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

The most general form of the $WWZ$ and $WW\gamma$ 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.Comment: 7 pages, LaTeX file, 5 ps figure

Neutralino Relic Density with a Cosmological Constant confronts Electroweak Precision Measurements

We discuss the relic density of the lightest of the supersymmetric particles ({\small LSP}) in view of new cosmological data, which favour the concept of an accelerating Universe with a non-vanishing cosmological constant. The new bound on the Cold Dark Matter density, $\Omega_{\mathrm{CDM}} h_0^2 \lesssim 0.22$, puts stringent constraints on supersymmetry preferring low supersymmetry breaking scales, in sharp contrast to electroweak precision measurements favouring large supersymmetry breaking scales. Supersymmetric predictions are in agreement with cosmological data and electroweak precision data in the window of the parameter space: m_0<200\GeV, 300\GeV, putting bounds on sparticle masses, which may be evaded if $m_{LSP} <m_{{\tilde{\tau}}_R} \lesssim 1.2 m_{LSP}$.Comment: 17 pages, LaTeX, 10 Postscript figures; version to appear in Phys. Lett.

Charge asymmetry in two-Higgs doublet models

We discuss the features of a two-Higgs doublet model exhibiting a two stage phase transition. At finite temperatures electric charge violating stationary points are developed. In conjunction with {\em CP} violation in the Higgs or the Yukawa sector, the phase transition to the charge conserving vacuum, generates a net charge asymmetry $\Delta Q$, in the presence of heavy leptons, which may be well above the astrophysical bounds put on $\Delta Q$ unless the heavy leptons are sufficiently massive. This type of transition may be of relevance for supersymmetric extensions of the Standard Model, since it shares the same features, namely two Higgs doublets and similar {\em CP} violating sources.Comment: 20 pages, LaTeX file, 5 eps figures included using epsfig macro. Major revisio

Radiative corrections to single Higgs boson production in e+e−e^+ e^- annihilation

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.

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 $\sim {{ \alpha_s} \over {\pi}} {1 \over 20} { {M^2_W} \over {M_S^2}} \Gamma_{u {\bar d}}$, where $M_S$ is the supersymmetry breaking scale and $\Gamma_{u {\bar d}}$ 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 $\sim {{ \alpha_s} \over {\pi}} \Gamma_{u {\bar d}}$ 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.Comment: 7 pages, LaTeX file with 2 figures, uses epsf macro

Single Higgs boson production at future linear colliders including radiative corrections

The next generation of high energy e+ e- linear colliders is expected to operate at \sqrt{s} \gtsim 500 GeV. In this energy range the WW fusion channel dominates the Higgs boson production cross section e+ e- -> \bar\nu \nu h^0/H^0. We calculate the one-loop corrections to this process due to fermion and sfermion loops within the MSSM. We perform a detailed numerical analysis of the total cross section and the distributions of the rapidity, the transverse momentum and the production angle of the Higgs boson. The fermion-sfermion correction is substantial being of the order of -10% and is dominated by the fermion loops. In addition, we explore the possibility of polarized e+ / e- beams. In the so-called "intense coupling" scenario the production of the heavy Higgs boson H^0 is also discussed.Comment: 23 pages, 9 figures, to be published in Nucl. Phys.

Refining the predictions of supersymmetric CP-violating models: A top-down approach

We explore in detail the consequences of the CP-violating phases residing in the supersymmetric and soft SUSY breaking parameters in the approximation that family flavour mixings are ignored. We allow for non-universal boundary conditions and in such a consideration the model is described by twelve independent CP-violating phases and one angle which misaligns the vacuum expectation values (VEVs) of the Higgs scalars. We run two-loop renormalization group equations (RGEs), for all parameters involved, including phases, and we properly treat the minimization conditions using the one-loop effective potential with CP-violating phases included. We show that the two-loop running of phases may induce sizable effects for the electric dipole moments (EDMs) that are absent in the one-loop RGE analysis. Also important corrections to the EDMs are induced by the Higgs VEVs misalignment angle which are sizable in the large tanb region. Scanning the available parameter space we seek regions compatible with accelerator and cosmological data with emphasis on rapid neutralino annihilations through a Higgs resonance. It is shown that large CP-violating phases, as required in Baryogenesis scenarios, can be tuned to obtain agreement with WMAP3 cold dark matter constraints, EDMs and all available accelerator data, in extended regions of the parameter space which may be accessible to LHC.Comment: 41 pages, 22 eps figures. A reference added and a typo corrected; version to appear in JHE

Trilinear Gauge Boson Couplings in the MSSM

We study the C and P even WW\gamma and 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.Comment: 16 pages, late

Implications of the pseudo-scalar Higgs boson in determining the neutralino dark matter

In the framework of the constrained minimal supersymmetric standard model (CMSSM) we discuss the impact of the pseudo-scalar Higgs boson in delineating regions of the parameters which are consistent with cosmological data and E821 data on the anomalous magnetic moment of the muon. For the large values of the parameter tan β &amp;gt; 50, cosmologically allowed corridors of large m 0, M1/2 are opened, due to the s-channel pseudo-scalar exchange in the pair annihilation of the lightest of the neutralinos to bb̄ or ττ̄, which dominates in this region. However, no such corridors are found for values tan β &amp;lt; 50. Combining cosmological and E821 data puts severe upper limits on the sparticle masses. We find that at LHC, but even at a e+e- linear collider with center of mass energy s1/2 = 800 GeV, such as TESLA, supersymmetry can be discovered, if it is based on the CMSSM

Dilaton dominance relaxes LHC and cosmological constraints in supersymmetric models

It has been pointed out recently that the presence of dilaton field in the early Universe can dilute the neutralino dark matter (DM) abundance, if Universe is not radiation dominated at DM decoupling, due to its dissipative-like coupling to DM. In this scenario two basic mechanisms compete, the modified Hubble expansion rate tending to increase the relic density and a dissipative force that tends to decrease it. The net effect can lead to an overall dramatic decrease of the predicted relic abundance, sometimes by amounts of the order of O(102) or so. This feature is rather generic, independent of any particular assumption on the underlying string dynamics, provided dilaton dominates at early eras after the end of inflation but before Big Bang Nucleosynthesis (BBN). The latter ensures that BBN is not upset by the presence of the dilaton. In this paper, within the context of such a scenario, we study the phenomenology of the constrained minimal supersymmetric model (CMSSM) by taking into account all recent experimental constraints, including those from the LHC searches. We find that the allowed parameter space is greatly enlarged and includes regions that are beyond the reach of LHC. The allowed regions are compatible with Direct Dark Matter searches since the small neutralino annihilation rates, that are now in accord with the cosmological data on the relic density, imply small neutralinonucleon cross sections below the sensitivities of the Direct Dark Matter experiments. It is also important that the new cosmologically accepted regions are compatible with Higgs boson masses larger than 120GeV, as it is indicated from the LHC experimental data. The smaller annihilation cross sections needed to explain WMAP data require that the detector performances of current and planned indirect DM search experiments through γ-rays should be greatly improved in order to probe the CMSSM regions. © 2012 SISSA