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String Theory Demystified

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220 <strong>String</strong> <strong>Theory</strong> Demystifi ed<br />

3. Consider the constraint equations in the compactifi cation section. Why is<br />

I<br />

( ∂ −∂ ) X = 0 the only constraint on the bosonic modes for the extra 16<br />

τ σ<br />

dimensions?<br />

4. Given the action<br />

16<br />

1 2 ⎛ i a<br />

I a<br />

− ⎞<br />

S =− d ∂ X ∂ X + ∂ X ∂ X + iS ∂ +∂ S<br />

a i a I<br />

4πα<br />

′ ∫ σ ∑<br />

Γ ( ) τ σ<br />

⎝<br />

⎜<br />

⎠<br />

⎟ , what are the<br />

I=<br />

i<br />

commutation relations satisfi ed by the bosonic modes?<br />

5. Consider the description of the heterotic string in the compactifi cation<br />

section and calculate ( 1+ Γ ) S = 0<br />

a<br />

.<br />

11

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