DOCSLIB.ORG

Topics in Gaussian Rough Paths Theory

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Topics in Gaussian Rough Paths Theory Topics in Gaussian rough paths theory vorgelegt von Diplom-Mathematiker Sebastian Riedel Hannover Von der Fakult¨atII - Mathematik und Naturwissenschaften der Technischen Universit¨atBerlin zur Erlangung des akademischen Grades Doktor der Naturwissenschaften Dr.rer.nat. genehmigte Dissertation Promotionsausschuss: Vorsitzende: Prof. Dr. Gitta Kutyniok Berichter/Gutachter: Prof. Dr. Peter K. Friz Berichter/Gutachter: Prof. Dr. Martin Hairer Tag der wissenschaftlichen Aussprache: 23. April 2013 Berlin 2013 D 83 Berlin, May 5, 2013 Acknowledgement At first, I would like to express my gratitude to my PhD advisor, Professor Peter Friz, who constantly supported me during the time of my doctorate. In particular, I would like to thank Peter for the time he always found for discussing with me and for the patience he had. His enduring encouragement laid the basis for the current work. Next, I would like to thank Professor Martin Hairer for being my second examiner, and Professor Gitta Kutyniok who kindly agreed to be the chair of the examination board. I am indebted to all my collaborators who worked with me during the last three years. Namely, I would like to thank Doctor Christian Bayer, Doctor Benjamin Gess, Professor Archil Gulisashvili, Professor Peter Friz, PD Doctor John Schoenmakers and Weijun Xu. Furthermore, I would like to thank Professor Terry Lyons for inviting me to Oxford during my PhD and for the valuable discussions we had. This work could have not been written without the financial support of the International Research Training Group \Stochastic models of complex processes" and the Berlin Mathematical School (BMS). I would like to thank all the people working there for their helpfulness and kindness they showed to me during the last years. Special thanks go to Joscha Diehl, Cl´ement Foucart, Birte Schr¨oderand Maite Wilke Berenguer for reading parts of this thesis and giving valuable comments. At this point, I would like to mention my colleagues and the friends I met in the mathematical institute of the Technische Universit¨atBerlin who gave me a very warm welcome and provided an open and friendly atmosphere during the time of my doctorate. In particular, I would like to thank Professor Michael Scheutzow, my BMS mentor, who gave me a lot of helpful advices concerning my PhD. I am also more than thankful to the following people: Michele, who made me laugh uncountably many times and who introduced me to the dark secrets of pasta and facebook. To Joscha for the possibility to ask the really relevant questions about rough paths. Thank you, Simon, for many fruitful discussions about and not about math. Maite, thank you for making me get up on Monday before 7:00 by offering coffee and for the joint exercise sessions. Thanks to Cl´ement for having many beers with me after work and for the first part of Brice de Nice. Last, thank you, Stefano, for B.F.H., the 1st of May and the 2nd chaos. At the end, I would like to thank my family, in particular my parents, who always had faith in what I am doing. Finally, my biggest thanks go to Birte for encouraging me during the last years, for sharing successes and defeats, joy and sorrow, and for chasing math away when it should not be there. ii To Birte iv Contents Introduction 1 Notation and basic definitions 17 1 Convergence rates for the full Brownian rough paths with applications to limit theorems for stochastic flows 21 1.1 Rates of Convergence for the full Brownian rough path . 24 2 Convergence rates for the full Gaussian rough paths 35 2.1 Iterated integrals and the shuffle algebra . 39 2.2 Multidimensional Young-integration and grid-controls . 43 2.3 The main estimates . 47 2.4 Main result . 66 3 Integrability of (non-)linear rough differential equations and integrals 73 3.1 Basic definitions . 74 3.2 Cass, Litterer and Lyons revisited . 76 3.3 Transitivity of the tail estimates under locally linear maps . 81 3.4 Linear RDEs . 83 3.5 Applications in stochastic analysis . 85 4 A simple proof of distance bounds for Gaussian rough paths 91 4.1 2D variation and Gaussian rough paths . 93 4.2 Main estimates . 98 4.3 Applications . 103 5 Spatial rough path lifts of stochastic convolutions 107 5.1 Main Result . 109 5.2 Conditions in terms of Fourier coefficients . 113 5.3 Lifting Ornstein-Uhlenbeck processes in space . 120 6 From rough path estimates to multilevel Monte Carlo 131 6.1 Rough path estimates revisited . 133 6.2 Probabilistic convergence results for RDEs . 137 6.3 Giles' complexity theorem revisited . 141 6.4 Multilevel Monte Carlo for RDEs . 