Letter of Intent for KEK Super B Factory Part I: Physics

for the left-handed (Q) and right-handed (U and D) quark sector,
for the left-handed (L) and right-handed (E) lepton sector, and
Li(1, 2, −1/2), Ei(1, 1, 1) (3.2)
H1(1, 2, −1/2), H2(1, 2, 1/2) (3.3)
for the Higgs fields. The representation (or charge) for the gauge group SU(3)C×SU(2)L×U(1)Y
is given in parentheses, and i (= 1, 2, or 3) is a generation index. Under the assumption of
R-parity conservation, which is required to avoid an unacceptably large proton decay rate, the
superpotential is written as
WMSSM = f ij
D DiQjH1 + f ij
U U iQjH2 + f ij
E EiLjH1 + µH1H2, (3.4)
where fU and fD are the quark Yukawa couplings. The soft supersymmetry breaking terms are
−Lsoft = (m 2 Q) i j ˜qi˜q †j + (m 2 D) j
i ˜ d †i dj
˜ + (m 2 U) j
i ũ†iũj + (m 2 E) i j˜ei˜e †j + (m 2 L) j
i ˜l †i˜lj +∆ 2 1h †
1h1 + ∆ 2 2h †
2h2 − (Bµh1h2 + h.c.)
+A ij
D ˜ di˜qjh1 + A ij
U ũi˜qjh2 + A ij
L ũi˜qjh2
+ M1
2 ˜ B ˜ B + M2
2 ˜ W ˜ W + M3
2
˜g˜g. (3.5)
These consist of mass terms for scalar fields (˜qi, ũi, ˜ di, ˜ li, ˜ei, h1, and h2), Higgs mixing terms,
trilinear scalar couplings, and gaugino ( ˜ B, ˜ W , and ˜g) mass terms.
Flavor physics already places strong restrictions on the possible structure of the SUSY breaking
sector, since arbitrary terms would induce many flavor violating processes which are easily
ruled out by present experimental data. Therefore, in order to comply with the requirement
of highly suppressed FCNC interactions one has to introduce some structure in the soft SUSY
breaking terms. Several scenarios have been proposed.
• Universality. The SUSY breaking terms have a universal flavor structure at a very high
energy scale, such as the Planck scale (∼ 10 18 GeV) or the GUT scale (∼ 10 16 GeV).
It could also be a lower scale (∼ 10 4−6 GeV). The universality comes from mediation
of the SUSY breaking effect by flavor-blind interactions, such as gravity (for a review of
gravity mediation see [5]), the Standard Model gauge interaction (gauge mediation [14–16]
the gaugino mediation [17–19]), or the super-Weyl anomaly (anomaly mediation [20, 21]).
Since the soft SUSY breaking terms are flavor-blind, the squark masses are degenerate at
the high energy scale where those terms are generated. The GIM mechanism then works
as long as the scalar triple coupling (squark-squark-Higgs), the A term, is proportional to
the Yukawa couplings in the Standard Model. An additional flavor violating effect could
appear through the renormalization group running of the squark masses to the low energy
scale, which depends on the flavor [22]. For the gauge mediation scenario the effect on
FCNC processes is extremely suppressed, since the SUSY breaking scale is low and there
is not enough room for the running.
• Alignment. Squark and slepton mass matrices could be diagonalized (no flavor changing
interaction) in the same basis as quarks and leptons, if one assumes some symmetries
involving different generations [23, 24]. Flavor violation is then suppressed and flavor
violating processes are induced by incomplete alignment.
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