Theta-problem and the String Swampland

Abstract

In the context of $\mathcal{N}=2$ supergravity without vector multiplets coupled to hypermultiplets, the coupling constant of graviphoton $\tau$ is apriori a free parameter. Stringy realization of this and using a mathematical conjecture leads to the statement that $j(\tau )\in \mathbb{R}$ so that the $\theta$-angle is $0$ or $\pi$. We conjecture that for any consistent realization of $\mathcal{N}=2$ supergravity theories coupled only to hypermultiplets this is the case and the rest belong to the swampland. This leads to the speculation that the $\theta$-angle for QCD or QED may also be fixed to $0$ for quantum gravitational consistency.

7 pages

References in corpus (4)

• Symmetries and Strings in Field Theory and Gravity
• The String Landscape, the Swampland, and the Missing Corner
• Periods of double octic Calabi--Yau manifolds
• Arithmetic and intermediate Jacobians of some rigid Calabi-Yau threefolds

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• The Weak Gravity Conjecture and Axion Strings
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• Moduli spaces of Calabi-Yau $d$-folds as gravitational-chiral instantons
• Dark energy, Ricci-nonflat spaces, and the Swampland
• Swampland geometry and the gauge couplings
• A Note on the dS Swampland Conjecture, Non-BPS branes and K-theory
• S-dual Inflation and the String Swampland
• Monopole Breaking of Chern-Weil Symmetries
• Topological susceptibility and information theory