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Implications for new physics solutions to the LSND and MiniBooNE anomalies after MicroBooNE results

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Waleed Abdallah, Raj Gandhi, Samiran Roy

High Energy Physics - Phenomenology · Submitted 12 Oct 2026 · 130 references

Pith's verdict: A capable but incremental model-building paper for the LSND/MiniBooNE anomalies that is thorough in its survey of MicroBooNE constraints and honest about its own limitations, though its central idea and parameter choices are not novel.

T0 · AI review

How this review was made: An AI referee (deepseek/deepseek-v4-flash) read the paper on October 14, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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arXiv ID2610.17207 (version 1)
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CitationRaj Gandhi, Samiran Roy, Waleed Abdallah. "Implications for new physics solutions to the LSND and MiniBooNE anomalies after MicroBooNE results." arXiv:2610.17207 (2026). https://pith.science/paper/GS47SED4
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The paper

The paper claims

A light pseudoscalar mediator with dominantly pseudoscalar couplings can account for the LSND and MiniBooNE anomalies after MicroBooNE constraints.

The reading

For over two decades, the LSND and MiniBooNE neutrino experiments have seen more electron-like events than expected from known backgrounds. These events could be caused by electrons, photons, or electron-positron pairs, since the detectors could not tell them apart. The newer MicroBooNE experiment, with its improved particle identification, has ruled out explanations based solely on extra electrons and placed strong limits on coherent photon or pair production. This paper reviews which theoretical proposals survive these new constraints and finds that models with a new light mediator that decays to electron-positron pairs via incoherent scattering are favored. The authors present a concrete model featuring a pseudoscalar particle about 17 MeV in mass that couples to quarks and a heavy neutral lepton. In the detector, a neutrino scatters off a nucleon, producing the heavy neutral lepton and the pseudoscalar, which then decays to an electron-positron pair. The model fits both the energy and angular distributions of the excess events in LSND and MiniBooNE. The paper also discusses necessary conditions, such as the neutrinos being Dirac particles to avoid large quantum corrections, and the need for extremely small CP violation to satisfy electric dipole moment limits. The authors acknowledge that the model is an effective theory and that its ultraviolet completion remains an open question.
Extended reading notes

Core claim

We point out that a light (m≤30 MeV) dark neutral spin zero mediator with dominantly pseudoscalar couplings, decaying to an e+e− pair, can account for the observations. (Section 1, sentence [b6])

Load-bearing premise

The assumption that neutrinos are Dirac particles (imposed via a Z2 symmetry in the Lagrangian of Section 3.1) is essential to avoid large one-loop corrections to SM neutrino masses from the a′-N loop. If neutrinos are Majorana, these corrections would likely rule out the model. This is explicitly discussed in Section 4 as a motivating reason for the Dirac choice.

Original abstract

Over the past couple of decades, the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE (MB) neutrino experiments have provided statistically significant evidence of persistent and as yet unexplained electron-like event excesses. The MicroBooNE experiment, with sensitive particle identification capabilities designed to shed light on these anomalous results, has conducted a number of analyses to test whether the excess is due to photons, electrons or $e^+e^-$ pair productions, all of which give almost identical signals in LSND and MB. Recent MicroBooNE searches, in addition to checking Standard Model (SM) processes, have focused on proposed new physics scenarios involving new mediators and dark portals beyond the SM. We study the consequences and effects of these analyses for the many theoretical proposals put forth to generate the three types of signals above in order to understand the observed excesses. We discuss which classes of solutions are allowed, disallowed or require further scrutiny involving theoretical and experimental efforts. We give an example of a new solution that survives the restrictions imposed by MicroBooNE results and other existing bounds. We point out that a light ($m\leq 30$ MeV) dark neutral spin zero mediator with dominantly pseudoscalar couplings, decaying to an $e^+e^-$ pair, can account for the observations. We indicate that if such a model is realised, it may point to the possibility that neutrinos are Dirac particles, and that there are dark Heavy Neutral Leptons (HNLs) of mass ${\cal O}(100)$ MeV. We discuss issues related to CP violation and ultra-violet completion of these models. Finally we stress that a search for the excess in incoherent scattering channels in MicroBooNE and SBND could help clarify the physics behind these persistent anomalies.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-10-14: 1 request, 7,857 input tokens.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.36 · human participants 0.02 · controlled comparison 0.11 · randomized assignment 0.01 · states quantitative result 0.91 · compares with prior results 0.78 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

