted.Comment: 21 pages, 7 figure

### Neutrino oscillation bounds on quantum decoherence

We consider quantum-decoherence effects in neutrino oscillation data. Working
in the open quantum system framework we adopt a phenomenological approach that
allows to parameterize the energy dependence of the decoherence effects. We
consider several phenomenological models. We analyze data from the reactor
experiments RENO, Daya Bay and KamLAND and from the accelerator experiments
NOvA, MINOS/MINOS+ and T2K. We obtain updated constraints on the decoherence
parameters quantifying the strength of damping effects, which can be as low as
$\Gamma_{ij} \lesssim 8 \times 10^{-27}$ GeV at 90% confidence level in some
cases. We also present sensitivities for the future facilities DUNE and JUNO.Comment: v2: matches published version, v1: 20 pages, 9 figures, 3 table

### Neutrino mass and mass ordering: No conclusive evidence for normal ordering

The extraction of the neutrino mass ordering is one of the major challenges
in particle physics and cosmology, not only for its implications for a
fundamental theory of mass generation in nature, but also for its decisive role
in the scale of future neutrinoless double beta decay experimental searches. It
has been recently claimed that current oscillation, beta decay and cosmological
limits on the different observables describing the neutrino mass parameter
space provide robust decisive Bayesian evidence in favor of the normal ordering
of the neutrino mass spectrum [arXiv:2203.14247]. We further investigate these
strong claims using a rich and wide phenomenology, with different sampling
techniques of the neutrino parameter space. Contrary to the findings of Jimenez
et al [arXiv:2203.14247], no decisive evidence for the normal mass ordering is
found. Neutrino mass ordering analyses must rely on priors and
parameterizations that are ordering-agnostic: robust results should be regarded
as those in which the preference for the normal neutrino mass ordering is
driven exclusively by the data, while we find a difference of up to a factor of
33 in the Bayes factors among the different priors and parameterizations
exploited here. An ordering-agnostic prior would be represented by the case of
parameterizations sampling over the two mass splittings and a mass scale, or
those sampling over the individual neutrino masses via normal prior
distributions only. In this regard, we show that the current significance in
favor of the normal mass ordering should be taken as $2.7\sigma$ (i.e. moderate
evidence), mostly driven by neutrino oscillation data.Comment: 10 pages, 4 figure

### Neutrino Mass Ordering from Oscillations and Beyond: 2018 Status and Future Prospects

The ordering of the neutrino masses is a crucial input for a deep understanding of flavor physics, and its determination may provide the key to establish the relationship among the lepton masses and mixings and their analogous properties in the quark sector. The extraction of the neutrino mass ordering is a data-driven field expected to evolve very rapidly in the next decade. In this review, we both analyse the present status and describe the physics of subsequent prospects. Firstly, the different current available tools to measure the neutrino mass ordering are described. Namely, reactor, long-baseline (accelerator and atmospheric) neutrino beams, laboratory searches for beta and neutrinoless double beta decays and observations of the cosmic background radiation and the large scale structure of the universe are carefully reviewed. Secondly, the results from an up-to-date comprehensive global fit are reported: the Bayesian analysis to the 2018 publicly available oscillation and cosmological data sets provides strong evidence for the normal neutrino mass ordering vs. the inverted scenario, with a significance of 3.5 standard deviations. This preference for the normal neutrino mass ordering is mostly due to neutrino oscillation measurements. Finally, we shall also emphasize the future perspectives for unveiling the neutrinomass ordering. In this regard, apart from describing the expectations from the aforementioned probes, we also focus on those arising from alternative and novel methods, as 21 cm cosmology, core-collapse supernova neutrinos and the direct detection of relic neutrinos