#paperOfTheDay "Non-Wilsonian ultraviolet completion via transseries" from 2021. A #quantumFieldTheory with marginally renormalizable coupling, such as the standard model of particle #physics usually leads to a power series solution that is divergent in two different ways: The number of #FeynmanDiagram s grows too fast, and the renormalized value of individual diagrams grows too fast. The latter is called #renormalon , and it can also be found in many other frameworks of QFT.
The present paper uses an analysis based on the renormalization group equation, truncated to low-order terms, to argue that the presence of the renormalon implies an ambiguity in the resummation. The technical machinery for this is called "resurgence", the basic mechanism is really intuitive: The Borel resummation is an integral along the positive real line, the renormalon is an algebraic singularity on that line, hence there is an ambiguity of which side (and how often, etc) one wants to pass the singularity. The paper arrives at two possible, mutually exclusive, interpretations of this finding.
I find these considerations really exciting, and they are closely related to my own work. However, I think it is fair to say that the many papers that have been written about renormalon chain resummation often raise more new questions than they answer, and at least to me the "big picture" of how this is supposed to work beyond leading-order is largely unclear. https://doi.org/10.1142/S0217751X21500160

Today's #paperOfTheDay is "Why there is Nothing rather than something: A theory of the cosmological constant" from 1988. Like yesterday's paper, it deals with the intersection between quantum field theory and #generalRelativity, but the 30 years between them clearly show. Coleman's 1988 paper is an argument in the style of that time (which structurally is quite similar to much of the older #renormalon literature): Heuristic manipulations of formal objects such as the wave function of the universe, or divergent sums over all spacetime geometries. The outcome of this argument is that if #wormholes exist (caused by quantum effects at a scale that is much smaller than observations, but larger than the Planck scale), they can drive the cosmological constant to zero in an Euclidean path integral formulation of general relativity. As always with Coleman, the language is quite funny and frank about the paper's limitations: He writes "Although I find this theory in many ways very attractive, I must honestly stress its speculative character. It rests on wormhole dynamics and the Euclidean formulation of quantum gravity. This is doubly a house built on sand. [...] the Euclideon formulation of gravity is not a subject with firm foundations and clear rules of procedure; indeed, it is more like a trackless swamp". Observations like these have by now, 30 years later, led to a style of theoretical physics that is much more systematic and mathematical than in the 1980s, but also sometimes less intuitive. #dailyPaperChallenge https://doi.org/10.1016%2F0550-3213(88)90097-1