Over the past couple of decades, the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE (MB) neutrino experiments have provided statistically significant evidence of persistent and as yet unexplained electron-like event excesses. The MicroBooNE experiment, with sensitive particle identification capabilities designed to shed light on these anomalous results, has conducted a number of analyses to test whether the excess is due to photons, electrons or $e^+e^-$ pair productions, all of which give almost identical signals in LSND and MB. Recent MicroBooNE searches, in addition to checking Standard Model (SM) processes, have focused on proposed new physics scenarios involving new mediators and dark portals beyond the SM. We study the consequences and effects of these analyses for the many theoretical proposals put forth to generate the three types of signals above in order to understand the observed excesses. We discuss which classes of solutions are allowed, disallowed or require further scrutiny involving theoretical and experimental efforts. We give an example of a new solution that survives the restrictions imposed by MicroBooNE results and other existing bounds. We point out that a light ($m\leq 30$ MeV) dark neutral spin zero mediator with dominantly pseudoscalar couplings, decaying to an $e^+e^-$ pair, can account for the observations. We indicate that if such a model is realised, it may point to the possibility that neutrinos are Dirac particles, and that there are dark Heavy Neutral Leptons (HNLs) of mass ${\cal O}(100)$ MeV. We discuss issues related to CP violation and ultra-violet completion of these models. Finally we stress that a search for the excess in incoherent scattering channels in MicroBooNE and SBND could help clarify the physics behind these persistent anomalies.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 Over the past couple of decades, the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE (MB) neutrino experiments have provided statistically significant evidence of persistent and as yet unexplained electron-like event excesses. background 1.00 0.04 0.02 asserted 0.99
s1 The MicroBooNE experiment, with sensitive particle identification capabilities designed to shed light on these anomalous results, has conducted a number of analyses to test whether the excess is due to photons, electrons or $e^+e^-$ pair productions, all of which give almost identical signals in LSND and MB. background 0.81 0.10 0.02 asserted 0.98
s2 Recent MicroBooNE searches, in addition to checking Standard Model (SM) processes, have focused on proposed new physics scenarios involving new mediators and dark portals beyond the SM. background 0.93 0.08 0.02 asserted 1.00
s3 We study the consequences and effects of these analyses for the many theoretical proposals put forth to generate the three types of signals above in order to understand the observed excesses. contribution 1.00 0.81 0.05 asserted 0.74
s4 We discuss which classes of solutions are allowed, disallowed or require further scrutiny involving theoretical and experimental efforts. contribution 0.90 0.70 0.07 asserted 0.59
s5 We give an example of a new solution that survives the restrictions imposed by MicroBooNE results and other existing bounds. contribution 0.84 0.86 0.17 asserted 0.98
s6 We point out that a light ($m\leq 30$ MeV) dark neutral spin zero mediator with dominantly pseudoscalar couplings, decaying to an $e^+e^-$ pair, can account for the observations. result 0.75 0.80 0.59 asserted 0.59
s7 We indicate that if such a model is realised, it may point to the possibility that neutrinos are Dirac particles, and that there are dark Heavy Neutral Leptons (HNLs) of mass ${\cal O}(100)$ MeV. interpretation 1.00 0.61 0.16 hedged possibility 1.00
s8 We discuss issues related to CP violation and ultra-violet completion of these models. contribution 0.79 0.52 0.03 unclear 0.86
s9 Finally we stress that a search for the excess in incoherent scattering channels in MicroBooNE and SBND could help clarify the physics behind these persistent anomalies. future work 1.00 0.22 0.19 hedged possibility 0.98

