arXiv subjects
Publications and source records attributed to Ernest Ma.
We propose to relate dark matter stability to the possible Dirac nature of neutrinos. The idea is illustrated in a simple scheme where small Dirac neutrino masses arise from a type--I seesaw mechanism as a result of a $Z_4$ discrete lepton number symmetry. The latter implies the existence of a viable WIMP dark matter candidate, whose stability arises from the same symmetry which ensures the Diracness of neutrinos.
We propose an extension of the standard model of quarks and leptons to include gauge $B-L$ symmetry with an exotic array of neutral fermion singlets for anomaly cancellation. With the addition of suitable scalars also transforming under $U(1)_{B-L}$, this becomes a model of radiative seesaw neutrino mass with possible multipartite dark matter. If leptoquark fermions are added, necessarily also transforming under $B-L$, the diphoton excess at 750 GeV, recently observed at the Large Hadron Collider, may also be explained.
A gauge $U(1)$ family symmetry is proposed, spanning the quarks and leptons as well as particles of the dark sector. The breaking of $U(1)$ to $Z_2$ divides the two sectors and generates one-loop radiative masses for the first two families of quarks and leptons, as well as all three neutrinos. We study the phenomenological implications of this new connection between family symmetry and dark matter. In particular, a scalar or pseudoscalar particle associated with this $U(1)$ breaking may be identified with the 750 GeV diphoton resonance recently observed at the Large Hadron Collider (LHC).
We study the 2010 specific version of the 2002 proposed $U(1)_X$ extension of the supersymmetric standard model, which has no $μ$ term and conserves baryon number and lepton number separately and automatically. We consider in detail the scalar sector as well as the extra $Z_X$ gauge boson, and their interactions with the necessary extra color-triplet particles of this model, which behave as leptoquarks. We show how the diphoton excess at 750 GeV, recently observed at the LHC, may be explained within this context. We identify a new fermion dark-matter candidate and discuss its properties. An important byproduct of this study is the discovery of relaxed supersymmetric constraints on the Higgs boson's mass of 125 GeV.
An anomaly-free U(1) gauge extension of the standard model (SM) is presented. Only one Higgs doublet with a nonzero vacuum expectation is required as in the SM. New fermions and scalars as well as all SM particles transform nontrivially under this U(1), resulting in a model of three active neutrinos and one sterile neutrino, all acquiring radiative masses. Charged-lepton masses are also radiative as well as the mixing between active and sterile neutrinos. At the same time, a residual $Z_2$ symmetry of the U(1) gauge symmetry remains exact, allowing for the existence of dark matter.
In 2002, I proposed a unique $U(1)$ extension of the supersymmetric standard model which has no $μ$ term and conserves baryon number and lepton number separately and automatically. This model, ${without~any~change}$, has all the necessary and sufficient ingredients to explain the possible 750 GeV diphoton excess, observed recently by the ATLAS Collaboration at the Large Hadron Collider (LHC). It is associated with the superfield which replaces the $μ$ parameter. If confirmed and supported by subsequent data, it may even be considered as the first evidence for supersymmetry.
A gauge U(1) framework was established in 2002 to extend the supersymmetric standard model. It has many possible realizations. Whereas all have the necessary and sufficient ingredients to explain the possible 750 GeV diphoton excess, observed recently by the ATLAS Collaboration at the Large Hadron Collider (LHC), they differ in other essential aspects. A compendium of such models is discussed.
I propose a model of radiative charged-lepton and neutrino masses with $A_4$ symmetry. The soft breaking of $A_4$ to $Z_3$ lepton triality is accomplished by dimension-three terms. The breaking of $Z_3$ by dimension-two terms allow cobimaximal neutrino mixing $(θ_{13} \neq 0, θ_{23} = π/4, δ_{CP} = \pm π/2)$ to be realized with only very small finite calculable deviations from the residual lepton triality. This construction solves a long-standing technical problem inherent in renormalizable $A_4$ models since their inception.
We consider a model of neutrino mass with a scalar triplet $(ξ^{++},ξ^+,ξ^0)$ assigned lepton number $L=0$, so that the tree-level Yukawa coupling $ξ^0 ν_i ν_j$ is not allowed. It is generated instead through the interaction of $ξ$ and $ν$ with dark matter and the soft breaking of $L$ to $(-1)^L$. We discuss the phenomenological implications of this model, including $ξ^{++}$ decay and the prognosis of discovering the dark sector at the Large Hadron Collider.
