this seems to be at odds with charge quantization, several possible resolutions immediately present themselves. One possibility is that the half-string is a mere artifact of some accounting scheme (see, e.g. [@BDS; @Taylor; @Mor; @3Q; @SS]) and that it is not in fact in conflict with charge quantization. Another possibility is that such symmetric boundary conditions for D8-branes are not actually allowed, and that the Ramond-Ramond gauge ten-form field strength $F_{10}$ must take integer values. A final possibility is that $F_{10}$ is allowed to take half-integer values but that, in such backgrounds, D0-brane charge is allowed to occur only in multiples of 2. We will conclude that this final scenario is in fact correct by considering the T-dual D2/D6 system and again using the description of D6-branes as Kaluza-Klein monopoles in M-theory.

The same question of course arises for the D2/D6 case. It is useful to first establish notation and we recall that, supposing the D6-brane is oriented along the $x_0,x_1,x_2...x_6$, the unit charged D6-brane solution takes the form

$$\begin{aligned}
\label{10Dsol}
ds^2_{string} &=&  V^{-1/2} dx_\parallel^2 + V^{1/2} dx_\perp^2, \cr
e^{2\phi} &=& V^{-3/2}, \cr
A_1 &=&  \frac{1}{2} (1 - \cos \theta) d \psi, \cr
F_2 &=& \frac{1}{2} \sin \theta  d \theta 