Effective Field Theory Description of Light Dilaton

Abstract

Dilatons, the CP-even pseudo-Nambu-Goldstone bosons arising from spontaneous scale symmetry breaking, offer a compelling alternative to axion-like particles (ALPs) yet lack a comprehensive low-energy framework. We address this by constructing a systematic effective field theory (EFT) for the dilaton based on a manifestly scale-invariant regularization scheme. This approach derives universal linear couplings to the trace anomaly while preserving consistent renormalization group evolution. We establish a hierarchical EFT tower connecting the ultraviolet conformal sector to the infrared, encompassing the dilaton-extended SMEFT, low-energy EFT up to dimension-7, and a chiral Lagrangian describing meson and baryon interactions. We perform a comprehensive phenomenological analysis across two distinct mass regimes, where dilaton manifests as either conventional particle or wave-like particle. For MeV-scale dilatons behaving as conventional particles, we obtain constraints from LHC production, semi-invisible $B$- and $K$-meson decays, and supernova cooling. For ultralight dilatons acting as dark matter, we project sensitivities for atomic clocks and atom interferometers. This unified EFT framework would pave the way for extended phenomenological studies across the full mass spectrum of the light dilaton.

Figures (6)

• Figure 1: Schematic hierarchy of energy scales associated with the dilaton EFTs constructed in this work. The figure also shows the dilaton couplings to gauge bosons, quarks and nucleons, which serve as inputs for the phenomenological analyses. These interactions can be probed via LHC searches, flavor-changing neutral currents (FCNCs), supernova cooling, and---assuming the dilaton accounts for the observed DM abundance---precision measurements of time-varying fundamental constants.
• Figure 2: Representative Feynman diagrams for the signal process $pp\to j\chi$.
• Figure 3: Representative one-loop Feynman diagrams for $B^+\rightarrow K^+\chi$ channel.
• Figure 4: Constraints on the dilaton VEV $f_\chi$. The purple shadows denotes the exclusion from HL-LHC. The blue shadows represents the exclusion at Belle II collaboration Belle-II:2023esi, while green shadow is the excluded regions at NA62 collaboration NA62:2021zjw. The gray dashed contour indicates the approximate exclusion derived from the SN1987A Kamiokande-II:1987idp.
• Figure 5: Sensitivity projections for the dilaton VEV $f_\chi$ as a function of dilaton mass $m_\chi$. Red curves depict the SNR = 1 sensitivity envelops of the Yb$^+$/Al$^+$ clock comparison experiment, for $\tau_\text{int}=10^4,10^8$ s (deep red, light coral). Also depicted are sensitivities of different AION stages.