The Distribution of Prime Geodesics for Γ \ H and Analogues for Free Groups
Outline The distribution of prime geodesics for Γ \ H and analogues for free groups Yiannis Petridis1 Morten S. Risager2 1The Graduate Center and Lehman College City University of New York 2Aarhus Universitet February 15, 2006 Hyperbolic surfaces Closed Geodesics Free groups and discrete logarithms Methods and ideas Outline 1 Hyperbolic surfaces 2 Closed Geodesics 3 Free groups and discrete logarithms 4 Methods and ideas Hyperbolic surfaces Closed Geodesics Free groups and discrete logarithms Methods and ideas Discrete groups The fundamental domain of SL2(Z) Upper-half space H = {z = x + iy, y > 0} Group: SL2(Z) az + b T (z) = , ad − bc = 1 cz + d a, b, c, d ∈ Z Hyperbolic surfaces Closed Geodesics Free groups and discrete logarithms Methods and ideas Congruence subgroups of SL2(Z) Example Fundamental Domain for Γ0(6) Hecke subgroups Γ0(N) a b ∈ SL ( ), N|c c d 2 Z Hyperbolic surfaces Closed Geodesics Free groups and discrete logarithms Methods and ideas Closed geodesics Closed geodesics {γ} = {aγa−1, a ∈ Γ} m 0 γ ∼ , m > 1 0 m−1 Lengths of closed geodesic: l(γ) = 2 log m Norm N(γ) = m2 Example (H/SL2(Z)) √ Hyperbolic metric Q( d), d > 0 fundamental unit dx2 + dy 2 d ds2 = y 2 l(γ) = 2 log d Hyperbolic surfaces Closed Geodesics Free groups and discrete logarithms Methods and ideas Distribution of primes Prime number theorem Prime geodesic theorem π(x) = |{p prime, p ≤ x}| π(x) = |{γ, N(γ) ≤ x}| x x π(x) ∼ , x → ∞ π(x) ∼ , x → ∞ ln x ln x Primes in progressions Chebotarev density theorem Z → Z/nZ ψ :Γ → G finite abelian, β ∈ G π(x, n, a) = |{p ≡ a mod n, p ≤ x}| π(x, β) = |{γ, N(γ) ≤ x, 1 x π(x, n, a) ∼ ψ(γ) = β}| φ(n) ln x 1 x π(x, β) ∼ |G| ln x Hyperbolic surfaces Closed Geodesics Free groups and discrete logarithms Methods and ideas Examples of the prime geodesic theorem X x2 Sarnak: h(d) ∼ 2 log x d ≤x ∼ 2g ∼ φ :Γ → H1(H/Γ, Z) = Z = Fix a shifted sublattice β ∈ Z2g/L Get density 1/6, the density of the sublattice.
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