No abstract available

No abstract available

[en] We compute the graviton-induced corrections to the trajectory of a classical test particle. We show that the motion of the test particle is governed by an effective action given by the expectation value (with respect to the graviton state) of the classical action. We analyze the quantum corrected equations of motion for the test particle in two particular backgrounds: a Robertson Walker spacetime and a (2+1)-dimensional spacetime with rotational symmetry. In both cases we show that the quantum corrected trajectory is not a geodesic of the background metric. copyright 1999 The American Physical Society

[en] We discuss cosmological solutions of Horava-Witten theory describing the strongly coupled heterotic string. At energies below the grand-unified scale, the effective theory is five, not four, dimensional, where the additional coordinate parametrizes an S¹/Z₂ orbifold. Furthermore, it admits no homogeneous solutions. Rather, the static vacuum state, appropriate for a reduction to four-dimensional N=1 supersymmetric models, is a BPS domain wall pair. Relevant cosmological solutions are those associated with this BPS state. In particular, such solutions must be inhomogeneous, depending on the orbifold coordinate as well as on time. We present two examples of this new type of cosmological solution, obtained by separation of variables rather than by exchange of the time and radius coordinates of a brane solution, as in previous work. The first example represents the analogue of a rolling radii solution with the radii specifying the geometry of the domain wall pair. This is generalized in the second example to include a nontrivial Ramond-Ramond scalar. copyright 1999 The American Physical Society

[en] Hierarchical quark masses and small mixing angles are shown to lead to a simple triangular form for U- and D-type quark mass matrices. In the basis where one of the matrices is diagonal, each matrix element of the other is, to a good approximation, the product of a quark mass and a CKM matrix element. The physical content of a general mass matrix can be easily deciphered in its triangular form. This parametrization could serve as a useful starting point for model building. Examples of mass textures are analyzed using this method. copyright 1999 The American Physical Society

[en] We analyze the signal at the Fermilab Tevatron for the doubly charged Higgs superfield of supersymmetric left-right models with gauge mediated supersymmetry breaking. Because of the presence of a new coupling, the lighter stau is usually less massive than the lightest neutralino and is frequently the next to lightest SUSY particle. The fermionic part of the doubly charged Higgs field decays dominantly into two τ leptons plus missing energy (gravitino). We find that the inclusive two τ jets (when they come from same sign τ jets) and three τ jets plus missing energy signatures could be observable at run II of the Tevatron. We also find that the distribution in angle between the two highest E_T τ jets when they come from same sign τ leptons can be used to distinguish this model from the others. copyright 1999 The American Physical Society

[en] We investigate a large class of supersymmetric SO(10) grand unified theories (GUT close-quote s) within the framework of gauge-mediated supersymmetry breaking. We start with the most general messenger sector and embed the standard model gauge group into either SU(2)_LxSU(2)_RxU(1)_B-L or SU(2)_LxU(1)_I3RxU(1)_B-L. We find that the conditions of the perturbativity of the gauge couplings and unification at the GUT scale severely restrict the messenger sector and lead to testable phenomenological predictions for the sparticle masses. One of the most notable features of the class of supersymmetric SO(10) grand unified theories introduced here is that among the many possible cases there are only a few consistent models, all of which share an essentially unique mass spectrum. copyright 1999 The American Physical Society

[en] In this Brief Report, a non-standard solution to the solar neutrino problem is reexamined. This solution assumes that neutrino flavors could have different couplings to gravity; hence, the equivalence principle is violated in this mechanism. The gravity induced mixing has the potential of accounting for the current solar neutrino data from several experiments even for massless neutrinos. We fit this solution to the total rate of neutrino events in the SuperKamiokande detector (first 504 days) together with the total rate from other detectors and also with the SuperKamiokande results for the recoil-electron spectrum. copyright 1999 The American Physical Society

[en] We study the pair production of neutral Higgs bosons through gluon fusion at hadron colliders in the framework of the minimal supersymmetric standard model. We present analytical expressions for the relevant amplitudes, including both quark and squark loop contributions, and allowing for mixing between the superpartners of left- and right-handed quarks. Squark loop contributions can increase the cross section for the production of two CP-even Higgs bosons by more than two orders of magnitude, if the relevant trilinear soft breaking parameter is large and the mass of the lighter squark eigenstate is not too far above its current lower bound. In the region of large tan and h;β, neutral Higgs boson pair production might even be observable in the 4b final state during the next run of the Fermilab Tevatron collider. copyright 1999 The American Physical Society

[en] We present a detailed description of a search for anomalous production of missing E_T (E/_T), jets, leptons (e,μ,τ), b quarks, or additional photons in events containing two isolated, central (|η|<1.0) photons with E_T>12 GeV. The results are consistent with standard model expectations, with the possible exception of one event that has, in addition to the two photons, a central electron, a high-E_T electromagnetic cluster, and large E/_T. We set limits using two specific SUSY scenarios for production of diphoton events with E/_T. copyright 1999 The American Physical Society