Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function

Starting from the known one-loop result for the $e^{+}e^{-}$-annihilation process $e^{+}e^{-}\stackrel{\gamma,Z} {\longrightarrow} q\bar{q}g$ with massless quarks we employ analyticity and crossing to determine the absorptive parts of the corresponding one-loop contributions in Deep Inelastic Scattering (DIS) and in the Drell-Yan process (DY). Whereas the ${\cal O}(\alpha_s^2)$ absorptive parts generate a non-measurable phase factor in the $e^{+}e^{-}$-annihilation channel one obtains measurable phase effects from the one-loop contributions in the deep inelastic and in the Drell-Yan case. We compare our results with the results of previous calculations where the absorptive parts in DIS and in the DY process were calculated directly in the respective channels. We also present some new results on the dispersive and absorptive contributions of the triangle anomaly graph to the DIS process.Comment: 23 pages, 5 figures, typos corrected. Version to appear in Phys. Rev.

Light bottom squark and gluino confront electroweak precision measurements

We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a light gluino (mass 12\sim 16 \gev) with electroweak precision measurements. Such light particles have been suggested to explain the observed excess in the $b$ quark production cross section at the Tevatron. The electroweak observables may be affected by the sbottom and gluino through the SUSY-QCD corrections to the $Zbb$ vertex. We examine, in addition to the SUSY-QCD corrections, the electroweak corrections to the gauge boson propagators from the stop which are allowed to be light from the SU(2)$_L$ symmetry. We find that this scenario is strongly disfavored from electroweak precision measurements unless the heavier sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in the stop sector is sufficiently large. This implies that one of the stops should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in Phys.Rev.Let

Probing the Weak Boson Sector in γe→Ze\gamma e\rightarrow Ze

We study possible deviations from the standard model in the reaction $\gamma e\rightarrow Ze$ at a 500 GeV $e^+e^-$ collider. As a photon source we use a laser backscattered photon beam. We investigate the most general $\gamma Z\gamma$ and $\gamma ZZ$ vertices including operators up to energy-dimension-six which are Lorentz invariant. These vertices require four extra parameters; two are CP-conserving, $h^\gamma_1$ and $h^Z_1$, and two are CP-violating, $h^\gamma_2$ and $h^Z_2$. We present analytical expressions of the helicity amplitudes for the process $\gamma e\rightarrow Ze$ for arbitrary values of anomalous couplings. Assuming Standard Model values are actually measured we present the allowed region in the ($h^\gamma_1,h^Z_1$) plane at the 90\% confidence level. We then show how the angular correlation of the $Z$ decay products can be used to extract detailed information on the anomalous (especially CP-violating) $\gamma Z\gamma$ and $\gamma ZZ$ couplings.Comment: Latex, 25 pages, 12 figures (not included). One compressed postscript file including all the figures available at ftp://ftp.kek.jp/kek/preprints/TH/TH-420/kekth420.ps.g

Studying trilinear gauge couplings at LEP2 using optimal observables

We study the sensitivity of the processes `e+ e- -> lepton (l) neutrino (v) quark (u) antiquark (d)' at LEP2 energies on the non-standard trilinear gauge couplings (TGC), using the optimal observables method. All relevant leading logarithmic corrections to the tree-order cross section, as well as experimental resolution effects have been studied. Taking into account correlations among the different TGC parameters we show that the limits on the TGC can reach the level of 0.15~(1sd) at 161 GeV with 100 pb$^{-1}$, a challenge for the first LEP2 phase. At higher energies this can be improved drastically, reaching the level of 0.02~(1sd).Comment: 14 pages, latex, minor typos correcte

Correlated decays of pair-produced scalar taus

We study the quantum mechanical correlation between two identical neutralinos in the decays of minimal supersymmetric standard model (MSSM) scalar tau (stau) pair produced in e+e- annihilation. Generally, the decay products of scalar (spinless) particles are not correlated. We show that a correlation between two neutralinos appears near pair production threshold, due to a finite stau width and mixing of the staus and/or neutralinos, and because the neutralinos are Majorana. Because the correlation is significant only in a specific kinematical configuration, it can be observed only in supersymmetric models where the neutralino momenta can be kinematically reconstructed, such as in models with R-parity violation.Comment: revtex, 10 pages, 8 eps figures; references added, version to appear in PR

