  We consider a simple modification of quadratic chaotic inflation. We add a
logarithmic correction to the mass term, and find that this model can be
consistent with the latest cosmological observations such as the Planck 2018
data, in combination with the BICEP2/Keck Array and the baryon acoustic
oscillation data. Since the model predicts the lower limit for the
tensor-to-scalar ratio r for the present allowed values of the spectral index
n_s, it could be tested by the cosmic microwave background polarization
observation in the near future. In addition, we consider higher-order
logarithmic corrections. Interestingly, we observe that the scalar spectral
index n_s and r stay in rather a narrow region of the parameter space.
Moreover, they reside in a completely different region from that for the
logarithmic corrections to the quartic coupling. Therefore, future observations
may distinguish which kind of corrections should be included, or even single
out the form of the interactions.
