Distribution of PCF cubic polynomials

Transcription

1 Distribution of PCF cubic polynomials Charles Favre June 28th, 2016

2 The parameter space of polynomials Poly d : degree d polynomials modulo conjugacy by affine transformations. {P = a d z d + + a 0, a d 0}/{P φ P φ 1, φ(z) = az + b} C C d / Aff(2, C). Complex affine variety of dimension d 1: finite quotient singularities.

3 Exploring the geometry of Poly 2 Interested in the geometry of the locus of polynomials with special dynamics in Poly d.

4 Exploring the geometry of Poly 2 Interested in the geometry of the locus of polynomials with special dynamics in Poly d. Work with a suitable ramified cover of Poly d by C d 1.

5 Exploring the geometry of Poly 2 Interested in the geometry of the locus of polynomials with special dynamics in Poly d. Work with a suitable ramified cover of Poly d by C d 1. d = 2: parameterization P c (z) = z 2 + c, c C. Critical point: 0. PCF maps: 0 is pre-periodic.

6 Exploring the geometry of Poly 2 Interested in the geometry of the locus of polynomials with special dynamics in Poly d. Work with a suitable ramified cover of Poly d by C d 1. d = 2: parameterization P c (z) = z 2 + c, c C. Critical point: 0. PCF maps: 0 is pre-periodic. PCF maps are defined over Q: c = 0, c 2 + c = 0, (c 2 + c) 2 + c = 0,...

7 Distribution of hyperbolic quadratic PCF polynomials

8 Distribution of hyperbolic quadratic PCF polynomials

9 Distribution of quadratic PCF polynomials PCF(n) = {P c, the orbit of 0 has cardinality n}. Theorem (Levin, Baker-H sia, F.-Rivera-Letelier,...) The probability measures µ n equidistributed on PCF(n) converge weakly towards the harmonic measure of the Mandelbrot set.

10 Distribution of quadratic PCF polynomials PCF(n) = {P c, the orbit of 0 has cardinality n}. Theorem (Levin, Baker-H sia, F.-Rivera-Letelier,...) The probability measures µ n equidistributed on PCF(n) converge weakly towards the harmonic measure of the Mandelbrot set. Levin: potential theoretic arguments Baker-H sia: exploit adelic arguments, and work over all completions of Q both Archimedean and non-archimedean: C, C p for p prime.

11 The cubic case Poly 3 Parameterization: P c,a (z) = 1 3 z3 c 2 z2 + a 3, a, c C. Crit(P c,a ) = {0, c} P c,a (0) = a 3, P c,a (c) = a 3 c3 6. PCF(n, m) = {orbit of 0 has cardinality n} & {orbit of c has cardinality m}

12 Finiteness of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Proposition (Branner-Hubbard) The set PCF(n, m) is finite and defined over Q.

13 Finiteness of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Proposition (Branner-Hubbard) The set PCF(n, m) is finite and defined over Q. PCF(n, m) is bounded in C 2 by Koebe distortion estimates;

14 Finiteness of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Proposition (Branner-Hubbard) The set PCF(n, m) is finite and defined over Q. in C p with p 5:

15 Finiteness of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Proposition (Branner-Hubbard) The set PCF(n, m) is finite and defined over Q. in C p with p 5: if a > max{1, c }, then Pc,a (0) = a 3, P 2 c,a(0) = a 9 and, P n c,a(0) = a 3n ;

16 Finiteness of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Proposition (Branner-Hubbard) The set PCF(n, m) is finite and defined over Q. in C p with p 5: if a > max{1, c }, then Pc,a (0) = a 3, P 2 c,a(0) = a 9 and, P n c,a(0) = a 3n ; PCF(n, m) { c, a 1}.

17 Finiteness of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Proposition (Branner-Hubbard) The set PCF(n, m) is finite and defined over Q. Proposition (Ingram) For any finite extension K /Q the set PCF K 2 is finite.

18 Distribution of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Theorem (F.-Gauthier) The probability measures µ n,m equidistributed on PCF(n, m) converge weakly towards the equilibrium measure µ of the connectedness locus C as n, m.

19 Distribution of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Theorem (F.-Gauthier) The probability measures µ n,m equidistributed on PCF(n, m) converge weakly towards the equilibrium measure µ of the connectedness locus C as n, m. C = {(c, a), Julia set of P c,a is connected} = {(c, a), 0 and c have bounded orbit};

20 Distribution of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Theorem (F.-Gauthier) The probability measures µ n,m equidistributed on PCF(n, m) converge weakly towards the equilibrium measure µ of the connectedness locus C as n, m. C = {(c, a), Julia set of P c,a is connected} = {(c, a), 0 and c have bounded orbit}; Green function G C : C 0 psh 0 function, C = {G C = 0}, G(c, a) = log max{1, c, a } + O(1);

21 Distribution of PCF maps P c,a (z) = 1 3 z3 c 2 z2 + a 3 Theorem (F.-Gauthier) The probability measures µ n,m equidistributed on PCF(n, m) converge weakly towards the equilibrium measure µ of the connectedness locus C as n, m. C = {(c, a), Julia set of P c,a is connected} = {(c, a), 0 and c have bounded orbit}; Green function G C : C 0 psh 0 function, C = {G C = 0}, G(c, a) = log max{1, c, a } + O(1); µ = Monge-Ampère(G C ) = (dd c ) 2 G C.

