Three papers as the tip of an iceberg

[mitchell porter]

http://arxiv.org/abs/0811.1341"

 

[Chronos]

It still looks like turtles all the way down to me.

 

[negru]

Yeah I don't know about the unitarity thing. It really annoys me that it's not explored more. Conformal gravity seems like a potentially very useful theory. I don't know if solving its problems is just hard, likely impossible, shown to be impossible, or what? For example, why do witten and berkovits write a whole paper about conformal gravity ( http://arxiv.org/abs/hep-th/0406051 ) and say:

This simple observation suggests that four-dimensional conformal supergravity theories
might be relevant to the real world – perhaps with the aid of some mechanism of
spontaneous breaking of conformal invariance. However, they in fact are generally considered
to be an unsuitable starting point for describing nature, because they lead to fourth
order differential equations for the fluctuations of the metric, and thus to a lack of unitarity.
We have no reason to question these beliefs and we will later describe some facts that
illustrate them.

Really, no reason to question these beliefs? Then why write a paper about something that doesn't make any sense...this is just beyond me..I mean, this ghost stuff in CG is just in perturbation theory (as far as I know). Non-perturbatively it might be ok. It just sounds silly to me to disregard the theory so easily

 

[negru]

Mitchell, that is in fact the only paper I knew. Is there really nothing more comprehensive out there? I'm particularly interested whether there's anything like the KLT relations in conformal gravity. Very interestingly, eq 4.14 shows that the 4 point ConformalG amplitude is proportional to the EinsteinG amplitude. I wonder if this holds for higher points?

And more generally, given the supposed non-unitarity of CG, does its S-matrix make any sense? Non-unitarity means probabilities not adding up to 1 due to ghosts, right? How about just tree level?

 

[mitchell porter]

Really, no reason to question these beliefs? Then why write a paper about something that doesn't make any sense...this is just beyond me..

It's the equivalent for theory of OPERA's FTL neutrino paper. They "know" it doesn't make sense, but it's "there" (in the twistor string), so they tell the world what they found and maybe the world will explain it for them.

I'm particularly interested whether there's anything like the KLT relations in conformal gravity.

Maybe yes - http://arxiv.org/abs/1108.3085" .