We study the classical field theoretical formulation of static generic
isolated horizons in a manifestly SU(2) invariant formulation. We show that the
usual classical description requires revision in the non-static case due to the
breaking of diffeomorphism invariance at the horizon leading to the non
conservation of the usual pre-symplectic structure. We argue how this
difficulty could be avoided by a simple enlargement of the field content at the
horizon that restores diffeomorphism invariance. Restricting our attention to
static isolated horizons we study the effective theories describing the
boundary degrees of freedom. A quantization of the horizon degrees of freedom
is proposed. By defining a statistical mechanical ensemble where only the area
A of the horizon is fixed macroscopically-states with fluctuations away from
spherical symmetry are allowed-we show that it is possible to obtain agreement
with the Hawking's area law---S = A/4 (in Planck Units)---without fixing the
Immirzi parameter to any particular value: consistency with the area law only
imposes a relationship between the Immirzi parameter and the level of the
Chern-Simons theory involved in the effective description of the horizon
degrees of freedom.Comment: Presentation improvements, published versio
