arXiv subjects
Publications and source records attributed to Stuart Raby.
In this talk I define what I call the minimal SO(10) SUSY model. I then discuss the phenomenological consequences of this theory, vis a vis gauge and Yukawa coupling unification, Higgs and super-particle masses, the anomalous magnetic moment of the muon, the decay $B_s \to μ^+ μ^-$ and dark matter.
In this talk I discuss the problems and virtues of SUSY GUTs in four dimensions. I then show how to solve some of these problems, without foregoing the virtues, by considering an SO(10) SUSY GUT in five dimensions. I discuss gauge coupling unification and neutrino masses. In particular, it is shown that the 5D compactification scale and cutoff scale are determined by fitting the low energy values of the three standard model gauge couplings. Neutrino masses can be accommodated.
We study neutrino physics in a 5D supersymmetric SO(10) GUT. We analyze several different choices for realizing the See-Saw mechanism. We find that the "natural" scale for the Majorana mass of right-handed neutrinos depends critically on whether the right-handed neutrinos are located in the bulk or localized on a brane. In the former case, the effective Majorana mass is "naturally" of order the compactification scale, about 10^{14} GeV. Note, this is the value necessary for obtaining a light tau neutrino mass approximately 10^{-2} eV which, within the context of hierarchical neutrino masses, is the right order of magnitude to explain atmospheric neutrino oscillations. On the other-hand when the right-handed neutrino is localized on the brane, the effective Majorana mass is typically larger than the compactification scale. Nevertheless with small parameters of order 1/10 - 1/30, an effective Majorana mass of order 10^{14} GeV can be accommodated. We also discuss the constraints on model building resulting from the different scenarios for locating the right-handed neutrinos.
In this letter we present a "natural" framework for obtaining bi-large neutrino mixing incorporating the FGY neutrino mass matrix ansatz. We show that an $SU(2) \times U(1)$ family symmetry can provide the desired FGY neutrino mass ansatz in the MSSM. We also show how to obtain an approximate FGY ansatz in an SO(10) SUSY GUT. In this context, the same $SU(2) \times U(1)$ family symmetry also generates the hierarchy of fermion masses as well as ameliorating SUSY flavor problems.
Gauge unification in a five dimensional supersymmetric SO(10) model compactified on an orbifold $S^1/(Z_2 \times Z_2^{\prime})$ is studied. One orbifolding reduces N=2 supersymmetry to N=1, and the other breaks SO(10) to the Pati-Salam gauge group $\ps$. Further breaking to the standard model gauge group is made through the Higgs mechanism on one of the branes. The differences of the three gauge couplings run logarithmically even in five dimensions and we can keep the predictability for unification as in four dimensional gauge theories. We obtain an excellent prediction for gauge coupling unification with a cutoff scale $M_* \sim 3 \times 10^{17}$ GeV and a compactification scale $M_c \sim 1.5 \times 10^{14}$ GeV. Finally, although proton decay due to dimension 5 operators may be completely eliminated, the proton decay rate in these models is sensitive to the placement of matter multiplets in the 5th dimension, as well as to the unknown physics above the cutoff scale.
In this talk we assume SO(10) boundary conditions at the GUT scale, including unification for the third generation Yukawa couplings $λ_t = λ_b = λ_τ$. We find that this assumption is only consistent with the low energy data in a narrow region of soft SUSY breaking parameter space. We discuss the consequences of this result for Higgs and SUSY searches.
We discuss the status of supersymmetric grand unified theories [SUSY GUTs] with regards to the observation of proton decay. In this talk we focus on SUSY GUTs in 4 dimensions. We outline the major theoretical uncertainties present in the calculation of the proton lifetime and then present our best estimate of an absolute upper bound on the predicted proton lifetime. Towards the end, we consider some new results in higher dimensional GUTs and the ramifications for proton decay.
We discuss magnetic monopoles in gauge theories with Wilson loops on orbifolds. We present a simple example in 5 dimensions with the fifth dimension compactified on an S^1/Z_2 orbifold. The Wilson loop in this SO(3) example replaces the adjoint Higgs scalar (needed to break SO(3) to U(1)) in the well-known 't Hooft - Polyakov construction. Our solution is a magnetic monopole string with finite energy, and length equal to the size of the extra dimension.
The origin of quark and lepton masses is one of the outstanding problems of physics. As the experimental data becomes more and more accurate, testing theories of fermion masses requires greater care. In this talk we discuss a theoretical framework for testing those theories with a high energy desert. It is only with precision tests that we can hope to narrow the set of viable, beyond the standard model theories.
In this talk I discuss the qualitative features of an SO(10) SUSY GUT with an SU(2)x U(1)$^n$ family symmetry. I then describe the global fit of this theory to precision electroweak data [including charged fermion masses and mixing angles]. Finally, the predictions of the model for neutrino masses and mixing are discussed. The most predictive version of the model naturally fits atmospheric neutrino data with maximal $ν_μ\longrightarrow ν_τ$ oscillations and solar neutrino data with small mixing angle MSW $ν_e \longrightarrow ν_{sterile}$ oscillations.
SO(10) supersymmetric grand unified theories [SUSY GUTs] provide a beautiful framework for physics beyond the standard model. Experimental measurements of the three gauge couplings are consistent with unification at a scale $M_G \sim 3 \times 10^{16}$ GeV. In addition predictive models for fermion masses and mixing angles have been found which fit the low energy data, including the recent data for neutrino oscillations. SO(10) boundary conditions can be tested via the spectrum of superparticles. The simplest models also predict neutron and proton decay rates. In this paper we discuss nucleon decay rates and obtain reasonable upper bounds. A clear picture of the allowed SUSY spectra as constrained by nucleon decay is presented.
