Graviton: Energy, Impulse, Frequency & Quantum

[mersecske]

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?

 

[Matterwave]

Gravitons do not arise from classical GR. GR is not quantized.

 

[mersecske]

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?

 

[haushofer]

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.

 

[mersecske]

Are there any useful equations for gravitons like E=h*nu for photons?

 

[tom.stoer]

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.

 

[mersecske]

It is not possible to introduce graviton simply based on wave mechanics?

 

[haushofer]

No, because you wouldn't know the properties of the graviton. According to GR, gravity is propagated by tensor modes.

 

[mersecske]

But I have read lots of papers in which graviton are mentioned,
like 1-2 graviton is emitted in the process for example.

 

[tom.stoer]

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.