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2005-06-06 15:16:22 UTC

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I'm doing some background reading forRaw Message

http://arxiv.org/abs/hep-th/0505188

and there is something very basic that

I'm getting badly confused about. We all know

that in string theory there are higher-order

corrections to the Einstein-Hilbert lagrangian

coming both from loops and from alpha' corrections.

Let's think about the alpha' corrections. Normally

people say that these higher-order curvature terms

are "suppressed" by powers of alpha'. My question

is this: in four dimensions, the coefficients would

really be things like alpha'/G, where G is Newton's constant.

This is [L_s/L_p]^2 , where L_s is the string length

scale and L_p is the Planck length. But normally,

if we believe in weakly coupled strings, this is a

*large* number, not a small one! So in what sense

are the string corrections to the EH lagrangian

"suppressed"? I know this has some very simple

answer, somebody please kick me........