  A novel superstring-inspired gravitational theory in four spacetime
dimensions is proposed as a sum of the modified $(R+\alpha R^2)$ gravity
motivated by the Starobinsky inflation and the Bel-Robinson-tensor-squared term
motivated by the eleven-dimensional M-theory dimensionally reduced to four
dimensions. The proposed Starobinsky-Bel-Robinson action has only two
parameters, which makes it suitable for verifiable physical applications in
black hole physics, cosmological inflation and Hawking radiation in the early
universe.
