Ordinary Fermions Research Articles

MASS GENERATION AND THE DYNAMICAL ROLE OF THE KATOPTRON GROUP

Heavy mirror fermions along with a new strong gauge interaction capable of breaking the electroweak gauge symmetry dynamically were recently introduced under the name of katoptrons. Their main function is to provide a viable alternative to the Standard-Model Higgs sector. In such a framework, ordinary fermions acquire masses after the breaking of the strong katoptron group which allows mixing with their katoptron partners. The purpose of this letter is to study the elementary-scalars-free mechanism responsible for this breaking and its implications for the fermion mass hierarchies.

Domain wall fermions in quenched lattice QCD

We study the chiral properties and the validity of perturbation theory for domain wall fermions in quenched lattice QCD at beta=6.0. The explicit chiral symmetry breaking term in the axial Ward-Takahashi identity is found to be very small already at Ns=10, where Ns is the size of the fifth dimension, and its behavior seems consistent with an exponential decay in Ns within the limited range of Ns we explore. From the fact that the critical quark mass, at which the pion mass vanishes as in the case of the ordinary Wilson-type fermion, exists at finite Ns, we point out that this may be a signal of the parity broken phase and investigate the possible existence of such a phase in this model at finite Ns. The rho and pi meson decay constants obtained from the four-dimensional local currents with the one-loop renormalization factor show a good agreement with those obtained from the conserved currents.

Weak-singlet fermions: Models and constraints

We employ data from precision electroweak tests and collider searches to derive constraints on the possibility that weak-singlet fermions mix with the ordinary standard model fermions. Our findings are presented within the context of a theory with weak-singlet partners for all ordinary fermions and theories in which only third-generation fermions mix with weak singlets. In addition, we indicate how our results can be applied more widely in theories containing exotic fermions.

Dirac magnetic monopole and the discrete symmetries

We examine several issues related to the processes of Dirac monopole–antimonopole production in high-energy collisions such as e + e − annihilation. Perturbative calculations for such processes are known to be inherently ambiguous due to the arbitrariness of direction of the monopole string this requires use of some prescription to obtain physical results. We argue that different prescriptions lead to drastically different physical results which suggests that at present we do not have an entirely satisfactory procedure for the elimination of string arbitrariness (this problem is quite separate from the problems caused by the large coupling constant). We then analyze the consequences of discrete symmetries (P and C) for the monopole production processes and for the monopole–antimonopole states. The P and C selection rules for the monopole–antimonopole states turn out to be different from those for the ordinary fermion–antifermion or boson–antiboson system. In particular, the spin 1/2 monopole and antimonopole should have the same helicities if they are produced through the one-photon annihilation of an electron and positron. A stronger selection rule holds for spinless monopoles: CP symmetry absolutely forbids the monopole–antimonopole production through the one-photon annihilation of an electron and positron. Single-photon e + e −→ g + g − amplitude has been a key input in calculating the contribution of virtual g + g − pairs to various physical processes such as the decay Z→3 γ and the anomalous magnetic moment of the electron. Applying our conclusions to these cases can lead to significant modifications of the results obtained in previous works.

Quons as su(2) irreducible tensor operators

We prove that, for the quon algebra, which interpolates between the Bose and Fermi statistics and depends on a free parameter q, it is possible to build an su(2) irreducible representation. One of the consequences of this fact is that the quons couple via the same angular momentum coupling rules obeyed by ordinary bosons and fermions.

Higgs- and Goldstone-boson-mediated long range forces

In certain mild extensions of the Standard Model, spin-independent long range forces can arise by exchange of two very light pseudoscalar spin--0 bosons. In particular, we have in mind models in which these bosons do not have direct tree level couplings to ordinary fermions. Using the dispersion theoretical method, we find a $1/r^{3}$ behaviour of the potential for the exchange of very light pseudoscalars and a $1/r^{7}$ dependence if the pseudoscalars are true massless Goldstone bosons.

