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Ultralight Scalar Dark Matter with Off-Diagonal Flavor Couplings

Jinhui Guo, Jia Liu, Chenhao Peng, Xiao-Ping Wang, Hang Zhao

Abstract

Ultralight dark matter can behave as a coherent background field and induce time-dependent modifications of Standard Model parameters. We study a scenario in which a real ultralight scalar $φ$ couples off-diagonally to down-type quarks, linking ultralight dark sectors to flavor physics. Working within an effective field theory, we diagonalize the quark mass matrix in a coherent $φ$ background and derive analytic expressions for oscillatory shifts in down-type quark masses and CKM parameters. These effects lead to signatures in both the classical regime, where $φ$ acts as a background field, and the quantum (particle) regime, where it contributes through on-shell production or off-shell mediation. Using precision flavor measurements, nuclear $β$ decays, atomic clocks, pulsar timing, and meson observables, we derive constraints on the flavor-violating couplings $λ_{ij}$ for $m_φ\sim 10^{-24}$--$10^{-12}\,\mathrm{eV}$, highlighting the complementarity of time-domain and flavor probes of ultralight dark sectors.

Ultralight Scalar Dark Matter with Off-Diagonal Flavor Couplings

Abstract

Ultralight dark matter can behave as a coherent background field and induce time-dependent modifications of Standard Model parameters. We study a scenario in which a real ultralight scalar couples off-diagonally to down-type quarks, linking ultralight dark sectors to flavor physics. Working within an effective field theory, we diagonalize the quark mass matrix in a coherent background and derive analytic expressions for oscillatory shifts in down-type quark masses and CKM parameters. These effects lead to signatures in both the classical regime, where acts as a background field, and the quantum (particle) regime, where it contributes through on-shell production or off-shell mediation. Using precision flavor measurements, nuclear decays, atomic clocks, pulsar timing, and meson observables, we derive constraints on the flavor-violating couplings for --, highlighting the complementarity of time-domain and flavor probes of ultralight dark sectors.
Paper Structure (18 sections, 78 equations, 4 figures)

This paper contains 18 sections, 78 equations, 4 figures.

Table of Contents

  1. Introduction
  2. A Flavor-violating ULDM Model
  3. Classical Interpretation
  4. Quantum Interpretation
  5. Constraints on ULDM as a Coherent Background Field
  6. Direct Measurement of CKM Matrix
  7. Nuclear Beta Decay
  8. Tritium Decays
  9. Constraints from Quark Mass Measurements
  10. Atomic Clocks
  11. Meson Mixing from a ULDM Background Field
  12. Constraints on the ULDM Field as a Quantum Particle
  13. Quark-flavor Violating Decays
  14. Constraint from Meson Oscillations
  15. Exotic Force Measurements
  16. ...and 3 more sections

Figures (4)

  • Figure 1: Two equivalent viewpoints: re-diagonalization in the presence of a ULDM background (mass mixing), and perturbation theory in the SM mass basis.
  • Figure 2: Representative one-loop diagram for the induced fifth force: $d_i(p_1)d_k(k_1)\to d_i(p_2)d_k(k_2)$ via exchange of two virtual mediators $\phi$, with $d_i$ the $i$th generation of down-type quarks and $p_i$, $k_i$, $\ell$ the momenta.
  • Figure 3: Periodogram corresponding to the dataset, along with the MC-derived $95\%$ confidence level threshold and upper limit. The data are compatible with the null hypothesis.
  • Figure 4: Comparison of the constraints on ULDM derived from NANOGrav NANOGrav:2023hvm and Yb/Cs clocks Sherrill:2023zahKobayashi:2022vsf as well as Sr/H/Si clocks Kennedy:2020bac, tritium beta decay tritiumdecay, ${}^{37}\mathrm{K}$ decay Shidling:2014ura, meson decay Belle-II:2023esiNA62:2020xlgBelle:2017oht, and $\mathrm{Rb/Quartz}$ clock Zhang:2022ewz. The black line represents $|\lambda_{ij}\bar{\phi}/(m_i-m_j)|$.