Definitions and background Outline Almost sure multifractal spectrum of SLE Ewain Gwynne (Joint with Jason Miller and Xin Sun) 1 Definitions and background 2 Upper bound 3 Lower bound 4 A few details of the proof 5 Conclusion Massachusetts Institute of Technology Conformally invariant scaling limits, University of Cambridge Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 1 / 59 Ewain Gwynne (MIT) Definitions and background Multifracal spectrum Let e s (D) := Θ The multifractal spectrum of D is a means of quantifying the behavior of |φ0 | (resp. |(φ−1 )0 |) near ∂D (resp. ∂D). Almost sure multifractal spectrum of SLE 2 / 59 Multifractal spectrum Let D ⊂ C be a simply connected domain (e.g. a complementary connected component of an SLEκ curve). Let φ : D → D be a conformal map. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE Definitions and background x ∈ ∂D : lim →0 log |φ0 ((1 − )x)| =s . − log e s (D)) ⊂ ∂D. Let Θs (D) := φ(Θ 3 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 4 / 59 Definitions and background Definitions and background Multifractal spectrum Multifractal spectrum φ e s (D) The multifractal spectrum of D is the two functions s 7→ dimH Θ and s 7→ dimH Θs (D). e s (D) = Θs (D) = ∅ for s ∈ We have Θ / [−1, 1], so this is only of D interest for s ∈ [−1, 1]. Related to, e.g., the harmonic measure spectrum of D, the integral means spectrum of D, the Hölder regularity of φ, and the Hausdorff dimension of ∂D. (1 − )x x Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 5 / 59 Ewain Gwynne (MIT) Definitions and background Related results 6 / 59 Multifractal spectrum Hausdorff dimension computed by Beffara (2008). Hölder exponent computed by Lawler and Viklund (2011) building on works by Rohde and Schramm (2005) and Lind (2008). Non-rigorous predictions for the multifractal spectrum by Duplantier as early as 2000. Lead Duplantier to conjecture SLE duality, the statement that the outer boundary of an SLEκ for κ > 4 locally looks like an SLE16/κ (rigorously established in works by Dubedát, Zhan, Miller-Sheffield) Almost sure multifractal spectrum of SLE Theorem: (Gwynne, Miller, Sun) Let κ > 0 and let η be an SLEκ in a smoothly bounded domain D ⊂ C. Let √ p √ p 4κ − 2 2 κ(2 + κ)(8 + κ) 4κ + 2 2 κ(2 + κ)(8 + κ) s− = , s+ = . (4 + κ)2 (4 + κ)2 Let s ∈ [s− , s+ ]. Almost surely, for each t > 0 and each complementary connected V of η([0, t]), we have Lawler and Viklund (2012) computed the multifractal spectrum at the tip of SLE. Beliaev and Smirnov (2009) computed the average integral means spectrum of SLE. Alberts, Binder, and Viklund (2015) computed a dimension spectrum for points where SLE hits the boundary. More in later talks today. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE Definitions and background 7 / 59 (4 + κ)2 s 2 8κ(1 + s) 8κ(1 + s − s 2 ) − 16s 2 − κ2 s 2 dimH Θs (V ) = . 8κ(1 − s 2 ) e s (V ) = 1 − dimH Θ e s (V ) = Θs (V ) = ∅. For s ∈ / [s− , s+ ], a.s. Θ Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 8 / 59 Definitions and background Definitions and background Multifractal spectrum Multifractal spectrum 1.2 1.0 s- 0.8 ξ(s) s+ ˜ ξ (s) Agrees with predictions of Duplantier. Invariant under replacing κ with 16/κ (SLE duality). s 7→ ξ(s) is maximized at s = κ/4, where is equals 1 + κ/8. 0.6 -1.0 Ewain Gwynne (MIT) 0.4 κ 0.2 4 0.0 -0.5 0.5 This yields an alternative proof that dimH η = 1 + κ/8 a.s. for κ ∈ (0, 4]. 1.0 Almost sure multifractal spectrum of SLE 9 / 59 Ewain Gwynne (MIT) Definitions and background Almost sure multifractal spectrum of SLE 10 / 59 Definitions and background Integral means spectrum Integral means spectrum The integral means spectrum of D is the function IMSD : R → R defined by R log ∂B1− (0) |φ0 (z)|a dz , IMSD (a) = lim sup − log →0 Average integral means spectrum of SLE computed by Beliaev-Smirnov (2009): R 2π log 0 E|(ft−1 )0 (re iθ )|a dθ . lim sup − log(r − 1) + r →1 where φ : D → D is a conformal map. Related to several conjectures in complex analysis. Usually hard to compute for deterministic fractals, but can be easier for random fractals. