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The "almost" de Sitter expansion of current cosmological model implies a puzzle for supersymmetry (SUSY) and also for string theory. A positive value of the cosmological constant implies a non-null vacuum energy that is, as far as I know, inconsistent with SUSY which has to be broken in order to get a tiny cosmological constant. Moreover, interacting theories in de Sitter spacetimes are hard to handle in current string theory due to some issues concerning the S-matrix and that field strengths become imaginary in those spacetimes. My question is:

Is the currently accepted LCDM model of cosmology a challenge for SUSY/string theory? Wouldn't it be saying that SUSY and string theory are "wrong" or at least incomplete (or they will be, since we will approach a pure dS spacetime in the cosmological future it nothing changes)? Afterall, to my knowledge, de Sitter spacetimes are not well behaved in interacting field theories and thus, even in superstring M-theory.

Remark: AdS/CFT is remarkably more "fit" to the SUSY/superstring idea, but it seems that the Universe has chosen the "wrong" sign for $\Lambda$!

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  • $\begingroup$ The behavior of de Sitter space in the presence of interacting quantum fields is very much an open area of research - with very little certainties (I spent about a year writing my bachelor's thesis on the topic)! $\endgroup$
    – Danu
    Commented Aug 31, 2014 at 16:18
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    $\begingroup$ Supersymmetry is broken isn't it? $\endgroup$
    – John Rennie
    Commented Aug 31, 2014 at 17:54
  • $\begingroup$ What makes you believe, that $\Lambda$ is a constant, to begin with, rather than a dynamic variable, that just happens to have a particular size and sign at this particular moment? Until someone shows me how to measure $\Lambda$ at all (or, at the very least several other) times in the past, I would be very careful to make any assumptions about the "choices" of the universe. $\endgroup$
    – CuriousOne
    Commented Aug 31, 2014 at 22:00
  • $\begingroup$ Curious: the Universe is accelerating, it implies a positive lambda NOW (just as it is expected it was in the inflationary epoch if you believe in inflation theory). It is obvious that lambda was not ALWAYS dominating the cosmic expansion (trivial from Cosmology lectures), and that it COULD be varying, BUT, the thing that Lambda is POSITIVE now it seems to be a "robust" experimental conclusion... $\endgroup$
    – riemannium
    Commented Sep 1, 2014 at 16:09
  • $\begingroup$ Related: physics.stackexchange.com/q/399038/2451 , physics.stackexchange.com/q/457834/2451 and links therein. $\endgroup$
    – Qmechanic ♦
    Commented Mar 11 at 7:00

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