3,775 research outputs found

### 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

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