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String Theory Demystified

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

Now since R= ( g N)<br />

s s<br />

/ 14 we can write<br />

N<br />

dof<br />

5<br />

AR<br />

=<br />

g<br />

8 2<br />

s s<br />

In fi ve-dimensions, the Newton gravitational constant is<br />

Hence we fi nd that<br />

G<br />

N<br />

5<br />

g<br />

= 5<br />

R<br />

<br />

dof =<br />

This agrees with the holographic principle, and is the same as the result obtained<br />

for black holes with the exception of the factor of 1/4.<br />

More Correspondence<br />

In this section we describe connections between the supergravity theory of the bulk<br />

and the SYM of the boundary. We can convert between bulk variables and SYM<br />

variables as follows. Let E SYM be energy on the boundary and M be the energy in the<br />

bulk. They are related as<br />

Temperature is related in the same way:<br />

8 2<br />

s s<br />

A<br />

G<br />

5<br />

E RM<br />

SYM =<br />

T RT<br />

SYM =<br />

where T is the temperature in the bulk. Now consider a thermal Yang-Mills state<br />

with temperature T SYM . The entropy is<br />

S = N TSYM 2 3<br />

( )<br />

A thermal state of temperature T SYM corresponds to an AdS Schwarzschild black<br />

hole at the center of the AdS ball.

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