arXiv subjects
Publications and source records attributed to Ernest Ma.
At greater than nuclear densities, matter may convert into a mixture of nucleons, hyperons, dibaryons, and strangelets, thus facilitating the formation of strange matter even before the onset of the quark-matter phase transition. From a nonstrange dibaryon condensate, it may even be possible to leapfrog into strange matter with a certain new interaction, represented by an effective six-quark operator which is phenomenologically unconstrained.
In the Higgs sector of the Minimal Supersymmetric Standard Model, the mass of the pseudoscalar $A$ is an independent parameter together with $\tan β\equiv v_2/v_1$. If $m_A$ is small, then the process $e^+ e^- \to h + A$ is kinematically allowed and is suppressed only if $\tan β$ is small. On the other hand, the mass of the charged Higgs boson is now near $M_W$, and the decay $t \to b + h^+$ is enhanced if $\tan β$ is small. Since the former has not been observed, and the branching fraction of $t \to b + W$ cannot be too small (by comparing the experimentally derived $t \bar t$ cross section from the leptonic channels with the theoretical prediction), we can infer a phenomenological lower bound on $m_A$ of at least 60 GeV for all values of $\tan β$.
We consider the decay of the $Z$ boson into three pseudoscalar bosons in a general two-Higgs-doublet model. Assuming $m_A$ to be very small, and that of the two physical neutral scalar bosons $h_1$ and $h_2$, $A$ only couples to $Z$ through $h_1$, we find the $Z \to A A A$ branching fraction to be negligible for moderate values of $\tan β\equiv v_2/v_1$, if there is no $λ_5 (Φ_1^\dagger Φ_2)^2 + h.c.$ term in the Higgs potential; otherwise there is no absolute bound but very large quartic couplings (beyond the validity of perturbation theory) are needed for it to be observable.
If the recently discovered anomalous events at HERA are due to a scalar leptoquark, then it is very likely to have weak isospin $I = 1/2$. In that case, present precision measurements of the oblique radiative parameters $S$ and $T$ provide strong constraints on the mass of the other component of this doublet. If the standard model is extended to include such a doublet, a slightly better fit may in fact be obtained. However, in specific proposed models where this doublet comes from a larger symmetry, there are often additional large and positive contributions to $S$ from exotic heavy fermions which far exceed the present experimental limit. A way to improve the Tevatron exploration of leptoquarks is proposed.
We consider 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. We assume that there is a singlet superfield S such that H_1 H_2 S is an allowed term in the superpotential. We discuss first the generic consequences of this hypothesis on the structure of the two-doublet Higgs sector at the electroweak energy scale, as well as Z-Z' mixing and the neutralino sector. We then assume the existence of a grand unified symmetry and universal soft supersymmetry breaking terms at that scale. We further assume that the additional U(1) is broken radiatively via a superpotential term of the form h h^c S, where h and h^c are exotic color-triplet fields which appear in E_6 models. We show that the U(1) breaking scale and the parameter tan(beta) \equiv v_2/v_1 are then both predicted as functions of the H_1 H_2 S coupling.
The appearance of a broken supersymmetric U(1) gauge factor at the TeV scale is relevant for several reasons. If it truly exists, then one important consequence is that at the 100 GeV energy scale, the two-doublet Higgs structure is of a more general form than that of the Minimal Supersymmetric Standard Model (MSSM). This is a prime example of tree-level nondecoupling. Furthermore, a particular U(1)_N from the superstring-inspired E_6 model allows for the existence of naturally light singlet neutrinos which may be necessary to accommodate the totality of neutrino-oscillation experiments.
Assuming the existence of a supersymmetric U(1) gauge factor at the TeV energy scale (motivated either by the superstring-inspired E_6 model or low-energy electroweak phenomenology), several important consequences are presented. The two-doublet Higgs structure at the 100 GeV energy scale is shown to be different from that of the Minimal Supersymmetric Standard Model (MSSM). A new neutral gauge boson Z' corresponding to the extra U(1) mixes with the Z. The supersymmetric scalar quarks and leptons receive new contributions to their masses from the spontaneous breaking of this extra U(1). The assumption of universal soft supersymmetry breaking terms at the grand-unification energy scale implies a connection between the U(1) breaking scale and the ratio of the vacuum expectation values of the two electroweak Higgs doublets.
If baryon-number nonconservation exists in the form of an effective six-quark operator which also changes strangeness by four units, it could have a tremendous impact on the absolute stability of strange quark matter. We show that such an operator is negligible in the supersymmetric standard model with $λ_{ijk} u_i^c d_j^c d_k^c$ terms in the superpotential, but may be of importance in models with exotic particle content. From the experimental lower limit of $10^{25}$ years on the stability of nuclei, we find a model-independent lower limit of the order $10^5$ years on the stability of strange matter against such decays.