149 Appendix 151 A Kolmogorov theorem for multiplicative functionals . 151 Contents vi Introduction \What I don't like about measure theory is that you have to say 'almost everywhere' almost everywhere." { Kurt Friedrichs \What is Ω? Cats?" { Michele Salvi In order to describe correctly the research contributions of this thesis, we begin by a brief history of the theory of stochastic integration with a focus on the attempt to define a pathwise integral. We will explain the very first goal of the precursors as well as the generalisations made by some of the leaders in the field. In particular, we will highlight the link between pathwise stochastic integration and Gaussian analysis. The introduction closes with an outline of our results. A basic problem in stochastic calculus is to give a meaning to differential equations of the form Y_t = f(Yt) X_ t; Y0 = ξ 2 W; (1) Y taking values in some Banach space W , X : [0;T ] ! V being some random signal with values in a Banach space V and f taking values in the space of linear maps from V to W . In a deterministic setting, these equations are also called controlled differential equations. In many cases in stochastics, it is natural to assume that X_ denotes some \noise" term which can formally be written as the differential of a Brownian motion B. However, this causes problems when we try to give a rigorous meaning to (1). In fact, a famous property of the trajectories t 7! !(t) of the Brownian motion, i.e. its sample paths, is their non-differentiability on a set of full measure. Therefore, we cannot apply the deterministic theory of controlled differential equations. One approach is to rewrite the differential equation (1) as an integral equation: Z t Yt = Y0 + f(Ys) dXs: (2) 0 By doing this, we shift the problem of defining (1) to the problem of how to define the (stochas- tic) integral in (2). More generally, we may ask the following question: How can we define a stochastic integral of the form Z t Ys dXs (3) 0 where X and Y are stochastic processes taking values in V resp. L(V; W )? There are basically two strategies we can follow. The first one ignores all the probabilistic structure the processes X and Y might have and tries to build up a deterministic theory of integration which is rich enough Introduction in order to integrate all sample paths of X and Y with respect to each other. We will call this the pathwise approach. The second strategy uses the probabilistic properties of the processes under consideration in order to define the integral, and we will call this the probabilistic approach. We will see that Lyons' rough paths theory can be seen as a pathwise approach, whereas the classical It¯otheory is rather a probabilistic approach. In the following, we will summarise the most important attempts of defining stochastic integrals of the form (3) in order to better understand the contribution of rough paths theory in the context of stochastic integration. This permits us to explain the notion of Gaussian rough paths which provides the framework for this thesis. Young's approach The first and probably most \natural" pathwise approach is to define the integral (3) as the limit (at least in probability) of Riemann-sums: Z t X Ys dXs = lim Yti (Xti+1 − Xti ); (4) 0 jΠj!0 ti2Π where the Π are finite partitions of the interval [0; t]. It is commonly known that this limit exists (pathwise) if the sample paths of X have bounded variation (which is the same as to say that the sample paths have finite length): X lim jXti+1 − Xti j < 1 a.s. jΠj!0 ti2Π Unfortunately, this is not the case for the Brownian motion and the above quantity will be infinite almost surely in this case. A more elaborated approach was developed by Laurence C. Young, starting from the article [You36] and further developed in a series of papers. Recall the notion of p-variation, a generalisation of the concept of bounded variation: If x: [0;T ] ! V is a path and p ≥ 1, the p-variation of x is defined as 1 0 1 p X p sup @ jxti+1 − xti j A : Π ti2Π The main theorem of Young can be stated as follows: If x and y are paths of finite p- resp. 1 1 1 q-variation with p + q > 1, the limit in (4) exists and can be bounded in terms of the p- and 1 1 q-variation of x and y. Let us note that the condition p + q > 1 is necessary; indeed, Young gives a counterexample by constructing paths x and y which have finite 2-variation only and for which the Riemann sums (4) diverge. Recall now that our initial aim was to solve integral equations of the form Z t yt = y0 + f(ys) dxs: (5) 0 If this equation has a solution, we expect (at least for smooth f) that the solution y has a regularity (on small scales) which is similar to the regularity of x.
