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Ernest Ma

Publications and source records attributed to Ernest Ma.

At least 127 records · Page 7Linked to original sources
arXiv2013

Radiative Scaling Neutrino Mass with $A_4$ Symmetry

A new idea for neutrino mass was proposed recently, where its smallness is not due to the seesaw mechanism, i.e. not inversely proportional to some large mass scale. It comes from a one-loop mechanism with dark matter in the loop consisting of singlet Majorana fermions $N_i$ with masses of order 10 keV and neutrino masses are scaled down from them by factors of about $10^{-5}$. We discuss how this model may be implemented with the non-Abelian discrete symmetry $A_4$ for neutrino mixing, and consider the phenomenology of $N_i$ as well as the extra scalar doublet $(η^+,η^0)$.

hep-ph↗
arXiv2012

Self-Organizing Neutrino Mixing Matrix

A new and novel idea for a predictive neutrino mass matrix is presented, using the non-Abelian discrete symmetry A(4) and the seesaw mechanism with only two heavy neutral fermion singlets. Given the components of the one necessarily massless neutrino eigenstate, the other two massive states are automatically generated. A realistic example is discussed with predictions of a normal hierarchy of neutrino masses and maximal CP violation.

hep-ph↗
arXiv2012

Radiative Scaling Neutrino Mass and Warm Dark Matter

A new and radical scenario of the simple 2006 model of radiative neutrino mass is proposed, where there is no seesaw mechanism, i.e. neutrino masses are not inversely proportional to some large mass scale, contrary to the prevalent theoretical thinking. The neutral singlet fermions in the loop have masses of order 10 keV, the lightest of which is absolutely stable and the others are very long-lived. All are components of warm dark matter, which is a possible new paradigm for explaining the structure of the Universe at all scales.

hep-ph↗
arXiv2012

Dirac neutrino mass generation from dark matter

In 2006, a simple extension of the Standard Model was proposed in which neutrinos obtain radiative Majorana masses at one-loop level from their couplings with dark matter, hence the term "scotogenic," from the Greek "scotos" meaning darkness. Here an analogous mechanism for Dirac neutrino masses is discussed in a minimal model. In different ranges of the parameter space, various candidates for dark matter are possible. In particular, the lightest Dirac fermion which appears in the loop diagram generating neutrino mass can be a viable dark matter candidate. Such a possibility does not exist for the Majorana case. Realistic neutrino mixing in the context of $A_4$ is discussed. A possible supersymmetric extension is also briefly discussed.

hep-ph↗
arXiv2012

Scotogenic $A_4$ Neutrino Model for Nonzero $θ_{13}$ and Large $δ_{CP}$

Assuming that neutrinos acquire radiative seesaw Majorana masses through their interactions with dark matter, i.e. scotogenic from the Greek 'scotos' meaning darkness, and using the non-Abelian discrete symmetry $A_4$, we propose a model of neutrino masses and mixing with nonzero $θ_{13}$ and necessarily large leptonic CP violation, allowing both the normal and inverted hierarchies of neutrino masses, as well as quasi-degenerate solutions.

hep-ph↗
arXiv2012

New Simple A_4 Neutrino Model for Nonzero θ_{13} and Large δ_{CP}

In a new simple application of the non-Abelian discrete symmetry $A_4$ to charged-lepton and neutrino mass matrices, we show that for the current experimental central value of $\sin^2 2 θ_{13} \simeq 0.1$, leptonic CP violation is necessarily large, i.e. $|\tan δ_{CP}| > 1.3$.

hep-ph↗
arXiv2012

Dark-Matter Fermion from Left-Right Symmetry

In an unconventional realization of left-right symmetry, the particle corresponding to the left-handed neutrino nu_L (with SU(2)_L interactions) in the right-handed sector, call it n_R (with SU(2)_R interactions), is not its Dirac mass partner, but a different particle which may be a dark-matter candidate. In parallel to leptogenesis in the SU(2)_L sector, asymmetric production of n_R may occur in the SU(2)_R sector. This mechanism is especially suited for n_R mass of order 1 to 10 keV, i.e. warm dark matter, which is a possible new paradigm for explaining the structure of the Universe at all scales.

hep-ph↗
arXiv2012

Supersymmetric Axion-Neutrino Model with a Higgs Hybrid

In 2001, a supersymmetric model was proposed to relate the axion scale to that of neutrino mass seesaw. Whereas this scenario is realistic, the particles associated with this mechanism are either too heavy or too weakly coupled for them to be observed (other than the axion itself or perhaps the axino). A variation of that model is here proposed which allows significant mixing of the Higgs boson with a new singlet related to the saxion (the scalar partner of the pseudoscalar axion), rendering it possible to be observed at the Large Hadron Collider (LHC). With the addition of exotic color superfields, this also becomes a specific realization of how the production of such a Higgs hybrid may be suppressed or enhanced at the LHC, which is very relevant to ongoing experimental efforts to find the Higgs boson.

