We introduce the first step of the TCV-ϕ programme, in which late-time cosmological expansion and cold dark matter are reinterpreted in terms of a cohesive vacuum carrying two scalar degrees of freedom. At the effective field theory level, the model contains a structural scalar field Φ1 and a light coherent field Φ2, coupled to gravity through a slightly non-minimal effective Planck mass and a simple cohesive potential. This first paper focuses on the homogeneous cosmological background and the linear matter power spectrum. For a reasonable benchmark set of parameters, the background expansion history H(z) is shown to be practically indistinguishable from standard ΛCDM, while Φ2 naturally behaves as an ultra-light dark matter component once H ≪ m2. Interfacing the framework with CLASS and using a fuzzy-dark-matter transfer function yields a matter power spectrum that remains ΛCDM-like on large scales and exhibits the expected small-scale suppression associated with ultra-light dark matter. In this first contribution, scalar masses, self-couplings and the initial misalignment of Φ2 are treated as phenomenological EFT parameters, with a full confrontation to CMB and large-scale structure data deferred to later work.
Cyrille Lecroq (Thu,) studied this question.