Solving Simple Poles: Why Does $\frac{e^{ikz}}{z^{2}+m^{2}}$ Have One?

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This is because the other pole at -im is outside of the contour and thus does not affect the integral.In summary, the mathematical text states that \frac{e^{ikz}}{z^{2}+m^{2}} has only one simple pole at im if k>0. While it does have two simple poles at im and -im, the contour used to evaluate the integral only encloses the pole at +im, making it the only one that contributes to the residue. This is due to the contour being closed upwards and the other pole being outside of the contour.
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nklohit
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In the mathematical text I've read, it says that [tex]\frac{e^{ikz}}{z^{2}+m^{2}}[/tex] has only one simple pole, that is, [tex]im[/tex], if [tex] k>0 [/tex]. Why?
Has it got 2 simple poles, [tex] I am [/tex] and [tex] -im [/tex] ?
 
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You are correct. It has simple poles at [tex]im[/tex] and [tex]-im[/tex]. Either your text is wrong or perhaps there's a restriction on the domain that you didn't notice.
 
  • #3
It does have two simple poles at I am and -im, but if k is positive the contour will be closed upwards (the contour's edges run along with x-axis, then form a half circle in the upper plane; taking the radius of the half circle to infinity, we find that this contour is exactly equal to the integral we are interested in) and the only pole enclosed will be the one at +im.

Therefore, there is only one pole that contributes to the residue.
 

1. What is a simple pole?

A simple pole is a singularity in a complex function, where the function approaches infinity as the variable approaches a specific point. In other words, the function has a pole at that point, but it is not a branch point.

2. How does a simple pole affect the behavior of a function?

A simple pole affects the behavior of a function by causing it to have a singularity at that point. This means that the function is undefined at the point of the pole, and the function's value becomes infinitely large as the variable approaches the pole.

3. Why does $\frac{e^{ikz}}{z^{2}+m^{2}}$ have a simple pole?

This function has a simple pole at $z = im$, where $i$ is the imaginary unit and $m$ is a constant. This is because when $z = im$, the denominator becomes 0, and the function becomes undefined at that point.

4. How can we solve for the simple pole in this function?

To solve for the simple pole in this function, we set the denominator equal to 0 and solve for $z$. In this case, we get $z = \pm im$, which are the poles of the function.

5. Can we use the residue theorem to solve for the simple pole in this function?

Yes, we can use the residue theorem to solve for the simple pole in this function. The residue at a simple pole is equal to the limit of the function as $z$ approaches the pole. In this case, the residue is equal to $e^{-mk}$.

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