Orbit Type Strata of C^3: 2-torus Action (a,b)

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Discussion Overview

The discussion revolves around the orbit type strata of C^3 under a 2-torus action defined by the mapping (a,b). Participants explore the implications of this action, particularly focusing on the nature of orbits and fixed points within the context of complex geometry.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant defines the action of the 2-torus on C^3 and suggests that the only fixed point is (0,0,0), proposing it as one strata.
  • Another participant argues that orbits are not fixed points and asserts that every point lies in an orbit, questioning the nature of the resulting space when fixing a point (u,v,w) and applying the torus action.
  • A participant clarifies that the mapping f: (a,b) → (abx, by/a, bz) is not injective under certain conditions, specifically when b=0 and a is not equal to 0, providing an example to illustrate this point.
  • Further inquiry is made into the nature of the image of the map f and its relevance to the orbit structure, with a specific example of the point (1,0,0) being raised to question its orbit under the group action.

Areas of Agreement / Disagreement

Participants express differing views on the nature of orbits and the implications of the mapping. There is no consensus on the interpretation of the action or the resulting orbit structure, indicating ongoing debate and exploration of the topic.

Contextual Notes

Participants note the importance of injectivity in determining the nature of orbits, but the discussion remains unresolved regarding the specific conditions and implications of the mapping.

HMY
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a 2-torus action on C^3 can be defined by
(a,b).(x,y,z)= (abx, a^-1by, bz)

What are the orbit type strata of C^3 here?

2-torus can be thought of (S^1)^2.
0 is the only fixed point I can tell, so it's one strata.
I just don't understand this seemingly simple action.
 
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Orbits are not fixed points. (0,0,0) is an orbit, agreed. But there is at least one other - every point lies in an orbit.

So fix a point (u,v,w) and look at where the torus maps it. What is the resulting space? It is a quotient space of the 2-torus, but by what? I.e.e when is the map (a,b)-->(abx,by/a,bz) not injective? (this is a constraint on x,y,z) Where it is injective impleis the orbits are 2-toruses, and where it isn't they are something else.
 
am I properly making sense of this?

Call this map f: (a,b)-->(abx,by/a,bz)

f is not injective when you look at (a, b) with b=0 &
a not= 0.

eg.
take another point (c,d) with d=0 & c not= a & c not= 0
So (a,b) not= (c,d). But f(a,b) = (0,0,0) & f(c,d) = (0,0,0)


matt grime said:
So fix a point (u,v,w) and look at where the torus maps it. What is the resulting space? It is a quotient space of the 2-torus, but by what? I.e.e when is the map (a,b)-->(abx,by/a,bz) not injective? (this is a constraint on x,y,z) Where it is injective impleis the orbits are 2-toruses, and where it isn't they are something else.
 
That f is a map from where to where? What is the alleged image? The set of all points (abx,by/a,bz) with x,y,z in C^3?

I don't see what that map has to do with the problem.

Here's a point in C^3: (1,0,0). What is the orbit of that point under group action?
 

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