arXiv subjects
Publications and source records attributed to E. Christova.
We calculate the CP-violating rate asymmetry of H^\pm decays into tau and neutrino at one loop in the MSSM with complex parameters. We find that the asymmetry is typically of the order of 10^-3, depending mainly on the phases of the trilinear coupling A_τand of the gaugino mass M_1.
Supersymmetric loop contributions can lead to different decay rates of H+\to t\bar b and H-\to b\bar t. We calculate the decay rate asymmetry δ^CP = \frac{Γ(H+\to t\bar b)-Γ(H-\to b\bar t)}{{Γ(H+\to t\bar b)+Γ(H-\to b\bar t)} at next-to-leading order in the MSSM with complex parameters. We analyse the parameter dependence of δ^CP with emphasis on the phases of A_t and A_b. It turns out that the most important contribution comes from the loop with stop, sbottom, and gluino. If this contribution is present, δ^CP can go up to 10-15% for tan(beta)~10, and to ~5% for large values of tan(beta).
Supersymmetric loop contributions can lead to different decay rates of H+\to t\bar b and H-\to b\bar t. We calculate the decay rate asymmetry δ^CP = \frac{Γ(H+\to t\bar b)-Γ(H-\to b\bar t)}{{Γ(H+\to t\bar b)+Γ(H-\to b\bar t)} at next-to-leading order in the MSSM with complex parameters. We analyse the parameter dependence of δ^CP with emphasis on the phases of A_t and A_b. It turns out that the most important contribution comes from the loop with stop, sbottom, and gluino. If this contribution is present, δ^CP can go up to 10-15%.
We extract the pion fragmentation functions and their uncertainties from a judicious choice of e+e- and semi-inclusive DIS data. These are used to study the error propagation in the extraction of polarized parton densities from semi-inclusive DIS asymmetries. We conclude that the uncertainties on polarized PDs have been underestimated in the past.
Analytic expressions for the angular distributions of the $b$-quarks associated with single $t$-quark production in $p \bar p \to W^* \to t \bar b \to b \bar b W$ and of the leptons from the subsequent decay $W \to lν$ are obtained in the laboratory system. CP violation in the $t$-production vertex is assumed. Different angular and total cross section CP violating asymmetries are considered. Relations testing CP violation solely in the $t$-decay vertex are also obtained. A numerical analysis is performed in the MSSM with a CP violating phase of the trilinear coupling $A_{\tilde t}$. The asymmetries are typically of the order $10^{-3}$ - $10^{-4}$.
By combining recent HERMES data on semi-inclusive DIS $π^\pm$-production with the singlet fragmentation function $D_Σ^{π^+}$, which is well determined from $e^+e^-$ data, we are able to extract, for the first time, the flavoured fragmentation functions $D_u^{π^+}$, $D_d^{π^+}$ and $D_s^{π^+}$ without making any assumptions about favoured and unfavoured transitions. Whereas $D_u^{π^+}$ and $D_d^{π^+}$ are very well determined, the accuracy of $D_s^{π^+}$ is limited by the uncertainty in evolving $D_Σ^{π^+}$ from the $Z^0$ pole down to the SIDIS scale of a few $(GeV)^2$. We discuss how the precision on $D_s^{π^+}$ could be improved. Knowledge of the $D_{q=u,d,s}^{π^+}$ will permit the extraction of the polarized parton densities from future polarized SIDIS asymmetry measurements. We study the precision that can be expected in such an extraction.
We discuss how to extract the polarized parton densities and fragmentation functions in a model independent way from SIDIS, and present results for D_{u,d,s}^{π^+}.
The energy spectra of the b and bbar quarks in e+e- -> t tbar with t -> b W (tbar -> bbar W) are calculated assuming CP violation in the production process. Expressions for the corresponding CP violating asymmetries and optimal observables that determine the imaginary parts of the electric and weak dipole moment form factors of the top are derived. It is shown that polarization of the initial lepton beams is essential to disentangle Im d^γ(s) and Im d^{Z}(s). Numerical results are given in the Minimal Supersymmetric Standard Model with complex phases.
