Theory HEP Seminar

Distant Strings on the Swampland

Irene Valenzuela

Harvard University

In this talk, I will explain recent developments on the Swampland Distance Conjecture and the asymptotic geometry of the field space in 4d N=1 EFTs. I will discuss a direct relation between the existence of fundamental axionic strings, dubbed EFT strings, and infinite distance limits in 4d N=1 EFTs coupled to gravity. The backreaction of EFT strings can be interpreted as an RG flow of their couplings, and allows one to probe different regimes within the field space of the theory. We propose that any 4d EFT infinite distance limit can be realised as an EFT string RG flow. We show that along such limits the EFT string becomes asymptotically tensionless, and so the EFT eventually breaks down. This provides an upper bound for the maximal field range of an EFT with a finite cut-off, and reproduces the Swampland Distance Conjecture from a bottom-up perspective. Our results hold even in the presence of a non-trivial potential, as long as its energy scale remains well below the cut-off. We check our proposal for large classes of 4d N=1 string compactifications and find that, even if there are typically other towers of particles becoming light, the mass of the leading tower always scales with the string tension as m²~T^w in Planck units with w=1,2,3. The presence of higher spin fields underlying the Distance conjecture is also clear from a CFT perspective.