Three Jet Events and New Strong Couplings at LEP and NLC

We study the effects of new dimension--6 operators, resulting from a general $SU(3)_C \otimes SU(2)_L \otimes U(1)_Y$ invariant effective Lagrangian, on three jet production at LEP and at the Next Linear Collider. Contributions to the total event rate and to some event shape variables are analysed in order to establish bounds on these operators.Comment: 5 pages, LaTeX, 1 Figur

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

Testing Anomalous Higgs Couplings in Triple Photon Production at the Tevatron Collider

We derive bounds on Higgs and gauge--boson anomalous interactions using the CDF data for the process $p \bar{p} \to \gamma\gamma\gamma + X$. We use a linearly realized $SU_L(2) \times U_Y(1)$ invariant effective Lagrangian to describe the bosonic sector of the Standard Model, keeping the fermionic couplings unchanged. All dimension--six operators that lead to anomalous Higgs interactions involving $\gamma$ and $Z$ are considered. We also show the sensitivity that can be achieved for these couplings at Fermilab Tevatron upgrades.Comment: 13 pages, RevTeX, 2 figures included using epsfi

Quartic Anomalous Couplings in eγe\gamma Colliders

We study the production of gauge boson pairs at the next generation of linear $e^+e^-$ colliders operating in the $e\gamma$ mode. The processes $e\gamma \rightarrow VV^\prime F$ ($V,V^\prime =W$, $Z$, or $\gamma$ and $F=e$ or $\nu$) can give valuable information on possible deviations of the quartic vector boson couplings from the Standard Model predictions. We establish the range of the new couplings that can be explored in these colliders based on a $3\sigma$ effect in the total cross section. We also present several kinematical distributions of the final state particles that could manifest the underlying new dynamics. Our results show that an $e\gamma$ collider can extend considerably the bounds on anomalous interactions coming from oblique radiative corrections and from direct searches in $e^+e^-$ colliders.Comment: 21 pages and 7 figures appended as a postscript file (uuencoded), MAD/PH/764, IFT-P.031/93, IFUSP-P 1047 (uses REVTeX3

Searching for Leptoquarks in electron-photon Collisions

We study the production of composite scalar leptoquarks in $e\gamma$ colliders, and we show that an $e^+e^-$ machine operating in its $e\gamma$ mode is the best way to look for these particles in $e^+e^-$ collisions, due to the hadronic content of the photon.Comment: 12 pages in REVTeX3. 6 figures appended as postcript files. Report: IFT-P.014/93 and IFUSP-P 104

Probing Higgs Couplings in e^+ e^- \to \gamma\gamma\gamma

We investigate the existence of anomalous Higgs boson couplings, $H\gamma\gamma$ and $HZ\gamma$, through the analysis of the process $e^+ e^- \to \gamma\gamma\gamma$ at LEP2 energies. We suggest some kinematical cuts to improve the signal to background ratio and determine the capability of LEP2 to impose bounds on those couplings by looking for a Higgs boson signal in this reaction.Comment: 12 pages, RevTeX, 9 embedded figure

Excited Fermion Contribution to Z Physics at One Loop

We investigate the effects induced by excited leptons at the one-loop level in the observables measured on the $Z$ peak at LEP. Using a general effective Lagrangian approach to describe the couplings of the excited leptons, we compute their contributions to both oblique parameters and $Z$ partial widths. Our results show that the new effects are comparable to the present experimental sensitivity, but they do not lead to a significant improvement on the available constraints on the couplings and masses of these states.Comment: 25 pages 6 figure

Two-photon final states in peripheral heavy ion collisions

We discuss processes leading to two photon final states in peripheral heavy ion collisions at RHIC. Due to the large photon luminosity we show that the continuum subprocess $\gamma \gamma \to \gamma \gamma$ can be observed with a large number of events. We study this reaction when it is intermediated by a resonance made of quarks or gluons and discuss its interplay with the continuum process, verifying that in several cases the resonant process ovewhelms the continuum one. It is also investigated the possibility of observing a scalar resonance (the $\sigma$ meson) in this process. Assuming for the $\sigma$ the mass and total decay width values recently reported by the E791 Collaboration we show that RHIC may detect this particle in its two photon decay mode if its partial photonic decay width is of the order of the ones discussed in the literature.Comment: 10 pages, 8 figure

Spinor formalism for massive fields with half-integral spin

In this article, we extend the %Weyl-van der Waerden spinor technique for calculating helicity amplitudes to general massive fields of half-integer spins. We find that the little group generators can be represented as first-order differential operators in the spinor formalism. We use the spinor forms of the generators to get the explicit form of the massive fields of any spin and any helicity. We also deal with the three-particle S-matrix by these spinor form generators, and find that we are able to extend the explicit form of the three-particle vertex obtained by Benincasa and Cachazo to the massive case. We present the explicit expressions for the amplitudes with external particles of the lowest helicities up to -3/2. Group theory, in the form of raising operators of the little group, then dictates other amplitudes with higher helicity in the same spin multiplets. The formalism allows, in principle, to determine the electromagnetic form-factors of charged particles of arbitrary helicities, without additional assumptions about the underlying lagrangian. We find that restrictions which follow from gauge and Lorentz invariance are nearly as restrictive as in the massless case.Comment: 21 pages, 1 figure