Higgs-Portal Scalar-Field Collapse From Non-Markovian Dynamics to Viable CSL Limit

We propose and analyze a model of objective wave-function collapse induced by a light real scalar field ϕ coupled to the mass density of matter via a Higgs portal interaction. The model aims to provide a microscopic origin for continuous spontaneous localization (CSL)–type dynamics while remaining compatible with particle physics, astrophysical, interferometric, and non-interferometric constraints.Starting from a concrete Higgs-portal Lagrangian, we derive the non-Markovian master equation for the reduced density matrix of matter obtained by integrating out ϕ in a general Gaussian state. We show that for a massive scalar field in thermal equilibrium (including the vacuum) the Markovian limit required to recover a CSL-like Lindblad term vanishes identically: the time-integrated symmetrized field correlator defining the would-be Markovian kernel is zero for mϕ= ̸ = 0, reflecting theabsence of noise power at zero frequency in the Kallen–Lehmann spectral represen tation. This provides a simple but robust “no-go” result: a standard equilibrium massive quantum field cannot generate a white-noise collapse term of CSL type.We then introduce a phenomenological non-equilibrium scalar noise parameterized by a dimensionless IR-enhancement factor Xϕ and derive the mapping between the scalar–nucleon coupling gs, the correlation length rC, and the effective CSLcollapse rate λ. Using the Higgs-portal structure, we relate gs to the mixing angle θ and the portal coupling λHS and confront the model with (i) astrophysical bounds on fifth forces and stellar cooling, (ii) collider limits on invisible Higgs decays andHiggs–scalar mixing, and (iii) non-interferometric CSL constraints from X-ray emission, bulk heating, cold atoms, LISA Pathfinder and planetary heating. We show that there exists a viable region of parameter space with mϕ ∼ eV, rC ∼ 200nm,gs ≲ 10e−13, λ_HS ∼ 10e−11 and λ ≲ 2×10e−12 s−1 which satisfies simultaneously all current bounds while remaining testable with next-generation experiments.The required non-equilibrium enhancement of the scalar noise is modest: match ing our conservative upper bound only demands Xϕ ∼ 2−20, which can be naturally realized in simple cosmological scenarios (such as a misalignment-like coherentcondensate or non-thermal freeze-in production of infrared modes) without overproducing the scalar energy density. For these parameters, we find that the predicted additional decoherence is utterly negligible (≲ 0.06%) for all matter-wave interference experiments performed to date (M ∼ 10^4−10^5 amu, coherence times ∼ 10 ms), but becomes potentially observable (0.2−2% loss of visibility for 10 ms, scaling to ∼10% for 50 ms) for next-generation interferometers targeting M ∼ 10^6 amu.Our analysis clarifies both the promise and the limitations of Higgs-portal scalar field collapse models: they offer a concrete, testable UV completion of CSL tightly linked to particle physics, but they necessarily require the scalar sector to reside ina persistent non-equilibrium,effectively classical state whose detailed microphysical origin remains to be fully understood.. NB: "This is personal/unfunded research."