Self Coupling of the Higgs boson in the processes   $p\,p\,\rightarrow\,ZHHH+X$ and $p\,p\,\rightarrow\,WHHH+X$
  To gain some sense about the likelihood of measuring the Higgs boson quartic coupling, we calculate the contribution to the triple Higgs production cross section from the subprocesses $q\bar{q}\to ZHHH$ and $q\bar{q}'\to WHHH$. Our results illustrate that determining this coupling, or even providing experimental evidence that it exists, will be very difficult. 
Duane A. Dicus, Chung Kao and Wayne W. Repko
hep-ph