arXiv subjects

Ernest Ma

Publications and source records attributed to Ernest Ma.

At least 325 records · Page 18Linked to original sources

arXiv1998

Baryogenesis with Scalar Bilinears

We show that if a baryon asymmetry of the universe is generated through the out-of-equilibrium decays of heavy scalar bilinears coupling to two fermions of the minimal standard model, it is necessarily an asymmetry conserving $(B-L)$ which cannot survive past the electroweak phase transition because of sphalerons. We then show that a surviving $(B-L)$ asymmetry may be generated if the heavy scalars decay into two fermions, \underline {and into two light scalars} (which may be detectable at hadron colliders). We list all possible such trilinear scalar interactions, and discuss how our new baryogenesis scenario may occur naturally in supersymmetric grand unified theories.

hep-ph↗

arXiv1998

Probing the Exotic Particle Content Beyond the Standard Model

We explore the possible exotic particle content beyond the standard model by examining all its scalar bilinear combinations. We categorize these exotic scalar fields and show that without the suppression of (A) their Yukawa couplings with the known quarks and leptons, and (B) the trilinear couplings among themselves, most are already constrained to be very heavy from the nonobservation of proton decay and neutron-antineutron oscillations, the smallness of $K^0 - \bar {K^0}$, $D^0 - \bar {D^0}$ and $B_d^0 - \bar {B_d^0}$ mixing, as well as the requirement of a nonzero baryon asymmetry of the universe. On the other hand, assumption (B) may be naturally violated in many models, especially in supersymmetry, hence certain exotic scalars are allowed to be below a few TeV in mass and would be easily detectable at planned future hadron colliders. In particular, large cross sections for the distinctive processes like $\bar p p \to tt,\bar t c$ and $p p \to t t, b b$ would be expected at the Fermilab Tevatron and CERN LHC, respectively.

hep-ph↗

arXiv1998

Alternative Interpretation of the Tevatron Top Events

We propose an alternative interpretation of the top events discovered at the Tevatron in 1995. Given that the charge of the $b$ quark jet cannot be measured for the whole sample with certainty, the signal can be due to a quark of charge -4/3 at the reported mass, i.e. 174 GeV, while the top quark is actually heavier, say above 230 GeV. We point out in this paper that such a scenario is actually hinted at by the latest precision electroweak measurements of $Z$ decay. To rule out this possibility in the future, the $b$ quark jet charge analysis has to become definitive, or the single "top" production cross section has to be measured.

hep-ph↗

arXiv1998

Dynamical Neutrino Mass Matrix: Large (Small) Mixing Solution to Atmospheric (Solar) Neutrino Oscillations

In the wake of the SuperKamiokande announcement of atmospheric neutrino oscillations which favor the large mixing of $ν_μ$ with $ν_τ$, there is considerable theoretical activity towards a possible understanding of the solar neutrino deficit also in terms of the mixing of $ν_e$ with the other two neutrinos. A specific dynamical model is presented here for the first time which naturally chooses the large (small) mixing solution to atmospheric (solar) neutrino oscillations.

hep-ph↗

arXiv1998

Gauged $B - 3 L_τ$ and Baryogenesis

It has recently been shown that by extending the minimal standard model to include a right-handed partner to $ν_τ$, it is possible to gauge the $B - 3 L_τ$ quantum number consistently. If we add two scalar triplets, one trivial ($ξ_1$) and one nontrivial ($ξ_2$) under $B - 3 L_τ$, it is possible also to have desirable neutrino masses and mixing for neutrino oscillations. At the same time, a lepton asymmetry can be generated in the early universe through the novel mechanism of the decay of the heavier $ξ_1$ into the lighter $ξ_2$ plus a neutral singlet ($ζ^0$). This lepton asymmetry then gets converted into a baryon asymmetry at the electroweak phase transition.

hep-ph↗

arXiv1998

Radiative neutrino mass matrix for three active plus one sterile species

A simple unifying mass matrix is presented for the three active and one sterile neutrinos $ν_e$, $ν_μ$, $ν_τ$ and $ν_s$, using an extension of the radiative mechanism proposed some time ago by Zee. The total neutrino-oscillation data are explained by the scheme $ν_e \leftrightarrow ν_s$ (solar), $ν_μ\leftrightarrow ν_τ$ (atmospheric) and $ν_e \leftrightarrow ν_μ$ (LSND). We obtain the interesting approximate relationship $(Δm^2)_{atm} \simeq 2[(Δm^2)_{solar} (Δm^2)_{LSND}]^{1/2}$ which is well satisfied by the data.

hep-ph↗

arXiv1998

Phenomenology of the $B - 3 L_τ$ Gauge Boson

Assuming the existence of a gauge boson $X$ which couples to $B - 3 L_τ$, we discuss the present experimental constraints on $g_X$ and $m_X$ from $Z \to l^+ l^-$ and $Z \to \bar f f X~(f = q, ν_τ, τ)$. We also discuss the discovery potential of $X$ at hadron colliders through its decay into $τ^+ τ^-$ pairs. In the scenario where all three charged leptons (and their neutrinos) mix, lepton flavor nonconservation through $X$ becomes possible and provides another experimental probe into this hypothesis.

hep-ph↗

arXiv1998

Neutrino Masses and Leptogenesis with Heavy Higgs Triplets

A simple and economical extension of the minimal standard electroweak gauge model (without right-handed neutrinos) by the addition of two heavy Higgs scalar triplets would have two significant advantages. \underline {Naturally} small Majorana neutrino masses would become possible, as well as leptogenesis in the early universe which gets converted at the electroweak phase transition into the present observed baryon asymmetry.

