# American Institute of Mathematical Sciences

July  2012, 32(7): 2437-2451. doi: 10.3934/dcds.2012.32.2437

## On the asymptotic behaviour of the Lebesgue measure of sum-level sets for continued fractions

 1 Universität Bremen, Fachbereich 3 - Mathematik und Informatik, Bibliothekstr. 1, 28359 Bremen, Germany, Germany

Received  December 2009 Revised  June 2010 Published  March 2012

In this paper we give a detailed measure theoretical analysis of what we call sum-level sets for regular continued fraction expansions. The first main result is to settle a recent conjecture of Fiala and Kleban, which asserts that the Lebesgue measure of these level sets decays to zero, for the level tending to infinity. The second and third main results then give precise asymptotic estimates for this decay. The proofs of these results are based on recent progress in infinite ergodic theory, and in particular, they give non-trivial applications of this theory to number theory. The paper closes with a discussion of the thermodynamical significance of the obtained results, and with some applications of these to metrical Diophantine analysis.
Citation: Marc Kessböhmer, Bernd O. Stratmann. On the asymptotic behaviour of the Lebesgue measure of sum-level sets for continued fractions. Discrete & Continuous Dynamical Systems - A, 2012, 32 (7) : 2437-2451. doi: 10.3934/dcds.2012.32.2437
##### References:
 [1] J. Aaronson, "An Introduction to Infinite Ergodic Theory," Mathematical Surveys and Monographs, 50,, American Mathematical Society, (1997).   Google Scholar [2] J. Aaronson, M. Denker and M. Urbański, Ergodic theory for Markov fibred systems and parabolic rational maps,, Trans. AMS, 337 (1993), 495.  doi: 10.2307/2154231.  Google Scholar [3] N. H. Bingham, C. M. Goldie and J. L. Teugels, "Regular Variation," Encyclopedia of Mathematics and its Applications, 27,, Cambridge University Press, (1989).   Google Scholar [4] A. Brocot, Calcul des rouages par approximation, nouvelle méthode,, Revue chronométrique, 3 (1981), 186.   Google Scholar [5] H. Bruin, M. Nicol and D. Terhesiu, On Young towers associated with infinite measure preserving transformations,, Stoch. and Dynamics, 9 (2009), 635.  doi: 10.1142/S0219493709002816.  Google Scholar [6] H. E. Daniels, Processes generating permutation expansions,, Biometrika, 49 (1962), 139.  doi: 10.1093/biomet/49.1-2.139.  Google Scholar [7] J. L. Doob, "Stochastic Processes,", John Wiley & Sons, (1953).   Google Scholar [8] M. J. Feigenbaum, I. Procaccia and T. Tél, Scaling properties of multifractals as an eigenvalue problem,, Phys. Rev. A (3), 39 (1989), 5359.  doi: 10.1103/PhysRevA.39.5359.  Google Scholar [9] J. Fiala and P. Kleban, Intervals between Farey fractions in the limit of infinite level,, Annales des Sciences Mathematiques du Québec, 34 (2010), 63.   Google Scholar [10] D. Hensley, The statistics of the continued fraction digit sum,, Pacific Jour. of Math., 192 (2000), 103.  doi: 10.2140/pjm.2000.192.103.  