22 The adelic approach Interpretation of the Green function in the parameter space: G C = max{g c,a (c), G c,a (0)} Dynamical Green function: G c,a = lim 1 3 n log max{1, Pn c,a }

23 The adelic approach Interpretation of the Green function in the parameter space: G C = max{g c,a (c), G c,a (0)} Dynamical Green function: G c,a = lim 1 3 n log max{1, Pn c,a } Same construction for any norm p on Q: G C,p

24 The adelic approach Interpretation of the Green function in the parameter space: G C = max{g c,a (c), G c,a (0)} Dynamical Green function: G c,a = lim 1 3 n log max{1, Pn c,a } Same construction for any norm p on Q: G C,p Key observation: P c,a PCF iff Height(c, a) := Apply Yuan s theorem! 1 deg(c, a) p c,a G C,p (c, a ) = 0

25 Special curves Problem (Baker-DeMarco) Describe all irreducible algebraic curves C in Poly 3 such that PCF C is infinite. motivated by the André-Oort conjecture in arithmetic geometry

26 Special curves Problem (Baker-DeMarco) Describe all irreducible algebraic curves C in Poly 3 such that PCF C is infinite. motivated by the André-Oort conjecture in arithmetic geometry Theorem (Baker-DeMarco, Ghioca-Ye, F.-Gauthier) Suppose C is an irreducible algebraic curve in Poly 3 such that PCF C is infinite. Then there exists a persistent critical relation.

27 The curves Per n (λ): DeMarco s conjecture Per n (λ) = {P c,a admitting a periodic point of period n and multiplier λ}

28 The curves Per n (λ): DeMarco s conjecture Per n (λ) = {P c,a admitting a periodic point of period n and multiplier λ} Geometry of Per n (0): Milnor, DeMarco-Schiff, irreducibility by Arfeux-Kiwi (n prime);

29 The curves Per n (λ): DeMarco s conjecture Per n (λ) = {P c,a admitting a periodic point of period n and multiplier λ} Geometry of Per n (0): Milnor, DeMarco-Schiff, irreducibility by Arfeux-Kiwi (n prime); Distribution of Per n (λ) when n described by Bassaneli-Berteloot.

30 The curves Per n (λ): DeMarco s conjecture Per n (λ) = {P c,a admitting a periodic point of period n and multiplier λ} Geometry of Per n (0): Milnor, DeMarco-Schiff, irreducibility by Arfeux-Kiwi; Distribution of Per n (λ) when n described by Bassaneli-Berteloot. Theorem (F.-Gauthier) The set PCF Per n (λ) is infinite iff λ = 0. n = 1 by Baker-DeMarco

31 Scheme of proof C irreducible component of Per n (λ) containing infinitely many PCF: λ Q. 1. One of the critical point is persistently preperiodic on C. 2. C contains a unicritical PCF polynomial = λ 3 < There exists a quadratic PCF polynomial having λ as a multiplier = λ 3 = 1.

32 Step 2 P c,a (z) = 1 3 z3 c 2 z2 + a 3 C contains a unicritical PCF polynomial, and λ 3 < 1. a) Existence of the PCF unicritical polynomial by Bezout and Step 1.

33 Step 2 P c,a (z) = 1 3 z3 c 2 z2 + a 3 C contains a unicritical PCF polynomial, and λ 3 < 1. a) Existence of the PCF unicritical polynomial by Bezout and Step 1. b) Suppose P(z) = z 3 + b is PCF b 3 1 periodic orbits are included in z 3 1 P (z) 3 = 3z 2 3 < 1 on the unit ball hence λ 3 < 1

34 Step 1 One of the critical point is persistently preperiodic on C.

35 Step 1 One of the critical point is persistently preperiodic on C. 1. Apply the previous theorem: there exists a persistent critical relation.

36 Step 1 One of the critical point is persistently preperiodic on C. 1. Apply the previous theorem: there exists a persistent critical relation. 2. Suppose Pc,a(0) m = Pc,a(c) m for all c, a C. a branch at infinity c of C induces a cubic polynomial P = P c(t),a(t) C((t))[z] both points 0 and c tend to on c Kiwi & Bezivin = all multipliers of P are repelling contradiction with the existence of a periodic point with constant multiplier λ

37 Construction of the quadratic renormalization Use more from Kiwi on the dynamics of P over the non-archimedean field C((t))!

38 Construction of the quadratic renormalization Use more from Kiwi on the dynamics of P over the non-archimedean field C((t))! Step 1 implies 0 is pre-periodic whereas c tends to. If 0 is in the Julia set, then all cycles are repelling (Kiwi).

39 Construction of the quadratic renormalization Use more from Kiwi on the dynamics of P over the non-archimedean field C((t))! Step 1 implies 0 is pre-periodic whereas c tends to. If 0 is in the Julia set, then all cycles are repelling (Kiwi). Non-wandering theorem of Kiwi-Trucco: 0 belongs to a periodic (closed) ball: P n (B) = B.

40 Construction of the quadratic renormalization Use more from Kiwi on the dynamics of P over the non-archimedean field C((t))! Step 1 implies 0 is pre-periodic whereas c tends to. If 0 is in the Julia set, then all cycles are repelling (Kiwi). Non-wandering theorem of Kiwi-Trucco: 0 belongs to a periodic (closed) ball: P m (B) = B. P m (z) = a 0 (t) + a 1 (t)z a k (t)z k P m { z 1} = { z 1} implies a i (t) C[[t]] The renormalization is a 0 (0) + a 1 (0)z a k (0)z k.

41 Dynamics of the quadratic renormalization The renormalization is a quadratic PCF polynomial Q. One multiplier of Q is λ: non-repelling orbits pass through B (Kiwi) All multipliers of Q have 3 = 1.

42 Happy Birthday Sebastian!