Load more

Recommended publications
  • Convergence Rates for the Full Gaussian Rough Paths
    Annales de l’Institut Henri Poincaré - Probabilités et Statistiques 2014, Vol. 50, No. 1, 154–194 DOI: 10.1214/12-AIHP507 © Association des Publications de l’Institut Henri Poincaré, 2014 www.imstat.org/aihp Convergence rates for the full Gaussian rough paths Peter Friza,b,1 and Sebastian Riedelc,2 aFakultät II, Institut für Mathematik, TU Berlin, MA 7-2, Strasse des 17. Juni 136, 10623 Berlin, Germany bWeierstrass Institut für Angewandte Analysis und Stochastik, Mohrenstrasse 39, 10117 Berlin, Germany. E-mail: [email protected] cFakultät II, Institut für Mathematik, TU Berlin, MA 7-4, Straße des 17. Juni 136, 10623 Berlin, Germany. E-mail: [email protected] Received 5 August 2011; revised 23 April 2012; accepted 22 June 2012 Abstract. Under the key assumption of finite ρ-variation, ρ ∈[1, 2), of the covariance of the underlying Gaussian process, sharp a.s. convergence rates for approximations of Gaussian rough paths are established. When applied to Brownian resp. fractional Brownian motion (fBM), ρ = 1resp.ρ = 1/(2H), we recover and extend the respective results of (Trans. Amer. Math. Soc. 361 (2009) 2689–2718) and (Ann. Inst. Henri Poincasé Probab. Stat. 48 (2012) 518–550). In particular, we establish an a.s. rate − − − k (1/ρ 1/2 ε),anyε>0, for Wong–Zakai and Milstein-type approximations with mesh-size 1/k. When applied to fBM this answers a conjecture in the afore-mentioned references. Résumé. Nous établissons des vitesses fines de convergence presque sûre pour les approximations des chemins rugueux Gaussiens, sous l’hypothèse que la fonction de covariance du processus Gaussien sous-jacent ait une ρ-variation finie, ρ ∈[1, 2).
    [Show full text]
  • Final Report (PDF)
    Foundation of Stochastic Analysis Krzysztof Burdzy (University of Washington) Zhen-Qing Chen (University of Washington) Takashi Kumagai (Kyoto University) September 18-23, 2011 1 Scientific agenda of the conference Over the years, the foundations of stochastic analysis included various specific topics, such as the general theory of Markov processes, the general theory of stochastic integration, the theory of martingales, Malli- avin calculus, the martingale-problem approach to Markov processes, and the Dirichlet form approach to Markov processes. To create some focus for the very broad topic of the conference, we chose a few areas of concentration, including • Dirichlet forms • Analysis on fractals and percolation clusters • Jump type processes • Stochastic partial differential equations and measure-valued processes Dirichlet form theory provides a powerful tool that connects the probabilistic potential theory and ana- lytic potential theory. Recently Dirichlet forms found its use in effective study of fine properties of Markov processes on spaces with minimal smoothness, such as reflecting Brownian motion on non-smooth domains, Brownian motion and jump type processes on Euclidean spaces and fractals, and Markov processes on trees and graphs. It has been shown that Dirichlet form theory is an important tool in study of various invariance principles, such as the invariance principle for reflected Brownian motion on domains with non necessarily smooth boundaries and the invariance principle for Metropolis algorithm. Dirichlet form theory can also be used to study a certain type of SPDEs. Fractals are used as an approximation of disordered media. The analysis on fractals is motivated by the desire to understand properties of natural phenomena such as polymers, and growth of molds and crystals.
