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Thermodynamics and phase transition of rotating regular-de Sitter black holes

We analyze thermodynamic properties of the rotating regular black holes having mass ($M$), angular momentum ($a$), and a magnetic charge $(g)$, and encompass Kerr black hole ($g=0$). The mass $M$ has a minimum at the radius $r_+=r_+^{\star}$, where both the heat capacity and temperature vanish. The thermal phase transition is because of the divergence of heat capacity at a critical radius $r_{+}^C$ with stable (unstable) branches for $r_+<r_+^C$ ($>r_+^C$). We also generalize the rotating regular black holes in de Sitter (dS) background and analyzed its horizon structure to show that for each $g$, there are two critical values of the mass parameter $M_{\text{cr1}}$ and $M_{\text{cr2}}$ which correspond to the degenerate horizons. Thus, we have rotating regular-dS black holes with an additional cosmological horizon apart from the inner (Cauchy) and the outer (event) horizons. Next, we discuss the effective thermodynamic quantities of the rotating regular-dS black holes in the extended phase space where the cosmological constant ($Λ$) is considered as thermodynamic pressure. Combining the first laws at the two horizons, we calculate the heat capacity at constant pressure $C_P$, the volume expansion coefficient $α$, and the isothermal compressibility $κ_T$. At a critical point, the specific heat at constant pressure, the volume expansion coefficient, and the isothermal compressibility of the regular-dS black holes exhibit an infinite peak suggesting a second-order phase transition.