Tachyons

[Pete]

It is now well established that in (perturbative) QFT tachyons are an artefact of "choosing the wrong vacuum" to expand about. They are inherently unstable.

 

Maybe we should start a new thread on this rather than hijack this one.

I never learned QFT so I'll have to take your word for this until I learn it myself.

 

Why did you qualify it with perturbative?

 

Pete

[ajb]

Because particles only really make sense in perturbative quantum field theory.

[Pete]

Because particles only really make sense in perturbative quantum field theory.

 

Does the same thing hold true if one does not assume the mass shell condition, since that is a postulate that is abandoned for Tachyons. Are you sure that QFT theory can't handle this since it seems that the author would have said something about this. How long has perturbative quantum field theory been around?

 

Pete

[ajb]

Tachyons have negative mass squared. So in that sense they don't obey the mass-shell condition. However, a slight redefinition and they do. This is in fact discussed in Wikipedia to a reasonable degree.

 

Only things on mass-shell can be though of as "real particles", but the formalism of quantum field theory means that we must deal with things off mass-shell. This fact is very important.

 

Quantum field theory can handle taychons, but such field configurations are inherently unstable. They will decay into non-taychonic configurations. This is the so called "tachyon condensation".

 

In quantum field theory the mass squared is the second derivative of the effective potential, at a point where the first derivative is zero. This means we have a local maximum and not a minimum of the potential for tachyons. The potential is like "W" shaped with the field sat at the middle apex. It will roll down the "hill" into the minima where it no longer has negative mass squared.

 

As for the "author" of QFT, well thousands of people have contributed here. If you want the true "originator" then that was Dirac in 1927. The people who really developed quantum electrodynamics into a usable theory were Tomonaga, Schwinger and Feynman (1946, 1949). They developed perubative methods and renormalisation and were awarded the 1965 Nobel prize. The history of QFT and gauge theory is quite interesting. I won't detail any of it here, but the book The Dawning of Gauge Theory by Lochlainn O'Raifeartaigh is the book to read.

[Zero]

Feynman, yeah!

No, seriously...good point about Dirac. Em...his notation confuses me, but I profess to be no QM specialist. ha! Just studying Tachyons...the whole Higgs-Kibble mechanism concept screws with me.

But, hey, kudos to you guys!