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| The last term vanishes if G<sub>1</sub>(x,x')and A(x) fall off sufficiently fast at <math>t\rightarrow\infin</math>. They do. So:<br> | | The last term vanishes if G<sub>1</sub>(x,x')and A(x) fall off sufficiently fast at <math>t\rightarrow\infin</math>. They do. So:<br> |
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− | <math>\int \nabla \cdot \mathbf{F} d^4x=A(x')</math><br> | + | <math>\int \nabla \cdot \mathbf{F} d^4x=A(x')</math><br><br><br> |
− | Now invoke the divergence theorem on the half space <math>z>0 \quad</math>:<br><br> | + | Now invoke the divergence theorem on the half space <math>z>0 \quad</math>:<br><br><br> |
| <math>A(x')=-\int d^2x\int cdt\left[A(x)\frac{\part}{\part t}G_1(x,x')-G_1(x,x')\frac{\part}{\part z}A(x)\right]</math>, where the last term is zero by the constriction of<math>G_1(z=0) \quad</math><br><br> | | <math>A(x')=-\int d^2x\int cdt\left[A(x)\frac{\part}{\part t}G_1(x,x')-G_1(x,x')\frac{\part}{\part z}A(x)\right]</math>, where the last term is zero by the constriction of<math>G_1(z=0) \quad</math><br><br> |
− | <math>A(x')=-c\int dt\int d^2xA(x)\frac{\part}{\part z}G_1(x,x')</math><br><br> | + | <math>A(x')=-c\int dt\int d^2xA(x)\frac{\part}{\part z}G_1(x,x')</math><br><br><br> |
− | To do the t integral, I need to bring out the z derivative. To do this, I first turn it into a z' derivative, using the relation: <br> | + | To do the t integral, I need to bring out the z derivative. To do this, I first turn it into a z' derivative, using the relation: <br><br><br> |
| <math>G_1(x,x')=\frac{-1}{4\pi}\left(\frac{\delta(|\mathbf{x}-\mathbf{x}'|-c(t-t'))}{|\mathbf{x}-\mathbf{x}'|}-\frac{\delta(|\mathbf{x}-\mathbf{x}''|-c(t-t'))}{|\mathbf{x}-\mathbf{x}''|}\right)</math>, where <math>\mathbf{x}''=\mathbf{x}'-2z'\hat{e_3}</math><br><br> | | <math>G_1(x,x')=\frac{-1}{4\pi}\left(\frac{\delta(|\mathbf{x}-\mathbf{x}'|-c(t-t'))}{|\mathbf{x}-\mathbf{x}'|}-\frac{\delta(|\mathbf{x}-\mathbf{x}''|-c(t-t'))}{|\mathbf{x}-\mathbf{x}''|}\right)</math>, where <math>\mathbf{x}''=\mathbf{x}'-2z'\hat{e_3}</math><br><br> |
| + | <math>\frac{\part}{\part z}G_1(x,x')=\frac{1}{4\pi}\left(\frac{\part}{\part z}\left(\frac{\delta(|\mathbf{x}-\mathbf{x}'|-c(t-t'))}{|\mathbf{x}-\mathbf{x}'|}-\frac{\delta(|\mathbf{x}-\mathbf{x}''|-c(t-t'))}{|\mathbf{x}-\mathbf{x}''|}\right)\right)</math>, |
| + | ∴ <math>A(x')=\frac{-1}{4\pi}\frac{\part}{\part z'}\int_{z=0} d^2x\left(2\frac{A(\mathbf{x},t'-\frac{\mathbf{x}-\mathbf{x}'}{c}}{\mathbf{x}-\mathbf{x}'}\right)</math? |
| + | |
| + | </math> |