Strong-deflection scaling in nearly symmetric thin-shell wormholes

Abstract

The angular winding of a returning light ray can grow while the family of admissible impacts disappears. We characterize this competition near reflection symmetry in a static thin-shell wormhole joining Schwarzschild exteriors of slightly different masses. Exact shell-frame matching fixes the reflected interval, and a normal coordinate at each nondegenerate photon-sphere maximum gives a composite angular expansion with controlled error on compact interior channel intervals. The result remains valid when the throat distance divided by the mass contrast tends to zero, stays finite or diverges. For a throat distance proportional to a positive power of the fractional mass difference, the width exponent increases from one toward two and then saturates, while the logarithmic winding coefficient decreases from three toward two. Fixed-throat configurations retain their finite-distance amplitude and coefficient three. Reference-subtracted profiles connect the intermediate sector to finite and vanishing scaled throat positions. Independent quadratures test the scaling laws and resolve the slower convergence associated with changing scale ratios. The shrinking solid-angle aperture follows directly from the critical-impact gap. For an axial observer and a transparent test disk confined to the same exterior, the return-phase condition selects the admitted intersections; sampled near-symmetric configurations shift the first available global crossing to a later label. The closing aperture and increasing winding are therefore linked by the accessible radial extent, with disk access determined by the phase accumulated on the emitting segment.