    [Show full text]
  • Arxiv:1712.01343V2 [Math.DS]
    MULTISCALE SYSTEMS, HOMOGENIZATION, AND ROUGH PATHS ILYA CHEVYREV, PETER K. FRIZ, ALEXEY KOREPANOV, IAN MELBOURNE, AND HUILIN ZHANG Dedicated to Professor S.R.S Varadhan on the occasion of his 75th birthday Abstract. In recent years, substantial progress was made towards under- standing convergence of fast-slow deterministic systems to stochastic differen- tial equations. In contrast to more classical approaches, the assumptions on the fast flow are very mild. We survey the origins of this theory and then re- visit and improve the analysis of Kelly-Melbourne [Ann. Probab. Volume 44, Number 1 (2016), 479-520], taking into account recent progress in p-variation and càdlàg rough path theory. Contents 1. Introduction 2 2. Emergence of randomness in deterministic dynamical systems 4 2.1. The weak invariance principle 4 2.2. First applications to fast-slow systems 5 2.3. Chaotic dynamics: CLT and the WIP 6 2.3.1. Uniformly and nonuniformly expanding maps 7 2.3.2. Hyperbolic diffeomorphisms 11 2.3.3. Hyperbolic flows 13 3. General rough path theory 13 3.1. Limit theorems from rough path analysis 13 3.2. WIPs in rough path theory 17 arXiv:1712.01343v2 [math.DS] 25 Mar 2019 4. Applications to fast-slow systems 18 4.1. Chaotic dynamics: enhanced WIP and moments 18 4.1.1. Expanding maps 18 4.1.2. Hyperbolic diffeomorphism 19 4.1.3. Hyperbolic flows 20 4.2. Continuous dynamics 20 4.3. Discrete dynamics 22 5. Extension to families and non-product case 23 References 24 Key words and phrases. Fast-slow systems, homogenization, rough paths.
    [Show full text]
  • Rough Paths and Rough Partial Differential Equations
    Weierstrass Institute for Applied Analysis and Stochastics Rough paths and rough partial differential equations Christian Bayer Mohrenstrasse 39 · 10117 Berlin · Germany · Tel. +49 30 20372 0 · www.wias-berlin.de March 18, 2016 Outline 1 Motivation and introduction 2 Rough path spaces 3 Integration against rough paths 4 Integration of controlled rough paths 5 Rough differential equations 6 Applications of the universal limit theorem 7 Rough partial differential equations Rough paths and rough partial differential equations · March 18, 2016 · Page 2 (48) Controlled differential equations Standard ordinary differential equation d y˙t = V(yt); y0 = ξ 2 R ; t 2 [0; 1] V : Rd ! Rd smooth Controlled differential equation d dyt = V(yt)dxt; y0 = ξ 2 R ; t 2 [0; 1] I V : Rd ! Rd×e smooth e I xt path taking values in R I xt may contain component t, i.e., includes dyt = V0(yt)dt + V(yt)dxt Rough paths and rough partial differential equations · March 18, 2016 · Page 3 (48) Controlled differential equations Standard ordinary differential equation d y˙t = V(yt); y0 = ξ 2 R ; t 2 [0; 1] V : Rd ! Rd smooth Controlled differential equation d dyt = V(yt)dxt; y0 = ξ 2 R ; t 2 [0; 1] I V : Rd ! Rd×e smooth e I xt path taking values in R I xt may contain component t, i.e., includes dyt = V0(yt)dt + V(yt)dxt Rough paths and rough partial differential equations · March 18, 2016 · Page 3 (48) Controlled differential equations Standard ordinary differential equation d y˙t = V(yt); y0 = ξ 2 R ; t 2 [0; 1] V : Rd ! Rd smooth Controlled differential equation d dyt
    [Show full text]
  • Diffusive and Rough Homogenisation in Fractional Noise Field
    Diffusive and rough homogenisation in fractional noise field Johann Gehringer and Xue-Mei Li Imperial College London * June 23, 2020 Abstract With recently developed tools, we prove a homogenisation theorem for a random ODE with short and long-range dependent fractional noise. The effective dynamics are not necessarily diffusions, they are given by stochastic differential equations driven simultaneously by stochastic processes from both the Gaussian and the non-Gaussian self-similarity universality classes. A key lemma for this is the ‘lifted’ joint functional central and non-central limit theorem in the rough path topology. keywords: passive tracer, fractional noise, multi-scale, functional limit theorems, rough differential equations MSC Subject classification: 34F05, 60F05, 60F17, 60G18, 60G22, 60H05, 60H07, 60H10 Contents 1 Introduction 2 2 Preliminaries 5 2.1 Hermiteprocesses................................ ........ 5 2.2 FractionalOrnstein-Uhlenbeckprocesses . ................ 