Google Scholar [11] B. Hu and J. Rudnik, Exact solutions to the Feigenbaum renormalization-group equations for intermittency,, Phys. Rev. Lett., 48 (1982), 1645.   Google Scholar [12] M. Kesseböhmer, S. Munday and B. O. Stratmann, Strong renewal theorems and Lyapunov spectra for $\alpha$-Farey and $\alpha$-Lüroth systems,, to appear in Ergod. Theory and Dyn. Syst., ().   Google Scholar [13] M. Kesseböhmer and M. Slassi, Limit laws for distorted critical return time processes in infinite ergodic theory,, Stochastics and Dynamics, 7 (2007), 103.   Google Scholar [14] M. Kesseböhmer and M. Slassi, A distributional limit law for the continued fraction digit sum,, Mathematische Nachrichten, 281 (2008), 1294.   Google Scholar [15] M. Kesseböhmer and M. Slassi, Large deviation asymptotics for continued fraction expansions,, Stochastics and Dynamics, 8 (2008), 103.   Google Scholar [16] M. Kesseböhmer and B. O. Stratmann, A multifractal formalism for growth rates and applications to geometrically finite Kleinian groups,, Ergodic Theory & Dynamical Systems, 24 (2004), 141.   Google Scholar [17] M. Kesseböhmer and B. O. Stratmann, Stern-Brocot pressure and multifractal spectra in ergodic theory of numbers,, Stochastics and Dynamics, 4 (2004), 77.  doi: 10.1142/S0219493704000948.  Google Scholar [18] M. Kesseböhmer and B. O. Stratmann, A multifractal analysis for Stern-Brocot intervals, continued fractions and Diophantine growth rates,, J. Reine Angew. Math., 605 (2007), 133.   Google Scholar [19] A. Ya. Khintchine, "Continued Fractions,", Univ. of Chicago Press, (1964).   Google Scholar [20] M. Lin, Mixing for Markov operators,, Z. Wahrsch. u. V. Geb., 19 (1971), 231.  doi: 10.1007/BF00534111.  Google Scholar [21] W. Parry, On $\beta$-expansions of real numbers,, Acta Math. Acad. Sci. Hung., 11 (1960), 401.  doi: 10.1007/BF02020954.  Google Scholar [22] W. Parry, Ergodic properties of some permutation processes,, Biometrika, 49 (1962), 151.  doi: 10.2307/2333475.  Google Scholar [23] T. Prellberg and J. Slawny, Maps of intervals with indifferent fixed points: Thermodynamical formalism and phase transition,, J. Stat. Phys., 66 (1992), 503.   Google Scholar [24] M. A. Stern, Über eine zahlentheoretische Funktion,, J. Reine Angew. Math., 55 (1958), 193.   Google Scholar [25] M. Thaler, Estimates of the invariant densities of endomorphisms with indifferent fixed points,, Israel J. Math., 37 (1980), 303.   Google Scholar [26] M. Thaler, Transformations on $[0,1]$ with infinite invariant measures,, Israel J. Math., 46 (1983), 67.  doi: 10.1007/BF02760623.  Google Scholar [27] M. Thaler, The asymptotics of the Perron-Frobenius operator of a class of interval maps preserving infinite measures,, Studia Math., 143 (2000), 103.   Google Scholar [28] M. Thaler, "Infinite Ergodic Theory,", Luminy lecture notes, (2001).   Google Scholar [29] E. Wirsing, On the theorem of Gauss-Kusmin-Lévy and a Frobenius-type theorem for function spaces,, V. Acta Arith., 24 (): 507.   Google Scholar

