Search

We have calculated the complete one-loop corrections to the sfermion pair production process e + e − → f i f j (f=t,b,τ,ν τ ) in the Minimal Supersymmetric Standard Model. Our results also include the previously calculated SUSY-QCD corrections. We present the details of the renormalization scheme used. It is found that the weak corrections are of the same magnitude as the SUSY-QCD corrections at higher energies ( s ∼1 TeV). At these energies an important part of the weak corrections stems from the box contribution. This is best seen in sneutrino production.

We calculate the full electroweak one-loop corrections to the decay of the CP-odd Higgs boson A 0 into scalar quarks in the minimal supersymmetric extension of the Standard Model (MSSM). Due to the complex structure of the electroweak sector a proper renormalization of many parameters in the on-shell renormalization scheme is necessary. For the decay into sbottom quarks, especially for large tan β , the corrections can be very large in the on-shell renormalization scheme, which makes the perturbation series unreliable. We solve this problem by an appropriate definition of the tree-level coupling in terms of running quark masses and running trilinear couplings A q . We also discuss the decay of heavy scalar quarks into light scalar quarks and A 0 . We find that the corrections are significant and therefore cannot be neglected.

For energies relevant to future linear colliders, $\sqrt{s} \gsim 500$ GeV, the WW fusion channel dominates the Higgs boson production cross section $e^+ e^- \to \bar{\nu} \nu h^0$. We have calculated the one-loop corrections to this process due to fermion and sfermion loops in the context of the MSSM. As a special case, the contribution of the fermion loops in the SM has also been studied. In general, the correction is negative and sizeable of the order of 10 percent, the bulk of it being due to fermion loops., Comment: Version to appear in Phys. Lett. B

Unless squarks and sleptons are in the multi-TeV region or above, CP violating induced electric dipole moments of elementary particles can pose significant puzzles for supersymmetric (SUSY) models. We study the dipole-moment-inducing one-loop amplitudes as a function of the fundamental SUSY parameters and show that these puzzles are removed if there is a sufficiently large hierarchy between the gaugino masses and the scalar mass. We comment on the experimental status of the low gaugino mass scenario., 13 pages, 3 figures

We perform a detailed study of the decays of the heavier τ slepton ( τ 2 ) and τ-sneutrino ( ν τ ) in the Minimal Supersymmetric Standard Model (MSSM). We show that the decays into Higgs or gauge bosons, i.e. τ − 2 → τ − 1 +(h 0 ,H 0 ,A 0 or Z 0 ) , τ − 2 → ν τ +(H − or W − ) , and ν τ → τ − 1 +(H + or W + ) , can be very important due to the sizable τ Yukawa coupling and large mixing parameters of τ . Compared to the decays into fermions, such as τ − 2 →τ − + χ 0 i and τ − 2 →ν τ + χ − j , these bosonic decay modes can have significantly different decay distributions. This could have an important influence on the search for τ 2 and ν τ and the determination of the MSSM parameters at future colliders.

We perform a detailed study of the decays of the heavier top and bottom squarks ( t 2 and b 2 ) in the Minimal Supersymmetric Standard Model (MSSM). We show that the decays into Higgs or gauge bosons, i.e. t 2 → t 1 +(h 0 ,H 0 ,A 0 or Z 0 ) , t 2 → b 1,2 +(H + or W + ) , and the analogous b 2 decays, can be dominant in a wide range of the model parameters due to the large Yukawa couplings and mixings of t and b. Compared to the conventional decays into fermions, such as t 2 →t+( χ 0 i or g ) and t 2 →b+ χ + j , these bosonic decay modes can have significantly different decay structures and distributions. This could have an important impact on the search for t 2 and b 2 and the determination of the MSSM parameters at future colliders.

We calculate the supersymmetric ${\cal O}(\alpha_s)$ QCD corrections to stop and sbottom decays into vector bosons within the Minimal Supersymmetric Standard Model. We give analytic formulae and perform a numerical analysis of these decays. We find that SUSY-QCD corrections to the decay widths are typically -5% to -10% depending on the squark masses, squark mixing angles, and the gluino mass.

