Frictionless UV-finite Instantons in Curved Spacetime

We identify a new class of UV-complete instanton solutions that describe the false vacuum- decay of a real scalar field in a particular curved spacetime background. To this end, we consider a simple scalar theory with a Coleman potential and calculate the Euclidean action $S_{\text{E}}$ by assuming an O(4)-symmetric curved spacetime. The function $a(r)$ dictating the geometry of spacetime may consistently be chosen to be a constant, thereby eliminating the drag forces from the equations of motion and ensuring that the gravitational backgrounds of both the false vacuum and bounce solutions are identical. By employing standard WKB and Gelfand-Yaglom methods, we compute the corresponding prefactor due to quantum fluctuations around this frictionless bounce solution which becomes UV finite after renormalization. The possible consequences of such frictionless UV-finite instantons are discussed.