arXiv subjects

F. M. Renard

Publications and source records attributed to F. M. Renard.

122 records · Page 7Linked to original sources

arXiv1995

Anomalous Couplings in Single Higgs Production through $γγ$ Collisions

We show that single Higgs production in $γγ$ collisions through laser backscattering provides the best way to look for New Physics (NP) effects inducing anomalous Higgs couplings. Our analysis is based on the four $dim=6$ operators $Ø_{UB}$, $Ø_{UW}$, $\olØ_{UB}$ and $\olØ_{UW}$ which describe New Physics effects in this sector. Using the Higgs production rate we establish observability limits for the couplings of the aforementioned operators at a level of $10^{-3}$, which means establishing lower bounds on the scale of NP of the order 30 to 200 TeV. Higgs branching ratios, especially the ratio $Γ(H\toγγ)/Γ(H\toγZ)$, are shown to provide powerful ways to disentangle the effects of the various operators.

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arXiv1995

Signatures of anomalous coupling in boson pair production through γγcollisions

We discuss possible New Physics (NP) effects on the processes $γγ\to W^+W^-$, $ZZ$, $Zγ$, $γγ$, $HH$ which are observable in $γγ$ collisions. Such collisions may be achieved through laser backscattering at a high energy $e^+e^-$ linear collider. To the extent that no new particles will be directly produced in the future colliders, it has already been emphasized that the new physics possibly hidden in the bosonic interactions, may be represented by the seven $dim=6$ operators $Ø_W$, $Ø_{BΦ}$, $Ø_{WΦ}$, $Ø_{UB}$, $Ø_{UW}$, $\olØ_{UB}$ and $\olØ_{UW}$ (the last two ones being CP-violating). In this paper, we show that the above processes are sensitive to NP scales at the several TeV range, and we subsequently discuss the possibility to disentangle the effects of the various operators.

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arXiv1995

Anomalous Weak Boson Couplings: Suggestions from Unitarity and Dynamics

Taking into account the constraints from LEP1 and lower energy experiments, we identify the seven $SU(2)\times U(1)$ gauge invariant purely bosonic $dim=6$ operators which provide a quite general description of how New Physics could reflect in the bosonic world, if it happens that all new degrees of freedom are too heavy to be directly produced in the future colliders. Five of these operators are CP conserving and the remaining ones are CP violating. We derive the unitarity constraints for the CP violating operators and compare them with the already known constraints for the CP conserving ones. Dynamical renormalizable models are also presented, which partly elucidate what the appearance of each of these operators can teach us on the mechanism of spontaneous gauge symmetry breaking.

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arXiv1995

Residual heavy quark and boson interactions: the role of the $Zb\bar b$ vertex

We establish the most general parametrization of the new physics tested by present precision measurements and possibly responsible for any deviation of the $Z\to b \bar b $ amplitude from its Standard Model result, under the assumption that it is CP symmetric and is induced by degrees of freedom which are too heavy to be ~directly produced at the future Colliders. This is achieved by writing the complete list of the $SU(3)_c\times SU(2) \times U(1) $ gauge invariant and CP symmetric $dim=6$ operators, involving only quarks of the third family and/or bosons. The quark ~containing operators are divided into two classes, according to whether they involve the $t_R$ field or not. Each class contains 14 quark operators. We then proceed to derive the constraints from present precision measurements, on the first class of the 14 $t_R$ involving operators. We show that the $Zb \bar b$ vertex plays a fundamental role to discriminate not only between these operators, but also between this whole scheme and an alternative one like \eg\@ an MSSM description with light chargino and neutral Higgs.

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arXiv1995

The Bosonic Sector of the Electroweak Interactions, Status and Tests at Present and Future Colliders

The status of the Standard Model (SM) is reviewed. We emphazize the fact that in spite of the success of the SM for the descrition of the fermionic sector, the status of the bosonic sector (gauge and scalar) suffers from many theoretical deficiencies and from the lack of empirical support. This situation, which leaves room for several types of extensions or alternatives to SM, strongly motivates the pursue of intense efforts for finding hints of New Physics (NP) effects. We present a phenomenological description valid for energies lying below the NP scale. We discuss the indirect constraints established from high precision tests at LEP1, as well as the direct tests that could be performed at future machines

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arXiv1994

A Probe of New Resonant Structures with Four Fermion Processes at a 1 TeV $e^+e^-$ Collider

Oblique contributions from vector particles that are strongly coupled to the known gauge bosons are calculated for the case of various observables at a 1 TeV $e^+e^-$ collider. Constraints provided by LEP 1 results are taken into account in a model-independent way through a dispersion relation technique. Depending on the assumed theoretical properties, mass limits of several TeV should be observable.

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arXiv1994

Unitarity Constraints for New Physics Induced by dim-6 Operators

We compute the helicity amplitudes for boson-boson scattering at high energy due to the operators $Ø_{BΦ}$, $Ø_{WΦ}$ and $Ø_{UB}$, and we derive the corresponding unitarity bounds. Thus, we provide relations between the couplings of these operators and the corresponding New Physics thresholds, where either unitarity is saturated or new degrees of freedom are excited. We compare the results with those previously obtained for the operators $Ø_W$ and $Ø_{UW}$ and we discuss their implications for direct and indirect tests at present and future colliders. The present treatment completes the study of the unitarity constraints for all blind bosonic operators.

