arXiv subjects

Stuart Raby

Publications and source records attributed to Stuart Raby.

105 records · Page 6Linked to original sources

arXiv1997

Global Analysis of Electroweak Data in SUSY GUTs

A $χ^2$ analysis of several SUSY GUTs recently discussed in the literature is presented. We obtain global fits to electroweak data, which include gauge couplings, gauge boson masses, BR($b\to sγ$) and masses of fermions of all three generations and their mixing angles. Thus we are able to test gauge unification, radiative electroweak symmetry breaking, SUSY sector (- in the context of supergravity induced SUSY breaking) and the Yukawa sector in each particular model self-consistently. One of the models studied provides a very good fit with $χ^2 \sim 1$ for 3 degrees of freedom, in a large region of the allowed SUSY parameter space. The Yukawa sector works so well in this case that the analysis ends up testing the MSSM constrained by unification. Adopting this point of view, in the second part of this talk we focus on the details of the fit for BR($b\to sγ$) and discuss the correlations among $δm_b^{SUSY}$, $α_s(M_Z)$ and a GUT threshold to $α_s(M_G)$. We conclude that an attractive SO(10)-derived regime of the MSSM remains a viable option.

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arXiv1997

Gauge-mediated SUSY Breaking at an Intermediate Scale

Gauge-mediated SUSY breaking with a messenger scale of order $10^{15}$ GeV has some interesting features. It can solve the flavor changing neutral current problem of supersymmetric models with predictions for superpartner masses which are identical to those of minimal supergravity models. It can however also lead to theories with novel experimental signatures. For example, we present a model in which the gluino is the lightest supersymmetric particle. We also review the present experimental status of a stable gluino.

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arXiv1996

A Global chi^2 Analysis of Electroweak Data in SO(10) SUSY GUTs

We present the details of a global $χ^2$ analysis of electroweak data, including fermion masses and mixing angles, in SO(10) SUSY GUTs. Just as precision electroweak data is used to test the Standard Model, the well determined Standard Model parameters are the precision electroweak data for testing theories beyond the Standard Model. In this paper we use the latest experimentally measured values for these parameters. We study several models discussed in the literature. One of these models provides an excellent fit to the low energy data with $χ^2 \sim 1$ for 3 degrees of freedom. We present graphs of constant $χ^2$ contours as functions of position in soft SUSY breaking parameter space, as well as our predictions for a few selected points in parameter space. We also study the sensitivity of our results to changes in various parameters. Finally, we discuss the consequences of our work in the context of a general MSSM analysis at the Z scale.

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arXiv1996

Nucleon Decay in a Realistic SO(10) SUSY GUT

In this paper, we calculate neutron and proton decay rates and branching ratios in a predictive SO(10) SUSY GUT which agrees well with low energy data. We show that the nucleon lifetimes are consistent with the experimental bounds. The nucleon decay rates are calculated using all one-loop chargino and gluino dressed diagrams regardless of their chiral structure. We show that the four-fermion operator $C_{jk} (u_R {d_j}_R)({d_k}_L {ν_τ}_L)$, commonly neglected in previous nucleon decay calculations, not only contributes significantly to nucleon decay, but, for many values of the initial GUT parameters and for large $\tanβ$, actually dominates the decay rate. As a consequence, we find that $τ_p/τ_n$ is often substantially larger than the prediction obtained in small $\tanβ$ models. We also find that gluino-dressed diagrams, often neglected in nucleon decay calculations, contribute significantly to nucleon decay. In addition we find that the branching ratios obtained from this realistic SO(10) SUSY GUT differ significantly from the predictions obtained from ``generic" SU(5) SUSY GUTS. Thus nucleon decay branching ratios, when observed, can be used to test theories of fermion masses.

