# Graviton and other particle interections

1. Aug 14, 2014

### Quarlep

We know that graviton spin is 2 so other lepton and quarks spin is 1/2 I am confused because If Graviton and a quark or maybe a lepton make an interaction than the last spin must be 3/2 or 5/2 but theres no particle exist in this spin quantity.It means theres no particle called graviton or I dont know I am confused

Thanks

2. Aug 14, 2014

### ShayanJ

You only add spins if you have a particle which is the bound state of other particles. But not all kinds of interactions give bound states!

3. Aug 14, 2014

### Quarlep

Whats bound state I googled but its hard to understand

4. Aug 14, 2014

### ShayanJ

5. Aug 14, 2014

### Quarlep

I lookes there But I didnt undertsand I am 16 years old and I dont know QM. Its complicated and I dont know english very well.

6. Aug 14, 2014

### Quarlep

Can you tell me more specific so you are trying to tell me theres a graviton but is not interact with other particles.
Or its interacts ?

7. Aug 14, 2014

### ShayanJ

OK. The point is, in some situations, the interaction is somehow that the particles are going to remain close to each other. In these situations, we say that they formed a bound state, a composite particle. Like a proton which is formed from two up quarks and one down quark.
But for some other situations, the particles just attract or repel each other for some time and then leave each other alone. These are called scattering processes or sometimes collisions.

8. Aug 14, 2014

### Quarlep

I ask it because I read a book about particle phyiscs and the author said that spin is conserved its true or not ?
And thanks for explanation Thanks I understand it

9. Aug 14, 2014

### Staff: Mentor

Total angular momentum is conserved. Spin is one part, but the motion of particles can contribute to the angular momentum as well.

We know that if it exists, its spin has to be 2.

Yes a (hypothetical) graviton would interact with other particles.

10. Aug 14, 2014

Staff Emeritus
Why? A spin-1 photon can interact with a spin-0 alpha particle and it will remain a spin-0 alpha particle?

11. Aug 14, 2014

### ChrisVer

As for the photon-alpha particle interactions, in case the alpha particle absorbs a photon, it's going to get excited and so will get orbital momentum to conserve the angular momentum. Is giving composite particles for this case good?

12. Aug 15, 2014

### Quarlep

I learned that total angular momentum is conserved as indicated above.But I am confused here because total angular momentum is equal spin angular momentum plus orbital angular momentum. In particle interactions like two electron collusions or proton proton collusion every collusions or decays there's no orbital angular momentum(my idea) so I guess total angular momentum must be equal spin angular momentum because theres no orbital momentum so If graviton interects with another particle total angular momentum must be conserved so I claimed that its equal spin angular momentum.Its the reason why I said that graviton and other particle interactions result of spin is 3/2 or 5/2.
Am I wrong.

13. Aug 15, 2014

Staff Emeritus
Let's not complicate things when we explain things. It doesn't have to absorb the photon.

14. Aug 15, 2014

### ChrisVer

if it doesn't absorb the photon then the alpha+gamma will give alpha+gamma

15. Aug 15, 2014

Staff Emeritus
Chris, you are not helping. What I am trying to get across is the idea that you can have an interaction with no exchange of angular momentum. Quibbling does not help.

16. Aug 16, 2014

### Staff: Mentor

As soon as there is more than one particle, you can have "orbital" angular momentum (not really as orbit, but as displaced relative motion).
Collision with i.