Parametric Resonance of Higgsed Vector Dark Matter: Inflationary Initial Conditions and Sourced Displacements

Parametric resonance in a Higgsed Abelian sector provides an efficient mechanism for producing vector dark matter, but its viability depends crucially on the origin of the initial dark-Higgs displacement that seeds the resonance. In this work, we investigate this initial-condition problem in a weakly coupled Abelian-Higgs theory with potential $V=\lambda_4(\phi^2-v^2)^2/4$, using the calibrated nonlinear broad-resonance relic map together with a stochastic inflationary analysis of the dark-Higgs condensate. We show that a minimal light-spectator realization fails under standard inflationary duration: while broad resonance and isocurvature constraints require $\phi_0/H_I \gtrsim 3.3\times10^4,$ the stochastic equilibrium and finite-duration random walk produce only $\phi/H_I=\mathcal O(1).$ This large displacement mismatch is robust against order-of-magnitude variations in the resonance efficiency and broadness threshold, establishing a model-independent obstruction to the stochastic branch. We then identify a distinct classically sourced branch, generated by a negative Hubble-induced mass, in which the condensate tracks a time-dependent minimum, $\phi_0=\kappa H_*/\sqrt{\lambda_4},$ and the radial fluctuation remains heavy during inflation. In this case, the fixed-$e/\lambda_D$ relic scaling shifts from $m_X\propto \lambda_4^{5/8}H_I^{-3/2}$ to $m_X\propto \kappa^{-3/2}\lambda_4 H_*^{-3/2}.$ We derive the simultaneous consistency conditions for this sourced branch, including broad resonance, adiabatic tracking, perturbativity, sub-Planckian displacement, thermal non-erasure, spectator backreaction, and control of inflationary vector fluctuations. Our results establish that Higgsed-vector resonance is not merely a dark-matter production mechanism, but a sensitive probe of the inflationary and reheating dynamics that determine its initial conditions.