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 alightreal scalar field ϕ coupled to the mass density of matter viaa Higgs-portal interaction. Themodel aims to provide a microscopic origin for continuous spontaneous localization (CSL)–type dynamics while remaining compatible with particle physics, astrophysical, and non-interferometric collapse 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 field correlator defining the would-be Markovian kernel is zero for m_ϕ= ̸=0. This provides a simple“no-go” result: a standard equilibrium 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 amplification factor X_ϕ and derive the mapping between the scalar–nucleon coupling gs and the CSL collapse rate λ as a function of the correlation length r_C. Using theHiggs-portal structure, we relate gs to the mixing angle θ and portal coupling λHS and confront the model with (i) astrophysical bounds on fifth-forces and stellar cooling, (ii) collider limits on invisible Higgs decays and Higgs–scalar mixing, and (iii) non-interferometric CSL constraints from X-ray emission, bulk heating, cold atoms, LISA Pathfinder and planetary heating. We show that the reexists aviable region of parameter space with mϕ∼eV, r_C∼200nm, gs≲10e-13, λ_HS∼10e−11 and λ∼10e12s−1 which satisfies simultaneously all current constraints while providing a potentially observable collapse rate for mesoscopic systems. Our analysis clarifies both the promise and limitations of Higgs-portal scalar field collapse models : they offer a concrete, testable UV completion for CSL, but require the scalar sector to be in a non-equilibrium, effectively classical state whose microscopic origin remains to be explained. NB: "This is personal/unfunded research."