Fixed point and scale invariance

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SUMMARY

The discussion centers on the concept of fixed points in quantum field theory (QFT), specifically regarding ultraviolet (UV) fixed points and their implications for coupling constants. A UV fixed point, denoted as ##\lambda^*##, indicates that as the energy scale increases, the coupling converges to this value, ensuring the theory remains meaningful at high energies. The Wilsonian perspective posits that changing the energy scale introduces a new theory with a new Lagrangian, with all Lagrangians converging to the UV fixed point. Additionally, it is established that theories at fixed points are scale invariant, as the beta function for the coupling is zero at these points.

PREREQUISITES
  • Understanding of quantum field theory (QFT)
  • Familiarity with the concept of running couplings and beta functions
  • Knowledge of Wilsonian renormalization group (RG) methods
  • Basic grasp of Lagrangian mechanics in theoretical physics
NEXT STEPS
  • Study the implications of UV fixed points in quantum field theory
  • Explore the concept of scale invariance in physical theories
  • Learn about the renormalization group flow and its applications
  • Investigate the role of beta functions in determining fixed points
USEFUL FOR

The discussion is beneficial for theoretical physicists, particularly those specializing in quantum field theory, as well as students and researchers interested in the concepts of fixed points and scale invariance in high-energy physics.

Einj
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Hello everyone. I'm studying the fixed point of theory in the context of QFT. First of all, let me say what I think I understood about fixed points and then I'll state my question.
Suppose we have a theory with a certain running coupling ##\lambda(\mu)##. If we have, for example, an UV fixed point, say ##\lambda^*##, this means that when the energy scale increases the coupling will converge towards this value and hence the theory is defined at arbitraty high energy since it remains meaningful.
In the Wilsonian point of view, everytime that we change our energy scale we are introducing a new theory with a new Lagrangian. In this languange a UV fixed point is that Lagrangian towards which every other Lagrangian converge when the energy scale increases.

First of all: is this correct?

Secondly, I found in my places that the theory at the fixed point is scale invariant. Can anyone explain to me why?

Thanks a lot
Cheers
 
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In this example, The fixed point is the position where the beta function for the coupling is zero.

Therefore it is scale independent by definition!
 
RGevo said:
In this example, The fixed point is the position where the beta function for the coupling is zero.

Therefore it is scale independent by definition!

RGevo is presumably not at the fixed point? :D
 

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