Swampland Constraints on No-Boundary Quantum Cosmology
  The Hartle-Hawking no-boundary proposal describes the quantum creation of the
universe. To have a non-negligible probability to obtain a classical expanding
universe, eternal inflation is required, which is severely constrained by
Swampland conjectures such as the refined de Sitter conjecture and the distance
conjecture. We discuss this issue in detail and demonstrate the
incompatibility. We show that the dimensionless parameters in the refined de
Sitter conjecture should be bounded from above by a positive power of the
scalar potential to realize the classical expanding universe. In other words,
the probability of the classical expanding universe is extremely small under
the Swampland conjectures unless the parameters are much smaller than unity. If
they are order unity, on the other hand, the saddle-point solution itself
ceases to exist implying a genuinely quantum universe.
