Bubble-resummation and critical-point methods for ${\hat{I}}^2$-functions at large $N$

Abstract

We investigate the connection between the bubble-resummation and critical-point methods for computing the ${\hat{I}}^2$-functions in the limit of large number of flavours, $N$, and show that these can provide complementary information. While the methods are equivalent for single-coupling theories, for multi-coupling case the standard critical exponents are only sensitive to a combination of the independent pieces entering the ${\hat{I}}^2$-functions, so that additional input or direct computation are needed to decipher this missing information. In particular, we evaluate the ${\hat{I}}^2$-function for the quartic coupling in the Gross-Neveu-Yukawa model, thereby completing the full system at $\mathcal{O}(1/N)$. The corresponding critical exponents would imply a shrinking radius of convergence when $\mathcal{O}(1/N^2)$ terms are included, but our present result shows that the new singularity is actually present already at $\mathcal{O}(1/N)$, when the full system of ${\hat{I}}^2$-functions is known.

11 pages, 7 figures; v2: references added, matches the published version