Radiative corrections to the semileptonic and hadronic Higgs-boson decays H -> W W/Z Z -> 4 fermions

The radiative corrections of the strong and electroweak interactions are calculated for the Higgs-boson decays H -> WW/ZZ -> 4f with semileptonic or hadronic four-fermion final states in next-to-leading order. This calculation is improved by higher-order corrections originating from heavy-Higgs-boson effects and photonic final-state radiation off charged leptons. The W- and Z-boson resonances are treated within the complex-mass scheme, i.e. without any resonance expansion or on-shell approximation. The calculation essentially follows our previous study of purely leptonic final states. The electroweak corrections are similar for all four-fermion final states; for integrated quantities they amount to some per cent and increase with growing Higgs-boson mass M_H, reaching 7-8% at M_H \sim 500 GeV. For distributions, the corrections are somewhat larger and, in general, distort the shapes. Among the QCD corrections, which include corrections to interference contributions of the Born diagrams, only the corrections to the squared Born diagrams turn out to be relevant. These contributions can be attributed to the gauge-boson decays, i.e. they approximately amount to \alpha_s/\pi for semileptonic final states and 2\alpha_s/\pi for hadronic final states. The discussed corrections have been implemented in the Monte Carlo event generator PROPHECY4F.Comment: 29 pages, LaTeX, 30 postscript figure

Lepton flavour violation in future linear colliders in the long-lived stau NLSP scenario

We analyze the prospects of observing lepton flavour violation in future e-e- and e+e- linear colliders in scenarios where the gravitino is the lightest supersymmetric particle, and the stau is the next-to-lightest supersymmetric particle. The signals consist of multilepton final states with two heavily ionizing charged tracks produced by the long-lived staus. The Standard Model backgrounds are very small and the supersymmetric backgrounds can be kept well under control by the use of suitable kinematical cuts. We discuss in particular the potential of the projected International Linear Collider to discover lepton flavour violation in this class of scenarios, and we compare the estimated sensitivity with the constraints stemming from the non-observation of rare decays.Comment: 30 pages, 12 figures. Discussion extended to include the efficiency of identifying long-lived staus, references added. To appear in JHE

Radiative corrections to scalar-fermion pair production in high energy e+e- collisions

We study the one-loop radiative corrections to pair production of the supersymmetric scalar partners of the standard fermions in e+e- annihilation. Both electroweak and SUSY-QCD corrections are considered. Applications are for production of scalar fermions of the third generation, e^+e^-\to \wt{f}_i \wt{f}_j^* (i,j=1,2), $f=t, b,\tau$, as well as for production of scalar quarks of the first and second generation. Effects on integrated cross sections are discussed and also the one-loop induced forward-backward asymmetries are studied. It is found that at low energy, \sqrt{s}\approx 500 \to 1000 GeV, the corrections are dominated by the QCD contributions, At high energy, $\sqrt{s}\geq 2$ TeV, the electroweak box diagrams give a substantial contribution and even dominate in some regions of parameters space. The purely loop-induced forward-backward asymmetry can reach values of several per cent.Comment: 23 pages, latex, 13 figure

A T-odd asymmetry in neutralino production and decay

We study CP-violating effects in neutralino production and subsequent decay within the Minimal Supersymmetric Standard Model with complex parameters M_1 and mu. The observable we propose is a T-odd asymmetry based on a triple product in neutralino production e^+ e^- -> tilde{chi}^0_i tilde{chi}^0_2, i = 1,...,4, with subsequent leptonic three-body decay tilde{chi}^0_2 -> tilde{chi}^0_1 l^+ l^-, l = e, mu, at an e^+ e^- linear collider with sqrt{s} = 500 GeV and polarised beams. We provide compact analytical formulae for the cross section and the T-odd asymmetry taking into account the complete spin correlations between production and decay. We give numerical predictions for the cross section and the T-odd asymmetry. The asymmetry can go up to 10 %.Comment: 28 pages, LaTeX, 10 figures; v2: typos corrected, published versio

Photon emission by an ultra-relativistic particle channeling in a periodically bent crystal

