Metrics and conformal transformations

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SUMMARY

This discussion focuses on conformal transformations within the context of conformal field theory. The key transformation condition is expressed as $$\Lambda (x) g_{\mu \nu} = g_{\rho \sigma} \frac {\partial x'^\rho}{\partial x^\mu} \frac {\partial x'^\sigma}{\partial x^\nu}$$, leading to the derived condition $$dx'^\mu dx'_\mu = \Lambda (x) dx^\mu dx_\mu$$. A query arises regarding the use of the metric $$g_{\mu \nu}$$ in the $$x^\mu$$ coordinates to lower indices of $$dx'^\mu$$, given that they originate from a different coordinate system. The transformation law for the metric is also discussed, emphasizing the importance of understanding the pullback of the metric by the conformal transformation.

PREREQUISITES
  • Understanding of conformal field theory concepts
  • Familiarity with metric tensors and their transformations
  • Knowledge of differential geometry and coordinate transformations
  • Basic grasp of mathematical notation used in physics
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  • Study the properties of conformal transformations in detail
  • Learn about metric tensor transformations in differential geometry
  • Explore the implications of the pullback operation on metrics
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This discussion is beneficial for theoretical physicists, mathematicians specializing in geometry, and students studying conformal field theory or related areas in advanced physics.

FuzzySphere
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Conformal field theory is way over my head at the moment, but I decided to "dip my toes into it," and I watched a little video talking about conformal transformations. Now, I know that in a conformal transformation, $$x^\mu \to x'^\mu ,$$ the metric must satisfy $$\Lambda (x) g_{\mu \nu} = g_{\rho \sigma} \frac {\partial x'^\rho}{\partial x^\mu} \frac {\partial x'^\sigma}{\partial x^\nu}.$$ From this I have been informed that we can derive the condition $$dx'^\mu dx'_\mu = \Lambda (x) dx^\mu dx_\mu .$$ I have tried using the condition on the metric to derive this, only to get to this condition: $$g_{\mu \nu} dx'^\mu dx'^\nu = \Lambda g_{\mu \nu} dx^\mu dx ^\nu ,$$ but I have one query: can we use the metric $$g_{\mu \nu}$$ in the $$x^\mu$$ coordinates to lower the indices of $$dx'^\mu ,$$ seeing as they are from a different coordinate system?
 
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FuzzySphere said:
the metric must satisfy Λ(x)gμν=gρσ∂x′ρ∂xμ∂x′σ∂xν.
I observe ' and without ' are upside down.
\Lambda g_{\mu\nu}=g'_{\mu\nu}=g_{\rho\sigma} \ (\partial x^{\rho}/\partial x'^{\mu}) \ ( \partial x^{\sigma}/ \partial x'^{\nu})
 
anuttarasammyak said:
I observe ' and without ' are upside down.
\Lambda g_{\mu\nu}=g'_{\mu\nu}=g_{\rho\sigma} \ (\partial x^{\rho}/\partial x'^{\mu}) \ ( \partial x^{\sigma}/ \partial x'^{\nu})
No, that is the transformation law for the metric, what I have is the coordinate representation of the pull back of the metric by the conformal transformation.
 

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