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We study the influence of running vacuum on the baryon-to-photon ratio inrunning vacuum models (RVMs). When there exists a non-minimal coupling betweenphotons and other matter in the expanding universe, the energy-momentum tensorof photons is no longer conserved, but the energy of photons could remainconserved. We discuss the conditions for the energy conservation of photons inRVMs. The photon number density and baryon number density, from the epoch ofphoton decoupling to the present day, are obtained in the context of RVMs byassuming that photons and baryons can be coupled to running vacuum,respectively. Both cases lead to a time-evolving baryon-to-photon ratio.However the evolution of the baryon-to-photon ratio is strictly constrained byobservations. It is found that if the dynamic term of running vacuum is indeedcoupled to photons or baryons, the coefficient of the dynamic term must beextremely small, which is unnatural. Therefore, our study basically rules outthe possibility that running vacuum is coupled to photons or baryons in RVMs.

Constraints on running vacuum models with the baryon-to-photon ratio