  Thermal emission spectra of exoplanets provide constraints on the chemical
compositions, pressure-temperature (P-T) profiles, and energy transport in
exoplanetary atmospheres. Accurate inferences of these properties rely on the
robustness of the atmospheric retrieval methods employed. While extant
retrieval codes have provided significant constraints on molecular abundances
and temperature profiles in several exoplanetary atmospheres, the constraints
on their deviations from thermal and chemical equilibria have yet to be fully
explored. Our present work is a step in this direction. We report HyDRA, a
disequilibrium retrieval framework for thermal emission spectra of exoplanetary
atmospheres. The retrieval code uses the standard architecture of a parametric
atmospheric model coupled with Bayesian statistical inference using the Nested
Sampling algorithm. For a given dataset, the retrieved compositions and P-T
profiles are used in tandem with the GENESIS self-consistent atmospheric model
to constrain layer-by-layer deviations from chemical and radiative-convective
equilibrium in the observable atmosphere. We demonstrate HyDRA on the Hot
Jupiter WASP-43b with a high-precision emission spectrum. We retrieve an H2O
mixing ratio of log(H2O) = -3.54^{+0.82}_{-0.52}, consistent with previous
studies. We detect H2O and a combined CO/CO2 at 8-sigma significance. We find
the dayside P-T profile to be consistent with radiative-convective equilibrium
within the 1-sigma limits and with low day-night redistribution, consistent
with previous studies. The derived compositions are also consistent with
thermochemical equilibrium for the corresponding distribution of P-T profiles.
In the era of high precision and high resolution emission spectroscopy, HyDRA
provides a path to retrieve disequilibrium phenomena in exoplanetary
atmospheres.

Earth and Planetary Astrophysics