  We report a high-resolution numerical study of two-dimensional (2D) miscible
Rayleigh-Taylor (RT) incompressible turbulence with the Boussinesq
approximation. An ensemble of 100 independent realizations were performed at
small Atwood number and unit Prandtl number with a spatial resolution of
$2048\times8193$ grid points. Our main focus is on the temporal evolution and
the scaling behavior of global quantities and of small-scale turbulence
properties. Our results show that the buoyancy force balances the inertial
force at all scales below the integral length scale and thus validate the basic
force-balance assumption of the Bolgiano-Obukhov scenario in 2D RT turbulence.
It is further found that the Kolmogorov dissipation scale $\eta(t)\sim
t^{1/8}$, the kinetic-energy dissipation rate $\varepsilon_u(t)\sim t^{-1/2}$,
and the thermal dissipation rate $\varepsilon_{\theta}(t)\sim t^{-1}$. All of
these scaling properties are in excellent agreement with the theoretical
predictions of the Chertkov model [Phys. Rev. Lett. \textbf{91}, 115001
(2003)]. We further discuss the emergence of intermittency and anomalous
scaling for high order moments of velocity and temperature differences. The
scaling exponents $\xi^r_p$ of the $p$th-order temperature structure functions
are shown to saturate to $\xi^r_{\infty}\simeq0.78\pm0.15$ for the highest
orders, $p\sim10$. The value of $\xi^r_{\infty}$ and the order at which
saturation occurs are compatible with those of turbulent Rayleigh-B\'{e}nard
(RB) convection [Phys. Rev. Lett. \textbf{88}, 054503 (2002)], supporting the
scenario of universality of buoyancy-driven turbulence with respect to the
different boundary conditions characterizing the RT and RB systems.
