A Sharp Sobolev--Strichartz estimate for the wave equation
  We calculate the the sharp constant and characterise the extremal initial data in $\dot{H}^{\frac{3}{4}}\times\dot{H}^{-\frac{1}{4}}$ for the $L^4$ Sobolev--Strichartz estimate for the wave equation in four space dimensions. 
Neal Bez, Chris Jeavons
math.AP math.CA