String Unification and Leptophobic Z′Z' in Flipped SU(5)

We summarize recent developments in the prediction for $\alpha_s(M_Z)$, self-consistent string unification and the dynamical determination of mass scales, and leptophobic $Z'$ gauge bosons in the context of stringy flipped SU(5). [To appear in Proceedings of Fourth International Conference on Supersymmetry (SUSY96), University of Maryland (May 1996).]Comment: 5 pages, LaTeX (uses espcrc2.sty), 5 figures (included

A Layman's guide to SUSY GUTs

The determination of the most straightforward evidence for the existence of the Superworld requires a guide for non-experts (especially experimental physicists) for them to make their own judgement on the value of such predictions. For this purpose we review the most basic results of Super-Grand unification in a simple and clear way. We focus the attention on two specific models and their predictions. These two models represent an example of a direct comparison between a traditional unified-theory and a string-inspired approach to the solution of the many open problems of the Standard Model. We emphasize that viable models must satisfy {\em all} available experimental constraints and be as simple as theoretically possible. The two well defined supergravity models, $SU(5)$ and $SU(5)\times U(1)$, can be described in terms of only a few parameters (five and three respectively) instead of the more than twenty needed in the MSSM model, \ie, the Minimal Supersymmetric extension of the Standard Model. A case of special interest is the strict no-scale $SU(5)\times U(1)$ supergravity where all predictions depend on only one parameter (plus the top-quark mass). A general consequence of these analyses is that supersymmetric particles can be at the verge of discovery, lurking around the corner at present and near future facilities. This review should help anyone distinguish between well motivated predictions and predictions based on arbitrary choices of parameters in undefined models.Comment: 25 pages, Latex, 11 figures (not included), CERN-TH.7077/93, CTP-TAMU-65/93. A complete ps file (1.31MB) with embedded figures is available by request from [email protected]

Exploring Discourse Ethics for Tourism Transformation

The 'critical turn' in tourism studies is defined as a research perspective that explores social transfor- mation in and through tourism by facing the negative impact of strategic-instrumental rationality on this activity. This work explores the features of discourse ethics that may normatively support tourism transformation, a gap that has not been thoroughly discussed in tourism research. For this purpose, the study combines the use of critical and ethical theory with an analysis of discourse ethics in tourism literature to demonstrate that the use of Habermasian discourse ethics needs to be complemented with the Apelian approach. Through these steps the work reveals the theoretical bases of discourse ethics to discuss whether understandings between stakeholders guided by strategic-instrumental rationality can be reached not only in the political sphere —Habermas—, but also in the ethical field —Apel

Vanishing Str M^2 in the presence of anomalous U_A(1)

We show that the presence of an anomalous $\rm U_A(1)$ factor in the gauge group of string-derived models may have the new and important phenomenological consequence of allowing the vanishing of ${\rm Str}\,{\cal M}^2$ in the ``shifted" vacuum, that results in the process of cancelling the anomalous $\rm U_A(1)$. The feasibility of this effect seems to be enhanced by a vanishing vacuum energy, and by a ``small" value of ${\rm Str}\,{\cal M}^2$ in the original vacuum. In the class of free-fermionic models with vanishing vacuum energy that we focus on, a necessary condition for this mechanism to be effective is that ${\rm Str}\,{\cal M}^2>0$ in the original vacuum. A vanishing ${\rm Str}\,{\cal M}^2$ ameliorates the cosmological constant problem and is a necessary element in the stability of the no-scale mechanism.Comment: 7 pages, no figures, LaTe

M-theory Inspired No-scale Supergravity

We propose a supergravity model that contains elements recently shown to arise in the strongly-coupled limit of the $E_8\times E_8$ heterotic string (M-theory), including a no-scale--like K\"ahler potential, the identification of the string scale with the gauge coupling unification scale, and the onset of supersymmetry breaking at an intermediate scale determined by the size of the eleventh dimension of M-theory. We also study the phenomenological consequences of such scenario, which include a rather constrained sparticle spectrum within the reach of present-generation particle accelerators.Comment: 8 pages, LaTeX, 3 figures (included

New Precision Electroweak Tests of SU(5) x U(1) Supergravity

We explore the one-loop electroweak radiative corrections in $SU(5)\times U(1)$ supergravity via explicit calculation of vacuum-polarization and vertex-correction contributions to the $\epsilon_1$ and $\epsilon_b$ parameters. Experimentally, these parameters are obtained from a global fit to the set of observables $\Gamma_{l}, \Gamma_{b}, A^{l}_{FB}$, and $M_W/M_Z$. We include $q^2$-dependent effects, which induce a large systematic negative shift on $\epsilon_{1}$ for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). The (non-oblique) supersymmetric vertex corrections to \Zbb, which define the $\epsilon_b$ parameter, show a significant positive shift for light chargino masses, which for $\tan\beta\approx2$ can be nearly compensated by a negative shift from the charged Higgs contribution. We conclude that at the 90\%CL, for m_t\lsim160\GeV the present experimental values of $\epsilon_1$ and $\epsilon_b$ do not constrain in any way $SU(5)\times U(1)$ supergravity in both no-scale and dilaton scenarios. On the other hand, for m_t\gsim160\GeV the constraints on the parameter space become increasingly stricter. We demonstrate this trend with a study of the m_t=170\GeV case, where only a small region of parameter space, with \tan\beta\gsim4, remains allowed and corresponds to light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). Thus $SU(5)\times U(1)$ supergravity combined with high-precision LEP data would suggest the presence of light charginos if the top quark is not detected at the Tevatron.Comment: LaTeX, 11 Pages+4 Figures(not included), the figures available upon request as an uuencoded file(0.4MB) or 4 PS files from [email protected], CERN-TH.7078/93, CTP-TAMU-68/93, ACT-24/9