Ordering-disordering dynamics of the voter model under random external bias

Abstract: We investigate a variant of the two-state voter model in which agents update their states under a random external field (which points upward with probability $s$ and downward with probability $1-s$) with probability $p$ or adopt the unanimous opinion of $q$ randomly selected neighbors with probability $ 1-p$. Using mean-field analysis and Monte Carlo simulations, we identify an ordering-disorder transition at $p_c$ when $s=1/2$. Notably, in the regime of $p>p_c$, we estimate the time for systems to reach polarization from consensus and find the logarithmic scaling $T_{\text{pol}} \sim \mathcal{B}\ln N$, with $\mathcal{B} = 1/(2p)$ for $q = 1$, while for $q > 1$, $\mathcal{B}$ depends on both $p > p_c$ and $q$. We observe that polarization dynamics slow down significantly for nonlinear strengths $q$ between $2$ and $3$, independent of the probability $p$. On the other hand, when $s=0$ or $s=1$, the system is bound to reach consensus, with the consensus time scaling logarithmically with system size as $T_{\text{con}} \sim \mathcal{B}\ln N$, where $\mathcal{B} = 1/p$ for $q = 1$ and $\mathcal{B} = 1$ for $q > 1$. Furthermore, in the limit of $p = 0$, we analytically derive a general expression for the exit probability valid for arbitrary values of $q$, yielding universal scaling behavior. These results provide insights into how bipolar media environment and peer pressure jointly govern the opinion dynamics in social systems.