6 2.3 HermiteRank..................................... ..... 7 2.4 JointfunctionalCLT/non-CLT . .......... 7 2.5 AssumptionsandConventions . .......... 8 3 Lifted joint functional limit theorem 9 arXiv:2006.11544v1 [math.PR] 20 Jun 2020 3.1 Relativecompactnessofiteratedintegrals . ................. 10 3.2 Young integral case (functional non-CLT in rough topology) ................. 14 3.3 Itô integral case (functionalCLT in roughtopology) . ................... 15 3.4 ProofofTheoremB................................. ...... 22 3.5 ProofoftheconditionalintegrabilityoffOU . ................. 22 4 Multi-scale homogenisation theorem 24 5 Appendix 26 5.1 Someroughpaththeory.... .... .... ... .... .... .... .. ........ 26 *[email protected], [email protected] 1 1 Introduction Fractional noise is the ‘derivative’of a fractional Brownian motion. Its covarianceat times separated by a span 2H 2 2H 1 1 s is ̺˜(s) 2H(2H 1) s − +2H s − δs where H is the Hurst parameter taking values in (0, 1) 2 ∼ − | | | |1 1 \{ } and δs is the Dirac measure.
    [Show full text]
  • A Note on the Continuity in the Hurst Index of the Solution of Rough
    A note on the continuity in the Hurst index of the solution of rough differential equations driven by a fractional Brownian motion Francesco C. De Vecchi∗ Luca Giordano† Daniela Morale‡ Stefania Ugolini‡ February 14, 2020 Abstract Within the rough path framework we prove the continuity of the solution to random dif- ferential equations driven by fractional Brownian motion with respect to the Hurst parameter H when H (1/3, 1/2]. ∈ 1 Introduction The importance of the study of stochastic equations driven by a fractional Brownian motion with parameter H (0, 1) naturally arises from the observation of many phenomena for which ∈ the assumption of independence of increments which is intrinsic, for example in the case of the standard Brownian motion, cannot be supposed ([7]). Indeed, in biology, meteorology, telecommunications, queueing theory and finance evidence of memory and autocorrelation effects are shown ([6,10,15]). The estimation of H is very important, since it determines the magnitude of the self-correlation of the noise in the models. As emphasized in [8], not only one has to deal with the problem of the estimation of the Hurst parameter H of the noise, as in [9,11,12], but one needs to check that the model does not exhibit a large sensitivity with respect to the values of H. Hence, the study of the continuity problem is important in the case of both time (SDE) and time-space (SPDE) stochastic differential equations driven by fractional noises, and it is a very interesting problem not only from a theoretical point of view, but also in the modeling applications ([1,2,4,13,14]).
    [Show full text]
  • Doob--Meyer for Rough Paths
    DOOB–MEYER FOR ROUGH PATHS PETER FRIZ, ATUL SHEKHAR Abstract. Recently, Hairer–Pillai proposed the notion of θ-roughness of a path which leads to a deterministic Norris lemma. In the Gubinelli framework (H¨older, level 2) of rough paths, they were then able to prove a H¨ormander type result (SDEs driven by fractional Brownian motion, H > 1/3). We take a step back and propose a natural ”roughness” condition relative to a given p-rough path in the sense of Lyons; the aim being a Doob-Meyer result for rough integrals in the sense of Lyons. The interest in our (weaker) condition is that it is immediately verified for large classes of Gaussian processes, also in infinite dimensions. We conclude with an application to non-Markovian system under H¨ormander’s condition. 1. Introduction Recently, Hairer–Pillai [11] proposed the notion of θ-roughness of a path which leads to a de- terministic Norris lemma, i.e. some sort of quantitative Doob-Meyer decomposition, for (level-2, H¨older) rough integrals in the sense of Gubinelli. It is possible to check that this roughness con- dition holds for fractional Brownian motion (fBm); indeed in [11] the author show θ-roughness for any θ>H where H denotes the Hurst parameter. (Recall that Brownian motion corresponds to H = 1/2; in comparison, the regime H < 1/2 should be thought of as ”rougher”.) All this turns out to be a key ingredient in their H¨ormander type result for stochastic differential equations driven by fBm, any H > 1/3, solutions of which are in general non-Markovian.
