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

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

CHANGES IN THE U.S. DEMAND FOR SUGAR AND IMPLICATIONS FOR IMPORT POLICIES

The thrust of this paper is to identify and measure structural changes in the U.S. demand for sugar and to derive subsequent implications for import restriction policies. Empirical results indicate that changes in consumer preferences and the availability of closer and cheaper sweeteners in food processing, especially high fructose corn syrup (HFCS), are exerting a downward pressure on sugar demand. As the U.S. demand for sugar decreases and the food industry adjusts faster to sweetener choices, the U.S. government would have to impose more restrictive import barriers to maintain prices to domestic sugar and HFCS producers. Furthermore, the welfare impact of U.S. sugar policy options on domestic consumers and food processors will be lessened.Demand and Price Analysis, International Relations/Trade,

Moduli and K\"ahler potential in fermionic strings

We study the problem of identifying the moduli fields in fermionic four-dimensional string models. We deform a free-fermionic model by introducing exactly marginal operators in the form of Abelian Thirring interactions on the world-sheet, and show that their couplings correspond to the untwisted moduli fields. We study the consequences of this method for simple free-fermionic models which correspond to $Z_2\times Z_2$ orbifolds and obtain their moduli space and K\"ahler potential by symmetry arguments and by direct calculation of string scattering amplitudes. We then generalize our analysis to more complicated fermionic structures which arise in constructions of realistic models corresponding to asymmetric orbifolds, and obtain the moduli space and K\"ahler potential for this case. Finally we extend our analysis to the untwisted matter sector and derive expressions for the full K\"ahler potential to be used in phenomenological applications, and the target space duality transformations of the corresponding untwisted matter fields.Comment: 27pp Latex text, no figs, CERN-TH.7259/94, CTP-TAMU-14/94 and ACT-06/9

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

Direct detection of dark matter in SU(5)xU(1) supergravity

We compute the scattering rates for the lightest neutralino $\chi^0_1$ in the forthcoming germanium $(^{73}{\rm Ge}+^{76}{\rm Ge})$ detector and a proposed lead detector $(^{207}{\rm Pb})$, within the framework of $SU(5)\times U(1)$ supergravity. We find that in only a small portion (\lsim10\%) of the parameter spaces of this class of models, are the rates in the germanium detector above the expected initial experimental sensitivity of 0.1 events/kg/day. However, a much larger portion (\lsim40\%) of the parameter spaces could be probed with an improved background rejection capability (0.01 events/kg/day) and/or a more sensitive detector $(^{207}{\rm Pb})$.Comment: 10 pages, Latex, 4 figures included (uuencoded

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

SUSY signals at HERA in the no-scale flipped SU(5) supergravity model

Sparticle production and detection at HERA are studied within the recently proposed no-scale flipped $SU(5)$ supergravity model. Among the various reaction channels that could lead to sparticle production at HERA, only the following are within its limit of sensitivity in this model: $e^-p\to \tilde e^-_{L,R}\chi^0_i+X, \tilde \nu_e\chi^-_1+X$, where $\chi^0_i(i=1,2)$ are the two lightest neutralinos and $\chi^-_1$ is the lightest chargino. We study the elastic and deep-inelastic contributions to the cross sections using the Weizs\"acker-Williams approximation. We find that the most promising supersymmetric production channel is right-handed selectron ($\tilde e_{R}$) plus first neutralino ($\chi^0_1$), with one hard electron and missing energy signature. The $\tilde\nu_e\chi^-_1$ channel leads to comparable rates but also allows jet final states. A right-handedly polarized electron beam at HERA would shut off the latter channel and allow preferentially the former one. With an integrated luminosity of {\cal L}=100\ipb, HERA can extend the present LEPI lower bounds on $m_{\tilde e_R}, m_{\tilde\nu_e},m_{\chi^0_1}$ by \approx25\GeV, while {\cal L}=1000\ipb will make HERA competitive with LEPII. We also show that the Leading Proton Spectrometer (LPS) at HERA is an excellent supersymmetry detector which can provide indirect information about the sparticle masses by measuring the leading proton longitudinal momentum distribution.Comment: 11 pages, 8 figures (available upon request as uuencoded file or separate ps files), tex (harvmac) CTP-TAMU-15/93, CERN/LAA/93-1