PHYS08200604017 Manimala Mitra - Homi Bhabha National Institute

0.08
0.25
0.06
0.2
10 -3
m
νee
(eV)
0.04
m t
(eV)
0.15
m β
2
(eV
2
)
10 -4
0.02
0.1
0
0 0.5 1
y 4
0.05
0 0.5 1
y 4
10 -5
0 0.5 1
y 4
Figure6.4: Scatter plotsshowing variationof|m νee |, m t andm 2 β withthemodel parameter
y 4 .
• y 3 = 0 and y 4 = 0 are not allowed here.
In the left panel of Figure 6.4 we show the variation of the effective neutrino mass
m νee with the model parameter y 4 . The effective mass predicted for neutrino-less
double beta decay in our model is |m νee | = |2v 1 y 4 |. We have allowed v 1 to vary
freely in the range 10 −1 −10 −2 . From Figure 6.4 one can clearly see that our model
predicts |m νee | < ∼0.07 eV. The next generation of neutrino-less double experiments
are expected to probe down to |m νee | = 0.01−0.05 eV [13]. The middle panel of this
figureshowsthetotalpredictedneutrinomassm t andrightpanelshowsm 2 β . Wefind
that the total neutrino mass m t (in eV) varies within the range 0.05 < m t < 0.28,
while the effective mass squared observable in beta decay m 2 β ≃ O(10−4 −10 −2 )eV 2 .
The KATRIN experiment will be sensitive to m β > 0.3 eV [14].
6.3.2 Mildly Broken µ−τ Symmetry Limit
So far we have assumed that the S 3 breaking in the neutrino sector is such that the
residual µ−τ symmetry is exact. This was motivated by the fact that S 2 is a subgroup
of S 3 and we took a particular VEV alignment given in Eq. (6.11). We will discuss about
VEV alignment in section 6.4. In this subsection we will assume that the µ−τ symmetry
is mildly broken. This could come from explicit µ−τ breaking terms in the Lagrangian.
In the next section we will see that in our model this comes after the minimization of
the scalar potential due to the deviation of the VEV alignments from that given in Eq.
(6.11). Small breaking of the VEV alignments could also come from radiative corrections
and/or higher order terms in the scalar part of the Lagrangian. Any breaking of µ − τ
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