In this paper we present a solution to the $μ$ problem in an SO(10) supersymmetric grand unified model with gauge mediated and D-term supersymmetry breaking. A Peccei-Quinn symmetry is broken at the messenger scale $M\sim 10^{12}$ GeV and enables the generation of the $μ$ term. The boundary conditions defined at $M$ lead to a phenomenologically acceptable version of the minimal supersymmetric standard model with novel particle phenomenology. Either the gluino or the gravitino is the lightest supersymmetric particle (LSP). If the gravitino is the LSP, then the gluino is the next-to-LSP (NLSP) with a lifetime on the order of one month or longer. In either case this heavy gluino, with mass in the range 25 - 35 GeV, can be treated as a stable particle with respect to experiments at high energy accelerators. Given the extensive phenomenological constraints we show that the model can only survive in a narrow region of parameter space resulting in a light neutral Higgs with mass $\sim 86 - 91$ GeV and $\tanβ\sim 9 - 14$. In addition the lightest stop and neutralino have mass $\sim 100 - 122$ GeV and $\sim 50 - 72$ GeV, respectively. Thus the model will soon be tested. Finally, the invisible axion resulting from PQ symmetry breaking is a cold dark matter candidate.
In this paper we consider a heavy gluino to be the lightest supersymmetric particle [LSP]. We investigate the limits on the mass of a heavy gluino LSP, using the searches for excess events in the jets plus missing momentum channel in Run I. The neutral and charged R-hadrons, containing a heavy gluino LSP, have distinct signatures at the Fermilab Tevatron. The range of excluded gluino masses depends on whether the R-hadron is charged or neutral and the amount of energy deposited in the hadronic calorimeter. The latter depends on the energy loss per collision in the calorimeter and the number of collisions; where both quantities require a model for R-hadron- Nucleon scattering. We show how the excluded range of gluino mass depends on these parameters. We find that gluinos with mass in the range between $\sim 35$ GeV and $\sim 115$ GeV are excluded by CDF Run I data. Combined with previous results of Baer et al., which use LEP data to exclude the range 3 - 22$\sim$25 GeV, our result demonstrates that an allowed window for a heavy gluino with mass between 25 and 35 GeV is quite robust. Finally we discuss the relevant differences of our analysis of Tevatron data to that of Baer et al.
New data on neutrino masses is very exciting. It is the first evidence for physics beyond the standard model. In this talk we discuss this data and how it may (or may not) be used to constrain theories of charged fermion masses. The talk is divided into two parts. In part I, we briefly discuss the theoretical framework for fermion masses and mixing angles as well as some of the most salient data for neutrino oscillations. In part II, we define the framework of a "predictive" theory of fermion masses. We then consider a particular theory which makes significant testable predictions.
In this paper we study the experimental consequences of a theory which naturally has a heavy, stable (or almost stable) gluino. We define the boundary conditions at a messenger scale $M \sim 10^{14}$ GeV which lead to this alternative phenomenologically acceptable version of the minimal supersymmetric standard model. In this theory, either the gluino or the gravitino is the lightest supersymmetric particle [LSP]. If the gravitino is the LSP, then the gluino is the next-to-LSP with a lifetime on the order of 100 years. In either case, the gluino is (for all practical purposes) a stable particle with respect to experiments at high energy accelerators. Thus the standard missing energy signature for SUSY fails. A stable gluino forms a color singlet hadron, the lightest of which is assumed to be an isoscalar gluino-gluon bound state ($R_0$). The $R_0$ has strong interactions and will interact in a hadronic calorimeter; depositing some fraction of its kinetic energy. Finally, in the case the gravitino is the LSP, bounds from searches for stable heavy isotopes of hydrogen or oxygen do not apply to the metastable $R_0$.
In this paper we present a dynamical model of SUSY breaking with a hybrid messenger sector. SUSY is broken dynamically at a scale of order $10^9$ GeV via strong SU(2) gauge interactions. SUSY breaking is then transmitted to the observable sector via two distinct sources: (1) messengers, carrying Standard Model gauge quantum numbers, with the messenger mass of order $10^{15}$ GeV, and (2) the D term of an anomalous U(1)$_X$. The model is quite constrained. The messenger scale is fixed by the Fayet-Iliopoulos term for the anomalous U(1)$_X$ interaction. In addition, we show that the D term SUSY breaking contributions to squark and slepton masses are "naturally" the same order as those coming from the messengers.
Lepton flavor violation may be a signature of "GUT scale" physics, if the messenger scale for SUSY breaking is above the "GUT scale." We elaborate on the details of this simple statement in the following talk.
Study of the MSSM in large tan$β$ regime has to include correlations between the constraints presented by the low energy values of the b quark mass and BR($b \to sγ$). Both quantities receive SUSY contributions enhanced by tan$β$ and have a major impact on the MSSM analysis. Here we summarize the results of such a study constrained by a complete SO(10) model. The dominant effects to the analysis come from third generation Yukawa couplings and a GUT threshold to $α_s$. We show that a small negative GUT correction to $α_s$ accommodates $α_s(M_Z) \leq 0.118$ and $δm_b^{SUSY} > 0$. The latter quantity being positive then opens up two options to fit the measured rate for $b \to sγ$. The two distinct fits differ by the overall sign of the amplitude for this process. They work equally well in complementary regions of the allowed SUSY parameter space. We show plots of the partial contributions to the coefficient $C_7(M_Z)$ in the ($m_0,M_{1/2}$) plane in each of these best fits. We conclude that an attractive SO(10)-derived regime of the MSSM remains a viable option.