2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/105638We construct a trajectory-based semiclassical theory of shot noise in clean chaotic cavities. In the universal regime of vanishing Ehrenfest time $\tE$, we reproduce the random matrix theory result, and show that the Fano factor is exponentially suppressed as $\tE$ increases. We demonstrate how our theory preserves the unitarity of the scattering matrix even in the regime of finite $\tE$. We discuss the range of validity of our semiclassical approach and point out subtleties relevant to the recent semiclassical treatment of shot noise in the universal regime by Braun et al. [cond-mat/0511292].Final version, to appear in Physical Review LettersMesoscale and Nanoscale PhysicsChaotic Dynamicstext