A new parametric study of f(Q, B) gravity with modified Chaplygin gas and recent observations

Abstract In this work, we explore the cosmological dynamics of a modified gravity framework based on the function $$f(Q,B)=\delta Q^{2}+\beta B$$ f ( Q , B ) = δ Q 2 + β B , where Q denotes the nonmetricity scalar and B is the boundary term that relates Q to the Ricci scalar. The matter sector is modeled using the Modified Chaplygin Gas (MCG) with the equation of state $$p=A\rho -\frac{D_{1}}{\rho ^{\alpha }}$$ p = A ρ - D 1 ρ α , allowing the model to interpolate between early-time matter behavior and late-time cosmic acceleration. By deriving an analytical expression for the Hubble parameter H ( z ), we perform a parameter estimation using Markov Chain Monte Carlo (MCMC) techniques in conjunction with the latest cosmological observations: 46 Hubble parameter measurements, 15 BAO data points, DESI DR2 BAO data and the Pantheon+ Type Ia supernovae compilation. The best-fit values are obtained as $$H_0=72.2814^{+3.4702}_{-4.5209}$$ H 0 = 72 . 2814 - 4.5209 + 3.4702 km/s/Mpc, $$A_s = 0.6964^{+0.0779}_{-0.1258}$$ A s = 0 . 6964 - 0.1258 + 0.0779 , $$\alpha = 0.0027^{+0.0225}_{-0.0209}$$ α = 0 . 0027 - 0.0209 + 0.0225 and $$A = 0.0024^{+0.0702}_{-0.0464}$$ A = 0 . 0024 - 0.0464 + 0.0702 . The deceleration parameter transitions at redshift $$z_{tr} \approx 0.946$$ z tr ≈ 0.946 , while the present-day value is $$q_0 = -0.789$$ q 0