From Phantom Divide Crossings to the Hubble Tension: A Non-Adiabatic Cyclic Universe with Third-Order Geometric Corrections 从幽灵分界线穿越到哈勃张力:带有三阶几何修正的非绝热循环宇宙

The standard cosmological model faces challenges regarding the nature of dark energy and the Hubble tension. We propose a non-adiabatic cyclic universe model characterized by a geometric correction term h(a,t). By introducing a third-order effective scale factor modification , we numerically solve the modified Friedmann equations. Our results reveal that the effective equation of state w_eff naturally crosses the phantom divide (w=-1) at approximately 6.6 Gyr ago. More importantly, this third-order geometric correction significantly enhances the late-time expansion rate. At z=0.05, the model yields an approximately 8.5% increase in H(z)/H₀ compared to the standard ΛCDM model. Crucially, this mechanism remains perfectly compatible with Big Bang Nucleosynthesis (BBN) constraints, as h → 1 in the early universe. This study demonstrates that entropy-driven geometric corrections in a cyclic universe provide a viable pathway to alleviate the Hubble tension.