  Combined analyses of WMAP 3-year and ACBAR Cosmic Microwave Anisotropies
angular power spectra have presented evidence for gravitational lensing >3
sigma level. This signal could provide a relevant test for cosmology. After
evaluating and confirming the statistical significance of the detection in
light of the new WMAP 5-year data, we constrain a new parameter A_L that scales
the lensing potential such that A_L=0 corresponds to unlensed while A_L=1 is
the expected lensed result. We find from WMAP5+ACBAR a 2.5 sigma indication for
a lensing contribution larger than expected, with A_L=3.1_{-1.5}^{+1.8} at 95%
c.l.. The result is stable under the assumption of different templates for an
additional Sunyaev-Zel'dovich foreground component or the inclusion of an extra
background of cosmic strings. We find negligible correlation with other
cosmological parameters as, for example, the energy density in massive
neutrinos. While unknown systematics may be present, dark energy or modified
gravity models could be responsible for the over-smoothness of the power
spectrum. Near future data, most notably from the Planck satellite mission,
will scrutinize this interesting possibility.
