During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled "The Neutrino Matrix" accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report [1] provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.2

The ProtoDUNE-SP detector is a single-phase liquid argon time projection chamber with an active volume of 7.2× 6.1× 7.0 m3. It is installed at the CERN Neutrino Platform in a specially-constructed beam that delivers charged pions, kaons, protons, muons and electrons with momenta in the range 0.3 GeV/c to 7 GeV/c. Beam line instrumentation provides accurate momentum measurements and particle identification. The ProtoDUNE-SP detector is a prototype for the first far detector module of the Deep Underground Neutrino Experiment, and it incorporates full-size components as designed for that module. This paper describes the beam line, the time projection chamber, the photon detectors, the cosmic-ray tagger, the signal processing and particle reconstruction. It presents the first results on ProtoDUNE-SP's performance, including noise and gain measurements, dE/dx calibration for muons, protons, pions and electrons, drift electron lifetime measurements, and photon detector noise, signal sensitivity and time resolution measurements. The measured values meet or exceed the specifications for the DUNE far detector, in several cases by large margins. ProtoDUNE-SP's successful operation starting in 2018 and its production of large samples of high-quality data demonstrate the effectiveness of the single-phase far detector design.

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A CPT violating decoherence scenario can easily account for all the experimental evidence in the neutrino sector including LSND. In this work it is argued that this framework can also accommodate the Dark Energy content of the Universe, as well as the observed matter-antimatter asymmetry.In a previous work [1], henceforth referred to as I, we have discussed a phenomenological way of accounting for the LSND results [2] on evidence for antineutrino oscillations ν e → ν µ , but with lack of corresponding evidence in the neutrino sector, by means of invoking CPT Violating (CPTV) decoherence, due to quantum gravity. Indeed, quantum decoherence in matter propagation occurs when the matter subsystem interacts with an 'environment' [3], according to the rules of open-system quantum mechanics. At a fundamental level, such a decoherence may be the result of propagation of matter in quantum gravity space-time backgrounds with 'fuzzy' properties, which may be responsible for violation of CPT symmetry[4] in a way not necessarily related to mass differences between particles and antiparticles. As demonstrated in I, it is possible to fit all the available neutrino data, including the results from LSND and Karmen[5] experiments, not by enlarging the neutrino sector or implementing CPTV mass spectra for neutrinos, but by invoking a CPTV difference in the decoherence parameters between particle and antiparticle sectors in three generation neutrino models (we refer the reader to the original work for technical details). From this point of view, then, the LSND result would evidence CPT violation in the sense of different decohering interactions between particle and antiparticle sectors, while the mass differences (and widths) between the two sectors remain the same. From I it became clear that both mixing and decoherence, the latter in the antineutrino sector only, were necessary to account for all the available experimental information, including LSND and Karmen results [2,5]. Mixing, in the sense of non trivial mass differences between energy eigenstates, was important, since pure decoherence, that is absence of any mass terms in the Hamiltonian, was not sufficient to fit the data. However, this does not mean that the mass terms are necessarily of conventional origin. As stressed in I, the Hamiltonian appearing in the decoherent evolution should be viewed as an "effective" one, receiving possible contributions from the environment as well. In this sense, one cannot exclude the possibility that some contribution to the neutrino masses have a quantum-decoherence origin, as a result of interactions with the foam, as happens for example when neutrinos interact with matter and the mass differences get modified (and mass degeneracies lifted) as a result of the interaction. Such an effect will disentangle neutrino masses from standard electroweak symmetry breaking scenaria. As we shall discuss below, this is an important feature that will allow us to associate the recently claimed amount of dark energy in the Universe by means of astroph...

Decoherence has the potential to explain all existing neutrino data including LSND results, without enlarging the neutrino sector. This particular form of CPT violation can preserve the equality of masses and mixing angles between particle and antiparticle sectors, and still provide seizable differences in the oscillation patterns. A simplified minimal model of decoherence can explain the existing neutrino data as well as the standard three oscillation scenario, while making dramatic predictions for the upcoming experiments. Such a model can easily accomodate the LSND result but cannot fit the spectral distortions seen by KamLAND. Some comments on the order of the decoherence parameters in connection with theoretically expected values from some models of quantum-gravity are given. In particular, the quantum gravity decoherence as a primary origin of the neutrino mass differences scenario is explored, and even a speculative link between the neutrino mass-difference scale and the dark energy density component of the Universe today is drawn.

The deep underground neutrino experiment (DUNE), a 40-kton underground liquid argon time projection chamber experiment, will be sensitive to the electron-neutrino flavor component of the burst of neutrinos expected from the next Galactic core-collapse supernova. Such an observation will bring unique insight into the astrophysics of core collapse as well as into the properties of neutrinos. The general capabilities of DUNE for neutrino detection in the relevant few- to few-tens-of-MeV neutrino energy range will be described. As an example, DUNE’s ability to constrain the $$\nu _e$$ ν e spectral parameters of the neutrino burst will be considered.

We consider a class of models predicting new heavy neutral fermionic states, whose mixing with the light neutrinos can be naturally significant and produce observable effects below the threshold for their production. We update the indirect limits on the flavour nondiagonal mixing parameters that can be derived from unitarity, and show that significant rates are in general expected for one-loop-induced rare processes due to the exchange of virtual heavy neutrinos, involving the violation of the muon and electron lepton numbers. In particular, the amplitudes for µ-e conversion in nuclei and for µ → ee + e − show a non-decoupling quadratic dependence on the heavy neutrino mass M, while µ → eγ is almost independent of the heavy scale above the electroweak scale. These three processes are then used to set stringent constraints on the flavour-violating mixing angles. In all the cases considered, we point out explicitly that the non-decoupling behaviour is strictly related to the spontaneous breaking of the SU(2) symmetry.

In this work we perform global fits of microscopic decoherence models of neutrinos to all available current data, including LSND and KamLAND spectral distortion results. In previous works on related issues the models used were supposed to explain LSND results by means of quantum gravity induced decoherence. However those models were purely phenomenological without any underlying microscopic basis. It is one of the main purposes of this article to use detailed microscopic decoherence models with complete positivity, to fit the data.The decoherence in these models has contributions not only from stochastic quantum gravity vacua operating as a medium, but also from conventional uncertainties in the energy of the (anti)neutrino beam. All these contributions lead to oscillation-length independent damping factors modulating the oscillatory terms from which one obtains an excellent fit to all available neutrino data, including LSND and Kamland spectral distortion.Comment: 27 pages, 2 figure