In the context of the non-Abelian discrete symmetry $A_4$, the neutrino mass matrix has been studied extensively. A brief update is presented to focus on the conceptual shift from tribimaximal mixing ($θ_{13} = 0$, $θ_{23} = π/4$, $\tan^2 θ_{12} = 1/2$) to $\underline{\rm cobimaximal}$ mixing ($θ_{13} \neq 0$, $θ_{23} = π/4$, $δ_{CP} = \pm π/2$) which agrees well with present data. Three specific realistic examples are proposed, two with three and the third with just two parameters.
A new theoretical insight into the pattern of neutrino mixing and leptonic $CP$ violation is presented. It leads naturally and uniquely to a specific dark sector of three real neutral scalar singlets, with the radiative implementation of the inverse seesaw mechanism for neutrino mass. The new simple but crucial enabling idea is that a familiar $A_4$ transformation turns any orthogonal $3 \times 3$ matrix into one which predicts $θ_{23} = π/4$ and $δ_{CP} = \pm π/2$ for the neutrino mixing matrix, in good agreement with present data.
We consider the case of light dark matter ($\sim 10$ GeV). We discuss a simple $Z_2$ model of scalar self-interacting dark matter, as well as a related model of unstable long-lived dark matter which can explain the anomalous Kolar events observed decades ago.
We study a gauge $B-L$ extension of the standard model of quarks and leptons with unconventional charges for the singlet right-handed neutrinos, and extra singlet scalars, such that a residual $Z_3$ symmetry remains after the spontaneous breaking of $B-L$. We discuss the phenomenological consequences of this scenario, including the possibility of long-lived self-interacting dark matter and $Z'$ collider signatures.
In all scalar extensions of the standard model of particle interactions, the one Higgs boson responsible for electroweak symmetry breaking always mixes with other neutral scalars at tree level unless a symmetry prevents it. An unexplored important option is that the mixing may be radiative, and thus guaranteed to be small. Two first such examples are discussed. One is based on the soft breaking of the discrete symmetry $Z_3$. The other starts with the non-Abelian discrete symmetry $A_4$ which is then softly broken to $Z_3$, and results in the emergence of an interesting dark-matter candidate together with a light mediator for the dark matter to have its own long-range interaction.
It is shown that in extensions of the standard model of quarks and leptons where additive lepton number $L$ is broken by two units, so that $Z_2$ lepton parity, i.e. $(-1)^L$ which is either even or odd, remains exactly conserved, there is the possibility of stable dark matter without additional symmetry. This applies to many existing simple models of Majorana neutrino mass with dark matter, including some radiative models. Several well-known examples are discussed. This new insight leads to the construction of a radiative Type II seesaw model of neutrino mass with dark matter where the dominant decay of the doubly charged Higgs boson $ξ^{++}$ is into $W^+W^+$ instead of the expected $l_i^+ l_j^+$ lepton pairs for the well-known tree-level model.
I propose the notion that there is only one Higgs doublet which is responsible for electroweak symmetry breaking and all other possible scalars in any extension of the standard model are prevented from mixing with it because of a symmetry which stabilizes dark matter. This leads naturally to radiative (scotogenic) neutrino mass as well as radiative quark and lepton masses if flavor symmetry is also considered.
The gauged $B - L$ symmetry is one of the simplest and well studied extension of standard model. In the conventional case, addition of three singlet right handed neutrinos each transforming as $-1$ under the $B - L$ symmetry renders it anomaly free. It is usually assumed that the $B - L$ symmetry is spontaneously broken by a singlet scalar having two units of $B - L$ charge, resulting in a natural implementation of Majorana seesaw mechanism for neutrinos. However, as we discuss in this proceeding, there is another simple anomaly free solution which leads to Dirac or inverse seesaw masses for neutrinos. These new possibilities are explored along with an application to neutrino mixing with $S_3$ flavour symmetry.
A special form of the $3 \times 3$ Majorana neutrino mass matrix derivable from $μ- τ$ interchange symmetry accompanied by a generalized $CP$ transformation was obtained many years ago. It predicts $θ_{23} = π/4$ as well as $δ_{CP} = \pm π/2$, with $θ_{13} \neq 0$. Whereas this is consistent with present data, we explore a deviation of this result which occurs naturally in a recent proposed model of radiative inverse seesaw neutrino mass.