4d strings at strong coupling

A bstract Weakly coupled regions of 4d EFTs to gravity are particularly suitable describe the backreaction BPS fundamental axionic strings, dubbed EFT in a local patch spacetime around their core. We study extension these solutions global ones, which implies probing strong coupling and provides an estimate string tension therein. conjecture that for charge generators such is always possible yields sub-Planckian tension. substantiate this claim by analysing strings made up from NS5-branes wrapping Calabi-Yau threefold divisors either type IIA or heterotic theory. argue case global, non-perturbative data can be simply encoded terms GLSM describing compactification, as we demonstrate explicit examples.