Probing Intermediate Mass Higgs Interactions at the CERN Large Hadron Collider

We analyze the potentiality of the CERN Large Hadron Collider to probe the Higgs boson couplings to the electroweak gauge bosons. We parametrize the possible deviations of these couplings due to new physics in a model independent way, using the most general dimension--six effective lagrangian where the SU(2)_L x U(1)_Y is realized linearly. For intermediate Higgs masses, the decay channel into two photons is the most important one for Higgs searches at the LHC. We study the effects of these new interactions on the Higgs production mechanism and its subsequent decay into two photons. We show that the LHC will be sensitive to new physics scales beyond the present limits extracted from the LEP and Tevatron physics.Comment: 13 pages, 1 figure included using epsfig, RevTe

Bounds on Higgs and Gauge--Boson Interactions from LEP2 Data

We derive bounds on Higgs and gauge--boson anomalous interactions using the LEP2 data on the production of three photons and photon pairs in association with hadrons. In the framework of $SU(2)_L \otimes U(1)_Y$ effective Lagrangians, we examine all dimension--six operators that lead to anomalous Higgs interactions involving $\gamma$ and $Z$. The search for Higgs boson decaying to $\gamma\gamma$ pairs allow us to obtain constrains on these anomalous couplings that are comparable with the ones originating from the analyses of $p\bar{p}$ collisions at the Tevatron. Our results also show that if the coefficients of all ``blind'' operators are assumed to have same magnitude, the indirect constraints on the anomalous couplings obtained from this analyses, for Higgs masses $M_H \lesssim$ 140 GeV, are more restrictive than the ones coming from the $W^+W^-$ production.Comment: 14 pages Latex file using RevTeX, 3 figures as .eps file

Bosonic Quartic Couplings at LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study anomalous quartic vector-boson interactions Z Z gamma gamma, Z Z Z gamma, W+ W- gamma gamma, and W+ W- Z gamma through the weak boson fusion processes q q -> q q gamma gamma and q q -> q q gamma Z(-> l+ l-) with l = electron or muon. After a careful study of the backgrounds and how to extract them from the data, we show that the process p p -> j j gamma l+ l- is potentially the most sensitive to deviations from the Standard Model, improving the sensitivity to anomalous couplings by up to a factor 10^4 (10^2) with respect to the present direct (indirect) limits.Comment: 18 pages, 2 figures, revised versio

Scrutinizing the ZW+W- vertex at the Large Hadron Collider at 7 TeV

We analyze the potential of the CERN Large Hadron Collider running at 7 TeV to search for deviations from the Standard Model predictions for the triple gauge boson coupling ZW+W- assuming an integrated luminosity of 1 fb^{-1}. We show that the study of W+W- and W^\pm Z productions, followed by the leptonic decay of the weak gauge bosons can improve the present sensitivity on the anomalous couplings \Delta g_1^Z, \Delta \kappa_Z, \lambda_Z, g_4^Z, and \tilde{\lambda}_Z at the 2\sigma level.Comment: 12 pages, 3 figures. One reference added, matches published versio

Tests of Higgs Boson Couplings at a mu+mu- Collider

We investigate the potential of a muon collider for testing the presence of anomalous Higgs boson couplings. We consider the case of a light (less than $160 GeV$) Higgs boson and study the effects on the Higgs branching ratios and total width, which could be induced by the non standard couplings created by a class of dim=6 $SU(3)\times SU(2)\times U(1)$ gauge invariant operators satisfying the constraints imposed by the present and future hadronic and $e^-e^+$ colliders. For each operator we give the minimal value of the $\mu^+\mu^-$ integrated luminosity needed for the muon collider ($\mu C$) to improve these constraints. Depending on the operator and the Higgs mass, this minimal $\mu C$ luminosity lies between $0.1 fb^{-1}$ and $100 fb^{-1}$.Comment: 18 pages and 4 figures; version to be published in Phys. Rev.D. e-mail: [email protected]

Constraints on Quartic Vector-Boson Interactions from Z Physics

We obtain the constraints on possible anomalous quartic vector-boson vertices arising from the precision measurements at the $Z$ pole. In the framework of $SU(2)_L \otimes U(1)_Y$ chiral Lagrangians, we examine all effective operators of order $D=4$ that lead to four-gauge-boson interactions but do not induce anomalous trilinear vertices. We constrain the anomalous quartic interactions by evaluating their one-loop corrections to the $Z$ pole physics. Our analysis is performed in a generic $R_\xi$ gauge and it shows that only the operators that break the $SU(2)_C$ custodial symmetry get limits close to the theoretical expectations. Our results also indicate that these anomalous couplings are already out of reach of the Next Linear $e^+ e^-$ Collider, while the Large Hadron Collider could be able to further extend the bounds on some of these couplings.Comment: 16 pages, 1 Postscript figures, uses RevTex and eps.st

R--Parity Violating Signals for Chargino Production at LEP II

We study chargino pair production at LEP II in supersymmetric models with spontaneously broken R-parity. We perform signal and background analyses, showing that a large region of the parameter space of these models can be probed through chargino searches at LEP II. In particular, we determine the attainable limits on the chargino mass as a function of the magnitude of the effective bilinear R-parity violation parameter $\epsilon$, demonstrating that LEP II is able to unravel the existence of charginos with masses almost up to its kinematical limit even in the case of R-parity violation. This requires the study of several final state topologies since the usual MSSM chargino signature is recovered as $\epsilon \to 0$. Moreover, for sufficiently large $\epsilon$ values, for which the chargino decay mode $\chi^\pm \to \tau^\pm J$ dominates, we find through a dedicated Monte Carlo analysis that the $\chi^\pm$ mass bounds are again very close to the kinematic limit. Our results establish the robustness of the chargino mass limit, in the sense that it is basically model-independent. They also show that LEP II can establish the existence of spontaneous R-parity violation in a large region of parameter space should charginos be produced.Comment: improved analyses; 31 pages and 9 figures (included

Anomaly Mediated Supersymmetry Breaking without R-Parity

We analyze the low energy features of a supersymmetric standard model where the anomaly--induced contributions to the soft parameters are dominant in a scenario with bilinear $R$--parity violation. This class of models leads to mixings between the standard model particles and supersymmetric ones which change the low energy phenomenology and searches for supersymmetry. In addition, $R$--parity violation interactions give rise to small neutrino masses which we show to be consistent with the present observations.Comment: 38 pages, 15 figures. For higher resolution figures go to http://www.fma.if.usp.br/~magro/figures

Searching for an Invisibly Decaying Higgs Boson in E^+E^-, E-Gamma, and Gamma-Gamma Collisions

Higgs bosons can have a substantial ``invisible'' branching ratio in many extensions of the Standard Model, such as models where the Higgs bosons decay predominantly into light or massless weakly interacting Goldstone bosons. In this work, we examine the production mechanisms and backgrounds for invisibly decaying Higgs bosons at the Next Linear $e^+e^-$ Collider operating in the modes $e^+e^-$, $e\gamma$, and $\gamma\gamma$. We demonstrate that such machine is much more efficient to survey for invisibly decaying Higgs bosons than the Large Hadron Collider at CERN.Comment: (LaTex file, 9 figures in postcript available upon request. MAD/PH/81