We present a detailed study of the decays of the neutral Higgs bosons $H^0$ and $A^0$ within the Minimal Supersymmetric Standard Model. We find that the supersymmetric modes ${\tilde{t}}\bar{\tilde{t}}$ and ${\tilde{b}}\bar{\tilde{b}}$ can dominate the $H^0$ and $A^0$ decays in a wide range of the model parameters due to large Yukawa couplings and mixings of ${\tilde{t}}$ and ${\tilde{b}}$. Compared to the conventional modes $t\bar{t}$ and $b\bar{b}$, these modes have very distinctive signatures. This could have a decisive impact on the neutral Higgs boson searches at future colliders., Comment: 15 pages, LaTeX, also available at ftp://physics.ge.seikei.ac.jp/Pub/preprint/itpsu9603.uu (uuencoded postscript)

We calculate the supersymmetric QCD corrections in order $\alpha_s$ to the cross section $e^+ e^- \to \sq_i \bar\sq_j$ $(i,j = 1, 2)$ within the Minimal Supersymmetric Standard Model. We pay particular attention to the case of the left--right squark mixing and to the renormalization of the mixing angle. The corrections due to gluino exchange turn out to be smaller than those due to gluon exchange, but they can be significant at higher energies even for a gluino mass of a few hundred GeV., Comment: 18 pages including 5 figures

We present a complete calculation of the O ( α s ) QCD corrections to the width of the decay H + → t b within the Minimal Supersymmetric Standard Model. We find that the QCD corrections are quite important, and that the supersymmetric QCD corrections (due to gluino, t and b exchange) can be comparable to or even larger than the standard QCD corrections in a large region of the supersymmetric parameter space. This is mainly due to the effect of large left-right mixings of stop ( t ) and sbottom ( b ). This could significantly affect the phenomennology of the H + search.

We calculate the supersymmetric O ( α s ) QCD corrections to the width of the decay within the Minimal Supersymmetric Standard Model. We find that the QCD corrections are significant, but that they do not invalidate our previous conclusion at tree-level on the dominance of the mode in a wide parameter region.

We present a detailed study of the decays of the charged Higgs boson H+ within the Minimal Supersymmetric Standard Model. We find that the supersymmtric mode t b can dominate the H+ decays in a wide range of the model parameters due to the large Yukawa couplings and mixings of t and b . Compared to the conventional modes τ+vτ and t b , this mode has very distinctive signatures. This could have a decisive impact on H+ searches at future colliders.

Proton elastic scattering off a polarized proton target has been measured at 150 GeV/ c , in the |; t |-range 0.2–3.0 GeV 2 . The results on polarization and differential cross section are presented.

An absorbed Regge model already proposed for kaon photoproduction is extended to electroproduction and describes well the recent experimental data on K+ Λ and K+Σ0 electroproduction. As K exchange alone cannot account for the large unnatural parity contribution being present, we consider in addition either KB(1+−) or KA(1++) −KA (2−−) exchange.

We study in detail production and decay of neutralinos in e + e − annihilation. Formulae for the cross section, the single lepton, lepton pair, and missing energy spectra are given. Particular attention is paid to the mixing of gauginos and higgsinos. In order to illustrate its importance numerical results for four different mixing scenarios are presented.

We treat in detail the production of selectrons and squarks in ep collisions, e + p → e + q + X. In particular we also study their most important decays. General mixing of gauginos and higgsinos is included. Formulae for the cross section, the energy and the angular distribution of the decay electron are given. We also calculate the cross section asymmetry when using polarized electron beams. Numerical results for three different mixing scenarios and various squark and selectron masses are presented.

We calculate the width for Z 0 → χ + χ − and all possible decay rates of the charginos. We systematically study their dependence on the supersymmetry parameters and work out the constraints experiments will provide.

We have considered the azimuthal angular correlation between a baryon and an antibaryon in a quark jet. It is shown that by measuring this correlation an accurate determination of the probability of diquark break-up is possible. Both analytical and Monte Carlo calculations are presented.

The relativistic matrix elements for possible spin-parity assignments of the L-meson decaying via special cascade decays are presented. The corresponding Dalitz plot distributions are compared with the non-relativistic cases.

A general analysis of single pion electroproduction with polarized leptons and polarized target but undetected final state polarizations is presented. Suitable asymmetries for cross section measurements are defined. A discussion of π + n production at high energies is given and predictions are made on the basis of a Born term model and a Regge model extrapolated from photoproduction.

Due to the high anomalous magnetic moment of the quark it can be explained on a pure electromagnetic basis why the n-quark is heavier than the p-quark. It then follows, within the quark model, that all isomultiplet splittings are of pure electromagnetic origin.