Why should we care about the top quark Yukawa coupling?
  In the cosmological context, for the Standard Model to be valid up to the
scale of inflation, the top quark Yukawa coupling $y_t$ should not exceed the
critical value $y_t^{crit}$, coinciding with good precision (about 0.02%) with
the requirement of the stability of the electroweak vacuum. So, the exact
measurements of $y_t$ may give an insight on the possible existence and the
energy scale of new physics above 100 GeV, which is extremely sensitive to
$y_t$. We overview the most recent theoretical computations of $y_t^{crit}$ and
the experimental measurements of $y_t$. Within the theoretical and experimental
uncertainties in $y_t$ the required scale of new physics varies from $10^7$ GeV
to the Planck scale, urging for precise determination of the top quark Yukawa
coupling.
