SITP sign on 3rd floor of the Varian Physics Building
Fifth force and equivalence principle tests search for new interactions by precisely measuring forces between macroscopic collections of atoms and molecules and their properties under free fall. In contrast, the early Universe plasma probes these interactions at a more fundamental level. In this talk, I will consider the case of a scalar mediating a fifth force, and show that the effects of dimensional transmutation, spontaneous symmetry breaking, and the running of the gauge couplings cause the scalar's low-energy interactions to mix, leading to nearly universal dynamics at early times. Known expressions for the pressure of the Standard Model during its various epochs can be used to compute the scalar's effective potential. We find that the cosmological dynamics of this scalar are very sensitive to the reheat temperature of the Universe. Given the unknown reheat temperature, scalar couplings to matter larger than ∼10^−6(m_ϕ/eV)^−1/4 relative to gravity produce the correct dark matter abundance, thereby linking fifth force experiments to the search for dark matter and motivating new physics searches in this part of parameter space.