Sterile Neutrino Search with MicroBooNE's Electron Neutrino Disappearance Data.

A sterile neutrino is a well motivated minimal new physics model that leaves an imprint in neutrino oscillations. Over the last two decades, a number of hints pointing to a sterile neutrino have emerged, many of which are pointing near m_{4}∼1 eV. Here, we show how MicroBooNE data can be used to search for electron neutrino disappearance using each of their four analysis channels. We find a hint for oscillations with the highest single channel significance of 2.4σ (using the Feldman-Cousins approach) coming from the Wire-Cell analysis and a simplified treatment of the experimental systematics. The preferred parameters are sin^{2}(2θ_{14})=0.35_{-0.16}^{+0.19} and Δm_{41}^{2}=1.25_{-0.39}^{+0.74} eV^{2}. This region of parameter space is in good agreement with existing hints from source experiments, is at a similar frequency but higher mixing than indicated by reactor antineutrinos, and is at the edge of the region allowed by solar neutrino data. Existing unanalyzed data from MicroBooNE could increase the sensitivity to the >3σ level.

Supermassive Black Holes, Ultralight Dark Matter, and Gravitational Waves from a First Order Phase Transition.

The formation of ultrarare supermassive black holes (SMBHs), with masses of O(10^{9} M_{⊙}), in the first billion years of the Universe remains an open question in astrophysics. At the same time, ultralight dark matter (DM) with mass in the vicinity of O(10^{-20} eV) has been motivated by small scale DM distributions. Though this type of DM is constrained by various astrophysical considerations, certain observations could be pointing to modest evidence for it. We present a model with a confining first order phase transition at ∼10 keV temperatures, facilitating production of O(10^{9} M_{⊙}) primordial SMBHs. Such a phase transition can also naturally lead to the implied mass for a motivated ultralight axion DM candidate, suggesting that SMBHs and ultralight DM may be two sides of the same cosmic coin. We consider constraints and avenues to discovery from superradiance and a modification to N_{eff}. On general grounds, we also expect primordial gravitational waves-from the assumed first order phase transition-characterized by frequencies of O(10^{-12}-10^{-9} Hz). This frequency regime is largely uncharted, but could be accessible to pulsar timing arrays if the primordial gravitational waves are at the higher end of this frequency range, as could be the case in our assumed confining phase transition.

CP-Violating Neutrino Nonstandard Interactions in Long-Baseline-Accelerator Data.

Neutrino oscillations in matter provide a unique probe of new physics. Leveraging the advent of neutrino appearance data from NOvA and T2K in recent years, we investigate the presence of CP-violating neutrino nonstandard interactions in the oscillation data. We first show how to very simply approximate the expected NSI parameters to resolve differences between two long-baseline appearance experiments analytically. Then, by combining recent NOvA and T2K data, we find a tantalizing hint of CP-violating NSI preferring a new complex phase that is close to maximal: ϕ_{eµ} or ϕ_{eτ}≈3π/2 with |ε_{eµ}| or |ε_{eτ}|∼0.2. We then compare the results from long-baseline data to constraints from IceCube and COHERENT.

Ultralight Boson Dark Matter and Event Horizon Telescope Observations of M87

The initial data from the Event Horizon Telescope (EHT) on M87^{*}, the supermassive black hole at the center of the M87 Galaxy, provide direct observational information on its mass, spin, and accretion disk properties. A combination of the EHT data and other constraints provides evidence that M87^{*} has a mass ∼6.5×10^{9} M_{⊙}. EHT also inferred the dimensionless spin parameter |a^{*}|≳0.5 from jet properties; a separate recent analysis using only the light from near M87^{*} as measured by the EHT Collaboration found |a^{*}|=0.9±0.1. These determinations disfavor ultralight bosons of mass µ_{b}∈(0.85,4.6)×10^{-21} eV for spin-one bosons and µ_{b}∈(2.9,4.6)×10^{-21} eV for spin-zero bosons, within the range considered for fuzzy dark matter, invoked to explain dark matter distribution on approximately kiloparsec scales. Future observations of M87^{*} could be expected to strengthen our conclusions.

Invisible Neutrino Decay Could Resolve IceCube's Track and Cascade Tension.

The IceCube Neutrino Observatory detects high energy astrophysical neutrinos in two event topologies: tracks and cascades. Since the flavor composition of each event topology differs, tracks and cascades can be used to test the neutrino properties and the mechanisms behind the neutrino production in astrophysical sources. Assuming a conventional model for the neutrino production, the IceCube data sets related to the two channels are in >3σ tension with each other. Invisible neutrino decay with lifetime τ/m=10^{2} s/eV solves this tension. Noticeably, it leads to an improvement over the standard nondecay scenario of more than 3σ while remaining consistent with all other multimessenger observations. In addition, our invisible neutrino decay model predicts a reduction of 59% in the number of observed ν_{τ} events which is consistent with the current observational deficit.