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Ernest Ma

Publications and source records attributed to Ernest Ma.

At least 289 records · Page 16Linked to original sources
arXiv2001

Naturally Small Seesaw Neutrino Mass with No New Physics Beyond the TeV Scale

If there is no new physics beyond the TeV energy scale, such as in a theory of large extra dimensions, the smallness of the seesaw neutrino mass, i.e. $m_ν= m_D^2/m_N$, cannot be explained by a very large $m_N$. In contrast to previous attempts to find an alternative mechanism for a small $m_ν$, I show how a solution may be obtained in a simple extension of the Standard Model, without using any ingredient supplied by the large extra dimensions. It is also experimentally testable at future accelerators.

hep-ph↗
arXiv2001

Realistic Gluino Axion Model Consistent with Supersymmetry Breaking at the TeV Scale

The recently proposed model of using the dynamical phase of the gluino to solve the strong CP problem is shown to admit a specific realization in terms of fundamental singlet superfields, such that the breaking of supersymmetry occurs only at the TeV scale, despite the large axion scale of 10^{9} to 10^{12} GeV. Phenomenological implications are discussed.

hep-ph↗
arXiv2000

Three Active and Two Sterile Neutrinos in an E_6 Model of Diquark Baryogenesis

In the U(1)_N extension of the supersymmetric standard model with E_6 particle content, the heavy singlet superfield N may decay into a quark and a diquark as well as an antiquark and an antidiquark, thus creating a baryon asymmetry of the Universe. We show how the three doublet and two singlet neutrinos in this model acquire mass from physics at the TeV scale without the benefit of using N as a heavy right-handed neutrino. Specifically, the active neutrinos get masses via the bilinear term μLX^c which conserves R-parity, and via the nonzero masses of the sterile neutrinos. We predict fixed properties of the extra Z' boson, as well as the new lepton doublets X and X^c, and the observation of diquark resonances at hadron colliders in this scenario.

hep-ph↗
arXiv2000

Allowable Low-Energy E_6 Subgroups from Leptogenesis

There are only two viable low-energy $E_6$ subgroups: $SU(3)_C \times SU(2)_L \times U(1)_Y \times U(1)_N$ or $SU(3)_C \times SU(2)_L \times SU(2)'_R \times U(1)_{Y_L + Y'_R}$, which would not erase any preexisting lepton asymmetry of the Universe that may have been created by the decay of heavy singlet (right-handed) neutrinos or any other mechanism. They are also the two most favored $E_6$ subgroups from a recent analysis of present neutral-current data. We study details of the leptogenesis, as well as some salient experimental signatures of the two models.

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arXiv2000

Leptogenesis: Neutrinos and New Lepton Flavor Violation at the Tev Energy Scale

Leptogenesis, i.e. the creation of a lepton asymmetry in the early Universe, may occur through the decay of heavy singlet (right-handed) neutrinos. If we require it not to be erased by physics beyond the Standard Model at the TeV energy scale, then only 2 candidates are possible if they are subgroups of $E_6$. These 2 solutions happen to be also the only ones within 1$σ$ of the atomic parity violation data and the invisible $Z$ width. Lepton flavor violation is predicted in one model, as well as in another unrelated model of neutrino masses where the observable decay of a doubly charged scalar would determine the relative magnitude of each element of the neutrino mass matrix.

hep-ph↗
arXiv2000

Relaxing b\to sγConstraints on the Supersymmetric Particle Mass Spectrum

We consider the radiative decay b \to s γin a supersymmetric extension of the standard model of particle interactions, where the $b$-quark mass is entirely radiative in origin. This is accomplished by the presence of nonholomorphic soft supersymmetry breaking terms in the Lagrangian. As a result, the contributions to the b \to s γamplitude from the charged Higgs boson and the charginos/neutralinos are suppressed by 1/\tan^2βand {\cal O}(α/α_s) respectively, allowing these particles to be lighter than in the usual supersymmetric model. Their radiatively generated couplings differ from the usual tree-level ones and change the collider phenomenology drastically. We also study how this scenario may be embedded into a larger framework, such as supersymmetric SU(5) grand unification.

hep-ph↗
arXiv2000

Neutrino Masses and Leptogenesis from R Parity Violation

In R parity violating supersymmetry (conserving baryon number B but violating lepton number L), Majorana neutrino masses may arise at tree level, in one loop, and in two loops. The L violating interactions work together with the B + L violating electroweak sphalerons to erase any preexisting B or L asymmetry of the Universe. To have successful leptogenesis nevertheless, a specific scenario is proposed.