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##### References:
 [1] J. Aaronson, "An Introduction to Infinite Ergodic Theory," Mathematical Surveys and Monographs, 50,, American Mathematical Society, (1997).   Google Scholar [2] J. Aaronson, M. Denker and M. Urbański, Ergodic theory for Markov fibred systems and parabolic rational maps,, Trans. AMS, 337 (1993), 495.  doi: 10.2307/2154231.  Google Scholar [3] N. H. Bingham, C. M. Goldie and J. L. Teugels, "Regular Variation," Encyclopedia of Mathematics and its Applications, 27,, Cambridge University Press, (1989).   Google Scholar [4] A. Brocot, Calcul des rouages par approximation, nouvelle méthode,, Revue chronométrique, 3 (1981), 186.   Google Scholar [5] H. Bruin, M. Nicol and D. Terhesiu, On Young towers associated with infinite measure preserving transformations,, Stoch. and Dynamics, 9 (2009), 635.  doi: 10.1142/S0219493709002816.  Google Scholar [6] H. E. Daniels, Processes generating permutation expansions,, Biometrika, 49 (1962), 139.  doi: 10.1093/biomet/49.1-2.139.  Google Scholar [7] J. L. Doob, "Stochastic Processes,", John Wiley & Sons, (1953).   Google Scholar [8] M. J. Feigenbaum, I. Procaccia and T. Tél, Scaling properties of multifractals as an eigenvalue problem,, Phys. Rev. A (3), 39 (1989), 5359.  doi: 10.1103/PhysRevA.39.5359.  Google Scholar [9] J. Fiala and P. Kleban, Intervals between Farey fractions in the limit of infinite level,, Annales des Sciences Mathematiques du Québec, 34 (2010), 63.   Google Scholar [10] D. Hensley, The statistics of the continued fraction digit sum,, Pacific Jour. of Math., 192 (2000), 103.  doi: 10.2140/pjm.2000.192.103.  Google Scholar [11] B. Hu and J. Rudnik, Exact solutions to the Feigenbaum renormalization-group equations for intermittency,, Phys. Rev. Lett., 48 (1982), 1645.   Google Scholar [12] M. Kesseböhmer, S. Munday and B. O. Stratmann, Strong renewal theorems and Lyapunov spectra for $\alpha$-Farey and $\alpha$-Lüroth systems,, to appear in Ergod. Theory and Dyn. Syst., ().   Google Scholar [13] M. Kesseböhmer and M. Slassi, Limit laws for distorted critical return time processes in infinite ergodic theory,, Stochastics and Dynamics, 7 (2007), 103.   Google Scholar [14] M. Kesseböhmer and M. Slassi, A distributional limit law for the continued fraction digit sum,, Mathematische Nachrichten, 281 (2008), 1294.   Google Scholar [15] M. Kesseböhmer and M. Slassi, Large deviation asymptotics for continued fraction expansions,, Stochastics and Dynamics, 8 (2008), 103.   Google Scholar [16] M. Kesseböhmer and B. O. Stratmann, A multifractal formalism for growth rates and applications to geometrically finite Kleinian groups,, Ergodic Theory & Dynamical Systems, 24 (2004), 141.   Google Scholar [17] M. Kesseböhmer and B. O. Stratmann, Stern-Brocot pressure and multifractal spectra in ergodic theory of numbers,, Stochastics and Dynamics, 4 (2004), 77.  doi: 10.1142/S0219493704000948.  Google Scholar [18] M. Kesseböhmer and B. O. Stratmann, A multifractal analysis for Stern-Brocot intervals, continued fractions and Diophantine growth rates,, J. Reine Angew. Math., 605 (2007), 133.   Google Scholar [19] A. Ya. Khintchine, "Continued Fractions,", Univ. of Chicago Press, (1964).   Google Scholar [20] M. Lin, Mixing for Markov operators,, Z. Wahrsch. u. V. Geb., 19 (1971), 231.  doi: 10.1007/BF00534111.  Google Scholar [21] W. Parry, On $\beta$-expansions of real numbers,, Acta Math. Acad. Sci. Hung., 11 (1960), 401.  doi: 10.1007/BF02020954.  Google Scholar [22] W. Parry, Ergodic properties of some permutation processes,, Biometrika, 49 (1962), 151.  doi: 10.2307/2333475.  Google Scholar [23] T. Prellberg and J. Slawny, Maps of intervals with indifferent fixed points: Thermodynamical formalism and phase transition,, J. Stat. Phys., 66 (1992), 503.   Google Scholar [24] M. A. Stern, Über eine zahlentheoretische Funktion,, J. Reine Angew. Math., 55 (1958), 193.   Google Scholar [25] M. Thaler, Estimates of the invariant densities of endomorphisms with indifferent fixed points,, Israel J. Math., 37 (1980), 303.   Google Scholar [26] M. Thaler, Transformations on $[0,1]$ with infinite invariant measures,, Israel J. Math., 46 (1983), 67.  doi: 10.1007/BF02760623.  Google Scholar [27] M. Thaler, The asymptotics of the Perron-Frobenius operator of a class of interval maps preserving infinite measures,, Studia Math., 143 (2000), 103.   Google Scholar [28] M. Thaler, "Infinite Ergodic Theory,", Luminy lecture notes, (2001).   Google Scholar [29] E. Wirsing, On the theorem of Gauss-Kusmin-Lévy and a Frobenius-type theorem for function spaces,, V. Acta Arith., 24 (): 507.   Google Scholar
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