Cosmological Evolution of the Higgs Vacuum Expectation Value in Emergent Gravity
In a generally covariant theory whose Lagrangian density contains no derivatives of the metric, the spacetime geometry is fixed algebraically by the scalar fields, and the simplest quadratic potential is known to generate exponentially expanding, recollapsing and big-rip cosmologies. We extend this emergent-gravity Higgs cosmology by one new spacelike scalar field - the vacuum-expectation-value generating field - coupled to the Higgs particle through the Standard Model potential, so that the electroweak vacuum expectation value becomes a dynamical quantity evolving with cosmological time. We show that the broken-symmetry valley of the potential is an exact and stable solution of the full nonlinear system, on which the background is solved in closed form in terms of a single conserved charge. The charge feeds the Friedmann equation with a radiation-like component of purely geometric origin, diluting with the inverse fourth power of the scale factor although no radiation fluid is present; as a consequence the universe is born at a finite cosmological time in a radiation-dominated big bang, and for vanishing constant term in the potential the expansion history realizes a spontaneous radiation-to-dark-energy sequence. The sign of the Higgs kinetic term is not an assumption of the model: the requirement that the broken phase be the physical vacuum fixes it dynamically, and the stable choice reproduces the Standard Model relation between the Higgs mass, the self-coupling and the vacuum expectation value with no adjustable parameter. Oscillations about the valley describe a Higgs condensate which is frozen at early times, begins to oscillate through a misalignment mechanism, obeys a parameter-free adiabatic amplitude law, and backreacts on the expansion history as a definite renormalization of the background constants that feeds the radiation-like component.