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Register a new userMajorana neutrino mass structure induced by rigid instatons on toroidal orbifold
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We study effects of D-brane instantons wrapping rigid cycles on Z2*Z2 toroidal orbifold. We compute Majorana masses induced by rigid D-brane instantons and realize bimaximal mixing matrices in certain models. We can also derive more generic mass matrices in other models. The bimaximal mixing Majorana mass matrix has a possibility to explain observed mixing angles. We also compute the mu-term matrix among more than one pairs of Higgs fields induced by rigid D-brane instantons.
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The Majorana neutrino mass matrix combines information from the neutrino masses and the leptonic mixing in the flavor basis. Its invariance under some transformation matrices indicates the existence of certain residual symmetry. We offer an intuitive display of the structure of the Majorana neutrino mass matrix, using the whole set of the oscillation data. The structure is revealed depending on the lightest neutrino mass. We find that there are three regions with distinct characteristics of structure. A group effect and the $mu$-$tau$ exchange symmetry are observed. Six types of texture non-zeros are shown. Implications for flavor models are discussed.
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We study the reasonable requirements of two anomalous $U(1)$s in a flavored-axion framework for the anomaly cancellations of both $U(1)$-mixed gravity and $U(1)_Ytimes[U(1)]^2$ which in turn determine the $U(1)_Y$ charges where $U(1)_Y$ is the hypercharge gauge symmetry of the standard model. We argue that, with a flavor symmetry group, axion-induced topology in symmetry-broken phases plays crucial roles in describing how quarks and leptons are organized at a fundamental level and make deep connections with each other. A unified model, as an example, is then proposed in a simple way to describe a whole spectrum of particles where both flavored-axion interactions with normal matter and the masses and mixings of fermions emerge from the spontaneous breaking of a given symmetry group. Once a scale of active neutrino mass defined at a seesaw scale is fixed by the commensurate $U(1)$ flavored-PQ charge of fermions, that of QCD axion decay constant $F_A$ is determined. In turn, fundamental physical parameters complementary to each other are predicted with the help of precision flavor experiments. Model predictions are extracted on the characteristics of neutrino and flavored-axion: $F_A=3.57^{,+1.52}_{,-1.53}times10^{10}$ GeV (consequently, QCD axion mass $m_a=1.52^{+1.14}_{-0.46}times10^{-4}$ eV, axion to photon coupling $|g_{agammagamma}|=2.15^{+1.61}_{-0.64}times10^{-14},text{GeV}^{-1}$, axion to electron coupling $g_{Aee}=3.29^{+2.47}_{-0.98}times10^{-14}$, etc.); atmospheric mixing angle $theta_{23}$, Dirac CP phase $delta_{CP}$, and $0 ubetabeta${it-decay rate} for normal mass ordering and inverted one by taking quantum corrections into account.
We study the flavor structure in intersecting D-brane models. We study anomalies of the discrete flavor symmetries. We analyze the Majorana neutrino masses, which can be generated by D-brane instanton effects. It is found that a certain pattern of mass matrix is obtained and the cyclic permutation symmetry remains unbroken. As a result, trimaximal mixing matrix can be realized if Dirac neutrino mass and charged lepton mass matrices are diagonal.
One-loop radiative Majorana neutrino masses through the exchange of scalars have been considered for many years. We show for the first time how such a one-loop mass is also possible through the exchange of vector gauge bosons. It is based on a simple variation of a recently proposed $SU(2)_N$ extension of the standard model, where a vector boson is a candidate for the dark matter of the Universe.
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