Noether Symmetry in a Non-Metricity Theory with a Boundary Term: Exact Solutions and Bayesian Cosmological Constraints

Abstract: We investigate the cosmological implications of a power-law $f(Q, B)$ gravity model, where $Q$ denotes the non-metricity scalar and $B$ is the associated boundary term. We employ the Noether symmetry approach to identify the admissible functional form of the gravitational Lagrangian and to obtain the corresponding conserved quantities and exact cosmological solutions. Using the exact solution, we find that for this model parameter condition $α+β&gt;\frac{3}{2}$, the model exhibits the accelerating phase of the Universe. Furthermore, we have also discussed the model with recent observational data using a Bayesian Markov Chain Monte Carlo analysis. We consider different combinations of Cosmic Chronometers (CC), Pantheon+ & SH0ES, and DESI DR2 observations to constrain the model parameters and the Hubble constant $H_0$. The inferred value of $H_0$ depends on the adopted dataset combination, ranging from a higher value for the CC+Pantheon+ combination to a lower value for CC+DESI DR2, with the latter yielding $$H_0=67.5^{{+1.4}_{-1.6}\,\mathrm{km\,s^{-1}\,} Mpc<sup>{-1}}$$, consistent with the Planck 2018 CMB-preferred value within the standard $Λ$CDM framework. The inferred (H_0) is strongly dataset dependent, spanning the range between the early-Universe and locally calibrated determinations. We further examine the posterior covariance and correlation matrices to identify parameter degeneracies and assess the robustness of the MCMC constraints. The background evolution also exhibits late-time accelerated expansion and remains compatible with the observational constraints. These results demonstrate that the $f(Q, B)$ model provides a viable alternative description of late-time cosmology.