Limits on Second-Order Non-Gaussianity from Minkowski Functionals of
  WMAP Data
  We analyze non-Gaussianity (NG) due to the primordial bispectrum and
trispectrum using CMB temperature maps of WMAP 7-year data. We first apply the
perturbative formulae of Minkowski functionals up to second-order NG derived by
Matsubara (2010), which enable us to give limits on cubic NG parametrized with
tau_NL and g_NL as well as various types of quadratic NG parametrized with
f_NL. We find no signature of primordial NG in WMAP 7-year data, but give
constraints on the local-type, equilateral-type, orthogonal-type f_NL:
f_NL(loc)=20+-42, f_NL(eq)=-121+-208, f_NL(ort)=-129+-171, respectively, and
tau_NL/10^4=-7.6+-8.7, and g_NL/10^5=-1.9+-6.4. We also find that these
constraints are consistent with the limits from skewness and kurtosis
parameters which characterize the perturbative corrections of MFs.
