How to look for supersymmetry under the lamppost at the LHC

We apply a model-independent, agnostic approach to the collider phenomenology of supersymmetry (SUSY), in which all mass parameters are taken as free inputs at the weak scale. We consider the gauginos, higgsinos, and the first two generations of sleptons and squarks, and analyze all possible mass hierarchies among them ($4\times 8!=161,280$ in total) in which the lightest superpartner is neutral, leading to missing energy. In each case, we identify the full set of the dominant (i.e. least suppressed by phase space, small mixing angles or Yukawa couplings) decay chains originating from the lightest colored superpartner. Our exhaustive search reveals several quite dramatic yet unexplored multilepton signatures with up to 8 isolated leptons (plus possibly up to 2 massive gauge or Higgs bosons) in the final state. Such events are spectacular, background-free for all practical purposes, and may lead to a discovery of SUSY in the very early stage ($\sim 10\ {\rm pb}^{-1}$) of LHC operations at 7 TeV.Comment: 4 pages, 4 figure

Contrasting Supersymmetry and Universal Extra Dimensions at Colliders

We contrast the experimental signatures of low energy supersymmetry and the model of Universal Extra Dimensions and discuss various methods for their discrimination at hadron and lepton colliders. We study the discovery reach of hadron colliders for level 2 Kaluza-Klein modes, which would indicate the presence of extra dimensions. We also investigate the possibility to differentiate the spins of the superpartners and KK modes by means of the asymmetry method of Barr. We then review the methods for discriminating between the two scenarios at a high energy linear collider such as CLIC. We consider the processes of Kaluza-Klein muon pair production in universal extra dimensions in parallel to smuon pair production in supersymmetry. We find that the angular distributions of the final state muons, the energy spectrum of the radiative return photon and the total cross-section measurement are powerful discriminators between the two models.Comment: 6 pages, 8 figures, to appear in the proceedings of the 2005 International Linear Collider Workshop, Stanford, US

Quintessential Kination and Leptogenesis

Thermal leptogenesis induced by the CP-violating decay of a right-handed neutrino (RHN) is discussed in the background of quintessential kination, i.e., in a cosmological model where the energy density of the early Universe is assumed to be dominated by the kinetic term of a quintessence field during some epoch of its evolution. This assumption may lead to very different observational consequences compared to the case of a standard cosmology where the energy density of the Universe is dominated by radiation. We show that, depending on the choice of the temperature T_r above which kination dominates over radiation, any situation between the strong and the super--weak wash--out regime are equally viable for leptogenesis, even with the RHN Yukawa coupling fixed to provide the observed atmospheric neutrino mass scale ~ 0.05 eV. For M< T_r < M/100, i.e., when kination stops to dominate at a time which is not much later than when leptogenesis takes place, the efficiency of the process, defined as the ratio between the produced lepton asymmetry and the amount of CP violation in the RHN decay, can be larger than in the standard scenario of radiation domination. This possibility is limited to the case when the neutrino mass scale is larger than about 0.01 eV. The super--weak wash--out regime is obtained for T_r << M/100, and includes the case when T_r is close to the nucleosynthesis temperature ~ 1 MeV. Irrespective of T_r, we always find a sufficient window above the electroweak temperature T ~ 100 GeV for the sphaleron transition to thermalize, so that the lepton asymmetry can always be converted to the observed baryon asymmetry.Comment: 13 pages, 8 figure