Abstract
We propose a scenario with string theory in the deep ultraviolet, an intermediate asymptotically safe scaling regime for gravity and matter, and the Standard Model in the infrared. This could provide a new perspective to tackle challenges of the two models: For instance, the gravitational Renormalization Group flow could connect a negative microscopic to a positive macroscopic cosmological constant, potentially rendering string theory on an anti-de Sitter background observationally viable. Further, the unitarity of a string-theoretic ultraviolet completion could be inherited by an asymptotically safe fixed point, despite the presence of higher-order interactions. We discuss necessary conditions on the scale of asymptotic safety and the string scale for our scenario to be viable. As a first test, we explore the weak-gravity conjecture in the context of asymptotically safe gravity.
Highlights
Asymptotic safety, string theory and the weak gravity conjecture de Alwis, Senarath; Eichhorn, Astrid; Held, Aaron; Pawlowski, Jan M.; Schiffer, Marc; Versteegen, Fleur
The transition scale ktr is defined as the energy scale at which a departure from scale-symmetry sets in, such that below ktr the couplings deviate from their values in the asymptotically safe scaling regime
It is key that the determination of infrared (IR) values of couplings following from scale-symmetry carries over if an asymptotically safe scaling regime is only realized over a finite, but large enough, range of scales, with new physics kicking in at very high energy scales
Summary
What is the fundamental nature of the building blocks of our universe? String theory and the asymptotically safe Standard Model (ASSM) are both possible candidates. We assume that additional states from string theory (such as heavy moduli and superpartners) decouple at high energies (i.e., directly below the string scale), so that the effective-field theory regime contains only the Standard Model and gravity This assumption can be relaxed to accommodate further matter fields that arise from string theory, if an asymptotically safe fixed point persists under extensions by the corresponding additional fields. This might include the intriguing consequence that the Higgs mass [1,74,75], the top quark mass [2], the bottom quark mass [5] and the Abelian gauge coupling [76,3] could emerge as predictions of string theory This follows since functional RG studies indicate that the respective couplings come out as irrelevant couplings with finite asymptotically safe fixed-point values.
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