Supersymmetry is still possible because it has many adjustable features that can be tweaked to remove it from the exclusion ranges of existing parameter space (keep in mind that SUSY is a class of theories and not just a single theory). But, the kinds of SUSY theories that are still possible are increasingly unlike the ones that theorists had hoped for when they came up with SUSY and the versions that remain possible do increasingly little to solve the unsolved problems in physics that it was invented to solve.Is supersymmetry still possible or has it been proven wrong?
Eddington said:The law that entropy always increases, holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.
This seems harsh. The standard model made no prediction for the mass of the Higgs. Experiments ruled out more and more parameter space until it was discovered. Supersymmetry makes very definite predictions given a choice of model and parameters. Experiments can rule out more parameter space until confirmation or loss of interest. Loss of interest does not necessarily mean supersymmetry is not part of nature.How did Eddington phrased it:
People will still publish theories on Supersymmetry, LQG, Superstring theories even if they don't provide any testable predictions, you could always argue we need more energies.
I don't think you can call these "theories" since you don't predict something, you just tweaking the parameters post experiments.
SUSY does provide predictions for any given set of parameters. Indeed, that is the main reason that so many LHC data are analyzed using hypothesis testing statistical methods that compare LHC data to both SM and SUSY predictions. Doing SUSY calculations to get predictions is frequently easier than in the SM and is rarely significantly more difficult. The problem that is has faced is that every experimental test it has been given for any particular set of parameters has either been falsified, or has proved impossible to confirm or deny due to a lack of statistical power in existing experiments.I don't think you can call these "theories" since you don't predict something, you just tweaking the parameters post experiments.
I think this is a very good summary. Lets add, it is not only naturalness, also the triple coincidence of renormalisated couplings needs SUSY to start near the TeV scale.From naturalness argument people expected SUSY to kick in at the 1TeV scale (this was motivated by radiative corrections for the Higgs boson). So our notion of naturalness seems to be wrong. Theoretically, SUSY could still be there, but it becomes more and more improbable (in a Bayesian sense).
I think in the future people will regard SUSY as a useful mathematical tool which aided us to get certain insights, like dualities. And, of course, in retrospect it's always easy to say "it was wrong", but the theoretical motivations for it were very solid. From e.g. SU(5)-unification we know however that nature does not always follow our notion of beauty.