Global curvature control in a regular black hole with Minkowski core and inner-extremal horizon

Abstract

We construct a static, spherically symmetric regular black hole with a Minkowski core, a non-extremal outer horizon, and a degenerate inner horizon with vanishing surface gravity. The spacetime exhibits two main features. First, in the large-mass regime with

, the maximal Kretschmann scalar becomes nearly independent of the ADM mass and is mainly controlled by the inner-horizon radius

$$r_-$$ r -

, providing a simple sufficient condition for the curvature to remain sub-Planckian everywhere. Second, the effective cubic zero of the metric function replaces the standard exponential near-horizon amplification with power-law behavior. A massless scalar test field shows that the geometric blueshift factor grows as

$$v^{3/2}$$ v 3 / 2

. Then, we use the double-null shell and Ori models to examine the corresponding effective mass dynamics. The nonlinear shell-crossing contribution decays at late times, while the Ori evolution with a Price-law ingoing flux keeps the internal Misner–Sharp mass bounded. In both descriptions, the late-time mass approaches

$$r_-/2$$ r - / 2

. The same inner-horizon scale therefore controls the global curvature bound and the finite mass scale reached by the shell dynamics.