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 11 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 12 / 59 Definitions and background Definitions and background Integral means spectrum Integral means spectrum 3.0 We obtain the a.s. bulk integral means spectrum of SLE (which is defined in the same way as the ordinary integral means spectrum, but with small neighborhoods of the tip and starting point of η removed). 2.5 1.5 1.0 0.5 -6 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 13 / 59 2.0 a- Corollary: Let κ > 0 and let η be an SLEκ in a smoothly bounded domain D ⊂ C. Almost surely, for each t > 0, each a ∈ R, and each complementary connected V of η([0, t]), we have a < a− −1 + s− a, √ 2 bulk IMSV (a) = −a + (4+κ)(4+κ− (4+κ) −8aκ) , a ∈ [a− , a+ ] 4κ −1 + s a, a > a+ . + Ewain Gwynne (MIT) Upper bound -4 -2 0 a+ 2 Almost sure multifractal spectrum of SLE 4 6 14 / 59 Upper bound Outline Setup 1 Definitions and background 2 Upper bound To establish an upper bound for the Hausdorff dimension of the sets e s (D), we need to estimate the probability that a point is Θs (D) and Θ contained in these sets. 3 Lower bound By SLE duality it suffices to consider κ ≤ 4. 4 A few details of the proof 5 Conclusion Ewain Gwynne (MIT) By a change of coordinates, we can assume that η is a chordal SLEκ from −i to i in D. Let Dη be the right complementary connected component of η. Also let Ψ : Dη → D be the conformal map which fixes −i, i, and 1. Almost sure multifractal spectrum of SLE 15 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 16 / 59 Upper bound Upper bound Setup Setup Ψ i i To establish an upper bound for the Hausdorff dimension of the sets e s (D), we need to estimate the probability that a point is Θs (D) and Θ contained in these sets. By SLE duality it suffices to consider κ ≤ 4. Dη 1 By a change of coordinates, we can assume that η is a chordal SLEκ from −i to i in D. Let Dη be the right complementary connected component of η. 1 Also let Ψ : Dη → D be the conformal map which fixes −i, i, and 1. Dη will be convenient for the two-point estimate because we can grow the curve from both directions. −i Ewain Gwynne (MIT) −i Almost sure multifractal spectrum of SLE 17 / 59 Ewain Gwynne (MIT) Upper bound Reverse SLE Reverse SLE/GFF coupling Pointwise derivative estimates for finite time inverse maps Reverse SLEκ is obtained by solving the reverse Loewner equation Change of variables Estimates for the area of the set where forward finite time maps have given derivative behavior ġt (z) = − Markov property Pointwise derivative estimates for time and regularity infinity map conditions Usual argument Upper bound for dimension of Ewain Gwynne (MIT) 18 / 59 Upper bound Upper bound Reverse SLE martingales Almost sure multifractal spectrum of SLE 2 . gt (z) − Ut The solution is a family of conformal maps gt : H → H \ Kt , for (Kt ) hulls in H. √ If Ut = κBt , then gt − Ut has the same law as the time t centered Loewner map of a forward SLEκ . Usual argument Upper bound for dimension of Almost sure multifractal spectrum of SLE 19 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 20 / 59 Upper bound Upper bound Reverse SLE One point estimate for inverse maps If z ∈ H and ρ ∈ R, then gt 2 /8κ Mt = |gt0 (z)|(8+2κ−ρ)ρ/8κ (Im gt (z))−ρ |gt (z) − √ κBt |ρ/κ is a martingale. Introduced by Lawler (2009). Reverse analogue of the Schramm-Wilson martingales for forward SLE. Re-weighting by Mt gives a reverse SLEκ (ρ) with a force point at z. Call this reweighted law Pz∗ . Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 21 / 59 Ewain Gwynne (MIT) Upper bound One point estimate for inverse maps If Im z = and z is not too close to 0 or ∞, then P |gt0 (z)| ≈ −s ≈ α Pz∗ |gt0 (z)| ≈ −s To show Pz∗ (|gt0 (z)| ≈ −s ) 1 we use a coupling with a Gaussian free field. where ≈ means −s+u ≤ |gt0 (z)| ≤ −s−u for u > 0 small but fixed. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 22 / 59 Upper bound One point estimate for inverse maps z We claim that if we take ρ = (4+κ)s 1+s , then P∗ Given this we obtain P (|gt0 (z)| ≈ −s ) ≈ α . Almost sure multifractal spectrum of SLE (|gt0 (z)| ≈ −s ) 1. 23 / 59 By a theorem of Sheffield (2011) we can find random distributions h d and ht (GFF’s plus harmonic functions) s.t. h ◦ gt + Q log |gt0 | = ht √ √ under P∗z , where Q = 2/ κ + κ/2. