An elusive vector dark matter

Even though the sensitivity of direct dark matter search experiments reaches the level of about 10^-45cm², no confident signal of dark matter has been observed. We point out that, if dark matter is a vector boson, the null result in direct dark matter search experiments may be due to the destructive effects in dark-matter-nucleon elastic scattering. We illustrate the scenario using a modified Higgs portal model that includes exotic quarks. The significant cancellation can occur for a certain mass gap between new heavy quark and dark matter. As a result, the spin-independent dark-matter-nucleon elastic scattering is so suppressed that the future direct search experiments will hardly observe the signal of dark matter.