AbstractThis second volume Book II of the Quantum Model of the Universe (QMU) presents a comprehensive,structurally organized analysis of late-time cosmology, focusing on the emergence, mechanisms, andconstraints of cosmic acceleration. Building on the foundational and early-universe regimes developedin Volume I, the present work investigates the structural, geometric, and vacuum–matter interactions thatgovern accelerated expansion, formulating each hypothesis as a self-contained, logically coherent unitwith explicit mathematical, structural, and observational status.The Book II systematically explores the vacuum–structure coupling, multi-sector interactions,phase-space saturation, backreaction effects, and covariant structural constraints that collectivelydetermine the onset and magnitude of cosmic acceleration. Classical ΛCDM dynamics are reinterpretedas limiting cases within a broader structural framework, and the effective dark energy contribution isderived from cumulative vacuum–matter interactions rather than ad hoc postulates. Each mechanism isanalyzed for structural necessity, testability, and parameter closure, ensuring that all statements are eithermathematically inevitable, observationally falsifiable, or clearly delineated as logically contingent.The collection serves as a rigorous map of admissible cosmological models at late times, highlightingthe structural boundaries of accelerated expansion and the universal constraints imposed by relativisticcosmology, vacuum invariance, and gravitational coherence. Volume II situates the QMU contributions asextensions that unify early-universe physics with late-time acceleration, closing previously unresolvedlogical spaces and providing a robust foundation for observational verification and falsification of thestructural acceleration framework. IntroductionThis work constitutes Book II of the Quantum Model of the Universe (QMU) Volume II, forming thecentral segment of a three-book structure within the second volume of the QMU framework. WhileVolume II as a whole addresses the transition from primordial regimes to multi-domain cosmology, BookII specifically develops the structural theory of late-time cosmic acceleration, extending the foundationaland early-universe dynamics established in Book I of Volume II.Book II is designed as a self-contained, logically coherent unit, yet it is inseparably linked to theother books: it builds directly upon the physical carriers, vacuum structure, quantum geometry, andearly-universe regimes analyzed in Book I, and it provides the necessary structural and multi-domainfoundations that are further expanded in Book III. This arrangement preserves a continuous logicaland mathematical narrative across Volume II while allowing each book to be read independently forspecialized study.The primary objective of Book II is to demonstrate that cosmic acceleration is not an anomalyrequiring additional microphysical postulates or ad hoc dark-energy models, but rather a structuralnecessity emerging from global vacuum–matter interactions, geometric invariants, and relativisticcosmology. Each hypothesis and mechanism is treated as a self-contained unit with explicitmathematical formulation, structural status, and observational interface, consistent with the QMUcanonical methodology.The chapters are organized into two interconnected layers. The first layer addresses vacuum–structureinteractions, multi-sector coupling, phase-space saturation, parameter closure, and effective cosmologicalbackreaction mechanisms. Classical ΛCDM and phenomenological dark energy models aresystematically reinterpreted as limiting or approximate cases within this structural framework.The second layer integrates cumulative and global effects, including external-mass contributions,bubble-in-bubble scenarios, multiverse interactions, and statistical coordination across vacuum sectors,connecting early-universe inheritance to late-time cosmic acceleration.For practical coherence, chapters in Book II are sequentially numbered from 36 to 98, reflectingcontinuity from Book I and alignment with the overarching Volume II structure. Transition chaptersexplicitly link the early-universe physics of Book I to the structural acceleration theorems andmulti-domain considerations that culminate in Book III.Through rigorous mathematical derivation, structural classification, and observational testability,Book II provides a complete, falsifiable, and publication-ready framework for understanding late-timecosmic acceleration. By situating acceleration as a structurally necessary phenomenon, it closes a keylogical gap between early-universe dynamics and the multi-domain cosmology addressed in Book III,firmly embedding Book II as the central segment of Volume II