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Stars as Laboratories for Fundamental Physics - MPP Theory Group

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218 Chapter 6<br />

Fig. 6.7. Contours <strong>for</strong> the vertex renormalization factor Z T <strong>for</strong> transverse<br />

electromagnetic excitations in a medium according to Eq. (6.52).<br />

Fig. 6.8. Modified vertex renormalization factor ˜Z L <strong>for</strong> longitudinal electromagnetic<br />

excitations in a medium according to Eq. (6.53).<br />

The longitudinal c<strong>as</strong>e is more complicated. Z L is a product of two<br />

factors ˜Z L and ω 2 /(ω 2 − k 2 ) where the <strong>for</strong>mer,<br />

˜Z L ≡ 2 (ω2 − v 2 ∗k 2 )<br />

3ω 2 P − (ω 2 − v 2 ∗k 2 ) , (6.53)<br />

is a function of the variable v ∗ k alone because <strong>for</strong> pl<strong>as</strong>mons ω is a<br />

function of v ∗ k alone. The function ˜Z L (v ∗ k) is shown in Fig. 6.8; <strong>for</strong><br />

v ∗ k ≫ ω P it quickly drops to zero. However, in a relativistic pl<strong>as</strong>ma

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