Dynamics of Units and Packing Constants of Ideals
Perspectives • Continued Fractions in Q(√D) Dynamics of units and • The Diophantine semigroup packing constants of ideals • Geodesics in SL2(R)/SL2(Z) • (Classical) Arithmetic Chaos • Well-packed ideals Curtis T McMullen 1 Harvard University • Dynamics of units on P (Z/f) • Link Littlewood & Zaremba conjectures Continued Fractions Diophantine numbers Q. How to test if a real number x is in Q? x = [a , a , a , a , ...] = a + 1 0 1 2 3 0 a + 1 Q. How to test if a real number x is in Q(√D)? 1 a2 + 1 a3 + ... 1 x = [a0, a 1, a 2, a 3, ...] = a0 + a1 + 1 a2 + 1 BN = {x real : ai ≤N} a3 + ... BN-Q is a Cantor set of dim→1 as N→∞. A. x is in Q(√D) iff ai’s repeat. Conjecture: x algebraic and Diophantine iff x is rational or quadratic Diophantine sets in [0,1] Examples BN = {x : ai ≤N} γ = golden ratio = (1+√5)/2 = [1,1,1,1....] = [1] σ = silver ratio = 1+√2 = [2] [1,2,2,2] (√30) B2 [1,2] Q(√3) Q [1,2,2] Q(√85) [1,1,1,2] Q(√6) [1,1,2] Q(√10) [1,1,2,2] Q(√221) B4 Question: Does Q(√5) contain infinitely many periodic continued fractions with ai ≤ M? Thin group perspective Theorem Every real quadratic field contains infinitely GN = Diophantine semigroup in SL2(Z) many uniformly bounded, periodic continued fractions. generated by Wilson, Woods (1978) 01 01 01 ( 11) , ( 12) ,...( 1 N ) . Example: [1,4,2,3], [1,1,4,2,1,3], [1,1,1,4,2,1,1,3]..
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