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\section{\usemenu{slacpub7237::context::slacpub7237001}{Introduction}}\label{section::slacpub7237001}
Supersymmetry provides an elegant framework
in which physics at the electroweak scale
can be decoupled from Planck scale physics.
The electroweak scale arises dynamically as the effective scale
of supersymmetry breaking in the visible sector.
The breaking of supersymmetry must be transmitted
from a breaking sector to the visible sector through
a messenger sector.
Most phenomenological studies of low energy
supersymmetry implicitly assume that messenger
sector interactions are of gravitational strength.
The intrinsic scale of supersymmetry breaking is
then necessarily of order $\sqrt{F} \sim 10^{11}$ GeV,
giving an electroweak scale of ${G_F^{1/2}} \sim F / M_p$.
While gravitational strength interactions represent a
lower limit, it is certainly possible that the messenger
scale, $M$, is anywhere between the Planck and just above
the electroweak scale,
with supersymmetry broken at
an intermediate scale, ${G_F^{1/2}} \sim F / M$.
If the messenger scale is well below the Planck scale,
it is likely that the usual gauge interactions of the
standard model play some role in the messenger sector.
This is because standard model gauginos couple
at the renormalizable level only through gauge interactions.
If the Higgs bosons received masses
predominantly from nongauge interactions in the messenger sector,
with only a small contribution from
gauge interactions,
the standard model gauginos would be unacceptably
lighter than the electroweak scale.\footnote{
The argument for light gauginos in the absence of
standard model gauge interactions within a messenger
sector well below the Planck scale
only applies if the gauginos
are elementary degrees of freedom. %up to the messenger scale.
If the standard model gauge group is magnetic at or below
the messenger scale the gauginos could in principle
receive a large mass from operators suppressed by the
confining magnetic scale.}
It is therefore interesting to consider theories in which
the standard model gauge interactions act as messengers of supersymmetry
breaking \cite{1,2,3}.
This mechanism occurs if supersymmetry is realized nonlinearly
in some sector which transforms under the standard model
gauge group.
Supersymmetry breaking in the visible sector spectrum
then arises as a radiative correction.
In this paper we consider the superpartner spectroscopy and
important phenomenological signatures that result
from gaugemediated supersymmetry breaking.
%With electroweak symmetry breaking properly imposed,
%The low energy theory is highly constrained and very
%predictive, with the superpartner spectrum depending
%primarily on only two parameters.
Since within this anzatz
the gauge interactions transmit supersymmetry breaking,
the standard model soft masses arise in proportion to
gauge charges squared.
This leads to a sizeable hierarchy among the superpartner masses
according to gauge quantum numbers.
%The $B$ino and right handed sleptons gain mass only through
%$U(1)_Y$ interactions and are therefore lightest.
%The $W$ino's and left handed sleptons, transforming under
%$SU(2)_L$, are somewhat heavier.
%The strongly interacting squarks and gluino are significantly
%heavier than the electroweak states.
In addition, for a large class of models, there are a number
of relations and sum rules among the superpartner masses.
%In this same class of models the gaugino masses satisfy
%``gaugino unification'' relations.
Electroweak symmetry breaking is driven by negative radiative
corrections to the uptype Higgs mass squared from the large top quark
Yukawa coupling and large stop masses
\cite{3}.
With the constraint of electroweak symmetry breaking
the minimal model of gaugemediation is highly constrained
and very predictive,
with the superpartner spectrum depending primarily
on two parameters  the overall scale and $\tan \beta$.
In addition, there is a logarithmic dependence
of various mass relations on the messenger scale.
%In the minimal model the Higgsinos are heavier than
%the electroweak gauginos.
%In addition, the nonstandard model Higgs bosons,
%$A^0$, $H^0$, and $H^{\pm}$ are heavy leaving the lightest
%Higgs boson,
%Most of these features are fairly stable under deviations
%away from the minimal model.
%A much smaller value of $\mu$ can however result with large
%corrections to the Higgs soft masses arising
%from nongauge interactions.
The precise form of the low lying superpartner spectrum
determines the signatures that can be observed at a high
energy collider.
With gaugemediated supersymmetry breaking, either
a neutralino or slepton is the lightest standard model
superpartner.
The signature for supersymmetry is then either the traditional
missing energy or heavy charged particle production.
In a large class of models the general form of the cascade decays
to the lightest standard model superpartner is largely fixed
by the anzatz of gaugemediation.
In addition,
for a low enough supersymmetry breaking scale, the lightest
standard model superpartner can decay to its partner plus
the Goldstino component of the gravitino within the
detector.
In the next subsection the natural lack of flavor
changing neutral currents with gaugemediated supersymmetry
breaking is discussed.
The minimal model of gaugemediated supersymmetry breaking
(MGM) and its variations are presented in section 2.
A renormalization group analysis of the minimal model
is performed in section 3,
with the constraint of proper radiative electroweak symmetry
breaking enforced.
Details of the resulting superpartner and Higgs boson spectra
are discussed.
Mass relations and sum rules are identified which can distinguish
gauge mediation from other theories for the soft terms.
Some mass relations allow a logarithmically sensitive probe of
the messenger scale.
In section 4 variations of the minimal model are studied.
With larger messenger sector representations
the lightest standard model superpartner is naturally a slepton.
Alternately, additional sources for Higgs sector masses, can lead
in some instances to a Higgsino as the lightest standard model
superpartner.
The phenomenological consequences of gaugemediated supersymmetry
breaking are given in section 5.
The supersymmetric contribution to
${\rm Br}(b \to s \gamma)$ in the minimal model, and resulting
bound on the overall scale for the superpartners, are quantified.
The collider signatures for superpartner production in both
the minimal model, and models with larger messenger sector
representations, are also detailed.
In the latter case, the striking signature of heavy charged
particles exiting the detector can result, rather than
the traditional missing energy.
The signatures resulting from decay of the lightest standard
model superpartner to its partner plus the Goldstino are
also reviewed.
In section 6 we conclude with a few summary remarks
and a comment about tuning.
The general expression for scalar and gaugino masses in a large
class of models is given in appendix A.
A nonminimal model is presented in appendix B which
demonstrates an approximate $U(1)_R$ symmetry, and has
exotic scalar and gaugino mass relations, even though
it may be embedded in a GUT theory.
Finally, in appendix C the couplings of the Goldstino
component of the gravitino
%to the lightest standard model superpartner
are reviewed.
In addition to the general expressions for the decay
rate of the lightest standard model superpartner
to its partner plus the Goldstino,
the severe suppression of the branching ratio to Higgs boson final
states in the minimal model is quantified.
%For the entire range of parameters of the minimal model
%At moderate values of $\tan \beta$, $\na$ is the lightest
%standard model superpartner, and decays
%predominantly a photon and
%the Goldstino component of the gravitino,
%$\na \to \gamma + G$.
%At large values of $\tan \beta$, however, $\stau_1$ is the
%lightest standard model superpartner, and decays by
%$\stau \to \tau + G$.
%Radiative corrections from topstop loops give a sizeable
%modification of $m_{h^0}$ since the squarks are so heavy.
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