We obtain analytical formulae for the cross section and the angular distributions of the b(bbar) quarks in the process e+e- -> t tbar, with t -> W+ b (tbar -> W- bbar) assuming CP violation in the γt tbar and Z t tbar vertices. We present CP violating asymmetries, which measure separately the real and imaginary parts of the electroweak dipole moment form factors of the top, d^γ(s) and d^{Z}(s). We give a numerical analysis of these asymmetries within the Minimal Supersymmetric Standard Model with complex parameters. They turn out to be of order <= 10^{-3}.
The CP violating electric and weak dipole moment form factors of the top quark appear in the process $e^{+}e^{-} --> t\bar{t}$. We present a complete analysis of these dipole moment form factors within the Minimal Supersymmetric Standard Model with complex parameters. We include gluino, chargino, and neutralino exchange in the loop of the $γt\bar{t}$ and $Z t\bar{t}$ vertex. We give the analytic expressions and present numerical results.
The CP violating electric and weak dipole moment form factors of the top quark, $\dgs$ and $\dzs$, appear in the process \mbox{$e^{+}e^{-} \to t \bar{t}$}. We present a complete analysis of these dipole moment formfactors within the Minimal Supersymmetric Standard Model with complex parameters. We include gluino, chargino, and neutralino exchange in the loop of the \mbox{$γt\bar{t}$} and \mbox{$Z t\bar{t}$} vertex. We give analytic expressions and present numerical results for the asymmetries that measure these formfactors.
We present a complete analysis of the electrtic and weak dipole moment form factors of the top quark within the Minimal Supersymmetric Standard Model with complex parameters. We include gluino, chargino, and neutralino exchange in the loops of the $γt\bar{t}$ and $Z t\bar{t}$ vertices.
We obtain analytic formulae for the cross section of the sequential processes of $e^+ e^- \to t \bar t$ and $t \to b l ν$ in the laboratory frame where the dependence on triple product correlations of the type ($\hat(q}_1 x \hat{q}_2 . \hat{q}_3$), induced by CP violation both in the production and the decay are explicitely shown. Different observables sensitive to CP violation are defined and calculated in the Minimal Supersymmetric Standard Model (MSSM). The observables sensitive to CP violation are of the order of $10^-3$. The dependence on the masses of the supersymmetric particles is also shown.
The minimal supersymmetric extension of the standard model allows for some of the coupling strengths to be complex parameters. The presence of such imaginary phases can lead to violations of time reversal invariance, which can be tested if correlations in products of an odd number of polarizations and momenta are measured and found to be different from zero. As an example, we consider the triple product $\mbox{\bf J} \cdot \left(\mbox{\bf p}_1 \times \mbox{\bf p}_ {2} \right)$ in the $β$-decay of the neutron, of the $Σ^-$, and in the decay $K^{+}_{3μ}$. For these low-energy decays, we find that the present experimental precision is not enough to provide useful bounds on combinations of such phases and the masses of the supersymmetric particles. At higher energies, the same time reversal violating correlation in the semileptonic decay of the $t$ quark is of the order of $α_s/π$, made bigger by the large mass of the decaying quark.
T-odd correlations of polarizations and momenta provide a promising testing ground for new physics beyond the standard model. We estimate the contribution of the minimal supersymmetric extension of the standard model to two such observables: in the production of $t\bar{t}$, we look for a term proportional to \mbox{${\bf J}_t \cdot ({\bf p}_q \times {\bf p}_{t})$}-where {\bf J}$_t$ is the polarization of the $t$ quark and {\bf p} $_{q,t}$ are the momenta of the initial and final particles-and find that it is of the order of $10^{-1} \times (α_s/π)$. In the production of $W^+W^-$, we look for a term proportional to \mbox{${\bf E}_W \cdot ({\bf p}_q \times {\bf p}_{W})({\bf p}_q \cdot {\bf E}_W)$}-where {\bf E}$_W$ is the transverse polarization of W- to find that it can be as large as $10^{-1} \times (α_w/π)$.