Ultralight Scalar Dark Matter with Off-Diagonal Flavor Couplings

TL;DR

This paper explores how ultralight scalar dark matter with off-diagonal flavor couplings can cause observable time-dependent effects in flavor physics, providing new constraints from various precision measurements.

Contribution

It introduces a novel model linking ultralight dark matter to flavor physics via off-diagonal couplings and derives analytic expressions for induced effects on quark masses and CKM parameters.

Findings

Constraints on flavor-violating couplings $bb_{ij}$ for $m_bphi \,\sim\, 10^{-24}$--$10^{-12}$ eV.

Identification of signatures in both classical and quantum regimes of ultralight scalar interactions.

Demonstration of the complementarity between time-domain measurements and flavor observables in probing dark sectors.

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 $\phi$ 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 $\phi$ 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 $\phi$ 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 $\beta$ decays, atomic clocks, pulsar timing, and meson observables, we derive constraints on the flavor-violating couplings $\lambda_{ij}$ for $m_\phi \sim 10^{-24}$--$10^{-12}\,\mathrm{eV}$, highlighting the complementarity of time-domain and flavor probes of ultralight dark sectors.