Why is ##\frac{1}{\sqrt{z}}## a branch point and ##\frac{1}{z}## a pole?

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The discussion clarifies that ##\frac{1}{\sqrt{z}}## is classified as a branch point due to its double-valued nature, necessitating a branch cut for integration. In contrast, ##\frac{1}{z}## is identified as a pole, which allows for the application of the Cauchy integral theorem without complications. The presence of a branch point complicates integration around singularities, as it requires careful consideration of the Riemann surface, which consists of two sheets. The confusion arises when attempting to integrate around the point ##z=0##, where the multi-valued aspect of the function leads to inconsistencies.

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I am a bit confused. Why ##\frac{1}{\sqrt{z}}## is branch point and ##\frac{1}{z}## is pole. And why we cannot use Cauchy integral theorem when we have branch point? Why we need to cut off branch point when we integrate? Thanks a lot for the answer.
 
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[itex]\frac{1}{\sqrt{z}}[/itex] is double valued. Riemann surface has two sheets - branch cut needed.
 
Yes I now that the problem is because is double valued. However I am not sure what is really happens. For example taking the circle around the point ##z=0## problem occurs. Could you explain where is the problem?
 

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