|Jul16-12, 10:27 PM||#1|
supergravity, does anyone work on it now?
It is with immense pleasure that I came across this passage in Brief History of Time. I remember reading this sentence when I was 16 but in the last 20 years I had forgotten where I read it. The only thing I could remember was that there were some physics calculations which took 3 years to complete and no one had the courage to take them on. Now I've found that passage again. I guess I did read BHOT when I was 16 and moreover I got to the end since this passage is in the final pages. I didn't understand the book though and probably just plowed through it just to say I had done it.
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|Jul17-12, 12:08 AM||#2|
|Jul18-12, 01:41 AM||#3|
You can do "SUGRA on its own", or "SUGRA derived from strings"; strings indicate that not arbitrary low-energy theories (gauge-, SUSY/gauge-, SUGRA-theories) are possible (consistent with gravity), but only those which follow from string / M-theory; the others are called "swampland".
Afaik Nicolai is still working on N=8 SUGRA related to E(10) and E(11) - whatever this means ;-)
Maximal N=8 SUGRA w/o relation to string theory is studied in order to understand whether it's well definied in perturbation theory - which would be an indication that it may be a viable theory of gravity w/o taking strings into account. Bern, Kallosh et al. are working on perturbative renormalizibility (even finiteness) of N=8 SUGRA.
Finiteness at all orders does not mean that the theory need to be consistent non-perturbatively b/c renormalizibility or finiteness at all orders does *not* imply convergence of the perturbation series. Therefore SUGRA may still require an UV completion; whether this could be strings or M-theory or something else is unclear to me, simply b/c neither have string / M-theory (whatever it may be) been shown to be renormalizable or finite to all orders, nor has it been possible to address a construction of these theories non-perturbatively.
So b/c we do not know if strings can redeem their promises it makes sense to study SUGRA as an alternative w/o any relation to strings.
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