  We propose a new method for identifying new physics imprints on present
observational data in cosmology whereby signatures of string theory are clearly
distinguished from imprints of possible features on the inflaton potential. Our
method relies on the cross-correlations spectra of cosmic shear from large
scale structure (LSS) with the CMB temperature anisotropies and E-mode
polarization, by using the following properties: inflationary cosmology
provides only one source term for all CMB spectra and LSS which highly
constrains any deviations from the standard predictions; string theory can add
new non-inflationary channels to the source of perturbations as well as modify
clustering properties at large scales. Discrepancies in the source terms of
correlations and clustering properties provide the evidence for new physics.
Models of single-field inflation with a feature are disfavored even with
present data. Upcoming WMAP results and future data from weak lensing of LSS
will further improve our ability to probe new physics in this manner and could
open the first direct window to string theory.