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 24 / 59 Upper bound Upper bound One point estimate for inverse maps One point estimate for inverse maps To show Pz∗ (|gt0 (z)| ≈ −s ) 1 we use a coupling with a Gaussian free field. h ◦ gt + Q log |gt0 | gt By a theorem of Sheffield (2011) we can find random distributions h h d and ht (GFF’s plus harmonic functions) s.t. h ◦ gt + Q log |gt0 | = ht √ √ under P∗z , where Q = 2/ κ + κ/2. By estimating the circle average processes for h and ht , we get that |gt0 (z)| ≈ −s with high probability under P∗z . This leads to P |gt0 (z)| ≈ −s ≈ α(s) . Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 25 / 59 Ewain Gwynne (MIT) Upper bound Upper bound Using stochastic calculus and a symmetry between forward and reverse SLEκ (ρ) due to Duplantier, Miller, and Sheffield (2014), we can also add extra regularity conditions to our lower bound. This is the most technical part of the one-point estimate. Our derivative estimates allow us to estimate the expected number of e s (H \ η([0, t])). -balls needed to cover Θ This gives an upper bound for the Hausdorff dimension of e s (H \ η([0, t])) and the integral means spectrum of H \ η([0, t]). Θ Basic complex analysis allows us to transfer these upper bounds to Dη . This is also the main reason why we can’t just cite other similar results in the literature (e.g. Rohde-Schramm, Beliaev-Smirnov). Almost sure multifractal spectrum of SLE 26 / 59 Upper bound One point estimate for inverse maps Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 27 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 28 / 59 Upper bound Upper bound Area estimate One point estimate for the forward maps Ψ i By a change of variables and the Koebe quarter theorem (|ft0 (z)| dist(z, η) Im ft (z)), we can estimate the area of the set of z ∈ H with |ft0 (z)| ≈ s and dist(z, η([0, t])) ≈ 1−s . i z Dη We then transfer this to an estimate for the area of the set As of z ∈ Dη for which |Ψ0 (z)| ≈ s and dist(z, η) ≈ 1−s . 1 −i Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE Ewain Gwynne (MIT) 29 / 59 1 −i Almost sure multifractal spectrum of SLE Upper bound 30 / 59 Lower bound One point estimate for the forward maps Outline Using the Markov property, one can argue that P (z ∈ As ) does not depend too strongly on z. This takes us from area estimates to pointwise estimates: P |Ψ0 (z)| ≈ s , dist(z, η) ≈ 1−s ≈ γ(s) . 1 Definitions and background 2 Upper bound 3 Lower bound 4 A few details of the proof 5 Conclusion This estimate leads to an upper bound for dimH Θs (Dη ). Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 31 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 32 / 59 Lower bound Lower bound Lower bound Lower bound We prove a lower bound for dimH Θs (Dη ) first. This will allow us to construct a Frostman measure on a self-similar subset of Θs (Dη ) (the “perfect points”), i.e. a positive finite measure satisfying Z Z 1 dν(z)dν(w ) < ∞ |z − w |α Let q := s/(1 − s). We define nested events En (z) for z ∈ D such that T∞ s n=1 En (z) ⊂ {z ∗∈ Θ (Dη )}. P (En (z)) ≈ e −βγ (q)n . P(En (z)∩En (w )) γ ∗ (q)+o|z−w | (1) . P(En (z))P(En (w )) ≤ |z − w | Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE for given α < ξ(s). 33 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE Lower bound 34 / 59 Lower bound Lower bound Lower bound φβ i Let η be the time reversal of η, which is an SLEκ from −i to i. i η̄ We will look at the behavior of η and η at the first time they hit Be −β (z). 1 1 η −i Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 35 / 59 Ewain Gwynne (MIT) −i Almost sure multifractal spectrum of SLE 36 / 59 Lower bound Lower bound Lower bound Lower bound i ψ0,j i Now we iterate this. Let η0,1 = η. Inductively let η0,j+1 be the curve obtained by running η0,j and η 0,j up to the first time they Be −β (0), then applying the map ψ0,j which takes the complement of the two sides of the curve to D, with 0 fixed. d η̄0,j η̄0,j+1 η0,j η0,j+1 −i −i Then we have η0,j = η, modulo perturbations of the endpoints (which we can deal with by growing out a little more of the curve). Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 37 / 59 Ewain Gwynne (MIT) Lower bound 38 / 59 Lower bound Lower bound Lower bound Let φ0,j be defined in the same manner as φβ above, but with η0,j in place of η. Let E0,j be the event that |φ0j (0)| ≈ e −βq (plus a bunch of regularity conditions). T Let En (0) = nj=1 E0,j . Define En (z) for z ∈ D by first mapping z to 0. Define the perfect points to be the (approximately) the set of z ∈ D for which En (z) occurs. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE Almost sure multifractal spectrum of SLE 39 / 59 Our events are set up so that T∞ n=1 En (z) ⊂ Θs (Dη ). The probability that |φ0β (0)| ≈ e −βq is of the same order as the probability that |Ψ0 (0)| ≈ e −βq and dist(z, η) ≈ e −β . We know the latter probability is e −βγ (with = e −β/(1−s) ). Hence P(En (z)) ≈ Ewain Gwynne (MIT) ∗ (q) by the one-point estimate ∗ e −nβγ (q) . Almost sure multifractal spectrum of SLE 40 / 59 Lower bound Lower bound Lower bound Lower bound ψz,k Consider two points z and w with |z − w | ≈ e −kβ . η̄z,k We need to estimate P(En (z) ∩ En (w )) for n ≥ k. w z The points 0 = ψz,k (z) and ψz,k (w ) are at constant order distance apart. ηz,k Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 41 / 59 Ewain Gwynne (MIT) Lower bound 42 / 59 Lower bound Lower bound Flow lines We can couple η with a GFF h on D in such a way that η is the “flow line” of h started from −i (in the sense of Miller and Sheffield’s Imaginary Geometry papers). We would like to say that the behaviors of the curve near the two points are approximately independent. However, we are interested in the derivative of a certain conformal map, which may depend on the whole curve. At each stage in the construction of En (z), we add auxiliary flow lines ± ηz,j for h started from the tip of the part of η we have grown so far. To get around this we need to localize. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE Almost sure multifractal spectrum of SLE 43 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 44 / 59 Lower bound Lower bound Flow lines Flow lines The auxiliary flow lines form “pockets” with the property that the intersection of η with each pocket is conditionally independent of what happens outside the pocket, given the pocket. η̄z,2 η̄ + ηz,2 + ηz,1 We re-define the curves ηz,j so that they only depend on the part of the curve inside the j − 1th pocket around z. − ηz,2 − ηz,1 ηz,2 η Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 45 / 59 Ewain Gwynne (MIT) Lower bound Almost sure multifractal spectrum of SLE 46 / 59 Lower bound Flow lines Lower bound This leads to an estimate for + ηw,k+1 η̄ − ηw,k+1 w z + ηz,k+1 + ηz,k η Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE in terms of |z − w |. Can use the same estimates (and some relatively minor tricks) to get e s (Dη ) and IMSbulk (Dη ). a lower bound for dimH Θ − ηz,k+1 − ηz,k P(En (z)∩En (w )) P(En (z))P(En (w )) Once we have such an estimate, we get a lower bound for dimH Θs (Dη ) via the usual (Frostman measure) argument. 47 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 48 / 59 A few details of the proof A few details of the proof Outline Reverse continuity conditions 1 Definitions and background 2 Upper bound 3 Lower bound 4 A few details of the proof 5 Conclusion Throughout this talk, all of our events have involved “regularity conditions”. The most important (but by no means the only) such regularity conditions are the following. Let A ⊂ D be a closed set. Let D be a connected component of D \ A and let f : D → D be a conformal map. Let µ : (0, ∞) → (0, ∞) be an increasing function. G(f , µ): for each δ > 0 and each x, y ∈ ∂D ∩ ∂D with |x − y | ≥ δ, we have |f (x) − f (y )| ≥ µ(δ). G 0 (A, µ): for each δ > 0, A lies at distance at least µ(δ) from ∂D \ (A ∩ ∂D). Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 49 / 59 Ewain Gwynne (MIT) A few details of the proof Almost sure multifractal spectrum of SLE 50 / 59 A few details of the proof Reverse continuity conditions Reverse continuity conditions f Bδ (i) A G(f , µ) and G 0 (A, µ) are “equivalent” in the sense that for each µ, there exists µ0 (depending only on µ) such that G(f , µ) ⇒ G 0 (A, µ0 ) and vice versa. D µ(δ) Bδ (−i) Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 51 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 52 / 59 A few details of the proof A few details of the proof Reverse continuity conditions Strict mutual absolute continuity G(f , µ) is useful because many of our maps are normalized so that they fix −i, i, and 1. In order to achieve such a normalization, we sometimes need to apply a Möbius transformation. The condition G(f , µ) ensures that such a transformation does not distort distances too much. The condition G 0 (A, µ) (typically with A = η or some part of η) is useful because many of our estimates degenerate near the boundary. G(f , µ) is well-behaved under compositions of maps. G 0 (A, µ) is easy to deal with geometrically. