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E. Keith

Publications and source records attributed to E. Keith.

At least 19 recordsLinked to original sources
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↗
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.

hep-ph↗
arXiv1997

Lower Bound on the Pseudoscalar Mass in the Minimal Supersymmetric Standard Model

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 $\tan β$.

hep-ph↗
arXiv1997

Decay of Z into Three Pseudoscalar Bosons

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.

hep-ph↗
arXiv1997

S, T, and Leptoquarks at HERA

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.

hep-ph↗
arXiv1997

Generic consequences of a supersymmetric U(1) gauge factor at the TeV scale

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.

hep-ph↗
arXiv1996

A grand unified model with $M_G\sim M_{string}$ and $M_I\sim 10^{12}$ GeV

We present a model based on the gauge group SU(2)_L\times SU(2)_R \times SU(4)_C with gauge couplings that are found to be unified at a scale near the string unification scale. This model breaks to the MSSM at an intermediate scale which is instrumental in producing a neutrino in a mass range that can serve as hot dark matter and can also solve the strong CP problem via a harmless invisible axion.

hep-ph↗
arXiv1996

Baryon-Number Nonconservation and the Stability of Strange Matter

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.

hep-ph↗
arXiv1996

Supersymmetry and the spontaneous breaking of a U(1) gauge factor

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.

hep-ph↗
arXiv1996

Exotic Decays of Strangelets

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.

nucl-th↗
arXiv1996

Electric dipole moments and b-$τ$ unification in the presence of an intermediate scale in SUSY grand unification

We show that an intermediate gauge symmetry breaking scale can be a significant source of electric dipole moments for the electron and neutron in supersymmetric grand unified theories. New phases, similar to that of the CKM matrix, appear which do not arise from the supersymmetry (SUSY) breaking operators. To illustrate, we choose some grand unified SUSY models having an intermediate gauge symmetry breaking scale with some attractive features. We also show how well the $b-τ$ unification hypothesis works in this class of models.

hep-ph↗
arXiv1996

Intermediate scale as a source of lepton flavor violation in SUSY SO(10)

In supersymmetric SO(10) grand unified models, we examine the lepton flavor violation process $μ\rightarrow eγ$ from having the SU(2)$_R\times $U(1)$_{B-L}$ gauge symmetry broken at an intermediate scale $M_I$ below the SO(10) grand unification scale $M_G$. Even in the case that supersymmetry is broken by universal soft terms introduced at the scale $M_G$, we find significant rates for $μ\rightarrow eγ$ with $M_I \sim 10^{12}$ GeV or less. These rates are further enhanced if the universal soft terms appear at a scale greater than $M_G$.

hep-ph↗
arXiv1996

Towards a viable grand unified model with $M_G\sim M_{\rm string}$ and $M_I\sim 10^{12}$ GeV

We present a model based on the gauge group SU(2)$_L\times$SU(2)$_R\times$SU(4)$_C$ with gauge couplings that are found to be unified at a scale $M_G$ near the string unification scale. The model breaks to the minimal supersymmetric standard model at a scale $M_I\sim 10^{12}$ GeV, which is instrumental in producing a neutrino in a mass range that can serve as hot dark matter and this scale can also solve the strong CP problem via Peccei-Quinn (PQ) mechanism with an invisible harmless invisible axion. We show how this model can accommodate low and high values of $\tanβ$ and ``exotic" representations that often occur in string derived models. We show that this model has lepton flavor violation which can lead to processes which are one or two orders of magnitude below the current experimental limits.

hep-ph↗
arXiv1996

Efficacious Extra U(1) Factor for the Supersymmetric Standard Model

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.

hep-ph↗
arXiv1996

Mutual cosideration of $b\to sγ$ and $μ\to eγ$ in supersymmetric SO(10) grand unification

We compare the branching ratios for $b\rightarrow sγ$ and $μ\rightarrow eγ$ in terms of constraining the parameter space in supersymmetric SO(10) grand unification models where supersymmetry is broken softly near the Planck scale by generationally symmetric operators. We observe two general cases. One with small $\tanβ=2$ and the other one with large $\tanβ$ having third generation Yukawa coupling unification at the GUT scale. \newline\indent We show that for small $\tanβ$ the branching ratio constraints allow only a smaller region of parameter space for $μ>0$ compared to $μ<0$ for gluino mass $\alt$ 500 GeV. With large $\tanβ$, we find acceptable regions of parameter space with $\left|μ\right|\alt 1$ TeV only for $μ<0$. The dominant constraint on large $\tanβ$ with $μ>0$ parameter space is found to be given by the $b\rightarrow sγ$ branching ratio, while for large $\tanβ$ with $μ<0$ it is found to be given by the $μ\rightarrow eγ$ branching ratio. In many of these acceptable regions, we find that the $μ\rightarrow eγ$ branching ratio is predicted to be within one order of magnitude of its current experimental bound. We also show that the usually neglected gluino mediated diagrams in $b\rightarrow sγ$ can not be ignored in some regions of parameter space, especially for large $\tanβ$ scenarios when the gluino mass is near its lower experimental bound.

hep-ph↗
arXiv1995

Effects of supersymmetric grand unification scale physics on $Γ\left( b\to sγ\right)$

Although calculations of the $b\rightarrow sγ$ rate in supersymmetric grand unified models have always either ignored the gluino mediated contribution or found it to be negligible, we show that taking universal supersymmetry breaking masses at the Planck scale, rather than at the gauge unification scale as is customary, leads to the gluino contribution being more significant and in fact sometimes even larger than the chargino mediated contributions when $μ>0$ and $\tanβ$ is of order 1. The impact is greatest felt when the gluinos are relatively light. Taking the universal boundary condition at the Planck scale also has an effect on the chargino contribution by increasing the effect of the wino and higgsino-wino mediated decays. The neutralino mediated contribution is found to be enhanced, but nevertheless it remains relatively insignificant.

hep-ph↗