
The author constructs a probabilistic version of Nevanlinna theory in general cases, improving the stochastic method by estimates of increasing processes for Brownian motions (Br.m.) and martingales (mart.) on manifolds. In Section 1 he establishes counterparts of the 1. and 2. Main Nevanlinna Theorems and of a defect relation in the general situation of a filtered probability space \((\Omega, {\mathcal F}, P, ({\mathcal F}_t)_{t\geq 0})\) for a nonnegative continuous \({\mathcal F}_t\)-local submart. \((V_t) {t\geq 0}\) on it, after decomposing \(V_t= M_t+ A_t\) with \(M_t\) a local mart. and \(A_t\) an increasing process. Thus an analogy of the 1. Theorem corresponds to \[ E[V_T]- E[V_0]+ N(T,V)= E[A_T], \] where \(T\) is an \({\mathcal F}_t\)-stopping time with \(E[A_T] \lambda)\), \(V^*_T= \sup\{V_t: 0\leq t\leq T\}\), and the 2. Theorem to \[ E[V_T] \leq-E [\log\rho_T] +\log E \biggl[ \exp \bigl(V_T+ h(V_T) \bigr)\rho_T\biggr] +h\bigl(E[V_T] \bigr), \] where \(\rho_t\) is a positive \({\mathcal F}_t\)-adapted process and \(h\) a convex function on \([0,\infty)\). Further taking a sequence of stopping times \(T_n\), and \(h\) such that convenient inequalities hold, a defect relation is obtained in the form \(\liminf_{n\to\infty} (E[V_{T_n}]/E) \leq\limsup_{n\to \infty} (-E [\log \rho_{T_n}]/E )\), \(\mathbb{E}= E[\int^{T_n}_0 \rho_s ds]\). Section 2 contains a main estimate relative to a Green function and a harmonic measure of a Br.m. on manifolds. The author considers two types of \(n\)-dimensional Riemannian manifolds \(M\): the Cartan-Hadamard in sense of Greene-Wu, in particular those which are also spherically symmetric, and the parabolic ones defined by an exhaustion function. He proves estimates for the image of a Br.m. \(X_t\) on \(M\) under a positive continuous function \(f\): \[ E \bigl[\log f(X_{T_r}) \bigr] \leq (\beta+1)^2 \log E \left[\int^{T_r}_0 f(X_s)ds \right]+ S(r), \] giving the expression of \(T_r\) and \(S(r)\) in all the three cases, \(\beta>0\), \(r\in (0,\infty) \smallsetminus E_\beta\), \(E_\beta\) of finite Lebesgue measure. Section 3 is dedicated to harmonic morphisms \(\Phi: M\to N\) between Riemannian \(n\)-manifolds \(M\) and \(N\), which are characterized (Darling, Fuglede) as mappings a Br.m. \(X_t\) on \(M\) to a diffusion process \(Y_t\) on \(N\), \(Y_{A_t} =\Phi (X_t)\) with \(A_t= \int^t_0 \lambda^2_\Phi (X_s) ds\), \(\lambda_\Phi\)= the dilatation of \(\Phi\). For \(M\) as above, \(u\) a nonnegative Borel measurable function on \(N\) such that \(u(Y_t)\) be a continuous local submart., and from the inequality \(\sup_x E_x [\int^1_0 (\exp (u+h(u)) (Y_s)ds] <\infty\), an analogy of the 2. Theorem is deduced. (Procedure works if the image is a general Markov process too). The results are illustrated for \(N\) a compact Riemannian manifold with strictly positive injective radius at every point, by constructing a function \(u_S\), \(S\) being a family of \(q\) disjoint smooth submanifolds in \(N\) of codimension 2. Again Nevanlinna type 1 and 2 theorems and a defect relation are given. The conformal case \(M=\) Riemann surface, \(N= \mathbb{P}^1\), \(\Phi\) a meromorphic function clarifies the relation to classical Nevanlinna theory, \(M = \mathbb{C}\) or the unit disc, as well as to the case \(M=a\) parabolic Riemann surface. Section 4 treats the case when the image of the Br.m. is a mart.: \(Y_t\) on a Riemannian manifold \(N\) with Levi-Civita connexion. New concepts are associated to \(Y_t\) and estimates given using Krylov's one. For \(M\) as in 2., \(N\) compact, \(u\) and \(h\) satisfying some conditions, a 2. type theorem is deduced if \(\Phi\) is a stochastic nondegenerate harmonic map. Then the holomorphic case is dealt with and conformal martingales on Kähler manifolds are considered. A 2. type theorem is proved for \(\Phi\) a nondegenerate holomorphic map: \(\mathbb{C}^n \to\mathbb{P}^n\), with interesting consequences on defect relations, in particular a relation on the defect of an algebraic hypersurface which improves a Carlson-Griffiths' one. The theorem extends to a complex projective algebraic \(n\)-manifold \(N\). Section 5 contains an averaging Bezout estimate via probabilistic methods, for a harmonic morphism \(\Phi\), which extends to maps preserving strong Markov processes up to time-change.
Diffusion processes and stochastic analysis on manifolds, Nevanlinna theory, martingales, Brownian motions, defect relation, Brownian motion, Value distribution theory in higher dimensions, Diffusion processes, harmonic morphism, Analysis
Diffusion processes and stochastic analysis on manifolds, Nevanlinna theory, martingales, Brownian motions, defect relation, Brownian motion, Value distribution theory in higher dimensions, Diffusion processes, harmonic morphism, Analysis
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