Shedding light on the $t bar t$ asymmetry: the photon handle

We investigate a charge asymmetry in $t bar t gamma$ production at the LHC that provides complementary information to the measured asymmetries in $t bar t$ production. We estimate the experimental uncertainty in its measurement at the LHC with 8 and 14 TeV. For new physics models that simultaneously reproduce the asymmetry excess in $t bar t$ at the Tevatron and the SM-like asymmetry at the LHC, the measurement in $t bar t gamma$ at the LHC could exhibit significant deviations with respect to the SM prediction.

Combined analysis of Z -> t tbar and Z -> t tbar j production for vector resonance searches at LHC

We have implemented a code for Z + n jets production in ALPGEN, with Z decays into several final states, including l+ l- and t tbar. The MLM prescription is used for matching the matrix element with the parton shower, including in this way the leading soft and collinear corrections. In order to demonstrate its capabilities, we perform a combined analysis of Z -> t tbar and Z -> t tbar j production for a heavy leptophobic gauge boson. It is found that the effect of the extra jet cannot only be accounted for by a K factor multiplying the leading-order cross section. In fact, the combined analysis for Z -> t tbar and Z -> t tbar j presented improves the statistical significance of the signal by 25% (8.55 sigma versus 6.77 sigma for a Z mass of 1 TeV), compared with the results of an inclusive analysis carried out on the same sample of t tbar + t tbar j events.

Looking for signals beyond the neutrino Standard Model

Any new neutrino physics at the TeV scale must include a suppression mechanism to keep its contribution to light neutrino masses small enough. We review some seesaw model examples with weakly broken lepton number, and comment on the expected effects at large colliders and in neutrino oscillations.