S. Nandi

W decay in supergravity guts

Abstract We discuss the decay of the W-boson into supersymmetric particles and the decays of these particles in a unified theory in which gravity breaks SU L (2) × U(1). If the decay W → WZ is kinematically possible, the subsequent decay of the gauginos may provide a definitive signature for supersymmetry.

New collider bound on the light gravitino mass

In supergravity theories with a very light gravitino, the gluino decays dominantly to a gluon and a gravitino. This results in a much larger missing E{sub T} for the multijet final states in hadronic colliders. We use the latest Fermilab Tevatron data for the multijet final states to set a new absolute lower bound of 3.0{times}10{sup {minus}13} GeV for the light gravitino mass. {copyright} {ital 1997} {ital The American Physical Society}

Can proton decay be rotated away

Abstract We examine the question of whether the gauge interactions leading to proton decay can be rotated away from grand unified models, via a suitable choice of values for the flavor mixing angles. Grand unified models with an arbitrary number of families and an arbitrary gauge group will be considered. In the case of the SU(5) model with three generations, it is shown that proton decay can be rotated away only if s 3 = 0. ( S 3 is the sine of the third Kobayashi-Maskawa mixing angle.)

The neutron electric dipole moment in supersymmetric theories

Abstract The contribution to the intrinsic quark electric dipole moment (no spectators) due to gauge interaction in supersymmetric SU(3) C × SU(2) × U(1) theories is studied. To order g 4 [where g is the weak SU(2) coupling constant], we find that the contribution vanishes, as in the non-supersymmetric case. When the gluon and gluino radiative corrections are included, and supersymmetry is broken, the intrinsic quark electric dipole moment (iqedm) may provide a contribution to the neutron electric dipole moment, d n several orders of magnitude bigger [ d n / e ≈ 10 −28 cm] than the standard SU(2) C × SU(2) × U(1) gauge iqedm prediction (≈ 10 −34 cm).

Higgs boson production at heavy Z-resonance

Abstract In theories with an extra U(1) gauge boson (Z 2 ) at low energy, the Higgs boson can be produced copiously by the process e + e − →Z 2 →Z 1 +H, at the Z 2 resonance. The cross section for this process is calculated and it is found that it is about 2 to 3 orders of magnitude larger than the conventional process e + e − →Z ∗ →Z+H. It is also shown that this off-diagonal coupling exists in general, and it is calculated for a simple model.

SU(5) with split fermion representations

Abstract We calculate the weak mixing angle, proton lifetime (to two loops) and the bottom quark to tau lepton mass ratio (to one loop) in the SU(5) model containing split fermions in the (5 + 5 )L and (10 + 10 )L representations. Three of the split models agree with the measured value of sin2θW and the bound on the proton lifetime. Two of these three models give τ(P→e+π0) = 3.3 × 1032yr. In all three models, the value of the bottom quark mass comes out somewhat larger (∼6 GeV) than that needed in the potential models.

Supersymmetric signature in quarkonium decays

Abstract We calculate the heavy quarkonium decay widths for decays to scalar fermion-scalar antifermion pairs. In the light of the supersymmetric interpretation of the recently observed monojets, these decays could be observable in the forthcoming e + −e − colliding beam machines. The scalar lepton-scalar antilepton pairs produced by toponium decays is comparable to those produced by direct photon exchanges. The decays of the scalar pair into an electron-positron (or muon-antimuon) pair (carrying about one-half of the total beam energy) together with the missing photinos will be a clean signature of supersymmetry.