arXiv subjects

G. J. Gounaris

Publications and source records attributed to G. J. Gounaris.

70 records · Page 4Linked to original sources

arXiv1997

Using e-e+ to b b(bar) to test properties of new interactions at LEP2 and higher energies

We show that in e-e+ colliders at energies above the Z-peak, the process e-e+ to b b(bar) becomes very sensitive to the presence of residual New Physics (NP) effects described by the dim=6 SU(3)*SU(2)*U(1) gauge invariant operators O(qW), O(qB) and O(bB). This observation should be combined with the already known great sensitivity of the light fermion production through e-e+ annihilation above the Z-peak, to the bosonic operators O(DW) and O(DB). It is important to emphasize that the effects of all these operators are largely hidden at the Z-peak; while they are enhanced above it through the use the "Z-peak subtracted representation". The observability limits for detecting these operators at LEP2 and NLC, through such light fermion production processes, are also established.

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arXiv1997

General description of New Physics in t, b and boson Interactions and its Unitarity Constraints

We list all possible dim=6 CP conserving and SU(3)* SU(2)*U(1) gauge invariant interactions, which could be generated in case no new particles would be reachable in the future Colliders, and the only observable New Physics would be in the form of new interactions affecting the scalar sector and the quarks of the third family. These interactions are described by operators involving the standard model scalar field, the quarks of the third family and the gauge bosons. Subsequently, we identify those operators which do not contribute to LEP1 (and lower energy) observables at tree level and are not purely gluonic. Since present measurements do not strongly constrain the couplings of these operators, we derive here the unitarity bounds on them. Finally, in order to get a feeling on the possible physical meaning of the appearance of any of these operators, we identify the operators generated in a class of renormalizable dynamical models which at the TeV scale, are fully described by the SU(3)*SU(2)*U(1) gauge group.

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arXiv1996

A Model-independent Description of New Physics effects in e+e- to t tbar

We study the potential of a future $e^+e^-$ collider for the search of anomalous gamma t t bar and Z t t bar couplings, assuming that CP-invariance holds. This is done in a model-independent way, considering that all six possible couplings do appear. Two experimental situations are envisaged, with and without electron beam polarization. Observability limits in the form of domains in the 6-dimensional parameter space are established. Illustrations for specific constrained models are also presented and implications for new physics searches are discussed.

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arXiv1996

Dynamical Scenarios for Anomalous Interactions involving t, b quarks and bosons

In the present paper we explore various dynamical scenarios for New Physics (NP) which could be generated by very heavy particles and observed in the form of non-standard "low energy" interactions affecting the scalar sector, the gauge bosons and the quarks of the third family. Such interactions have been previously expressed in terms of 48 CP-conserving gauge invariant operators. We show that each scenario is characterized by a specific subset of such operators. Thus, if some traces of NP are ever found in the experimental data, then the comparison with the predictions of the various scenarios, should be able to guide the search towards the underlying dynamics generating it.

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arXiv1996

Effective lagrangian description of top production and decay

We propose a rather general description of residual New Physics (NP) effects on the top quark couplings. These effects are described in terms of 20 gauge invariant $dim=6$ operators involving gauge and Higgs bosons as well as quarks of the third family. We compute their implications for the $γt\bar t$, $Z t \bar t$ and $tbW$ vertices and study their observability in the process $e^-e^+ \to t\bar t$ with $t\to bW \to b\ell^+ν_\ell$. We present results for the integrated cross section, the angular distribution and various decay distribution and polarization asymmetries for NLC energies of $0.5-2~TeV$. Observability limits are discussed and interpreted in terms of the NP scales associated to each operator through the unitarity constraints. The general landscape of the residual NP effects in the heavy quark and bosonic sectors is also presented.

