  We perform a wavelet analysis of the temperature and polarization maps of the
Cosmic Microwave Background (CMB) delivered by the WMAP experiment in search
for a parity violating signal. Such a signal could be seeded by new physics
beyond the standard model, for which the Lorentz and CPT symmetries may not
hold. Under these circumstances, the linear polarization direction of a CMB
photon may get rotated during its cosmological journey, a phenomenon also
called cosmological birefringence. Recently, Feng et al. have analyzed a subset
the WMAP and BOOMERanG 2003 angular power spectra of the CMB, deriving a
constraint that mildly favors a non zero rotation. By using wavelet transforms
we set a tighter limit on the CMB photon rotation angle \Delta\alpha= -2.5 \pm
3.0 (\Delta\alpha= -2.5 \pm 6.0) at the one (two) \sigma level, consistent with
a null detection.
