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Searches for lepton flavor violation in tau decays constitute one of
the most theoretically and experimentally clean and powerful probes to
extend our knowledge in particle physics.  In this specific area,
\superb has clear advantages over the LHC experiments and SuperKEKB,
and it is complementary to muon LFV searches.
Experimental investigations on
\CP\ violation in tau decay and on the tau EDM and $g\! -\!\! 2$ provide \superb with
additional experimentally clean tools to shed light on unexplored
territories, with the ability to test some specific New Physics  scenarios.
Furthermore, precise tests of lepton universality can
reveal new phenomena, although attaining the required precision is
challenging, \superb is once again the best-positioned project, due
to its very high luminosity.

With an integrated luminosity of 75\invab, \superb will be able to
explore a significant portion of the parameter space of most New Physics
scenarios by searching for LFV in tau decays.  While the MEG
experiment~\cite{Grassi:2005ac} will search for $\mu \to e\gamma$ with
great sensitivity, \superb will uniquely explore transitions between the
third and first or second generations, providing crucial information to
determine the specific New Physics model that produces LFV.
The LHC experiments are, in general, not competitive in LFV searches;
SuperKEKB, with 10\invab, will also be able to explore LFV in tau decay,
but with a sensitivity that does not challenge the majority of New
Physics models. \superb has the
advantage of higher luminosity, which increases its tau LFV
sensitivity by a factor 2.7 in the worst hypothesis of background-dominated
analyses, even assuming no improvement in analysis
techniques. For analyses which are background-free, \superb
will have a sensitivity at least 7.5 times better, and will also profit from
reduced machine background. Furthermore, \superb can have a 85\%
linearly polarized electron beam, which will produce tau leptons with
known and well-defined polarization that can be exploited either to
improve the selection of LFV final states, given a specific LFV
interaction, or to better determine the features of the LFV
interaction, once they are found.

Experimental studies on \CP\ violation in tau decay and on the tau EDM and
$g\! - \!\! 2$ are especially clean tools, because they rely on measurement of
asymmetries with relatively small systematic uncertainties from the
experiment. The beam polarization also improves the experimental sensitivity
for tau EDM and $g\! - \!\! 2$ determinations, by allowing measurements of the polarization
of a single tau, rather than measurements of correlations between
two taus produced in the same events. with this technique,  \superb can test whether
supersymmetry is a viable explanation for the present discrepancy on
the muon $g\! - \!\! 2$.  Although the most plausible New Physics  models constrained
with the available experimental results predict \CP\ violation in tau decay
and the tau EDM in a range that is not measurable, \superb can test
specific models that enhance those effects to measurable levels.