    [Show full text]
  • Stochastic Control with Rough Paths Joscha Diehl, Peter Friz, Paul Gassiat
    Stochastic control with rough paths Joscha Diehl, Peter Friz, Paul Gassiat To cite this version: Joscha Diehl, Peter Friz, Paul Gassiat. Stochastic control with rough paths. Applied Mathematics and Optimization, Springer Verlag (Germany), 2016, 10.1007/s00245-016-9333-9. hal-01419763 HAL Id: hal-01419763 https://hal.archives-ouvertes.fr/hal-01419763 Submitted on 19 Dec 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. STOCHASTIC CONTROL WITH ROUGH PATHS JOSCHA DIEHL, PETER K. FRIZ, PAUL GASSIAT Abstract. We study a class of controlled differential equations driven by rough paths (or rough path realizations of Brownian motion) in the sense of T. Lyons. It is shown that the value function satisfies a HJB type equation; we also establish a form of the Pontryagin maximum principle. Deterministic problems of this type arise in the duality theory for controlled diffusion processes and typically involve anticipating stochastic analysis. We make the link to old work of M. H. A. Davis and G. Burstein [A deterministic approach to stochastic optimal control with application to anticipative optimal control. Stochastics and Stochastics Reports, 40:203–256, 1992] and then prove a continuous-time generalization of Roger’s duality formula [L.
    [Show full text]
  • An Introduction to Rough Paths Antoine Lejay
    An Introduction to Rough Paths Antoine Lejay To cite this version: Antoine Lejay. An Introduction to Rough Paths. J. Azéma; M. Ledoux; M. Emery; M. Yor. Seminaire de Probabilités XXXVII, 1832 (1832), Springer Berlin / Heidelberg, pp.1-59, 2003, Lecture Notes in Mathematics, 978-3-540-20520-3. 10.1007/b94376. inria-00102184 HAL Id: inria-00102184 https://hal.inria.fr/inria-00102184 Submitted on 25 Feb 2009 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. An Introduction to Rough Paths Antoine Lejay1 | Projet Tosca (INRIA / IECN) Abstract: This article aims to be an introduction to the theory of rough paths, in which integrals of di®erential forms against irregu- lar paths and di®erential equations controlled by irregular paths are de¯ned. This theory makes use of an extension of the notion of iter- ated integrals of the paths, whose algebraic properties appear to be fundamental. This theory is well-suited for stochastic processes. Keywords: controlled di®erential equations, integration against irregular paths, p-variation, stochastic processes, iterated integrals, Chen series, geometric multiplicative functional AMS Classi¯cation: Primary 60H10, 34A10; Secondary 34F05 Published in S¶eminaire de probabilit¶esXXXVII.
    [Show full text]
  • Topics in Stochastic Differential Equations and Rough Path Theory
    Topics in Stochastic Differential Equations and Rough Path Theory vorgelegt von Dipl.-Math. Joscha Diehl Von der Fakult¨atII { Mathematik und Naturwissenschaften der Technischen Universit¨atBerlin zur Erlangung des akademischen Grades Doktor der Naturwissenschaften { Dr. rer. nat. { genehmigte Dissertation Promotionsausschuss Vorsitzender: Prof. Dr. Dietmar H¨omberg Berichter: Prof. Dr. Peter Friz Prof. Dr. Terry Lyons Tag der wissenschaftlichen Aussprache: 22. M¨arz2012 Berlin 2012 D 83 Acknowledgment I want to express my deep gratitude towards my advisor Prof. Peter Friz, who set me on an interesting collection of problems. He was always ready to discuss any piece of mathematics and his unyielding enthusiasm was a constant source of joy. I want to thank Prof. Terry Lyons for accepting to be co-examiner of this thesis. Financial support by the DFG through the IRTG \Stochastic Models of Complex Processes" as well as the SPP1324 is gratefully acknowledged. Contents 1 Introduction 2 2 Stochastic differential equations with rough drift 5 2.1 Notation . .5 2.2 Main results . .5 2.3 The Young case . 21 2.4 Applications . 32 2.4.1 Robust filtering . 33 2.4.2 Pathwise stochastic control . 40 2.4.3 Mixed stochastic differential equations . 45 3 Backward stochastic differential equations with rough driver 46 3.1 Notation . 47 3.2 Main results . 47 3.3 The Markovian Setting - Connection to rough PDEs . 58 3.4 Connection to BDSDEs . 64 3.5 Technical results . 66 3.5.1 Comparison for BSDEs . 66 3.5.2 Properties of rough flows . 70 3.5.3 Comparison for PDEs . 71 1 1.