hep-ph↗
arXiv2012

CP Phases of Neutrino Mixing in a Supersymmetric B-L Gauge Model with T_7 Lepton Flavor Symmetry

In a recently proposed renormalizable model of neutrino mixing using the non-Abelian discrete symmetry T_7 in the context of a supersymmetric extension of the Standard Model with gauged U(1)_{B-L}, a correlation was obtained between θ_{13} and θ_{23} in the case where all parameters are real. Here we consider all parameters to be complex, thus allowing for one Dirac CP phase δ_{CP} and two Majorana CP phases α_{1,2}. We find a slight modification to this correlation as a function of δ_{CP}. For a given set of input values of Δm^2_{21}, Δm^2_{32}, θ_{12}, and θ_{13}, we obtain \sin^2 2 θ_{23} and m_{ee} (the effective Majorana neutrino mass in neutrinoless double beta decay) as functions of \tan δ_{CP}. We find that the structure of this model always yields small |\tan δ_{CP}|.

hep-ph↗
arXiv2012

Vector-Boson-Induced Neutrino Mass

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.

hep-ph↗
arXiv2011

Scalar Neutrino as Asymmetric Dark Matter: Radiative Neutrino Mass and Leptogenesis

In the Minimal Supersymmetric Standard Model (MSSM), the scalar neutrino $\tildeν_L$ has odd R parity, yet it has long been eliminated as a dark-matter candidate because it scatters elastically off nuclei through the $Z$ boson, yielding a cross section many orders of magnitude above the experimental limit. We show how it can be reinstated as a dark-matter candidate by splitting the masses of its real and imaginary parts in an extension of the MSSM with scalar triplets. As a result, radiative Majorana neutrino masses are also generated. In addition, decays of the scalar triplets relate the abundance of this asymmetric dark matter to the baryon asymmetry of the Universe through leptogenesis.

hep-ph↗
arXiv2011

Exceeding the MSSM Higgs Mass Bound in a Special Class of U(1) Gauge Models

A special class of supersymmetric U(1) gauge extensions of the standard model was proposed in 2002. It is anomaly-free, has no mu term, and conserves baryon and lepton numbers automatically. It also allows the lightest Higgs boson to have a mass exceeding the MSSM (Minimal Supersymmetric Standard Model) bound, i.e. about 130 GeV, which is of current topical interest from LHC (Large Hadron Collider) data. This and other new aspects of this 2002 proposal are discussed.

hep-ph↗
arXiv2011

Hiding the Higgs Boson from Prying Eyes

There are two simple ways that the Higgs boson H of the Standard Model (SM) may be more difficult to observe than expected at the Large Hadron Collider (LHC) or the Tevatron. One is well-known, i.e. H decays invisibly, into dark-matter scalar particles for example. The other is that H mixes with a heavy singlet scalar S which couples to new colored fermions and scalars. Of the two mass eigenstates, the lighter one could (accidentally) have a suppressed effective coupling to two gluons, and the heavy one could be kinematically beyond the reach of the LHC.

hep-ph↗
arXiv2011

Dark Vector-Gauge-Boson Model

A model based on SU(3)_C X SU(2)_L X U(1)_Y X SU(2)_N has recently been proposed, where the SU(2)_N vector gauge bosons are neutral, so that a vector dark-matter candidate is possible and constrained by data to be less than about 1 TeV. We explore further implications of this model, including a detailed study of its Higgs sector. We improve on its dark-matter phenomenology, as well as its discovery reach at the LHC (Large Hadron Collider).

hep-ph↗
arXiv2011

Nonzero theta(13) for neutrino mixing in the context of A(4) symmetry

In the original 2004 paper which first derived tribimaximal mixing in the context of A(4), i.e. the non-Abelian finite symmetry group of the tetrahedron (Plato's fire), as its simplest application, it was also pointed out how theta(13) nonzero may be accommodated. On the strength of the new T2K result that 0.03 (0.04) < sin^2 2 theta(13) < 0.28 (0.34) for delta(CP)=0 and normal (inverted) neutrino mass hierarchy, we perform a more detailed analysis of how this original idea may be realized in the context of A(4).

hep-ph↗
arXiv2011

Probing Lepton Flavor Triality with Higgs Boson Decay

If neutrino tribimaximal mixing is explained by a non-Abelian discrete symmetry such as $A_4$, $T_7$, $Δ(27)$, etc., the charged-lepton Higgs sector has a $Z_3$ residual symmetry (lepton flavor triality), which may be observed directly in the decay chain $H^0 \to ψ_2^0 \barψ_2^0$, then $ψ_2^0 (\barψ_2^0) \to l_i^+ l_j^- ~(i \neq j)$, where $H^0$ is a standard-model-like Higgs boson and $ψ_2^0$ is a scalar particle needed for realizing the original discrete symmetry. If kinematically allowed, this unusual and easily detectable decay is observable at the LHC with 1 fb$^{-1}$ for E_{cm} = 7 TeV.

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