How Is the Exponential Map Defined for Lie Groups Without a Metric?

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SUMMARY

The exponential map for Lie groups is defined using one-parameter subgroups associated with given tangent vectors, rather than relying on a metric or the Levi-Civita connection. While traditional definitions involve the geodesic ordinary differential equation (ODE) and Christoffel symbols, these are not necessary for defining the exponential map in the context of Lie groups. The discussion emphasizes the importance of understanding connections in this framework, highlighting that metric compatibility is irrelevant without a metric.

PREREQUISITES
  • Understanding of Lie groups and their properties
  • Familiarity with one-parameter subgroups
  • Knowledge of connections in differential geometry
  • Basic concepts of geodesics and their role in manifolds
NEXT STEPS
  • Study the definition and properties of one-parameter subgroups in Lie groups
  • Explore the role of connections in differential geometry, focusing on non-Levi-Civita connections
  • Learn about the geodesic ODE and its applications in various contexts
  • Investigate the implications of metric compatibility in the absence of a metric
USEFUL FOR

Mathematicians, physicists, and students of differential geometry seeking to deepen their understanding of Lie groups and the exponential map without relying on traditional metric-based approaches.

wacki
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I’ve read about the exponential map that for Lie groups the exponential map is actually the exponential function. But the exponential map is based on the geodesic ODE, so you need Christoffel symbols and thus the metric. But usually nobody gives you a metric with a Lie group. So how can I get the exponential map (and finally see that it’s just the exponential function)?
 
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wacki said:
But the exponential map is based on the geodesic ODE, so you need Christoffel symbols and thus the metric.
No you do not. You need a connection, not necessarily the Levi-Civita connection. In fact, asking for metric compatibility is senseless without a metric.
 
Ahh yes, thanks Orodruin.
I clearly lack experience and intuition with non-Levi-Civita connections.
 
You need to be careful when you say the exponential map. The exponential map for a Lie group is defined using the one parameter subgroup with a given tangent vector. For a manifold with a connection the geodesic is used.
 

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