Pochhammer contour over normal Riemann surface?

In summary, the contour of the function ##w=z^{1/3}(1-z)^{1/2}## on the torus surface of the Riemann surface for the function ##w=z^{1/3}(1-z)^{1/2}## appears to be a figure-8.
  • #1
jackmell
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What do all possible combinations of the pochhammer contour over the normal Riemann surface for the function ##w=z^{1/2}(1-z)^{1/3}## look like? I imagine like a pumpkin with six ridges longitudinally from north pole to south, one for each joining along the cut between zero and one, the contour then encircling the poles as it weaves along the ridges in various ways. I'd like to see a picture of that. Shouldn't that be possible to draw (analytically precisely I mean)? I've had trouble drawing these things in the past and was wondering if I have the general topology correct?

Edit: Dang it. I think the genus is one so not a pumpkin. Here's my genus calculations. We have:

$$g=1/2 \sum (r-1)-n+1$$

At zero it ramifies into three 2-cycle branches so that's 3. At one it ramifies into two 3-cycle branches so that's 4 more, and at infinity it fully ramifies so 5 more. Thus we have:

$$g=1/2(3+4+5)-6+1=1$$

I just don't understand how it could be a torus though.

Ok thanks,
Jack
 
Last edited:
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  • #2
I was wondering if someone could confirm my suspicion about a particular property of Riemann surfaces of algebraic functions:

Are singular points on Riemann surfaces duplicated according to the number of branches about the point?

Take for example the function ##w=z^{1/3}(1-z)^{1/2}##. This function ramifies into three 2-cycle branches at the origin, two 3-cycle branches at one, and a fully-ramified branch at infinity. The Riemann surface is a torus and the function should map the torus to a six-sheeted covering of the complex plane. Does that mapping have three points labeled ##(0,0)##, two labeled ##(1,0)## and a single point ##\infty##? If true, then we should at least be able to construct such a mapping qualitatively according to the following diagram. An actual mapping may not of course have the singular points located where I've placed them.

torus mapping.jpg


Correct or no?

Ok thanks,
Jack
 
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  • #3
Hi guys,

Don't wish to kick a sleeping dog with this. It's a very interesting problem though. I believe I know what the following contour looks like on the torus surface of this function. It's a figure-8 isn't it? I don't even have to know how to map the torus to a 6-sheeted covering of the complex plane either. No matter how we map it, that (analytically-continuous) contour has to be a figure-8 I believe..

Anyway, I'm thinking of taking a Topology class this fall and hopefully, that will help me with some interests of mine including this one.

2-branch loop.jpg
 

What is a Pochhammer contour?

A Pochhammer contour, also known as a Pochhammer path, is a complex contour on the complex plane that is used in the study of special functions, specifically the Gamma function and its generalizations. It is named after the mathematician Leo Pochhammer.

What is a normal Riemann surface?

A normal Riemann surface is a complex manifold that is locally biholomorphic to the complex plane. It is a generalization of the concept of a complex analytic curve, and is used in complex analysis and algebraic geometry.

What is the significance of the Pochhammer contour over a normal Riemann surface?

The Pochhammer contour over a normal Riemann surface is significant because it allows for the analytic continuation of the Gamma function and other special functions. It provides a way to evaluate these functions at points where they are not defined, and is an important tool in complex analysis and number theory.

How is the Pochhammer contour related to the Gamma function?

The Pochhammer contour is closely related to the Gamma function, as it is used to evaluate the Gamma function at points where it is not defined. The contour is also used in the study of the properties and behavior of the Gamma function, such as its zeros and poles.

Are there other applications of the Pochhammer contour over normal Riemann surfaces?

Yes, the Pochhammer contour has applications beyond the study of special functions. It is also used in the theory of modular forms, in the proof of the Riemann hypothesis, and in the study of complex differential equations.

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