  We explore discovery signatures of techni-dilaton (TD) at LHC. The TD was
predicted long ago as a composite pseudo Nambu-Goldstone boson (pNGB)
associated with the spontaneous breaking of the approximate scale symmetry in
the walking technicolor (WTC). Being pNGB, whose mass arises from the explicit
scale-symmetry breaking due to the dynamical mass generation, the TD should
have a mass MTD lighter than other techni-hadrons, say MTD \simeq 600GeV for
the typical WTC model, which is well in the discovery range of the ongoing LHC
experiment. We develop a spurion method of nonlinear realization to calculate
the TD couplings to the standard model (SM) particles and explicitly evaluate
the TD LHC production cross sections at sqrt{s}=7TeV times the branching ratios
in terms of MTD as an input parameter for 200GeV<MTD<1TeV in the typical WTC
models: one-doublet model (1DM) and one-family model (1FM). It turns out that
the TD signatures are quite different from those of the SM Higgs. We compare
the TD->WW/ZZ signature with the recent ATLAS and CMS bounds and find that in
the case of 1DM the signature is consistent over the whole mass range due to
the large suppression of TD couplings, and by the same token the signal is too
tiny for the TD to be visible through this channel at LHC. As for the 1FM, on
the other hand, a severe constraint is given on MTD to exclude the TD with
MTD<600GeV, which, however, would imply an emergence of somewhat dramatic
excess as the TD signature at MTD>600GeV in the near future. We further find a
characteristic signature coming from the gamma gamma mode in the 1FM. In sharp
contrast to the SM Higgs case, it provides highly enhanced cross
section~0.10--1.0fb at around MTD \simeq 600GeV, which is large enough to be
discovered during the first few year's run at LHC.
