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

In this work, we explore the cosmological dynamics of a modified gravity framework based on the function f(Q,B)=δ Q²+β 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=Aρ -D₁ρ α 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 H₀=72.2814+3.4702-4.5209 H 0 = 72 . 2814 - 4.5209 + 3.4702 km/s/Mpc, Aₛ = 0.6964+0.0779-0.1258 A s = 0 . 6964 - 0.1258 + 0.0779 , α = 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 zₜᵣ ≈ 0.946 z tr ≈ 0.946 , while the present-day value is q₀ = -0.789 q 0