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Anomaly mediation is a special case of gravity mediation
where there is no direct tree level coupling that
transmits the SUSY breaking in the hidden sector
to the observable one.
In this case the masses of the gauginos are
generated at oneloop, while
those of the scalars are generated at twoloop level,
because of the superconformal anomaly
that breaks scale invariance[6,7].
Since the anomaly is topological in origin, it
naturally conserves flavor, thereby inducing
no new FCNC amplitudes.
AMSB models thus preserve virtues of the gravitymediated
models with the FCNC problem resolved.
The scale invariant oneloop gaugino mass expressions are
M_{i} 
= 


where b_{i}'s are related to the oneloop beta functions through
and numerically
b_{1} = 33/5, b_{2} = 1, b_{3} = 3.
In the minimal AMSB model, however, the sleptons
become tachyonic, which necessitated, for instance,
introduction of a universal scalar mass parameter
m_{0}^{2}:

= 


where
's are related to the RG functions
through
.
As already stressed in Section 3.2,
the first and the most important message from
the gaugino mass formula
above is the hierarchy:
M_{1} : M_{2} : M_{3} = 2.8 : 1 : 8.3
as opposed to
M_{1} : M_{2} : M_{3} = 1 : 2 : 7that is expected for the gravity or gaugemediated models.
This implies that the lightest neutralino (
)
and the lighter chargino (
)
are almost pure winos and consequently
massdegenerate^{8}.
This degeneracy is lifted by
the treelevel gauginohiggsino mixing
and loop corrections, resulting in a small
but finite mass splitting as depicted in
Fig. 3.34
for
,
,
and
.
Figure 3.34:
Mass difference
as a function of the gravitino mass for
(upper curve)
and
(lower curve), , and
.

The lighter chargino thus decays mostly (9698 %)
into the lightest neutralino and a soft ,
possibly with a visibly displaced vertex.
Ref. [43] discusses search strategies for
the chargino pair production:
,
where the additional photon will be very useful to
suppress the huge twophoton
background
expected for the
range shown above, or to
tag the chargino pair production when the finalstate pions are
too soft to be detected.
When the decay length is comparable or larger than the detector
size, the charginos will appear as heavily ionizing particles
as in the case of the slepton LSP in the GMSB models.
If the daughter pions are too soft to be detected, one may
observe abruptly terminating tracks in the central tracker.
Fig. 3.35 summarizes the search methods and
corresponding discovery limits shown in
the

plane.
Figure:
3.35
Viable search modes in different regions
in the
(
) plane.
Discovery reach is given
for
and also for
accumulated at
.
The vertical band and vertical line (the band for
and the line for
)
is the reach of the
detection mode, which
is relevant only if the 's are too soft to detect[43].

The figure tells us that,
with all the methods combined,
one can cover the parameter space almost to
the kinematical limit.
The scalar mass formula also contains a phenomenologically
important message that is the near degeneracy of the
left and righthanded sleptons, which
means that left and righthanded sleptons can be
produced simultaneously, with relative rates
controlled by the beam polarization.
Slepton productions are studied[44,45]
in the context of the AMSB models
assuming
^{9}.
For instance, let us consider the lefthanded selectron
pair production:
followed by the mixed decays:
and
with
decaying slowly into
.
This results in a final state:
.
The signal is a fast
and a soft .
The soft
can give rise to a visibly displaced vertex,
if the decay length of the chargino is less than 3cm.
If it is longer than 3cm,
then one sees a heavily ionizing track of the chargino
as discussed above.
Fig. 3.36 shows the effective cross sections
after cuts to select the signal events
as contours in the m_{3/2}m_{0} plane.
Figure:
3.36
Effective cross section contours in the m_{3/2}m_{0} plane
expected for the
signal from
at
:
(a)
, and (b)
.
The shaded regions are ruled out by various constraints[45].

Note that the effective cross sections include
branching fraction as well as the selection efficiency
due to the selection cuts.
We can see that large regions, allowed by all the
current constraints, have large effective cross sections
fb at
= 1000 GeV.
Next: 3.4.5 Parity Violation
Up: 3.4 Other Scenarios
Previous: 3.4.3 Gauge Mediated Supersymmetry
ACFA Linear Collider Working Group
EMail:acfareport@acfahep.kek.jp