Past exam of the mathematics course of the University of Cambridge 2010 iii Paper 27 4 b Solution 2026-10-14
Let be the inverse image-capacity clock. Part (a) and the quadratic variation of a stochastic integral giveThe Dambis-Dubins-Schwarz theorem, or the Lévy characterization of Brownian motion, now shows that is standard Brownian motion up to the terminal image time. If that terminal clock is finite, it can be extended by a fresh Brownian continuation; this does not assert anything about the subsequent image trace. The initial value is zero because .
Differentiating the image Loewner chain with respect to its own half-plane capacity time givesThus, until its first hit of , the reparametrized image has the ordinary chordal SLE law from to infinity. This follows from the uniqueness of the Chordal Loewner equation for a given continuous driver; the continuous Loewner trace is recovered from the inverse-map limit. Localization can be removed by exhausting times strictly before this boundary contact. The terminal event is defined from the trace itself, so equality of the stopped trace laws follows as well.
On the other hand, the definition of Conformal invariance of SLE says that the full unparameterized image has the law of chordal from to , namely the law of . Its stopping event at is exactly the image of the original stopping event at . Therefore the same stopped image has both laws: ordinary from to infinity stopped at , and from to stopped at . We concludeThe statement does not identify with in their original clocks. It is target-change locality of SLE6, derived from the zero drift and capacity time change rather than assumed as a theorem.
Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 203 4 d Solution Created 2026-10-03 Updated 2026-10-06
For the SLE driver , apply the Itô formula to . At a fixed spatial point, has finite variation locally in time by the derivative formula in part (c); there is no extra spatial martingale term. ConsequentlyThis exact cancellation is the target-change locality of SLE6. For a general parameter the transformed SLE driving function would have drift .
Define the increasing clock and its inverse byThe derivative is real and strictly positive before , so this is a valid continuous time change of a continuous process. The driver is a continuous local martingale with quadratic variation and initial value zero. The Dambis-Dubins-Schwarz theorem gives a standard Brownian motion such thatIf the terminal clock is finite, the Brownian motion may be extended beyond that stopping time; only its stopped part is used here. Reparameterizing the image maps givesThese are exactly the defining Chordal Loewner equation and half-plane-capacity parameterization for . The trace is . Hence the image curve is also ordinary chordal after this time change, up to the specified stopping time:
Target-dependent continuation of SLE6 2026-10-14
At parameter six, changing a boundary target preserves the initial unparameterized SLE law until the growing hull separates the two possible targets. After separation, each curve continues in the complementary component whose boundary contains its own target. A curve targeted at infinity follows the unbounded component, whereas a finite separated target lies on a different component. The target-change locality of SLE6 proof no longer applies: its conformal automorphism of the upper half-plane conjugates corresponding surviving domains only before this separation. A zero drift before contact does not give equality of complete curve laws afterwards.