arXiv subjects

V. C. Spanos

Publications and source records attributed to V. C. Spanos.

23 records · Page 2Linked to original sources

arXiv1996

Supersymmetric QCD corrections to the W-boson width

We calculate the one-loop supersymmetric QCD corrections to the width of the $W$-boson. We find that these are of order $\sim {{ α_s} \over π} {1 \over 20} { {M^2_W} \over {M_S^2}} Γ_{u {\bar d}}$, where $M_S$ is the supersymmetry breaking scale and $ Γ_{u {\bar d}}$ the tree level hadronic width for $W^+ \rightarrow u {\bar d} $. Due to the appearance of the suppression factor $\sim {1 \over 20}$ these are at least two orders of magnitude smaller than the standard QCD corrections $\sim {{ α_s} \over π} Γ_{u {\bar d}}$ and hence of the order of the two-loop electroweak effects. Therefore supersymmetric QCD corrections will only be of relevance once experiments reach that level of accuracy.

hep-ph↗

arXiv1996

Constraining a CP-violating WWV coupling from the W^+W^- threshold cross section at LEP2

The most general form of the $WWZ$ and $WWγ$ interaction contains a $CP$-violating term which has the same threshold behaviour as the Standard Model $\ee \to \ww$ cross section. We calculate the cross section as a function of the corresponding anomalous coupling, and estimate the bounds which can be obtained from a measurement of the threshold cross section at LEP2. We show how the effect of the coupling is most pronounced in the angular distributions of the final-state fermions.

hep-ph↗

arXiv1996

Trilinear Gauge Boson Couplings in the MSSM

We study the C and P even WWγand WWZ trilinear gauge boson vertices (TGV's), in the context of the MSSM assuming that the external W's are on their mass shell. We find that for energies less than 200 GeV squark and slepton contributions to the aforementioned couplings are two orders of magnitude smaller than those of the Standard Model (SM). In the same energy range the bulk of the supersymmetric Higgs corrections to the TGV's is due to the lightest neutral Higgs, h_0, whose contribution is like that of a Standard Model Higgs of the same mass. The contributions of the Neutralinos and Charginos are sensitive to the input value for the soft gaugino mass M_{1/2}, being more pronounced for values M_{1/2} < 100 GeV. In this case and in the unphysical region, 0 < \sqrt{s} < 2 M_W , their contributions are substantially enhanced resulting in large corrections to the static quantities of the W boson. However, such an enhancement is not observed in the physical region. In general for 2 M_W < \sqrt{s} < 200 GeV the MSSM predictions differ from those of the SM but they are of the same order of magnitude. To be detectable deviations from the SM require sensitivities reaching the per mille level and hence unlikely to be observed at LEP200. For higher energies SM and MSSM predictions exhibit a fast fall off behaviour, in accord with unitarity requirements, getting smaller,in most cases, by almost an order of magnitude already at energies \sqrt{s} 0.5 TeV.

hep-ph↗

arXiv1995

Trilinear Gauge Boson Vertices in the MSSM

We study the $C$ and $P$ even $WWγ$ and $WWZ$ trilinear gauge boson vertices (TGV's), in the context of the MSSM as functions of the soft SUSY breaking parameters $A_0, m_0, M_{1/2}$ and the momentum $q$ carried by $γ, Z$, assuming the external $W$'s are on their mass shell. We follow a complete renormalization group analysis taking into account all constraints imposed by the radiative breaking of the electroweak symmetry. It is found that for energies ${\sqrt{s}} \equiv q^2 \le 200 \; GeV$ squark and slepton contributions to the aforementioned couplings are two orders of magnitude smaller than those of the Standard Model (SM). In the same energy range the bulk of the supersymmetric Higgs corrections to the TGV's is due to the lightest neutral Higgs, $h_0$, whose contribution is like that of a Standard Model Higgs of the same mass. The rest have negligible effect due to their heaviness. The contributions of the Neutralinos and Charginos are sensitive to the input value for the soft gaugino mass $M_{1/2}$ being more pronounced for values $M_{1/2} < 100 \; GeV$. In this case and in the unphysical region, $0 < \sqrt{s} < 2 M_W $ their contributions are substantially enhanced resulting to large corrections to the static quantities of the $W$ boson. However such an enhancement is not observed in the physical region and their corrections to the TGV's are rather small. In general for $2 M_W < \sqrt{s} < 200 \; GeV $ the MSSM predictions differ from those of the SM but they are of the same order of magnitude. Deviations from the SM predictions to be detectable require sensitivities reaching the per mille level and hence unlikely to be observed at LEP200. For higher energies SM and MSSM predictions exhibit a fast fall off behaviour, in accord with unitarity requirements, getting smaller by almost an

hep-ph↗

arXiv1994

Static Quantities of the W-Boson in the MSSM

We systematically analyze the anomalous dipole $Δk_γ$ and quadrupole $ΔQ_γ$ moments of the W gauge bosons in the context of the minimal supersymmetric standard model as functions of the soft SUSY breaking parameters $A_0,m_0,M_{1/2}$ and the top quark mass. The severe constraints imposed by the radiative breaking mechanism of the electroweak symmetry\,$ SU(2)\times U(1)$\, are duly taken into account. The supesymmetric values of $Δk_γ$ and $ΔQ_γ$ can be largely different, in some cases, from the standard model predictions but of the same order of magnitude for values of \quad $A_0,m_0,M_{1/2} \leq {\cal O}(1 TeV) $. Therefore possible supersymmetric structure can be probed provided the accuracy of measurements for $Δk_γ$, $ΔQ_γ$ reaches $10^{-2}-10^{-3}$ and hence hard to be detected at LEP2. If deviations from the standard model predictions are observed at LEP2, most likely these are not due to an underlying supersymmetric structure. In cases where $M_{1/2} \ll A_0,m_0 $, the charginos and neutralinos may give substantial contributions saturating the LEP2 sensitivity limits. This occurs when their masses $m_{\tilde C},m_{\tilde Z}$ turn out to be both light satisfying $m_{\tilde C}+m_{\tilde Z} \simeq M_W $. However these extreme cases are perturbatively untrustworthy and besides unnatural for they occupy a small region in the parameter space. }

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