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arXiv1994

Dynamical Scenarios for $SU(2)_c$ Symmetric New Physics Interactions

We study a picture of effective interactions among the $W$ and Higgs bosons which is consistent with the precision tests at present energies, and at the same time allows for large observable New Physics (NP) effects in the bosonic sector. Toy dynamical models containing new heavy particles are used to indicate how such a picture could be created by integrating out the heavy particles. In these models custodial $SU(2)_c$ symmetry is realized at a certain large scale $Λ_{NP}$, either naturally or at a certain limit of a single coupling. In the derivation of the effective lagrangian we keep operators of dimension up to six. These operators involve only the known gauge boson and Higgs particles. They provide a valid description of NP up to an energy scale which is just below the mass of the new heavy degrees of freedom.

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arXiv1994

Higgs Production in $SU(2)_c$ Symmetric Interactions

We study the sensitivity of Higgs production and decay processes to the $SU(2)_c$ symmetric couplings $O_W$ and $O_{UW}$. Remarkable results are obtained in the case of $γγ\to H$ and for certain ratios of Higgs decay widths. We also discuss and complete previous results on unitarity constraints for such couplings.

hep-ph↗

arXiv1994

Information and Discrimination from b Quark Production on Z Resonance

We introduce and define operatively in a model independent way a new ``heavy" b-vertexparameter, $η_b$, that can be derived from the measurement of a special polarization asymmetry for production of b-quarks on Z resonance. We show that the combination of the measurement of $η_b$ with that of a second and previously defined ``heavy" b-vertex parameter $δ_{bV}$ can discriminate a number of models of New Physics that remain associated to different ``trajectories" in the plane of the variations of the two parameters. This is shown in particular for some popular SUSY and technicolor-type models. In general, this discrimination is possible if a measurement of \underline{both} parameters is performed.

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arXiv1993

The Potential of a New Linear Collider for the Measurement of the Trilinear Couplings among the Electroweak Vector Bosons

We study the accuracy to be obtained in measuring trilinear $Z^0W^+W^-$ and $γW^+W^-$ couplings in the reaction $e^+e^- \to W^+W^-$ at "New Linear Collider" energies of $500GeV$ to $1000GeV$. We derive simple scaling laws for the sensitivity in the measurement of these couplings. For most couplings the sensitivity increases as $\sqrt{L\cdot s}$, where $L$ denotes the integrated luminosity and $\sqrt s$ denotes the $e^+e^-$ center-of-mass energy. Detailed investigations based on various fits confirm these scaling laws and show that an accuracy of the order of the standard radiative corrections can be reached at the NLC for the design values of the luminosity.

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arXiv1993

Unitarity Constraints for Transverse Gauge Bosons at LEP and Supercolliders

Using asymptotic helicity amplitudes for Vector-Vector, Vector-Higgs and Higgs-Higgs scattering, we establish the unitarity constraints on the $SU(2)_c$ conserving and $W_μ$ depending interactions, which at sufficiently high energies may create strong forces among the transverse vector boson and Higgs states. We then derive upper bounds for the couplings of these interactions, which depend on the high energy scale where unitarity is saturated. If \eg\, unitarity is saturated at 1TeV, then $λ_W \lsim 0.12$ is obtained. The implied relations between the present and future LEP results, and the possible observations of strong effects at supercolliders, are also discussed

hep-ph↗

arXiv1993

Four Fermion Processes at Future $e^+e^-$ Colliders as a Probe of New Resonant Structures

Possible oblique effects from vector particles that are strongly coupled to the known gauge bosons are calculated for the case of final hadronic states produced at future $e^+e^-$ colliders, using a formalism that was recently proposed and that exploits the information and the constraints provided by LEP 1 results. Combining the hadronic channels with the previously analysed leptonic ones we derive improved limits for the masses of the resonances that,in technicolour-like cases, would range from one to two TeV for a 500 GeV linear collider, depending on the assumed theoretical constraints.

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arXiv1993

Vector boson Pair Production at Supercolliders; useful approximate helicity amplitudes

We study vector boson pair production at $LHC$ and $SSC$, taking into account the effects generated by the anomalous vector boson and Higgs couplings induced by the operators ${\cal O}_W$ and ${\cal O}_{UW}$, which are the only dim=6 operators preserving $SU(2)_c$. These operators lead to enhanced production of transverse vector bosons, as opposed to the enhanced production of longitudinal gauge bosons, induced in case $M_H\gsim 1\ TeV$, by dim=4 terms already existing in the Standard Model lagrangian. For vector boson pair masses larger than $1\ TeV$, we establish very simple approximate expressions for the standard as well as the non-standard helicity amplitudes for $q\bar q$ annihilation and vector boson fusion, which accurately describe the physics. These expressions should simplify the experimental search for such interactions. We finally discuss the observability and the disentangling of these interactions.

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