Chaotic Behavior of Multidimensional Hamiltonian Systems: Disordered lattices, granular chains and DNA models Haris Skokos Department of Mathematics and Applied Mathematics University of Cape Town Cape Town, South Africa E-mail: haris.skokos@uct.ac.za URL: http://math_research.uct.ac.za/~hskokos/ Work supported by the UCT Research Committee
Outline The quartic disordered • Different dynamical behaviors Klein-Gordon (DKG) model • Lyapunov exponents and the disordered discrete nonlinear Schrödinger • Deviation Vector Distributions (DVDs) equation (DDNLS) Chaotic behavior of • Do granular nonlinearities and the resulting chaotic granular chains dynamics destroy energy localization? If yes, how? (coexistence of smooth and • Comparison with the disordered Fermi-Pasta-Ulam- non-smooth nonlinearities) Tsingou (FPUT) model • Lyapunov exponents and different dynamical regimes The Peyrard-Bishop-Dauxois • Behavior of DVDs (PBD) model of DNA • Effect of heterogeneity on system’s chaoticity Future works - Summary
The DKG and DDNLS models
Work in collaboration with Bob Senyange (PhD student): DKG model Bertin Many Manda (PhD student): DDNLS model
Interplay of disorder and nonlinearity Waves in disordered media – Anderson localization [Anderson, Phys. Rev. (1958)]. Experiments on BEC [Billy et al., Nature (2008)] Waves in nonlinear disordered media – localization or delocalization? Theoretical and/or numerical studies [Shepelyansky, PRL (1993) – Molina, Phys. Rev. B (1998) – Pikovsky & Shepelyansky, PRL (2008) – Kopidakis et al., PRL (2008) – Flach et al., PRL (2009) – S. et al., PRE (2009) – Mulansky & Pikovsky, EPL (2010) – S. & Flach, PRE (2010) – Laptyeva et al., EPL (2010) – Mulansky et al., PRE & J.Stat.Phys. (2011) – Bodyfelt et al., PRE (2011) – Bodyfelt et al., IJBC (2011)] Experiments: propagation of light in disordered 1d waveguide lattices [Lahini et al., PRL (2008)]
The disordered Klein – Gordon (DKG) model ε 2 N p 1 1 2 2 4 l l H = + u + u + u - u K l l l+1 l 2 2 4 2 W l=1 with fixed boundary conditions u 0 =p 0 =u N+1 =p N+1 =0 . Typically N=1000. 1 3 ε , chosen uniformly from . Parameters: W and the total energy E. l 2 2 4 /4 ) Linear case (neglecting the term u l Ansatz: u l =A l exp(i ω t). Normal modes (NMs) A ν, l - Eigenvalue problem: λ A l = ε l A l - (A l+1 + A l-1 ) with λ =Wω -W - 2, ε =W(ε -1) 2 l l The disordered discrete nonlinear Schrödinger (DDNLS) equation We also consider the system: β N 2 4 ε ψ ψ - ψ ψ +ψ ψ * * H = + D l l l l+1 l l+1 l 2 l=1 W W ε , where chosen uniformly from and is the nonlinear parameter. l 2 2 2 Conserved quantities: The energy and the norm of the wave packet. S l l
Distribution characterization E ν z We consider normalized energy distributions ν E m m ε 2 p 1 1 2 ν ν 2 4 E = + u + u + u - u with for the DKG model, ν ν ν ν+1 ν 2 2 4 4W 2 ν z and norm distributions for the DDNLS system. ν 2 l l N N 2 ν - ν z ν = νz m = with Second moment: ν ν 2 ν=1 ν=1 1 P = Participation number: N 2 z ν ν=1 measures the number of stronger excited modes in z ν . Single site P=1 . Equipartition of energy P=N .
Different Dynamical Regimes Three expected evolution regimes [Flach, Chem. Phys (2010) - S. & Flach, PRE (2010) - Laptyeva et al., EPL (2010) - Bodyfelt et al., PRE (2011)] Δ : width of the frequency spectrum, d: average spacing of interacting modes, δ : nonlinear frequency shift. Weak Chaos Regime: δ< d, m 2 t 1/3 Frequency shift is less than the average spacing of interacting modes. NMs are weakly interacting with each other. [Molina, PRB (1998) – Pikovsky, & Shepelyansky, PRL (2008)]. Intermediate Strong Chaos Regime: d< δ<Δ , m 2 t 1/2 m 2 t 1/3 Almost all NMs in the packet are resonantly interacting. Wave packets initially spread faster and eventually enter the weak chaos regime. Selftrapping Regime: δ > Δ Frequency shift exceeds the spectrum width. Frequencies of excited NMs are tuned out of resonances with the nonexcited ones, leading to selftrapping, while a small part of the wave packet subdiffuses [Kopidakis et al., PRL (2008)].
