A0[m^2]
is the Passarino-Veltman one-point integral
A_0..
By default A_0 is not expressed in terms of B_0.
[m^2] A0
\text{A}_0\left(m^2\right)
SetOptions[A0, A0ToB0 -> True];
[m^2] A0
-\frac{2 m^2 \;\text{B}_0\left(0,m^2,m^2\right)}{2-D}
SetOptions[A0, A0ToB0 -> False];
According to the rules of dimensional regularization A_0(0) is set to 0.
[0] A0
0
[SmallVariable[M^2]] A0
0