Invisible Axion-Like Dark Matter from Electroweak Bosonic Seesaw

We explore a model based on the classically-scale invariant standard model (SM) with a strongly coupled vector-like dynamics, which is called hypercolor (HC). The scale symmetry is dynamically broken by the vector-like condensation at the TeV scale, so that the SM Higgs acquires the negative mass-squared by the bosonic seesaw mechanism to realize the electroweak symmetry breaking. An elementary pseudoscalar S is introduced to give masses for the composite Nambu-Goldstone bosons (HC pions): the HC pion can be a good target to explore through a diphoton channel at the LHC. As the consequence of the bosonic seesaw, the fluctuating mode of S, which we call s, develops tiny couplings to the SM particles and is predicted to be very light. The s predominantly decays to diphoton and can behave as an invisible axion-like dark matter. The mass of the s-dark matter is constrained by currently available cosmological and astrophysical limits to be 10eV < ∼ ms < ∼ 1 eV. We find that the sufficient amount of relic abundance for the s-dark matter can be accumulated via the coherent oscillation. The detection potential in microwave cavity experiments is also addressed.