On the short-distance constraints from K_{L,S} -> mu^+ mu^-
Abstract
Motivated by new precise results on several
K
L
decays, sensitive to the
K
L
→γγ
form factor, we present a new analysis of the
K
L
→
μ
+
μ
−
long-distance amplitude based on a semi-phenomenological approach. Particular attention is devoted to the evaluation of the uncertainties of this method and to the comparison with alternative approaches. Our main result is a conservative upper bound of
2.5×
10
−9
on
B(
K
L
→
μ
+
μ
−
)
short
, which is compatible with the SM expectation and which provides significant constraints on new-physics scenarios. The possibility to extract an independent short-distance information from future searches on
K
S
→
μ
+
μ
−
is also briefly discussed.