Testing Cosmological Models Against the Quasar Dipole Anomaly: A Systematic Investigation of Eleven Hypotheses

This preprint presents a systematic investigation of eleven cosmological hypotheses proposed to explain the quasar dipole anomaly observed by the CatWISE survey (D = 0.0155, 4.9 sigma), which exceeds the kinematic expectation from the Cosmic Microwave Background by a factor of 2.2. The hypotheses tested include:- Khronon-Tensor (KT) theory variants: adiabatic tilt, late-onset tilt, smooth transitions, fine-tuned initial conditions, varying khronon fraction, transient profiles, and temporal gradient interpretations.- Disformal coupling to photons.- Directional Lorentz violation (Standard Model Extension).- Lemaitre-Tolman-Bondi (LTB) inhomogeneous cosmology.- A novel "Expansion Temporal Anisotropy" (ETA) hypothesis, tested against 1,701 Pantheon+ Type Ia supernovae. For each hypothesis, we derive quantitative predictions and compare them against observational constraints from Planck (CMB, shear limits), Pantheon+ (supernovae), and CatWISE (quasar dipole). Ten of the eleven hypotheses are ruled out by explicit calculations. Only the LTB model survives within known physics, but it requires extreme fine-tuning of the curvature function E(r) to approximately 3 x 10^-5. The document includes mathematical derivations, numerical estimates, a falsification test using real Pantheon+ data, a consolidated summary table, and a proposed testable hypothesis (Cosmological Clock Anisotropy, CCA) for future research. This work is intended as a research roadmap documenting both viable and non-viable paths, so that future investigators may build upon these results without retracing dead ends.