Talk:Mandelstam variables

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Call me stupid but isn't the u channel a twist of the s channel, not the t channel

I'm just learning I'll leave it to the true scholars (ie those get paid rather than pay) amongst us to make the edit

  • No, the u-channel is just like the t-channel with the final-state particles' roles exchanged. You may be referring to the fact that on the graphic in this article the u-channel looks like the s-channel, but the relevant bit is whether the two initial-state particles annihilate or not, which they don't in the u-channel. The graphic should be changed to better reflect this, though; in particular, the intermediate particle in the s-channel has a timelike momentum, whereas it is spacelike in the t- and u-channels, and it is pedagogically useful for the direction of the lines in the diagrams to reflect this. 142.3.164.195 23:51, 10 May 2006 (UTC)


  • Wrong sign: if it is p1 + p2 = - p3 - p4 then it should be t = (p1 + p3)^2 = (p2 + p4)^2, u = (p1 + p4)^2 = (p2 + p3)^2.

[edit] wrong sign

I think the conservation of 4-momentum should be p1 + p2 = p3 + p4 instead of p1 + p2 = − p3 − p4 ... -- Cheesus 14:47, 10 November 2006 (UTC)