Graviton: Energy, Impulse, Frequency & Quantum

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SUMMARY

The graviton is a hypothetical particle associated with theories of quantum gravity, particularly in the context of linearized General Relativity (GR) and string theory. In linearized GR, the graviton is massless and has a spin of 2, while string theory posits a UV-complete framework that includes gravitons in its spectrum. The energy of a graviton is complex due to the equivalence principle, and while equations like E=h*nu exist for photons, analogous formulas for gravitons remain elusive. Other approaches to quantum gravity, such as Loop Quantum Gravity (LQG), do not fundamentally rely on gravitons, instead emerging in specific semiclassical limits.

PREREQUISITES
  • Understanding of General Relativity (GR) and its linearization
  • Familiarity with quantum field theory (QFT) concepts
  • Knowledge of string theory and its implications for quantum gravity
  • Basic principles of quantum mechanics (QM) and wave mechanics
NEXT STEPS
  • Research the linearized General Relativity and the Fierz-Pauli theory
  • Explore string theory and its role in quantum gravity, focusing on its UV-completeness
  • Investigate Loop Quantum Gravity (LQG) and its alternative approaches to quantum gravity
  • Examine the implications of the equivalence principle on graviton energy calculations
USEFUL FOR

Physicists, researchers in quantum gravity, and students of theoretical physics seeking to deepen their understanding of gravitons and their role in modern physics theories.

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Graviton is an analogy or an exact object in he framework of classical GR?

What bout the energy and impulse of a graviton with frequency nu? What is the quantum?
 
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Gravitons do not arise from classical GR. GR is not quantized.
 
So what is a graviton? And in which kind of theory? And what is the most useful formulas, like energy as a function of frequency?
 
The best thing we can do up to now, is to linearize GR (which gives a theory called "Fierz-Pauli") and try to quantize it. The particle associated to this quantization is called the "graviton", and should be massless and have spin 2.

So the theory a graviton in appears is in this case "linearized GR".

However, string theory claims to be a UV-complete (so beyond the linear level!) theory of quantum gravity, and also has a graviton in its spectrum. At low energies, so at the linear level, it reproduces linearized GR.

What "the energy of a graviton" would be is a tricky question due to the equivalence principle; I would have to think about that.
 
Are there any useful equations for gravitons like E=h*nu for photons?
 
The graviton is a hypothetical particle in certain theories about quantum gravity.

Naive (perturbative) quantization of GR leads to a theory (unfortunately ill-defined in the UV) which is based on gravitons.
String theory leads to low-energy effective theories (SUGRA) which contain both spin-2 gravitons and their SUSY-partner, the spin-3/2 gravitino.
Other theories regarding quantum gravity, e.g. LQG, use very different concepts, and gravitons are not their basic building blocks but do emerge only in a certain semiclassical limit.
 
It is not possible to introduce graviton simply based on wave mechanics?
 
No, because you wouldn't know the properties of the graviton. According to GR, gravity is propagated by tensor modes.
 
But I have read lots of papers in which graviton are mentioned,
like 1-2 graviton is emitted in the process for example.
 
  • #10
Wave mechanics is a concept of QM, but the graviton is a concept based on (second quantized) QFT. There is no photon in Maxwells theory.
 

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