The Physics of Branes
Is an elementary particle really: (i) a particle? (ii) elementary?
Quantum mechanics tells us that particles are “fuzzy”:
Moreover, “elementary” and “composite” are just words..
In Quantum Field Theory this is true in a very precise sense.
Another distinction that is less basic than one would think:
In string theory, the fundamental string has a typical length scale.
This is why string theory is an approach to particle physics.
Consider a string wrapped around a compact spatial dimension:
If strings can look like particles, can membranes look like strings?
In string theory, the fundamental string is really a membrane.
This means that string theory is not just a theory of strings!
At strong coupling, string theory turns into “M-theory”.
Consider the following membrane configuration in M-theory:
Let the vertical part be wrapped on a small compact dimension.
This observation turns out to be very profound and powerful.
Such membranes are called “D2-branes”.
A simple generalisation of D2-branes: “Dp-branes”.
We need to use our branes!
Some application of brane physics:
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