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arXiv1996

A Global $χ^2$ Analysis of Electroweak Data (including Fermion Masses and Mixing Angles) in SO(10) SUSY GUTs

We present a global $χ^2$ analysis of electroweak data, including fermion masses and mixing angles, in SO(10) SUSY GUTs. Just as precision electroweak data is used to test the Standard Model, the well determined Standard Model parameters are the precision electroweak data for testing theories beyond the Standard Model. In this talk we use the latest experimentally measured values for these parameters. We study several models discussed in the literature. One of these models provides an excellent fit to the low energy data with $χ^2 \sim 1$ for 3 degrees of freedom. We present our predictions for a few selected points in parameter space.

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arXiv1996

Phenomenological Implications of Low Energy Supersymmetry Breaking

The experimental signatures for low energy supersymmetry breaking are presented. The lightest standard model superpartner is unstable and decays to its partner plus a Goldstino, $G$. For a supersymmetry breaking scale below a few 1000 TeV this decay can take place within a detector, leading to very distinctive signatures. If a neutralino is the lightest standard model superpartner it decays by $χ_1^0 \to γ+ G$, and if kinematically accessible by $χ_1^0 \to (Z^0, h^0, H^0, A^0) + G$. These decays can give rise to displaced vertices. Alternately, if a slepton is the lightest standard model superpartner it decays by $\tilde{l} \to l + G$. This can be seen as a greater than minimum ionizing charged particle track, possibly with a kink to a minimum ionizing track.

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arXiv1996

Experimental Signatures of Low Energy Gauge Mediated Supersymmetry Breaking

The experimental signatures for gauge mediated supersymmetry breaking are presented. The phenomenology associated with this class of models is distinctive since the gravitino is naturally the LSP. The next lightest supersymmetric particle (NLSP) can be a gaugino, Higgsino, or right handed slepton. Decay of the NLSP to its partner plus the LSP proceeds through the Goldstino component of the gravitino. For a significant range of parameters this decay can take place within the detector, and can be measured as a displaced vertex or kink in a charged particle track. In the case that the NLSP is mostly gaugino, we identify the discovery modes as $e^+e^- \rightarrow γγ+ \Emiss$, and $p \bar{p} \rightarrow l^+ l^- γγ+ \EmissT$. If the NLSP is a right handed slepton the discovery modes are $e^+ e^- \rightarrow l^+ l^- + \Emiss$ and $p \bar{p} \rightarrow l^+ l^- + \EmissT$. An NLSP which is mostly Higgsino is also considered. Finally, these theories can contain scalar particles which mediate sub-millimeter range coherent forces of gravitational strength.

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arXiv1996

GUT Scale Threshold Corrections in a Complete Supersymmetric SO(10) Model: $α_s(M_Z)$ vs. Proton Lifetime

We show that one loop GUT scale threshold corrections to gauge couplings are a significant constraint on the GUT symmetry breaking sector of the theory. The one loop threshold corrections relate the prediction for $α_s(M_Z)$ to the proton lifetime. We have calculated these corrections in a new complete SO(10) SUSY GUT. The results are consistent with the low energy measurement of $α_s(M_Z)$. We have also calculated the proton lifetime and branching ratios in this model. We show that proton decay rates provide a powerful test for theories of fermion masses.

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arXiv1995

Finite Supersymmetric Threshold Corrections to CKM Matrix Elements in the Large $tanβ$ Regime

We evaluate the finite 1-loop threshold corrections, proportional to $tanβ$, to the down quark mass matrix. These result in corrections to down quark masses and to Cabibbo-Kobayashi-Maskawa [CKM] matrix elements. The corrections to CKM matrix elements are the novel feature of this paper. For grand unified theories with large $\tanβ$ these corrections may significantly alter the low energy predictions of four of the CKM matrix elements and the Jarlskog parameter J, a measure of CP violation. The angles $α,\: β$ and $γ$ of the unitarity triangle and the ratio $|{V_{ub} \over V_{cb}}|$, however, are not corrected to this order. We also discuss these corrections in the light of recent models for fermion masses. Here the corrections may be useful in selecting among the various models. Moreover, if one model fits the data, it will only do so for a particular range of SUSY parameters.