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arXiv1996

Residual New Physics Effects in $e^+e^-$ and $γγ$ Collisions at NLC

We report on a set of studies concerning the description of New Physics (NP) effects characterized by a scale much higher than the electroweak scale. We concentrate on the residual effects described by an effective lagrangian involving only bosonic fields and restrict to the case that the Higgs field is described linearly, so that the Higgs particle exists. It has already been emphasized that this lagrangian may be represented by eight $dim=6$ operators; namely the blind CP-conserving operators $Ø_W$, $Ø_{BΦ}$, $Ø_{WΦ}$, $Ø_{UB}$, $Ø_{UW}$, the ''superblind'' ${\cal O}_{Φ2}$ and the two CP-violating ones $\olØ_{UB}$ and $\olØ_{UW}$. To each operator and for any given value of its coupling, we associate an unambiguous NP scale determined by the energy where unitarity is saturated. Our study of the possible NP tests realizable at a future linear $e^+e^-$ collider concentrates on $(e^+e^-\to HZ ~,~ Hγ)$, and on $γγ$ collisions producing boson pairs ($γγ\to W^+W^-$, $ZZ$, $Zγ$, $γγ$, $HH$), or a single Higgs ($γγ\to H$). The sensitivities to the various operators involved in the effective lagrangian are estimated. We find that the testable NP scales vary from a few tens of TeV in the boson pair processes, up to 65 TeV in single H production. Ways to disentangle the various operators are also proposed. In this respect a comparison of the NP effects in the various boson pair processes, like \eg\@ a comparison of $e^+e^-\to HZ$ versus $e^+e^-\to Hγ$, should be very fruitful. This is applied also to the study of the Higgs branching ratios, and especially the ratio $Γ(H\toγγ)/Γ(H\toγZ)$.

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arXiv1995

Tests of Anomalous Higgs Boson Couplings through $e^-e^+ \to HZ$ and $Hγ$

We show how the processes $e^- e^+ \to ZH, ~ γH$, which will be studied at LEP2 and at high energy colliders, could be used to search for types of New Physics (NP) characterized by an effective NP scale in the few TeV range and affecting the scalar sector only. In particular, for $e^- e^+ \to Z H$, we propose the measurement of suitable azimuthal asymmetries determined from the angular distribution of the $Z$-decay plane with respect to the $Z$-production one. Such asymmetries, together with the $ZH$ angular distribution, may allow a complete disentangling of the five $dim=6$ operators $ {\cal O }_{UB}$, $ {\cal O }_{UW}$, $\overline{\cal O }_{UB}$, $\overline{\cal O }_{UW}$, ${\cal O }_{\Phi2}$, describing the residual NP effects to the Higgs couplings. We note that the first four of these operators contribute to processes relevant to LEP1 precision measurements only at the 1-loop level, while the last operator remains completely unconstrained at this level. The process $e^- e^+ \to γH$ is also very sensitive to NP and should bring important independent information.

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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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arXiv1994

Searching for Exotic Mesons in e^+e^- Annihilation at Dafne

$DAΦNE$ should be useful for testing the nature of the vector mesons directly produced in $e^-e^+$ annihilation, as well as the nature of the $C=+$ states produced in the radiative decays of these vector mesons. In the $DAΦNE$ energy range, these latter states may have spin up to two and any parity. Provided the background can be handled and the spin of the produced state is known, the study of the angular distributions in these decays can measure the parity of the produced meson as well as the ratios of the independent production helicity amplitudes. These ratios provide sensitive tests for quark model classification of the states, in particular the enigmatic $f_1(1420)$. Thus, they can be used to indicate whether the mesons involved are consistent with the usual $q \bar q$ interpretation, or whether other interpretations like \eg\,hybrid, glueball or multiquark, are more favorable for some of them.

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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.

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arXiv1993

Probes of Heavy Meson Substructure in $e^+ e^-$ annihilation

We apply Heavy Quark Effective Theory to the production of $0^-$ and $1^-$ $Q\bar{q}$ states in $e^+ e^-$ annihilation. We show that HQET implies that the electric quadrupole amplitudes vanish and we propose tests for this theory. We also show how HQET can be applied to distinguish the $^3D_1$ and $^3S_1$ $Q\bar{Q}$ states.

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