4D spacetime as intersection of multiple D-branes Brane-world scenarios usually consider 4D spacetime to be a 3-brane or a collection of coincident 3-branes. Is it possible that 4D spacetime is instead an intersection (not coincidence) of multiple branes, e.g. two 6-branes, or 8-brane and 4-brane, etc (in 9+1 dimensions)? Or are there any inconsistencies/limitations on such scenario?
 A: Yes. 
The fluctuations of a D-brane (extending in D spatial directions and time) are described in terms of strings ending on the brane. The excitations of these strings are in the low energy limit described as a 'worldvolume' quantum field theory living on the brane, where the different fields encode the fluctuations of the brane in different directions and describe for example how the brane carries various charges. See for example Barton Zwiebach's 'A First Course in String Theory'.
When you have a stack of several D3 branes, the low energy fluctuations of this system will be described by strings beginning and ending on the different branes. In the case of parallel D3 branes the strings can move along the tangential directions to the branes and their low energy fluctuations will be described by a 3+1 dimensional quantum field theory.
When you have two intersecting branes, the low energy fluctuations of the entire system will be the strings going from one brane to the other, at the point of intersection. For two D3 branes that intersect along one common direction, the low energy fluctuations of the strings will, therefore, give rise to a 1+1 dimensional quantum field theory. Similarly, you can come up with 3+1 dimensional quantum field theories by letting higher dimensional branes intersect in various ways. Depending on what branes intersect each other and in what way you will obtain different field contents for the resulting 3+1 dimensional worldvolume theory describing the intersection.