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arXiv1995

Introduction to Theories of Fermion Masses

This paper is based on four lectures given at the Trieste Summer School 1994 on theories of fermion masses. The first two lectures introduce three mechanisms which have been used to construct models of fermion masses. We then discuss some recent applications of these ideas. In the last lecture we briefly review SO(10) and some predictive theories of fermion masses.

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arXiv1995

Fermion Masses and SO(10) SUSY GUTs

In this talk I summarize published work on a systematic operator analysis for fermion masses in a class of effective supersymmetric SO(10) GUTs\cite{adhrs}~\footnote{This work is in collaboration with G. Anderson, S. Dimopoulos, L.J. Hall, and G. Starkman.}. Given a minimal set of four operators at $M_G$, we have just 6 parameters in the fermion mass matrices. We thus make 8 predictions for the 14 low energy observables (9 quark and charged lepton masses, 4 quark mixing angles and $\tan β$). Several models, i.e. particular sets of dominant operators, are in quantitative agreement with the low energy data. In the second half of the talk I discuss the necessary ingredients for an SO(10) GUT valid below the Planck (or string) scale which reproduces one of our models. \footnote{These are preliminary results of work in progress with Lawrence Hall.} This complete GUT should still be interpreted as an effective field theory, i.e. perhaps the low energy limit of a string theory.

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arXiv1994

SO(10) SUSY GUTs and Fermion Masses

In this talk~\footnote{Talk presented at the IFT Workshop on Yukawa Couplings, Gainesville, FL, February 1994.} I summarize published work on a systematic operator analysis for fermion masses in a class of effective supersymmetric SO(10) GUTs \cite{adhrs}~\footnote{This work is in collaboration with G. Anderson, S. Dimopoulos, L.J. Hall, and G. Starkman.}. Given a minimal set of four operators at $M_G$, we have just 6 parameters in the fermion mass matrices. We thus make 8 predictions for the 14 low energy observables (9 quark and charged lepton masses, 4 quark mixing angles and $\tan β$). Several models, i.e. particular sets of dominant operators, are in quantitative agreement with the low energy data. In the second half of the talk I discuss the necessary ingredients for an SO(10) GUT valid below the Planck (or string) scale which reproduces one of our models. \footnote{These are preliminary results of work in progress with Lawrence Hall.} This complete GUT should still be interpreted as an effective field theory, i.e. perhaps the low energy limit of a string theory.}

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arXiv1993

Deducing L_{fermion} at M_{GUT} using Low Energy Data or Towards a Theory of Fermion Masses

In the last 20 years we have accumulated an enormous amount of data on elementary particles and their interactions. This data serves two purposes: to fix the phenomenological parameters of the Standard Model [SM] and to verify that the SM is an excellent description of nature. It is our goal to understand the origin of these many arbitrary parameters. In this talk we consider a supersymmetric [SUSY] SO(10) grand unified theory [GUT]. We present a straightforward procedure, incorporating a general operator analysis, which allows us to use low energy data to determine the fermionic sector of the theory at the GUT scale.

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arXiv1992

Precise predictions for mt, Vcb and tan

The fermion mass and mixing angle predictions of a recently proposed framework are investigated for large b and $τ$ Yukawa couplings. A new allowed region of parameters is found for this large $\tan β$ case. The two predictions which are substantially altered, $m_t$ and $\tan β$, are displayed, including the dependence on the inputs $|V_{cb}|$, $m_c$, $m_b$ and $α_s$. A simple restriction on this framework yields an additional prediction, for $|V_{cb}|$. If the b,t, and $τ$ Yukawas are equal at the GUT scale then $|\Vcb|$ is predicted and the top quark mass is constrained to lie in the range $\mt = 179. \pm 4.$ GeV.

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arXiv1992

Predictions for neutral K and B meson physics

Using supersymmetric grand unified theories, we have recently invented a framework which allows the prediction of three quark masses, two of the parameters of the Kobayashi-Maskawa matrix and tan $β$, the ratio of the two vevs. These predictions are used to calculate $ε$ and $ε'$ in the kaon system, B meson mass mixing and the size of CP asymmetries in the decays of neutral B mesons to explicit final states of given CP.

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