This paper is devoted to a detailed analysis of the new type of the undulator radiation generated by an ultra-relativistic charged particle channeling along a crystal plane, which is periodically bent by a transverse acoustic wave, as well as to the conditions limiting the observation of this phenomenon. This mechanism makes feasible the generation of electromagnetic radiation, both spontaneous and stimulated, emitted in a wide range of the photon energies, from X- up to gamma-rays

Radiative production of invisible charginos in photon photon collision

If in a supersymmetric model, the lightest chargino is nearly degenerate with the lightest neutralino, the former can decay into the latter alongwith a soft pion (or a lepton-neutrino pair). Near degeneracy of the chargino and neutralino masses can cause the other decay products (the pion or the lepton) to be almost invisible. Photon-photon colliders offer a possibility of clean detection of such an event through a hard photon tag.Comment: 12 pages, 5 postscript figure

Non-universal gauge boson Z′Z' and the spin correlation of top quark pair production at e−e+e^{-}e^{+} colliders

In the off-diagonal basis, we discuss the contributions of the non-universal gauge boson $Z'$ predicted by the topcolor-assisted technicolor ($TC2$) model to the spin configurations and the spin correlation observable of the top quark pair production via the process $e^{-}e^{+}\to t\bar{t}$. Our numerical results show that the production cross sections for the like-spin states, which vanish in the standard model, can be significantly large as $M_{Z'}\approx \sqrt{S}$. With reasonable values of the $Z'$ mass $M_{Z'}$ and the coupling parameter $k_{1}$, $Z'$ exchange can generate large corrections to the spin correlation observable.Comment: 16 pages, 5 figure

Higgs boson pair production process e+e−→ZHHe^+e^-\to ZHH in the littlest Higgs model at the ILC

The physics prospect at future linear $e^{+}e^{-}$ colliders for the study of the Higgs triple self-coupling via the process of $e^{+}e^{-}\to ZHH$ is investigated. In this paper, we calculate the contribution of the new particles predicted by the littlest Higgs model to the cross sections of this process in the future high energy $e^{+}e^{-}$ collider($ILC$). The results show that, in the favorable parameter spaces preferred by the electroweak precision, the deviation of the total cross sections from its $SM$ value varies from a few percent to tens percent, which may be detected at the future $ILC$ experiments with $\sqrt{s}$=500GeV.Comment: 13 pages,4 figure

Constraining Supersymmetry

We review constraints on the minimal supersymmetric extension of the Standard Model (MSSM) coming from direct searches at accelerators such as LEP, indirect measurements such as b -> s gamma decay and the anomalous magnetic moment of the muon. The recently corrected sign of pole light-by-light scattering contributions to the latter is taken into account. We combine these constraints with those due to the cosmological density of stable supersymmetric relic particles. The possible indications on the supersymmetric mass scale provided by fine-tuning arguments are reviewed critically. We discuss briefly the prospects for future accelerator searches for supersymmetry.Comment: 21 LaTeX pages, 9 eps figures, Invited Contribution to the New Journal of Physics Focus Issue on Supersymmetr

Properties of the Volume Operator in Loop Quantum Gravity I: Results

We analyze the spectral properties of the volume operator of Ashtekar and Lewandowski in Loop Quantum Gravity, which is the quantum analogue of the classical volume expression for regions in three dimensional Riemannian space. Our analysis considers for the first time generic graph vertices of valence greater than four. Here we find that the geometry of the underlying vertex characterizes the spectral properties of the volume operator, in particular the presence of a `volume gap' (a smallest non-zero eigenvalue in the spectrum) is found to depend on the vertex embedding. We compute the set of all non-spatially diffeomorphic non-coplanar vertex embeddings for vertices of valence 5--7, and argue that these sets can be used to label spatial diffeomorphism invariant states. We observe how gauge invariance connects vertex geometry and representation properties of the underlying gauge group in a natural way. Analytical results on the spectrum on 4-valent vertices are included, for which the presence of a volume gap is proved. This paper presents our main results; details are provided by a companion paper arXiv:0706.0382v1.Comment: 36 pages, 7 figures, LaTeX. See also companion paper arXiv:0706.0382v1. Version as published in CQG in 2008. See arXiv:1003.2348 for important remarks regarding the sigma configurations. Subsequent computations have revealed some minor errors, which do not change the qualitative results but modify some of the numbers presented her