    [Show full text]
  • On the Theory of Rough Paths, Fractional and Multifractional Brownian Motion with Applications to Finance Fabian Andsem Harang, MAT5960 Master’S Thesis, Autumn 2015
    On the Theory of Rough Paths, Fractional and Multifractional Brownian Motion With Applications to Finance Fabian Andsem Harang, MAT5960 Master’s Thesis, Autumn 2015 , 1 On the Theory of Rough Paths, Fractional and Multifractional Brownian motion - with applications to finance. Fabian Andsem Harang. Department of Mathematics,University of Oslo. December 10, 2015 Abstract In recent years the theory of rough paths has become increasingly popular. The theory gives simple and “free of probability” way of looking at random noise. In this thesis we will give existence and uniqueness results of a differential equation of the form dYt = f(Yt)dXt,Y0 = y Where X is a rough signal in the sense that X X t s ↵ where ↵ ( 1 , 1 ].Further t | t − s| . | − | 2 4 3 we will use rough path theory to study fractional and multifractional Brownian motion, and construct two Itô formulas for different regularities of the respective processes. At last we will apply this theory to a square root process (as used in Heston[8] and CIR[12]), and show existence of solutions to the square root process driven by a multifractional brownian motion with a regularity function h, when h :[0,T] [a, b] (0, 1) . ! ⇢ 2 Acknowledgements I want to thank my supervisors Dr. Torstein K. Nilssen and Professor Frank Proske for the inspiring ideas and discussions, and their patience. I will especially thank Torstein for his support, and for introducing me to the field of Rough Path theory. I am also very grateful to my girlfriend, and family for supporting me along the way of writing this thesis.
    [Show full text]
  • Ballistic Random Walks in Random Environment As Rough Paths: Convergence and Area Anomaly
    Ballistic random walks in random environment as rough paths: convergence and area anomaly Olga Lopusanschi∗ and Tal Orenshteiny Abstract Annealed functional CLT in the rough path topology is proved for the standard class of ballistic random walks in random environment. Moreover, the `area anomaly', i.e. a deterministic linear correction for the second level iterated integral of the rescaled path, is identified in terms of a stochastic area on a regeneration interval. The main theorem is formulated in more general settings, namely for any discrete process with uniformly bounded increments which admits a regeneration structure where the regeneration times have finite moments. Here the largest finite moment translates into the degree of regularity of the rough path topology. In particular, the convergence holds in the α-H¨olderrough path topology for all α < 1=2 whenever all moments are finite, which is the case for the class of ballistic random walks in random environment. The latter may be compared to a special class of random walks in Dirichlet environments for which the regularity α < 1=2 is bounded away from 1=2, explicitly in terms of the corresponding trap parameter. 2020 Mathematics Subject Classification: 60K05, 60K37, 60K40, 60L20, 82B41 Key words: Levy area, rough paths, annealed invariance principles, area anomaly, random walks in random environment, ballisticity conditions, regeneration structure 1 Introduction Rough path theory has been extensively developing since it was introduced by T. Lyons in `98 [Lyo98]. The theory provides a framework to solutions to SDEs driven by non-regular signals such as Brownian motions, while keeping the solution map continuous with respect to the signal.
    [Show full text]