Sign up ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

I obviously have a problem with basics of group theory. consider an open string in flat spacetime. there are usually two common gauge to solve the classical problem and quantize the strings:

  1. lightcone gauge
  2. conformal gauge.

After quantization, you study the state space, and here I have a problem with probably the representations of the $SO(24)$ (I focus on bosonic strings). I explain my problem explicitly below:

1-in lightcone gauge: for the second excited state, $N=2$ : the mass is $M^2=1/\alpha'$ and the bases for this subspace are : $a^\mu_2 |0\rangle $ and $a^\mu_1a^\nu_1|0\rangle $

2- in the conformal gauge: for the second excited state, $N=2$ : $M^2=1/\alpha'$ and the bases for this subspace are: $a^\mu_1a^\nu_1|0\rangle$ and, not $a^\mu_2|0\rangle$. (see Polchinski problem 4.1)

Now the problem is: Do we have a spin one particle with the mass :$M^2=1/\alpha'$ ? in lightcone gauge's state space we have it but, in conformal gauge we have only spin 2 particles with this mass. Is it really a problem?! or just a paradox comes from two different representations of the $SO(24)$ ?

I hope you got my question.

thank you very much

share|cite|improve this question
thank you, I used it ;) – Mohsen Aug 24 '13 at 14:12
By "spin", do you mean the kind of $SO(D−2)$ representation (vector, traceless symmetric tensor), or do you mean the component of the spin, for instance $S^{12}$, for some specific state ? – Trimok Aug 24 '13 at 14:51
I actually mean the first one. – Mohsen Aug 24 '13 at 22:57
Are you not satisfied with the solution of the problem $4.1$ given with details in the corrected exercices p. $33-34$ ? – Trimok Aug 25 '13 at 15:19

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.