N dimensional objects.

[MathematicalPhysicist]

Superstring theories attest that the building block is a one dimensional object, a string, now I wonder why stop there, why not two dimensional objects?

[Dmitry67]

N dimensional objects are called N-branes.

[Dmitry67]

Hm....
http://www.google.com/trends?q=superstring&ctab=0&geo=all&date=all&sort=0

[MathematicalPhysicist]

How does it differ from d-branes, and how many types of branes are there?

[Naty1]

I've read of p branes and d branes.

d branes are the ones discovered by Joe Polchinsky in the mid 1990's. I think I've read these are called Dirichlet branes

p branes are the type discovered by Ed Witten and strings I think are one dimensional versions of these....

Try this for an overview: http://en.wikipedia.org/wiki/P-branes

got to go....

[javierR]

P-branes are objects in supergravity and were studied first. They are described by a specific form of the spacetime metric and other background fields in the theory. You can consider them in string theories that have the supergravity theory as a low energy limit. D-branes are p-branes further adapted to the string framework. The "D" stands for "Dirichlet boundary conditions" for the string endpoints on the branes. The fluctuations of the D-branes are considered to be stringy excitations on the brane in contrast to sugra p-branes with (quantum) field fluctuations.

Bergshoeff, Sezgin and Townsend (Phys. Lett. 189B, 1986) first considered p-branes based on observations of Hughes, Liu and Polchinski (Phys Lett B180 1986).

Fundamental strings of string theory are a specific type of 1-brane, "electric", while magnetic 1-branes are solitonic solutions to a given theory. (This is a general thing: An electric 0,1,2,...-brane is not a true solution to a set of equations of motion; rather, they are objects coupling to a singular "solution" of the theory. On the other hand, magnetic branes are true solutions to the equations of motion.

[Dox]

Superstring theories attest that the building block is a one dimensional object, a string, now I wonder why stop there, why not two dimensional objects?

Those are the branes... Isn't it?

Look at the Lagrangian of Dp-branes, those are just the generalization of the Nambu-Goto action of the strings.