I can find a string theory background by requiring that the world sheet(adsbygoogle = window.adsbygoogle || []).push({});

beta-functions vanish, as conformal invariance of the world sheet

theory is necessary for consistency. This gives me what is called

background field equations. Or I can just look at low-energy limit of

strings. So I compute some string scattering amplitudes and look what

becomes of them in the IR-limit. Then I try to write down a field

theory Lagrangian which reproduces those low-energy amplitudes. Then

the Euler-Lagrange equations of that Lagrangian tell me what

backgrounds I can have.

Is there a theorem that says that the two different ways of getting

spacetime field equations must give the same answer in the low-energy

limit? If the two answers were to differ it would seem to indicate an

inconsistency, so we don't expect that. On the other hand it could just

mean that the low-energy method isn't quite "kosher". Do I remember

well that Michael Douglas complained about the effective field theory

appraoch to string theory. What was the gist of his argument? Is it

related to my question? Is it being taken seriously by string theorists

these days?

Thanks,

Jack

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# String backgrounds

Can you offer guidance or do you also need help?

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