Searches for new physics at the Hyper-Kamiokande experiment

We investigate the ability of the upcoming Hyper-Kamiokande (Hyper-K) neutrino experiment to detect new physics phenomena beyond the standard, three-massive-neutrinos paradigm; namely the existence of a fourth, sterile neutrino or weaker-than-weak, non-standard neutrino interactions. With both beam-based neutrinos from the Japan Proton Accelerator Research Complex (J-PARC) and atmospheric neutrinos, Hyper-K is capable of exploring new ranges of parameter space in these new-physics scenarios. We find that Hyper-K has comparable capability to the upcoming Deep Underground Neutrino Experiment (DUNE), and that combining both beam- and atmospheric-based data can clear up degeneracies in the parameter spaces of interest. We also comment on the potential improvement in searches for new physics if a combined analysis were performed using Hyper-K and DUNE data.Comment: 14 pages, 8 figures. Minor changes to results; matches published versio

Proton Fixed-Target Scintillation Experiment to Search for Minicharged Particles

We propose a low-cost and movable setup to probe minicharged particles (or milli-charged particles) using high-intensity proton fixed-target facilities. This proposal, FerMINI, consists of a milliQan-type detector, requiring multi-coincident (nominally, triple-coincident) scintillation signatures within a small time window, located downstream of the proton target of a neutrino experiment. During the collisions of a large number of protons on the target, intense minicharged particle beams may be produced via meson photo-decays and Drell-Yan production. We take advantage of the high statistics, shielding, and potential neutrino-detector-related background reduction to search for minicharged particles in two potential sites: the MINOS near detector hall and the proposed DUNE near detector hall, both at Fermilab. We also explore several alternative designs, including the modifications of the nominal detector to increase signal yield, and combining this detector technology with existing and planned neutrino detectors to better search for minicharged particles. The CERN SPS beam and associated experimental structure also provide a similar alternative. FerMINI can achieve unprecedented sensitivity for minicharged particles in the MeV to few GeV regime with fractional charge $\varepsilon=Q_{\chi}/e$ between $10^{-4}$ (potentially saturating the detector limitation) and $10^{-1}$.Comment: A spelling error corrected, 10 pages, 2 figure

Neutrino vs. Antineutrino Oscillation Parameters at DUNE and Hyper-Kamiokande

Testing, in a non-trivial, model-independent way, the hypothesis that the three-massive-neutrinos paradigm properly describes nature is among the main goals of the current and the next generation of neutrino oscillation experiments. In the coming decade, the DUNE and Hyper-Kamiokande experiments will be able to study the oscillation of both neutrinos and antineutrinos with unprecedented precision. We explore the ability of these experiments, and combinations of them, to determine whether the parameters that govern these oscillations are the same for neutrinos and antineutrinos, as prescribed by the CPT-theorem. We find that both DUNE and Hyper-Kamiokande will be sensitive to unexplored levels of leptonic CPT-violation. Assuming the parameters for neutrino and antineutrinos are unrelated, we discuss the ability of these experiments to determine the neutrino and antineutrino mass-hierarchies, atmospheric-mixing octants, and CP-odd phases, three key milestones of the experimental neutrino physics program. Additionally, if the CPT-theorem is violated in nature in a way that is consistent with all present neutrino and antineutrino oscillation data, we find that DUNE and Hyper-Kamiokande have the potential to ultimately establish CPT-invariance violation.Comment: 14 pages, 6 figure

Non-standard Neutrino Interactions at DUNE

We explore the effects of non-standard neutrino interactions (NSI) and how they modify neutrino propagation in the Deep Underground Neutrino Experiment (DUNE). We find that NSI can significantly modify the data to be collected by the DUNE experiment as long as the new physics parameters are large enough. For example, If the DUNE data are consistent with the standard three-massive-neutrinos paradigm, order 0.1 (in units of the Fermi constant) NSI effects will be ruled out. On the other hand, if large NSI effects are present, DUNE will be able to not only rule out the standard paradigm but also measure the new physics parameters, sometimes with good precision. We find that, in some cases, DUNE is sensitive to new sources of CP-invariance violation. We also explored whether DUNE data can be used to distinguish different types of new physics beyond nonzero neutrino masses. In more detail, we asked whether NSI can be mimicked, as far as the DUNE setup is concerned, by the hypothesis that there is a new light neutrino state.Comment: 14 pages, 9 figures. Matches version submitted to journal. Bug fixed: quantitative results changed, qualitative results and conclusions unchange

