A First Course in String Theory
14.1 Counting bosonic states
is the number of ‘s.
is the number of different ‘s.
For , .
(Indices and are not powers. Instead, they are just upper indices for representing different ‘s.)
When all ‘s commute, and , for example, represent the same state. So we have to avoid double-counting, except for the same ‘s states, such as .
By direct counting, without using the formula, the number of products of the form can be built is
Let , the number of ways to put indistinguishable balls into boxes.
By using the formula, the number of products of the form can be built is
— Me@2015-07-26 08:43:22 AM
2015.07.26 Sunday (c) All rights reserved by ACHK