This is tremendously interesting. In particular their suggestion that one solution to the conundrum is the existence of additional very light force carriers.
Perhaps a more up to date particle physicist than I can chip in bu such particles must presumably be outside of the Standard Model (as iirc from my particle physics, which is admittedly getting on for 20 years ago, there ain't any more slots left). I know there are some interesting new theories which are very widely disputed and which have a lot of other problems, such as the Exceptionally Simple Theory, which predict a whole host of additional particles - but there are reasons such things are on the fringe right now.
With all the progress in the last couple of decades, and all these new results pointing to new Physics in all kinds of areas, it's a fascinating time for the field - and makes one wonder where we'd be if the entire faculty hadn't dedicated decades down the String theory rabbit hole.
such particles must presumably be outside of the Standard Model
Yes, they are. With the detection of the Higgs we have now detected experimentally all of the Standard Model particles. Any new "very light force carriers" would definitely be outside of the Standard Model.
Gravitons are not included in the Standard Model, which doesn't cover gravity at all, and is not intended to.
As far as whether gravitons could be the "very light force carriers", I don't see how that would be possible; gravity is way too weak a force to make that much of a difference in measurements on hydrogen atoms, even muonic ones.
As a fascinated layman, strings always reminded me quite a bit of epicycles and I've had an impression that string theory had been falling out of favor for some time now.
The "popular fad" aspect of string theory has certainly lost much of its luster, no question, particularly as far as the general public is concerned. (The early excitement about the theory in the 1980's was apparently rather over the top.) The fact that folks like Peter Woit and Lee Smolin were able to publish popular books about their distaste for string theory reflects that (and those books in turn did a lot to establish the "string theory is overrated" counter-meme).
But within actual physics departments, as far as I've been able to tell string theory holds much the same position that is has for many years: it's the direction that most people interested in pursuing a "theory of everything" seem to find most promising. (Plenty of physicists have other interests, of course, even within particle physics: the phenomenology involved in interpreting LHC data and predicting new phenomena to look for at that scale is a big deal these days, and string theory really isn't relevant to those questions.) As far as I can tell from the inside, that's primarily a genuine process of ongoing scientific judgement rather than pure groupthink.
As a string theorist, I can see to some degree why you'd say it reminds you of epicycles: I think most of us would agree that there's got to be some deeper underlying truth that would make the structures of string theory seem more unified and elegant. The difference between that and epicycles, at least to a string theorist, is that we're optimistic that string theory as we know it is a valid, well-defined approximation to the underlying theory, whatever form that may take. Epicycles, on the other hand, were (as I understand it) sort of a hack, without any intrinsic connection to the true heliocentric model.
"The phenomenology involved in interpreting LHC data and predicting new phenomena to look for at that scale is a big deal these days, and string theory really isn't relevant to those questions."
I think "string theory is overrated" meme is mainly fueled by the fact that it "really isn't relevant to those questions". I got the impression that many string theorists claimed string theory to be relevant to those questions, and only changed position once it became clear that won't be the case.
From what I understand (as a fellow fascinated layman) is that String Theory is still the dominant StandardModel++ theory in academia but there are a few who are being more vocal about its validity.
Peter Woit is a notable skeptic of the viability of String Theory and has a blog which contains links to a number of interesting physics blogs.
http://www.math.columbia.edu/~woit/wordpress/
The dominant StandardModel++ theory is the standard model + super symmetry. String Theory is still in its formative years and best described as a collection of ideas than as a proper theory.
Perhaps a more up to date particle physicist than I can chip in bu such particles must presumably be outside of the Standard Model (as iirc from my particle physics, which is admittedly getting on for 20 years ago, there ain't any more slots left). I know there are some interesting new theories which are very widely disputed and which have a lot of other problems, such as the Exceptionally Simple Theory, which predict a whole host of additional particles - but there are reasons such things are on the fringe right now.
With all the progress in the last couple of decades, and all these new results pointing to new Physics in all kinds of areas, it's a fascinating time for the field - and makes one wonder where we'd be if the entire faculty hadn't dedicated decades down the String theory rabbit hole.