hep-ph↗
arXiv2000

Low-Scale Axion from Large Extra Dimensions

The mass of the axion and its decay rate are known to depend only on the scale of Peccei-Quinn symmetry breaking, which is constrained by astrophysics and cosmology to be between $10^9$ and $10^{12}$ GeV. We propose a new mechanism such that this effective scale is preserved and yet the fundamental breaking scale of $U(1)_{PQ}$ is very small (a kind of inverse seesaw) in the context of large extra dimensions with an anomalous U(1) gauge symmetry in our brane. Unlike any other (invisible) axion model, there are now possible collider signatures in this scenario.

hep-ph↗
arXiv2000

Light Sterile Neutrinos from Large Extra Dimensions

An experimentally verifiable Higgs-triplet model of neutrino masses from large extra dimensions was recently proposed. We extend it to accomodate a light sterile neutrino which also mixes with the three active neutrinos. A previously proposed phenomenological model of four neutrinos (\underline {the only viable such model now left}, in view of the latest atmospheric and solar neutrino-oscillation data) is specifically realized.

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arXiv2000

Leptogenesis from Neutralino Decay with Nonholomorphic R-Parity Violation

In supersymmetric models with lepton-number violation, hence also R-parity violation, it is easy to have realistic neutrino masses, but then leptogenesis becomes difficult to achieve. After explaining the general problems involved, we study the details of a model which escapes these constraints and generates a lepton asymmetry, which gets converted into the present observed baryon asymmetry of the Universe through the electroweak sphalerons. This model requires the presence of certain nonholomorphic R-parity violating terms. For completeness we also present the most general R-parity violating Lagrangian with soft nonholomorphic terms and study their consequences for the charged-scalar mass matrix. New contributions to neutrino masses in this scenario are discussed.

hep-ph↗
arXiv2000

Neutrino Masses and Leptogenesis

I discuss the connection between neutrino masses and leptogenesis. I use three prime examples: (1) canonical seesaw, (2) triplet Higgs, and (3) $R$ parity violation.

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arXiv2000

Verifiable Model of Neutrino Masses from Large Extra Dimensions

We propose a new scenario of neutrino masses with a Higgs triplet $(ξ^{++},ξ^+,ξ^0)$ in a theory of large extra dimensions. Lepton number violation in a distant brane acts as the source of a very small trilinear coupling of $ξ$ to the standard Higgs doublet in our brane. Small realistic Majorana neutrino masses are \underline{naturally} obtained with the fundamental scale $M_* \sim {\cal O}(1)$ TeV, foretelling the possible discovery of $ξ$ $(m_ξ\lsim M_*)$ at future colliders. Decays of $ξ^{++}$ into same-sign dileptons are fixed by the neutrino mass matrix. Observation of $μ-e$ conversion in nuclei is predicted.

hep-ph↗
arXiv2000

Neutrino Masses and the Gluino Axion Model

We extend the recently proposed gluino axion model to include neutrino masses. We discuss how the canonical seesaw model and the Higgs triplet model may be realized in this framework. In the former case, the heavy singlet neutrinos are contained in superfields which do not have any vacuum expectation value, whereas the gluino axion is contained in one which does. We also construct a specific renormalizable model which realizes the mass scale relationship $M_{SUSY} \sim f_a^2/M_U$, where $f_a$ is the axion decay constant and $M_U$ is a large effective mass parameter.

hep-ph↗
arXiv2000

Relaxation of the Dynamical Gluino Phase and Unambiguous Electric Dipole Moments

We propose a new axionic solution of the strong CP problem with a Peccei-Quinn mechanism using the gluino rather than quarks. The spontaneous breaking of this new global U(1) at 10^{11} GeV also generates the supersymmetry breaking scale of 1 TeV (solving the so-called μproblem at the same time) and results in the MSSM (Minimal Supersymmetric Standard Model) with R parity conservation. In this framework, electric dipole moments become calculable without ambiguity.

hep-ph↗
arXiv2000

Three Inequivalent Mass-Degenerate Majorana Neutrinos and a Model of Their Splitting for Neutrino Oscillations

The mass matrix of three Majorana neutrinos of equal mass is not necessarily proportional to the identity matrix, but expressible in terms of two angles and one phase. We discuss how such a mass matrix may be stable or unstable against radiative corrections. We then propose a model with additional explicit breaking of the threefold degeneracy to account for the atmospheric neutrino data, while the radiative breaking explains the solar neutrino data, using the large-angle Mikheyev-Smirnov-Wolfenstein solution. Our model requires a nonzero effective $ν_e$ mass for neutrinoless double beta decay close to the present experimental upper limit of 0.2 eV.

hep-ph↗
arXiv2000

Neutrino Exotica in the Skew E_6 Left-Right Model

With the particle content of the 27 representation of E_6, a skew left-right supersymmetric gauge model was proposed many years ago, with a variety of interesting phenomenological implications. The neutrino sector of this model offers a natural framework for obtaining small Majorana masses for nu_e, nu_mu, and nu_tau, with the added bonus of accommodating 2 light sterile neutrinos.

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