SUSY 2015, this year’s version of the big annual conference on supersymmetry, has been going on for the past week at Lake Tahoe. Joe Lykken began his summary talk by explaining how as a kid he was a big fan of the Bonanza TV show, about a ranch along the shores of Lake Tahoe. He always wanted to travel to Lake Tahoe and visit the Ponderosa ranch, was bitterly disappointed when he finally got to Lake Tahoe and found that the Ponderosa did not exist. The relevance of the story to his talk is “left as an exercise for the audience”, with a hint in the next slide, which gives the executive summary of the search for SUSY at the LHC: “We haven’t found it.” He ends the summary talk with this now well-known prediction for the SUSY 2215 conference.
In his discussion of “naturalness” (see slide 25), he makes what to me has always been an obvious point, but I haven’t seen it made ever at a conference like this:
Is the Standard Model (almost) all there is?
Maybe the naturalness argument applied to the Higgs is just wrong (well, it was apparently wrong for the vacuum energy too)
The Standard Model plus some TeV scale renormalizable additions (like dark matter) might be all there is
The Standard Model itself, or with such modest additions, is completely natural (EW scale is not a prediction)
Usual counterargument involves the putative Planck scale and unification thresholds, but this is speculative
An unsatisfying scenario, leaving many questions unanswered, but has a certain minimalist appeal
Some of the other talks included:
- Nima Arkani-Hamed’s slides and title aren’t available, but the Twitter coverage of the conference included a picture of one of his slides. This tweet reports that he announced that he was “rather annoyed” and “sick of thinking” about naturalness. I guess if you’ve spent most of your career arguing that the LHC would “resolve the naturalness problem” (because it would move fine-tuning from the Tevatron 10% to 1% if it saw nothing), gearing up now for an argument that a 100 TeV collider is needed to “resolve the naturalness problem” (by going from 1% to .1%) would be kind of annoying… In the slide he makes the same argument as in Particle Fever: no SUSY means particle theory should commit suicide and embrace the multiverse.
- In Gordon Kane’s talk he gave his latest string theory-based predictions for the masses of superpartners. For the last twenty years or so, his gluino mass prediction has always been the same: just a little bit higher than the current bounds. These bounds however keep moving up, so his prediction has moved from 250 GeV in 1997 to 1.5 TeV today (“Detectable soon”!). I think one very solid prediction that one could make is that Kane’s SUSY 2016 gluino mass prediction will be 2 TeV.
- Joe Polchinski’s talk defended moduli stabilization schemes such as the KKLT one that came out of his original work with Bousso, ending with the claim that
The KKLT construction has been thoroughly vetted, and it seems to me has survived robustly.
The de Sitter vacua are still there, as is the landscape.
Besides his pre-KKLT role in moduli stabilization, Polchinski is one of the most prominent exponents of the idea that particle theorists should just give up, using the KKLT moduli-stabilized string vacua as a reason for why string theory can never be tested, but we should believe it anyway. He’s been promoting this heavily since 2004, when he got Scientific American to publish this article with Raphael Bousso. My take on that article seems to have upset him greatly, and had a lot to do with the arXiv policy of not allowing trackbacks to this blog (which continues to this day).
This blog does seem to have played an odd role in the topic of Polchinski’s talk. Back in early 2014 someone wrote to me to suggest that I might want to discuss a series of papers by Bena, Grana et al. which pointed out problems with KKLT. I responded that I didn’t think this was a good idea: while I was no expert, it seemed to me that the KKLT construction was an absurdly complex one involving poorly controlled approximations (thus hard to conclusively decide if it was “right” or “wrong”), and it had entered the realm of ideology, as a bedrock for explaining why string theory could never predict anything. What I didn’t say was that I’m a fan of arguments showing string theory can never predict anything, so why should I publicize work challenging them?
Later in 2014, the same person wrote to me again to suggest that I change my mind, that there was a new preprint about this. I weakened and mentioned it here. A couple months later Polchinski published this, which mounts a defense of KKLT against criticisms like those of Bena, Grana, et al. I didn’t know about this, but did write a long posting about another arXiv preprint he had posted the same day, which was about “dualities” in general, and which I found quite interesting. Only after he and Bousso appeared in the comment section to criticize me about KKLT did I realize that they saw me as responsible for promoting anti-KKLT views, not realizing that I’m actually a KKLT fan. Some strange things have happened over the years at this blog, that Christmas Eve discussion was right up there.
In any case, just to make my views clear: I’m a big fan of KKLT, glad to hear that it now has been “thoroughly vetted”. Back when I first heard about it in 2003, I thought “this is great! now that string theorists have proved to themselves that their theory isn’t predictive, they’ll move on to something else”. I’ve been surprised though about how long that is taking to happen…