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 53 / 59 The parts of η inside the “pockets” used in the proof of the lower bound are SLEκ (ρL ; ρR )’s, not ordinary SLEκ ’s. However, if we grow out a little bit of the curves, then map back, we get curves whose laws are strictly mutually absolutely continuous with respect to the law of ordinary SLEκ curve, meaning that their laws are absolutely continuous, with Radon-Nikodym derivative bounded above and below by deterministic constants. We can do this at the same time we move the endpoints to −i and i. Ewain Gwynne (MIT) A few details of the proof Almost sure multifractal spectrum of SLE 54 / 59 A few details of the proof Strict mutual absolute continuity Strict mutual absolute continuity i i η̄ Growing the initial (purple) segments of the curve means that the starting point for the auxiliary flow lines is not a stopping time for η. ≈ SLEκ SLEκ (ρL ; ρR ) One has to be careful to make sure that the results of the imaginary geometry papers are applicable (this actually involves growing a second pair of auxiliary flow lines). η −i Ewain Gwynne (MIT) −i Almost sure multifractal spectrum of SLE 55 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 56 / 59 A few details of the proof A few details of the proof “o(1)” errors “o(1)” errors In our events, we require that the derivative of the conformal map is “≈ ”, i.e. between s−u and s+u , where u is a small parameter. In order to ensure that the perfect points are actually contained in the set Θs (Dη ), we need to shrink u a little bit at each stage. To counteract the increasing constants in the estimates, we also need to increase β a little bit at each stage. The diameter of the nth pocket is e −β n (1+on (1)) , where β n = Pn j=1 βj . To make sure the pockets surrounding z and w are disjoint, we need to skip non (1) scales when we do the two-point estimate. This is okay, as it just leads to an on (1) error in the exponent. So, the nth event in the definition of the perfect points is defined using the ball of radius e −βn , rather than e −β , where βn → ∞ (at approximately a logarithmic rate) as n → ∞. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 57 / 59 Ewain Gwynne (MIT) Conclusion 58 / 59 Conclusion Outline Future directions 1 Definitions and background 2 Upper bound 3 Lower bound 4 A few details of the proof 5 Conclusion Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE Winding spectrum of SLE—asymptotics of arg φ0 rather than |φ0 | Can also consider mixed spectrum. Predictions by Duplantier and Duplantier/Binder Upper bound for winding proven by Aru (2014). Probably lower bound can be done in a similar manner as for the multifractal spectrum. Multifractal spectrum for SLEκ (ρ) near where it intersects the boundary. Almost sure multifractal spectrum of SLE Same as for ordinary SLE away from the boundary by absolute continuity. Maybe could be done using techniques similar to those of our paper and/or or those of Alberts-Binder-Viklund. 59 / 59 Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 60 / 59 Conclusion References E. Gwynne, J. Miller, and X. Sun. Almost sure multifractal spectrum of SLE. ArXiv. B Duplantier. Conformally invariant fractals and potential theory. Physical Review Letters. G. Lawler and F. J. Viklund. Almost sure multifractal spectrum for the tip of an SLE curve. Acta Math. D. Beliaev and S. Smirnov. Harmonic measure and SLE. Comm. Math. Phys. S. Sheffield. Conformal weldings of random surfaces: SLE and the quantum gravity zipper. ArXiv. J. Miller and S. Sheffield. Imaginary Geometry I-IV. ArXiv. Ewain Gwynne (MIT) Almost sure multifractal spectrum of SLE 61 / 59