Closing the Universe by relaxing the cosmological constant

We propose a string-inspired model which correlates several aspects of particle physics and cosmology. Inspired by the flat directions and the absence of adjoint Higgs representations found in typical string models, we consider a no-scale $SU(5)\times U(1)$ supergravity model. This model entails well determined low-energy phenomenology, such as the value of the neutralino dark matter relic abundance and a negative contribution to the vacuum energy. A positive contribution to the vacuum energy is also typically present in string theory as a consequence of the running of the fundamental constants towards their fixed point values. If these two contributions cancel appropriately, one may end up with a vacuum energy which brings many cosmological observations into better agreement with theoretical expectations. The present abundance of neutralinos would then be fixed. We delineate the regions of parameter space allowed in this scenario, and study the ensuing predictions for the sparticle and Higgs-boson masses in this model.Comment: 5 pages, 2 figures (included), Latex, CTP-TAMU-06/9

A supergravity explanation of the CDF eeγγee\gamma\gamma event

We present a unified no-scale supergravity model with a light gravitino that can naturally explain the observed $ee\gamma\gamma$ event at CDF via right-handed selectron pair-production. The full spectrum of our model can be described in terms of a single parameter and can be distinguished from alternative proposals in the literature. Ongoing and future runs at LEP 2 should be able to probe the full allowed parameter space via acoplanar diphoton events from $e^+e^-\to\chi^0_1\chi^0_1$ production.Comment: 10 pages, LaTeX, 4 figures (included

RbR_b in supergravity models

We compute the supersymmetric contribution to $R_{b}\equiv \Gamma (Z\to b{\bar b})/\Gamma (Z\to {\rm hadrons})$ in a variety of supergravity models. We find R^{\rm susy}_b\lsim0.0004, which does not shift significantly the Standard Model prediction ($R^{\rm SM}_b=0.2162$ for m_t=160\GeV). An improvement in experimental precision by a factor of four would be required to be sensitive to such an effect.Comment: 5 pages, LaTeX, 1 figure (included)

No-scale supergravity confronts LEP diphoton events

We examine the possibility that some anomalous acoplanar diphoton events observed at LEP may be consistent with the predictions of our previously proposed one-parameter no-scale supergravity model with a light gravitino, via the process e^+e^- -> chi chi -> gamma gamma+E_miss. We find that one such event may indeed be consistent with the model predictions for m_chi \approx (60-70) GeV. This region of parameter space is also consistent with the selectron and chargino interpretations of the CDF ee gamma gamma + E_T,miss event.Comment: 9 pages, LaTeX, 4 figures (included). Updated to include full LEP161 dat