Quantitative Analyticity for Lyapunov Exponents of Random Products of Matrices with Explicit Polydiscs and Cauchy Coefficient Bounds

The top Lyapunov exponent ${\lambda }_{+}(A,p)$ of a random product of matrices in $\mathrm{G}\mathrm{L}(d,\mathbb{R})$, $d\ge 2$, with simple top spectrum, depends real-analytically on the probability weights $p$ and the matrix coefficients $A$. We establish a quantitative form of this analyticity through a single Kato perturbation argument on the complexified Markov operator on Hölder functions on projective space, yielding seven main theorems with explicit closed-form constants: (i) an explicit polydisc of holomorphy for $p\mapsto {\lambda }_{+}(A,p)$ in ${\mathbb{C}}^N$, giving the quantitative form of the Peres and Bezerra-Sánchez-Tall analyticity theorem; (ii) closed-form Cauchy bounds on its Taylor coefficients; (iii) joint analyticity in the weights $p$ and the matrix entries $A$, with explicit radii in both; (iv) an extension to Markov-chain driven cocycles, with polydisc radius explicit in the chain spectral gap; (v) explicit polynomial boundary-decay rates as $p$ approaches $\mathrm{\partial }{\mathrm{\Delta }}_N$, conditional on a spectral-gap-decay hypothesis; (vi) extension to $\mathrm{G}\mathrm{L}(d,\mathbb{R})$ for all $d\ge 2$ via the Fubini-Study metric; and (vii) a Grassmannian variant giving quantitative analyticity of the partial sums ${\mathrm{\Lambda }}_k={\lambda }_1+\cdots +{\lambda }_k$ under strong $k$-irreducibility, hence of each individual sub-top Lyapunov exponent. The polydisc radius is method-optimal within the Kato class, and a Bernstein-type result shows the Cauchy growth $\alpha !\cdot M_{\ast }\mathrm{/}{r}_{\ast }^{\mathrm{\mid }\alpha \mathrm{\mid }}$ is sharp up to constants. A two-matrix example with numerical values connects the bounds to the Hölder estimates of the companion paper Thiam (Nov. 2025).