Single site excitations DDNLS W=4, β = 0.1, 1, 4.5 DKG W = 4, E = 0.05, 0.4, 1.5 No strong chaos regime slope 1/3 slope 1/3 In weak chaos regime we averaged the measured exponent α (m 2 ~t α ) over 20 realizations: slope 1/6 slope 1/6 α=0.33± 0.05 (DKG) α=0.33± 0.02 (DDLNS) Flach et al., PRL (2009) S. et al., PRE (2009)
DKG: Different spreading regimes
Crossover from strong to weak chaos (block excitations) DDNLS β = 0.04, 0.72, 3.6 DKG E= 0.01, 0.2, 0.75 W=4 Average over 1000 realizations! d log m 2 (log ) t d log t α= 1/2 α= 1/3 Laptyeva et al., EPL (2010) Bodyfelt et al., PRE (2011)
Variational Equations We use the notation x = (q 1 ,q 2 , … ,q N ,p 1 ,p 2 , … ,p N ) T . The deviation vector from a given orbit is denoted by v = ( δ x 1 , δ x 2 ,…,δ x n ) T , with n=2N The time evolution of v is given by the so-called variational equations: dv = -J P v dt where 2 0 -I H N N J = , P = i, j = 1, 2, , n i j I 0 x x N N i j Benettin & Galgani, 1979, in Laval and Gressillon (eds.), op cit, 93
Maximum Lyapunov Exponent Chaos: sensitive dependence on initial conditions. Roughly speaking, the Lyapunov exponents of a given orbit characterize the mean exponential rate of divergence of trajectories surrounding it. Consider an orbit in the 2N-dimensional phase space with initial condition x(0) and an initial deviation vector from it v(0). Then the mean exponential rate of divergence is: v(t) 1 mLCE = λ = limΛ(t) = lim ln 1 t v(0) t t λ 1 =0 Regular motion λ 1 0 Chaotic motion
Symplectic integration We apply the 2-part splitting integrator ABA864 [Blanes et al., Appl. Num. Math. (2013) – Senyange & S., EPJ ST (2018)] to the DKG model: ε 2 N p 1 1 2 2 4 l l H = + u + u + u - u K l l l+ 1 l 2 2 4 2W l= 1 [SS] [S. et al., Phys. Let. A (2014) – and the 3-part splitting integrator ABC 6 Gerlach et al., EPJ ST (2016) – Danieli et al., MinE (2019)] to the DDNLS system: β 1 2 4 ε ψ + ψ - ψ ψ +ψ ψ ψ = q + ip * * H = , D l l l l+1 l l+1 l l l l 2 2 l ε β 2 2 2 2 2 l H = q + p + q + p - q q - p p D l l l l n n+1 n n+1 2 8 l By using the so-called Tangent Map method we extend these symplectic integration schemes in order to integrate simultaneously the variational equations [S. & Gerlach, PRE (2010) – Gerlach & S., Discr. Cont. Dyn. Sys. (2011) – Gerlach et al., IJBC (2012)].
DKG: Weak Chaos Block excitation L=37 sites, E=0.37, W=3
DKG: Weak Chaos Individual runs Linear case E=0.4, W=4 slope -1 Average over 50 realizations Single site excitation E=0.4, W=4 Block excitation (L=21 sites) α L = -0.25 E=0.21, W=4 Block excitation (L=37 sites) slope -1 E=0.37, W=3 d log S. et al., PRL (2013) L d log t
Weak Chaos: DKG and DDNLS DKG DDNLS α Λ = -0.25 α Λ = -0.25 Average over 100 realizations [Senyange, Many Manda & S., PRE (2018)] Block excitation (L=21 sites) β= 0.04, W=4 Block excitation (L=37 sites) E=0.37, W=3 Single site excitation β= 1, W=4 Single site excitation E=0.4, W=4 Single site excitation β=0.6 , W=3 Block excitation (L=21 sites) E=0.21, W=4 Block excitation (L=21 sites) β =0.03, W=3 Block excitation (L=13 sites) E=0.26, W=5
Strong Chaos: DKG and DDNLS DKG DDNLS α Λ = -0.3 α Λ = -0.3 Average over 100 realizations [Senyange, Many Manda & S., PRE (2018)] Block excitation (L=21 sites) β= 0.62, W=3.5 Block excitation (L=83 sites) E=0.83, W=2 Block excitation (L=21 sites) β=0. 5, W=3 Block excitation (L=37 sites) E=0.37, W=3 Block excitation (L=21 sites) β =0.72, W=3.5 Block excitation (L=83 sites) E=0.83, W=3
Deviation Vector Distributions (DVDs) Energy DVD DKG weak chaos L=37 sites, E=0.37, W=3 2 2 u p D l l Deviation vector: DVD: l 2 2 v(t)=( δ u 1 (t), δ u 2 (t), … , δ u N (t), δ p 1 (t), δ p 2 (t), … , δ p N (t)) u p l l l
Deviation Vector Distributions (DVDs) DKG: weak chaos. L=37 sites, E=0.37, W=3 DVD Energy
Weak Chaos: DKG and DDNLS Energy DVD Norm DVD DDNLS: W=4, L=21, β =0.04 DKG: W=3, L=37, E=0.37
Deviation Vector Distributions (DVDs) DDNLS: strong chaos W=3.5, L=21, β =0.72 DVD Norm
Strong Chaos: DKG and DDNLS Energy DVD Norm DVD DDNLS: W=3.5, L=21, β =0.72 DKG: W=3, L=83, E=8.3
Characteristics of DVDs Weak chaos Strong chaos DKG DDNLS DKG DDNLS
Characteristics of DVDs KG weak chaos DKG DDNLS L=37, E=0.37, W=3 Weak chaos Range of the lattice Strong visited by the DVD chaos R t ( ) max l t ( ) min l t ( ) w w [0, ] t [0, ] t N l D l w l l 1
Granular chains
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