Counting states in heterotic string theory | A First Course in String Theory

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(a) Consider the left NS’ sector. Write the precise mass-squared formula with normal-ordered oscillators and the appropriate normal-ordering constant.

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**What is normal-ordering?**

Put all the creation operators on the left.

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**What for?**

p.251 “It is useful to work with normal-ordered operators since they act in a simple manner on the vacuum state. We cannot use operators that do not have a well defined action on the vacuum state.”

“The vacuum expectation value of a normal ordered product of creation and annihilation operators is zero. This is because, denoting the vacuum state by , the creation and annihilation operators satisfy”

— Wikipedia on *Normal order*

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— This answer is my guess. —

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c.f. p.251:

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Equation at Problem 14.5:

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Equation (14.29):

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— This answer is my guess. —

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— Me@2018-08-06 10:23:48 PM

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2018.08.06 Monday (c) All rights reserved by ACHK