What kind of paper the classifier reports this is: theoretical result 0.54 · evidence from analysis of existing data 0.42.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Feynman diagram of the scattering process via the trilinear pseudoscalar coupling, which leads to the MB and LSND excesses in our model. finds the following coupling strengths of the scalars h, H, A, and a ′ with fermions: y h f = √ 2 mf v , yH f = yf , yA f = yf cξ, ya ′ f = yf sξ, λA N = λN sξ, and λ a ′ N = λN cξ . (3.12) 3.2 The interaction in MB and LSND The relevant renormalizable interaction Lagrangian is −L ⊃ κ a′3 + y a ′ q a ′ q γ¯ 5 q + (y a ′ νµN a ′ N γ ¯ 5 PL νµ + h.c.), (3.13) where PL = 1 2 (1 − γ5) and κ, in our model, is given by: κ = 3
Figure 2. Reduced chi-squared, χ 2/dof, as a function of the heavy neutrino mass MN . The colored points show the individual contributions from the MB energy (red), MB angular (green), LSND energy (blue), and LSND angular (orange) distributions, while the black curve represents the total reduced chi-squared obtained by summing all contributions. bin, respectively. Assuming Poisson statistics, the statistical uncertainty is approximated by the observed number of events (σ 2 stat,i ≃ Nobs i ). The MB collaboration has provided only the systematic uncertainty in the energy distribution [92],…
Figure 3. Top panels: These show, for neutrino runs, the MB electron-like events (backgrounds and signal). They are plotted against the visible energy Evis (left panel) and the emitted angle of the Cerenkov light (right panel). The blue solid line denotes the central prediction of excess events in our model. Bottom panels: These show the energy distribution (left panel) of the LSND data the angular distribution (right panel) of the light originating from the electron-like final state. In both panels, the shaded blue region represents our fit with an uncertainty band, and other shaded regions…
Figure 4. Sample Feynman diagrams of dipole moment contributions. (a) Two-loop Barr-Zee diagram with the SM fermions f running in the loop. The same diagram with the W-boson and charged Higgses instead of f can contribute to the eEDM. (b) Three-loop Barr-Zee diagram through the trilinear coupling of a ′ . (c) Four-quark diagram contributing to the neutron dipole moment. de γ(a') de γ(h) dn 4 f ACME 10-5 10-4 0.001 0.010 0.100 10-33 10-31 10-29 10-27 θCP eEDM (e cm )
Figure 5. Left: The eEDM contributions from the a ′ , h and neutron diagrams versus the CP phase angle θCP. The horizontal gray dashed line refers to the ACME upper bound (1.1 × 10−29 e cm). Right: Regions allowed by the ACME upper bound in the θ − θCP plane. and d γ e (a ′ ), respectively. However, the a ′ contribution to the two-loop Barr-Zee diagrams is larger than the SM Higgs contribution by two orders of magnitude, as shown in left panel of figure 5. The reason is that the a ′ coupling with the SM light fermions in our model, in particular with the electron pair, is enhanced by a
Figure 6. Prediction of incoherent events in MicroBooNE and SBND. Future experiments: Experimentally, important avenues for further investigation are linked to the Fermilab Short Baseline Neutrino (SBN) program [120, 121]. This consists of three liquid Argon based Time-Projection Chamber detectors fed by the Booster Neutrino Beam (BNB) and includes MicroBooNE. Their overall improved particle-identification capabilities provide greater discriminating power between electron, photon and e +e − events. In the near future, data from MicroBooNE on incoherent scattering events (to complement their…

Figures reproduced from arXiv:2610.17207 by the authors.

References

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