Theory HEP Seminar

Tensionless Strings in Four Dimensions and the Swampland

Timo Weigand

Heidelberg

We describe recent progress towards proving various general conjectures about the nature of quantum gravity within string theory. The focus will be on compactifications to four dimensions with N=1 supersymmetry, including the effect of quantum corrections. In the first part of the seminar we will study the Swampland Distance Conjecture, which posits that an infinite tower of states should become asymptotically light as one approaches the boundaries of moduli space at infinite distance in a gravitational theory. According to the Emergent String Conjecture, this tower must either correspond to a Kaluza-Klein tower or to the excitations of a weakly coupled fundamental string emerging at infinite distance. We will verify this general claim in the context of non-perturbative compactifications of F-theory to four dimensions by classifying their infinite distance limits in the Kahler moduli space. An important part is played by quantum corrections: They conspire such that the tension of the asymptotically light emergent string cannot drop below the Kaluza-Klein scale, as required by general consistency conditions. We then discuss the effect of quantum corrections on the Weak Gravity Conjecture in theories with four supercharges: We argue that both the superextremality condition and the mass of the string excitations which become light at weak coupling are modified by quantum corrections in such a way that the Weak Gravity Conjecture continues to be satisfied.