Multimessenger Astronomy and New Neutrino Physics

We discuss how to constrain new physics in the neutrino sector using multimessenger astronomical observations by the IceCube experiment. The information from time and direction coincidence with an identifiable source is used to improve experimental limits by constraining the mean free path of neutrinos from these sources. Over the coming years, IceCube is expected to detect neutrinos from a variety of neutrino-producing sources, and has already identified the Blazar TXS 0506+056 as a neutrino-producing source. We explore specific phenomenological models: additional neutrino interactions, neutrinophilic dark matter, and lepton-number-charged axion dark matter. For each new physics scenario, we interpret the observation of neutrinos from TXS 0506+056 as a constraint on the parameters of the new physics models. We also discuss mergers involving neutron stars and black holes, and how the detection of neutrinos coincident with these events could place bounds on the new physics models.Comment: 9 pages, 2 figures, matches published version. Results changed to include pseudoanalysis of TXS 0506+056 blazar neutrino data -- resulting limits improve

CP-Invariance Violation at Short-Baseline Experiments in 3+1 Neutrino Scenarios

New neutrino degrees of freedom allow for more sources of CP-invariance violation (CPV). We explore the requirements for accessing CP-odd mixing parameters in the so-called 3+1 scenario, where one assumes the existence of one extra, mostly sterile neutrino degree of freedom, heavier than the other three mass eigenstates. As a first step, we concentrate on the nu_e to nu_mu appearance channel in a hypothetical, upgraded version of the nuSTORM proposal. We establish that the optimal baseline for CPV studies depends strongly on the value of Delta m^2_14 -- the new mass-squared difference -- and that the ability to observe CPV depends significantly on whether the experiment is performed at the optimal baseline. Even at the optimal baseline, it is very challenging to see CPV in 3+1 scenarios if one considers only one appearance channel. Full exploration of CPV in short-baseline experiments will require precision measurements of tau-appearance, a challenge significantly beyond what is currently being explored by the experimental neutrino community.Comment: 11 pages, 4 figures. Matches published version; results and conclusions unchange

Origin of Sterile Neutrino Dark Matter via Vector Secret Neutrino Interactions

Secret neutrino interactions can play an essential role in the origin of dark matter. We present an anatomy of production mechanisms for sterile neutrino dark matter, a keV-scale gauge-singlet fermion that mixes with active neutrinos, in the presence of a new vector boson mediating secret interactions among active neutrinos. We identify three regimes of the vector boson's mass and coupling where it makes distinct impact on dark matter production through the dispersion relations and/or scattering rates. We also analyze models with gauged $L_\mu-L_\tau$ and $B-L$ numbers which have a similar dark matter cosmology but different vector boson phenomenology. We derive the parameter space in these models where the observed relic abundance is produced for sterile neutrino dark matter. They serve as well-motivated target for the upcoming experimental searches.Comment: 29 pages, 8 figures, comments welcome. Typos fixed. Results and conclusions unchange

Leptonic Unitarity Triangles

We present a comprehensive analysis of leptonic unitarity triangles, using both current neutrino oscillation data and projections of next-generation oscillation measurements. Future experiments, sensitive to the degree of CP violation in the lepton sector, will enable the construction of precise triangles. We show how unitarity violation could manifest in the triangles and discuss how they serve as unitarity tests. We also propose the use of Jarlskog factors as a complementary means of probing unitarity. This analysis highlights the importance of testing the unitarity of the leptonic mixing matrix, an understanding of which is crucial for deciphering the nature of the neutrino sector.Comment: Significantly updated analysis: latest NOvA and T2K results included, as well as future projections of IceCube-Gen2 and T2HK added. Matches version to appear in Phys. Rev.

Hunting On- and Off-Axis for Light Dark Matter with DUNE-PRISM

We explore the sensitivity of the Deep Underground Neutrino Experiment (DUNE) near detector and the proposed DUNE-PRISM movable near detector to sub-GeV dark matter, specifically scalar dark matter coupled to the Standard Model via a sub-GeV dark photon. We consider dark matter produced in the DUNE target that travels to the detector and scatters off electrons. By combining searches for dark matter at many off-axis positions with DUNE-PRISM, sensitivity to this scenario can be much stronger than when performing a measurement at one on-axis position.Comment: 16 pages (including 5 appendices), 11 figures. Version 2 matches published version with significant rearrangement of results (results unchanged). Version 1 contains nuclear scattering results not present in v

Constraining the Self-Interacting Neutrino Interpretation of the Hubble Tension

Large, non-standard neutrino self-interactions have been shown to resolve the $\sim 4\sigma$ tension in Hubble constant measurements and a milder tension in the amplitude of matter fluctuations. We demonstrate that interactions of the necessary size imply the existence of a force-carrier with a large neutrino coupling ($> 10^{-4}$) and mass in the keV -- 100 MeV range. This mediator is subject to stringent cosmological and laboratory bounds, and we find that nearly all realizations of such a particle are excluded by existing data unless it carries spin 0 and couples almost exclusively to $\tau$-flavored neutrinos. Furthermore, we find that the light neutrinos must be Majorana, and that a UV-complete model requires a non-minimal mechanism to simultaneously generate neutrino masses and appreciable self-interactions.Comment: 11 pages, 1 figure, 4 appendices. Version 2 matches published versio