hep-ph↗

arXiv1998

Pathways to Naturally Small Neutrino Masses

In the minimal standard electroweak gauge model, there is an effective dimension-five operator which generates neutrino masses, and it has only three tree-level realizations. One is the canonical seesaw mechanism with a right-handed neutrino. Another is having a heavy Higgs triplet as recently proposed. The third is to have a heavy Majorana fermion triplet, an example of which is presented here in the context of supersymmetric SU(5) grand unification. The three generic one-loop realizations of this operator are also discussed.

hep-ph↗

arXiv1998

New interactions in neutrino oscillations with three light flavors

If one assumes solar and LSND neutrino oscillations to explain the corresponding data, then the atmospheric neutrino deficit cannot be accommodated within the Standard Model with three light flavors, unless one ignores the data's zenith-angle dependence. We propose a novel solution to this problem by postulating large anomalous diagonal $ν_τ$-quark interactions which affect $ν_μ- ν_τ$ oscillations traversing the Earth and induce the observed zenith-angle dependence.

hep-ph↗

arXiv1998

Shifting $R_b$ with $A^b_{FB}$

Precision measurements at the $Z$ resonance agree well with the standard model. However, there is still a hint of a discrepancy, not so much in $R_b$ by itself (which has received a great deal of attention in the past several years) but in the forward-backward asymmetry $A^b_{FB}$ together with $R_b$. The two are of course correlated. We explore the possibilty that these and other effects are due to the mixing of $b_L$ and $b_R$ with one or more heavy quarks.

hep-ph↗

arXiv1998

Supersymmetric U(1) at the TeV Scale

If there exists an arbitrary supersymmetric U(1) gauge factor at the TeV scale, under which the two Higgs superfields H_{1,2} of the standard model are nontrivial, and if there is also a singlet superfield S such that the H_1 H_2 S term is allowed in the superpotential, then the structure of the two-doublet Higgs sector at the electroweak scale is more general than that of the MSSM (Minimal Supersymmetric Standard Model). Under further assumptions of grand unification and universal soft supersymmetry breaking terms, the scale of U(1) breaking is related to the parameter tan(beta) = v_2/v_1.

hep-ph↗

arXiv1998

Neutrino Masses and Anomalous Interactions

The interplay between neutrino masses and the interactions of neutrinos with matter is discussed with an eye to extending the latter to include possible new interactions. This conjecture may resolve the conundrum posed by the present experimental data on neutrino oscillations which suggest the existence of four neutrinos, whereas Z decay and Big Bang Nucleosynthesis allow only three. The case of a possible sterile neutrino is also briefly discussed.

hep-ph↗

arXiv1998

Models of Neutrino Mass and Interactions for Neutrino Oscillations

I review the various mechanisms for obtaining nonzero neutrino masses. I focus on the possibility of adding one light singlet neutrino to the three known doublet neutrinos nu_e, nu_mu, and nu_tau to accommodate the totality of neutrino-oscillation experiments. I review the various theoretical suggestions for this singlet. I discuss also a scenario in which there are only the three doublet neutrinos but a large anomalous interaction is assumed for nu_tau as an attempt to explain all present data.

hep-ph↗

arXiv1998

Symmetries of the Standard Model without and with a Right-Handed Neutrino

Given the particle content of the standard model without and with a right-handed neutrino, the requirement that all anomalies cancel singles out a set of possible global symmetries which can be gauged. I review this topic and propose a new gauge symmetry B - 3L_tau in the context of the minimal standard model consisting of the usual three families of quarks and leptons plus just one nu_R. The many interesting phenomenological consequences of this hypothesis are briefly discussed.

hep-ph↗

arXiv1998

Enhanced Three-Body Decay of the Charged Higgs Boson

If the charged Higgs boson H+ exists with mh < mt + mb, the conventional expectation is that it will decay dominantly into c s-bar and tau+ nu-tau. However, the three-body decay mode H+ --> W+ b b-bar is also present and we show that it becomes very important in the low tan(beta) region for mh >~ 140 GeV. We explore its phenomenological implications for the charged-Higgs-boson search in top-quark decay.

hep-ph↗

arXiv1997

Gauged B-3L_tau and Radiative Neutrino Masses

If the minimal standard model of quarks and leptons is extended to include just a righthanded partner to nu_tau, then the quantum number B-3L_tau can be added as a gauge symmetry without the appearance of anomalies. A suitable extension of the scalar sector allows one neutrino to have a seesaw mass, and the other two to have radiative masses, with acceptable phenomenological values for neutrino oscillations. The B-3L_tau gauge boson may be light and be observable through its decay into tau^+ tau^-.

hep-ph↗

arXiv1997

Revelations of the U(1)-Extended Supersymmetric Standard Model

If an extra supersymmetric U(1) gauge factor exists at the TeV energy scale, which is then broken together with the supersymmetry, there will be several interesting and important phenomenological consequences, not only at the TeV scale, but also at the 100 GeV scale. For one, the generic two-doublet Higgs structure will involve 3 additional parameters beyond that of the Minimal Supersymmetric Standard Model (MSSM), thereby raising the upper bound on the mass of the lighter of the two neutral Higgs scalars. For another, the supersymmetric scalar quarks and leptons receive new contributions to their masses from the spontaneous breaking of this extra U(1). Assuming a grand-unified E_6 gauge symmetry and universal soft supersymmetry-breaking terms at the grand-unification energy scale, we find solutions relating the U(1) breaking scale and the ratio of the vacuum expectation values of the two electroweak Higgs doublets.

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