We examine decoherence in neutrino oscillations induced by an ultralight scalar field coupled to neutrinos. The scalar induces time- and position-dependent shifts in the neutrino mass matrix. Neutrinos sample different field configurations throughout an experimental data-taking period, which leads to damping effects in the oscillation pattern in the form of decoherence. By recasting the neutrino-scalar dynamics within the open quantum systems framework, we establish a mapping between a complete model and phenomenological decoherence approaches. We find that the parameter driving decoherence scales as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>L</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><msup><mrow><mi>E</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>, where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>L</mi></math> is the baseline and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>E</mi></math> is the neutrino energy, as opposed to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>L</mi><mo>/</mo><mi>E</mi></math> typically assumed in phenomenological studies of open system approaches to neutrino oscillations.

United States

Brazil

Lua F.T. Airoldi

Gustavo F.S. Alves

Pedro A.N. Machado

Peter Vander Griend

Open system approach to neutrinos propagating in an ultralight scalar background

The determination of the neutrino mass ordering is one of the flagship goals in particle physics. A well-known and powerful synergy emerges when combining high-precision measurements of the effective atmospheric mass-squared splitting from electron antineutrino disappearance in reactor experiments with that from muon (anti)neutrino disappearance in accelerator-based long-baseline experiments. To fully exploit this synergy, percent-level precision in the atmospheric mass splitting is required—a target that JUNO is expected to achieve within a few months of data taking. This motivated the formulation of a mass ordering sum rule for neutrino disappearance channels, which shows that by combining data from T2K and NOvA with JUNO after one year of operation, the neutrino mass ordering can be determined at the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3</mn><mi>σ</mi></math> confidence level. Since JUNO has recently started taking data, it is timely to ask whether this sum rule remains robust in the presence of new physics. We identify the necessary conditions for new physics to affect the sum rule and demonstrate that, in some cases, such effects could lead to an incorrect inference of the mass ordering. As concrete examples, we consider scalar nonstandard interactions (SNSI) and neutrinos coupled to an ultralight scalar field. We find that, for SNSI, current constraints render any modification of the sum rule negligible, whereas in the latter case, the inference of the ordering requires caution. Nevertheless, these effects can be disentangled, illustrating how the sum rule can also be used to search for new physics.

Hiroshi Nunokawa

Renata Zukanovich Funchal

Impact of new physics on the JUNO-long-baseline synergy in the neutrino mass ordering determination

Current data on ultrahigh-energy (UHE) cosmic rays suggest they are predominantly made of heavy nuclei. This indicates that, in the absence of a subdominant proton component, the flux of neutrinos produced from cosmic ray collisions on the cosmic microwave background is small and hard to observe. Motivated by the recent extremely high-energy muon event reported by KM3NeT, we explore the possibility of enhancing the energy-flux of cosmogenic neutrinos through nuclear photodisintegration in the presence of new physics. Specifically, we speculate that UHE neutrons may oscillate into a new state, dark (or mirror) neutron <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>n</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow></math> that in turn decays injecting large amount of energy to neutrinos, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>n</mi><mo stretchy="false">→</mo><msup><mi>n</mi><mo>′</mo></msup><mo stretchy="false">→</mo><msub><mi>ν</mi><mi mathsize="small">UHE</mi></msub></math>. While this mechanism does not explain the tension between the KM3NeT event and null results from IceCube, it reconciles the experimental preference for a heavier cosmic ray composition with a large diffuse cosmogenic flux of UHE neutrinos.

Matheus Hostert

Maxim Pospelov

Neutron portal to ultrahigh-energy neutrinos

A black hole is expected to end its lifetime in a cataclysmic runaway burst of Hawking radiation, emitting all standard model particles with ultrahigh energies. Thus, the explosion of a nearby primordial black hole (PBH) has been proposed as a possible explanation for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><mn>220</mn><mtext> </mtext><mtext> </mtext><mi>PeV</mi></math> neutrino-like event recently reported by the KM3NeT Collaboration. If the event originated from a PBH, the source would need to lie at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>1</mn><mi>–</mi><mn>7</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>pc</mi></mrow></math>—depending on the assumed effective area—thus within the Solar System. At such proximity, the resulting flux of gamma rays and cosmic rays would be detectable at Earth. By incorporating the time-dependent field of view of gamma-ray observatories, we show that LHAASO should have recorded <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mn>10</mn><mn>8</mn></msup><mo stretchy="false">)</mo></math> events between fourteen and seven hours prior to the KM3NeT detection. IceCube and KM3NeT itself should likewise have detected of order a few hundred events in the range <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi><mo>≲</mo><msub><mrow><mi>E</mi></mrow><mrow><mi>ν</mi></mrow></msub><mo>≲</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>PeV</mi></mrow></math> during the 24 h preceding the burst. The absence of any such multimessenger signal, particularly in gamma-ray data, strongly disfavors the interpretation of the KM3-230213A event as arising from evaporation in a minimal four-dimensional Schwarzschild scenario.

Spain

Yuber F. Perez-Gonzalez

Gabriel M. Salla

Could a Primordial Black Hole Explosion Explain the Extremely High-Energy KM3NeT Neutrino Event?

The Sun is not quite a perfect sphere, and its oblateness, thought to be induced through its rotation, has been measured using optical observations of its radius. Its gravitational quadrupole moment can then be deduced using solar models, or through helioseismology, and it can also be determined from measurements of its gravitational effects on Mercury’s orbit. The various assessments do not appear to agree, with the most complete and precise orbital assessments being in slight excess of other determinations. This may speak to the existence of a nonluminous disk or ring, where we also note evidence for a circumsolar dust ring within Mercury’s orbit from the Solar TErrestrial RElations Observatory (STEREO) mission. Historically, too, a protoplanetary disk may have been key to reconciling the Sun’s metallicity with its neutrino yield. The distribution of the nonluminous mass within Mercury’s orbit can modify the relative size of the optical and orbital quadrupole moments in different ways. We develop how we can use these findings to limit the mass of a dark disk, ring, or halo in the immediate vicinity of the Sun, and we note how future observational studies of the inner Solar System can not only refine these constraints but can also help to identify and to assess the mass of its dark-matter component.

Susan Gardner

Pedro Machado

Mohammadreza Zakeri

Does the Sun have a dark disk?

Heavy neutral leptons (HNLs), depending on their mass and mixing, can be efficiently produced in meson decays from the target or absorber in short- to medium-baseline accelerator neutrino experiments, leaving detectable signals through their decays inside the neutrino detectors. We show that the currently running ICARUS experiment at Fermilab can reconstruct the HNL mass and explore new HNL parameter space in the mass range of 70–190 MeV. The mass reconstruction is enabled by two ingredients: (i) simple two-body kinematics of HNL production from stopped kaon decays at the NuMI absorber, followed by HNL decay into a charged-lepton pair and neutrino at the detector, and (ii) high resolution of Liquid Argon Time Projection Chamber (LArTPC) detectors in reconstructing final state particles. Our mass reconstruction method is robust under realistic energy resolution and angular smearing of the charged leptons, and is applicable to any LArTPC detector. We also discuss the synergy between ICARUS and future facilities like DUNE near detector and PIP-II beam dump in probing the HNL parameter space.

P.S. Bhupal Dev

Kevin J. Kelly

Mass reconstruction of heavy neutral leptons from stopped mesons