Low-Energy Constraints on New Physics Revisited

It is possible to place constraints on non-Standard-Model gauge-boson self-couplings and other new physics by studying their one-loop contributions to precisely measured observables. We extend previous analyses which constrain such nonstandard couplings, and we present the results in a compact and transparent form. Particular attention is given to comparing results for the light-Higgs scenario, where nonstandard effects are parameterized by an effective Lagrangian with a linear realization of the electroweak symmetry breaking sector, and the heavy-Higgs/strongly interacting scenario, described by the electroweak chiral Lagrangian. The constraints on nonstandard gauge-boson self-couplings which are obtained from a global analysis of low-energy data and LEP/SLC measurements on the Z pole are updated and improved from previous studies. Replaced version: tables and figures of Section VIb recalculated. There were roundoff problems, especially in Fig. 8. Text unchanged.Comment: \documentstyle[preprint,aps,floats,psfig]{revtex}, 10 figures, postscript version available from ftp://ftp.kek.jp/kek/preprints/TH/TH-51

Weak boson fusion production of supersymmetric particles at the LHC

We present a complete calculation of weak boson fusion production of colorless supersymmetric particles at the LHC, using the new matrix element generator SUSY-MadGraph. The cross sections are small, generally at the attobarn level, with a few notable exceptions which might provide additional supersymmetric parameter measurements. We discuss in detail how to consistently define supersymmetric weak couplings to preserve unitarity of weak gauge boson scattering amplitudes to fermions, and derive sum rules for weak supersymmetric couplings.Comment: 24 p., 3 fig., 9 tab., published in PRD; numbers in Table IV corrected to those with kinematic cuts cite

Bottom Quark Mass Determination from low-n Sum Rules

We study the uncertainties in the MSbar bottom quark mass determination using relativistic sum rules to O(alpha_S^2). We include charm mass effects and secondary b bbar production and treat the experimental continuum region more conservatively than previous analyses. The PDG treatment of the region between the resonances Upsilon (4S) and Upsilon (5S) is reconsidered. Our final result reads: m_b(m_b)=(4.20 \pm 0.09) GeV.Comment: 4 pages, Talk given at QCD 03, Montpellier, France, 2-9 July 200

Resonance Contributions to η\eta Photoproduction on Protons Found Using Dispersion Relations and an Isobar Model

The contributions of the resonances $D_{13}(1520)$, $S_{11}(1535)$, $S_{11}(1650)$, $D_{15}(1675)$, $F_{15}(1680)$, $D_{13}(1700)$, $P_{11}(1710)$, $P_{13}(1720)$ to $\gamma p\to \eta p$ are found from the data on cross sections, beam and target asymmetries using two approaches: fixed-t dispersion relations and an isobar model. Utilization of the two approaches and comparison of the results obtained with different parametrizations of the resonance contributions allowed us to make conclusions about the model-dependence of these contributions. We conclude that the results for the contributions of the resonances $D_{13}(1520)$, $S_{11}(1535)$, $F_{15}(1680)$ to corresponding multipole amplitudes are stable. With this the results for $D_{13}(1520)$ and $F_{15}(1680)$, combined with their PDG photoexcitation helicity amplitudes, allowed us to find the branching ratios $Br (D_{13}(1520)\to \eta N)=0.05\pm 0.02$, $Br (F_{15}(1680)\to \eta N)=0.16\pm0.04$ which have significantly better accuracy than the PDG data. The total Breit-Wigner width of the $S_{11}(1535)$ is model-dependent, we have obtained $\Gamma (S_{11}(1520))=142 MeV$ and $195 MeV$ using dispersion relations and the isobar model, respectively. The results for the $S_{11}(1650)$, $D_{15}(1675)$, $P_{11}(1710)$, $P_{13}(1720)$ are model dependent, only the signs and orders of magnitude of their contributions to multipole amplitudes are determined. The results for the $D_{13}(1700)$ are strongly model-dependent.Comment: 26 pages, 6 figure