arXiv subjects
Publications and source records attributed to Ernest Ma.
It is proposed that dark matter is the origin of neutrino mass, thereby linking inexorably two undisputed (and seemingly unrelated) pieces of evidence for physics beyond the Standard Model. Leptogenesis at the TeV scale may also be possible, as well as a measurable contribution to the muon anomalous magnetic moment.
In an improved application of the tetrahedral symmetry A_4 first introduced by Ma and Rajasekaran, supplemented by the discrete symmetry Z_3 as well as supersymmetry, a two-parameter form of the neutrino mass matrix is derived which exhibits the tribimaximal mixing of Harrison, Perkins, and Scott. This form is the same one obtained previously by Altarelli and Feruglio, and the inverse of that obtained by Babu and He. If only A_4 is used, then corrections appear, making tan^2(theta_{12}) differenet from 0.5, without changing significantly sin^2(2 theta_{23}) from one or theta_{13} from zero.
Instead of creating the observed baryon asymmetry of the universe by the decay of right-handed (RH) neutrinos to left-handed leptons, we propose to generate it dominantly by the decay of the RH neutrinos to RH leptons. This mechanism turns out to be successful in large regions of parameter space. It may work, in particular, at a scale as low as $\sim$~TeV, with no need to invoke quasi-degenerate RH neutrino masses to resonantly enhance the asymmetry. Such a possibility can be probed experimentally by the observation at colliders of a singlet charged Higgs particle and of RH neutrinos. Other mechanisms which may lead to successful leptogenesis from the RH lepton sector interactions are also briefly presented. The incorporation of these scenarios in left-right symmetric and unified models is discussed.
The evidence for dark matter signals a new class of particles at the TeV scale, which may manifest themselves indirectly through loop effects. In a simple model we show that these loop effects may be responsible for the enhanced muon anomalous magnetic moment, for the neutrino mass, as well as for leptogenesis in a novel way. This scenario can be verified at LHC experiments.
Two of the most important and pressing questions in cosmology and particle physics are: (1) What is the nature of cold dark matter? and (2) Will near-future experiments on neutrinoless double beta decay be able to ascertain that the neutrino is a Majorana particle, i.e. its own antiparticle? We show that these two seemingly unrelated issues are intimately connected if neutrinos acquire mass only because of their interactions with dark matter.
The successful A4 family symmetry for leptons is applied to quarks, motivated by the quark-lepton assignments of SU(5). Realistic quark masses and mixing angles are obtained, in good agreement with data. In particular, we find a strong correlation between |V_{ub}| and the CP phase beta, thus allowing for a decisive future test of this model.
In the recent successful applications of the non-Abelian discrete symmetry A_4 to the tribimaximal mixing of neutrinos, lepton doublets and singlets do not transform in the same way. It appears thus to be unsuitable as a family symmetry in grand unification. A simple resolution of this dilemma is proposed.
The radiative seesaw mechanism proposed recently is minimally extended to include supersymmetry in a specific model. Relevant related issues such as leptogenesis and dark matter are discussed.
Combining one established idea with two recent ones, it is pointed out for the first time that three of the outstanding problems of particle physics and cosmology, i.e. neutrino mass, dark matter, and baryogenesis, may have a common solution, arising from the interactions of a single term, with experimentally verifiable consequences.
The discrete subgroup Delta(27) of SU(3) has some interesting properties which may be useful for understanding charged-lepton and neutrino mass matrices. Assigning leptons to the 3 and 3* representations of Delta(27), a simple form of the Majorana neutrino mass matrix is obtained and compared to present data.
I review some of the recent progress (up to December 2005) in applying non-Abelian discrete symmetries to the family structure of leptons, with particular emphasis on the tribimaximal mixing ansatz of Harrison, Perkins, and Scott.
I review some of the recent progress (up to September 2005) in applying non-Abelian discrete symmetries to the family structure of leptons, with particular emphasis on the tribimaximal mixing ansatz of Harrison, Perkins, and Scott.
In the supersymmetric seesaw model of neutrino masses, augmented by the non-Abelian discrete tetrahedral symmetry A_4, a specific pattern of neutrino mixing is automatically generated if one of the three heavy singlet neutrino superfields acquires a nonzero vacuum expectation value. This pattern turns out to be exactly that of tribimaximal mixing, i.e. sin^2 theta_23 = 1/2, sin^2 theta_12 = 1/3, and sin^2 theta_13 = 0, in good agreement with data.
We show that a modification of a recently proposed model by Altarelli and Feruglio with softly broken $A_4$ symmetry leads naturally to nonvanishing $U_{e3}$ with $θ_{13}\simeq 2^o - 4^o$. The observed mass squared differences for solar and atmospheric neutrinos have been fitted without fine tuning among model parameters. The predicted solar neutrino mixing angle is brought down from the tri-bimaximal prediction to be in concordance with the latest global analysis including experimental data from KamLAND and SNO.
The observed baryon asymmetry of the Universe is suitably created in thermal leptogenesis through the out-of-equilibrium decay of $N_1$, the lightest of the three heavy singlet neutral fermions which anchor the seesaw mechanism to obtain small Majorana neutrino masses. However, this scenario suffers from the incompatibility of a generic lower bound on the mass of $N_1$ and the upper bound on the reheating temperature of the Universe after inflation. A modest resolution of this conundrum is proposed.
To connect the scalar field (acceleron) responsible for dark energy to neutrinos, the usual strategy is to add unnaturally light neutral singlet fermions (right-handed neutrinos) to the Standard Model. A better choice is actually a Higgs triplet, through the coupling of the acceleron to the trilinear Higgs triplet-double-doublet interaction. This hypothesis predicts an easily observable doubly-charged Higgs boson at the forthcoming Large Hadron Collider (LHC).
A minimal extension of the Standard Model is proposed, where the observed left-handed neutrinos obtain naturally small Majorana masses from a one-loop radiative seesaw mechanism. This model has two candidates (one bosonic and one fermionic) for the dark matter of the Universe. It has a very simple structure and should be verifiable in forthcoming experiments at the Large Hadron Collider.
We consider $SU(3)_{C}\times SU(2)_{AL}\times SU(2)_{BL}\times U(1)_{Y}$ as the low-energy subgroup of supersymmetric $SU(3)^{6}$ unification. This may imply small deviations from quark-lepton universality at the TeV scale, as allowed by neutron-decay data. New particles are predicted with specific properties. We discuss in particular the new heavy gauge bosons corresponding to $SU(2)_{AL} \times SU(2)_{BL} \to SU(2)_L$.