Pochhammer contour over normal Riemann surface?

Click For Summary
SUMMARY

The discussion revolves around the Pochhammer contour over normal Riemann surfaces for the function w=z^{1/2}(1-z)^{1/3}. The user, Jack, calculates the genus of the surface to be one, indicating a toroidal structure. He explores the ramifications at specific points, confirming that singular points on Riemann surfaces are duplicated according to the number of branches. Jack also speculates that the contour resembles a figure-8, emphasizing the importance of understanding the mapping of the torus to a six-sheeted covering of the complex plane.

PREREQUISITES
  • Understanding of Riemann surfaces and their properties
  • Familiarity with algebraic functions and their ramifications
  • Knowledge of genus calculations in topology
  • Basic concepts of covering spaces in complex analysis
NEXT STEPS
  • Study the properties of Riemann surfaces in detail
  • Learn about genus calculations and their implications in topology
  • Explore the mapping of toroidal surfaces to covering spaces
  • Investigate the Pochhammer contour and its applications in complex analysis
USEFUL FOR

Mathematicians, topology students, and anyone interested in complex analysis and Riemann surfaces will benefit from this discussion.

jackmell
Messages
1,806
Reaction score
54
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:
Physics news on Phys.org
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
 
Last edited:
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
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 5 ·
Replies
5
Views
4K
  • · Replies 7 ·
Replies
7
Views
5K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 10 ·
Replies
10
Views
4K
  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 5 ·
Replies
5
Views
4K