Because of the existence of cubic scalar couplings, there are in general nondecoupling effects at tree level in the scalar sector of any theory with two or more very different mass scales. We show this explicitly in the minimal nonsupersymmetric SU(5) model of grand unification. We show also how tree-level decoupling is guaranteed if supersymmetry is imposed. On the other hand, if the gauge symmetry is larger than that of the standard model at the mass scale of supersymmetry breaking, the two-Higgs-doublet structure at the presumably lower electroweak energy scale will be different from that of the minimal supersymmetric standard model, as shown already previuosly in a number od specific examples. We add here one example involving four Higgs doublets.
We investigate a supersymmetric theory with an extra U(1) gauge symmetry surviving down to low energies. The extra U(1) is assumed to originate from an E$_6$ grand unified theory (GUT). We show that if one assumes universal soft supersymmetry breaking scalar masses at the GUT scale, and requires the mass of the additional U(1) gauge boson to satisfy phenomenological bounds, then the conditions for electroweak symmetry breaking will provide stringent restrictions on the allowed parameter space of such a theory. We also determine the masses of standard as well as exotic sfermions and find that it is possible for the latter to be lighter than the former. An interesting specific observation is that a light stop is difficult to accommodate with an extra U(1) gauge symmetry.
The totality of present neutrino data seems to require four light neutrinos, but only three of them can be the neutral components of left-handed lepton doublets. To accommodate one or more naturally light singlet neutrino(s), an extra U(1) gauge factor is proposed to implement an analogous seesaw mechanism which accounts for the light doublet neutrinos. Using the constraints of anomaly cancellation, the property of this U(1) is determined. The most attractive theoretical framework is that of a supersymmetric $SU(3)_C \times SU(2)_L \times U(1)_Y \times U(1)_N$ model already proposed.
The stability of strange matter depends on the implicit assumption that baryon number is conserved. We examine the relevant effective operators which allow strangelets to decay by violating the conservation of baryon number. From the experimental lower limit of 10$^{25}$ years on the stability of nuclei, we find a lower limit of the order 10$^6$ years on the stability of strangelets against such exotic decays.
The totality of neutrino-oscillation phenomena appears to require the existence of a light singlet neutrino. As pointed out recently, this can be naturally accommodated with a specific extra U(1) factor contained in the superstring-inspired E$_6$ model and its implied particle spectrum. We analyze this model for other possible consequences. We discuss specifically the oblique corrections from Z-Z' mixing, the phenomenology of the two-Higgs-doublet sector and the associated neutralino sector, as well as possible scenarios of gauge-coupling unification.
The superstring-inspired E_6 model is reduced to the supersymmetric standard model extended by a specific U(1) factor. This choice allows for the existence of naturally light singlet neutrinos which also mix with the known three doublet neutrinos, thus making it possible to accommodate all present neutrino data. Other consequences of this model are also discussed: oblique corrections from Z-Z' mixing, phenomenology of the two-Higgs-doublet sector, and possible scenarios of gauge-coupling unification.
If the b and c quarks mix with new heavy quarks of weak isospin I_3 = -1 and 0 respectively, then the Z -> b b(bar) (c c(bar)) rate is necessarily greater (smaller) than that of the standard model. This may be the reason for the R_b excess and R_c deficit observed at LEP. A possible consequence of this scenario is the prospective discovery of a new quark x with the dominant decay x -> c h, then h -> b b(bar), where h is a neutral Higgs boson.
The apparent excess of $Z \rightarrow b \bar b$ events at LEP may be an indication of new physics beyond the standard model. However, in either the two-Higgs-doublet model or the minimal supersymmetric standard model, any explanation would lead to an important new decay mode of the top quark and suppresses the $t \rightarrow W b$ branching fraction, which goes against what has been observed at the Tevatron. In the two-Higgs-doublet model, the branching fraction of $Z \rightarrow b \bar b$ + a light boson which decays predominantly into $b \bar b$ would be at least of order 10$^{-4}$.
Naturally light singlet neutrinos which mix with the usual doublet neutrinos are possible if the supersymmetric standard gauge model is extended to include a specific additional U(1) factor derivable from E_6 decomposition. The low-energy particle content of the model is limited to the fundamental 27 representations of E_6.
If the standard electroweak gauge model is extended to include two or more Higgs doublets, there may be a neutral Higgs boson $h$ which is light (with a mass of say 10 GeV) but the $hZZ$ coupling is suppressed so that it has so far escaped experimental detection. However, the effective $hhZZ$ coupling is generally unsuppressed, hence the decay of Z into two light Higgs bosons plus a fermion-antifermion pair may have an observable branching fraction, especially if $h$ decays invisibly as for example in the recently proposed doublet Majoron model.