3,864 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 ( 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 () 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
Theoretical Expectations for the Muon's Electric Dipole Moment
We examine the muon's electric dipole moment \dmu from a variety of theoretical perspectives. We point out that the reported deviation in the muon's g-2 can be due partially or even entirely to a new physics contribution to the muon's {\em electric} dipole moment. In fact, the recent g-2 measurement provides the most stringent bound on \dmu to date. This ambiguity could be definitively resolved by the dedicated search for \dmu recently proposed. We then consider both model-independent and supersymmetric frameworks. Under the assumptions of scalar degeneracy, proportionality, and flavor conservation, the theoretical expectations for \dmu in supersymmetry fall just below the proposed sensitivity. However, non-degeneracy can give an order of magnitude enhancement, and lepton flavor violation can lead to \dmu of order e cm, two orders of magnitude above the sensitivity of the \dmu experiment. We present compact expressions for leptonic dipole moments and lepton flavor violating amplitudes. We also derive new limits on the amount of flavor violation allowed and demonstrate that approximations previously used to obtain such limits are highly inaccurate in much of parameter space
Kaluza-Klein Dark Matter: Direct Detection vis-a-vis LHC
We explore the phenomenology of Kaluza-Klein (KK) dark matter in very general
models with universal extra dimensions (UEDs), emphasizing the complementarity
between high-energy colliders and dark matter direct detection experiments. In
models with relatively small mass splittings between the dark matter candidate
and the rest of the (colored) spectrum, the collider sensitivity is diminished,
but direct detection rates are enhanced. UEDs provide a natural framework for
such mass degeneracies. We consider both 5-dimensional and 6-dimensional
non-minimal UED models, and discuss the detection prospects for various KK dark
matter candidates: the KK photon , the KK -boson , the KK
Higgs boson and the spinless KK photon . We combine collider
limits such as electroweak precision data and expected LHC reach, with
cosmological constraints from WMAP, and the sensitivity of current or planned
direct detection experiments. Allowing for general mass splittings, we show
that neither colliders, nor direct detection experiments by themselves can
explore all of the relevant KK dark matter parameter space. Nevertheless, they
probe different parameter space regions, and the combination of the two types
of constraints can be quite powerful. For example, in the case of in
5D UEDs the relevant parameter space will be almost completely covered by the
combined LHC and direct detection sensitivities expected in the near future.Comment: 52 pages, 29 figure
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