On the minimal monochromatic K4-density

We use Razborov's flag algebra method to show a new asymptotic lower bound for the minimal density $m_4$ of monochromatic $K_4$'s in any 2-coloring of the edges of the complete graph $K_n$ on $n$ vertices. The hitherto best known lower bound was obtained by Giraud, who proved that m_4>1/46, whereas the best known upper bound by Thomason states that m_4<1/33. We can show that m_4>1/35.