Constraints on Top Couplings in Models with Exotic Quarks

The extension of the Standard Model with exotic quark singlets and doublets introduces large flavor changing neutral couplings between ordinary fermions. We derive inequalities which translate the precise determination of the diagonal Z couplings, in particular at LEP, into stringent bounds on the off-diagonal ones. The resulting limits can be saturated in minimal extensions with one vector doublet or singlet. In this case, 23 and 6 single top events, respectively, are predicted at LEP2 for an integrated luminosity of 500 1/pb per experiment.

Current Algebra and Exotic Statistics in Six Dimensions

By studying ordinary chiral fermions in background gauge fields we show that in the case of gauge group SU(3) and space-time dimension 5+1 localized solitons obey $q-$ commutation relations with $q$ not equal to $\pm 1$ but a third root of unity.

Production of neutral scalar Higgs bosons ateγcolliders

We study the production of neutral scalar (CP even) Higgs bosons in the process $e\gamma\to e h$ by including supersymmetric corrections to the dominant $t$-channel photon exchange amplitude. In addition to the standard model $W^{\pm}$ and fermion loops, there are substantial contributions from chargino loops. For some cases, these contributions can exceed those of the $W$'s and ordinary fermions. The cross sections in this channel are generally one or two orders of magnitude larger than those in the related channel $e\bar{e}\to\gamma h$.

Phenomenological aspects of a fermiophobic SU (2) × SU (2) × U ( l) extension of the standard model

We consider an extension of the standard electroweak theory with gauge group SU(2) L × SU(2) R × U(1) Y ̃ , where the gauge bosons of the extra SU(2) R factor do not couple to ordinary fermions. We show that precision electroweak data and flavour physics provide quite stringent indirect constraints on its parameter space, but still allow for relatively light non-standard gauge and Higgs bosons. We then consider the model phenomenology at high-energy colliders, and observe that in the gauge boson sector present bounds and possible future signals are dominated by Z′ production. In summary, indirect constraints on the charged gauge boson sector are so tight that observable new effects must be connected either with the neutral gauge boson sector or with the extended Higgs sector of the model.

Flavor physics and the triviality bound on the Higgs mass

The triviality of the scalar sector of the standard one-doublet Higgs model implies that this model is only an effective low-energy theory valid below some cut-off scale Λ. The underlying high-energy theory must include flavor dynamics at a scale of order Λ or greater in order to give rise to the different Yukawa couplings of the Higgs to ordinary fermions. This flavor dynamics will generically produce flavor-changing neutral currents and non-universal corrections to Z → b b . We show that the experimental constraints on the neutral D-meson mass difference imply that Λ must be greater than of order 21 TeV. We also discuss bounds on Λ from the constraints on extra contributions to the K L - K S mass difference and to the coupling of the Z boson to b-quarks. For theories defined about the infrared-stable Gaussian fixed-point, we estimate that this lower bound on Λ yields an upper bound of approximately 460 GeV on the Higgs boson's mass, independent of the regulator chosen to define the theory.

Extended Technicolor Contribution to theZbbVertex

The deviation of the experimental value of $R_b \equiv \Gamma_b/\Gamma_h$ from the standard-model prediction can be naturally explained in the extended technicolor scenario.The diagonal extended technicolor gauge boson which flavor-diagonally couples with both the ordinary fermions and the techni-fermions plays an important role in order to have the appropriate radiative correction to the $Zbb$ vertex. But since the diagonal extended technicolor gauge boson gives too large positive contribution to the $T$ parameter, we need some new mechanisms which generate negative contribution to the $T$ parameter.

Electroweak symmetry breaking by vectorlike fermion condensation with small S and T parameters.

In order to build realistic models in which electroweak symmetry is dynamically broken we should explain the smallness of the Peskin-Takeuchi {ital S} and {ital T} parameters. In accordance with the decoupling theorem, these parameters must be suppressed by SU(2){sub {ital L}}{times}U(1){sub {ital Y}} invariant masses. From this fact we can expect that if fermions with large SU(2){sub {ital L}}{times}U(1){sub {ital Y}} invariant masses undergo condensation and break electroweak symmetry, the {ital S} and {ital T} parameters can be small. It is intersting that not only the {ital S} but also the {ital T} parameter can become small even if there exists a large isospin violation in fermion condensation. In this paper we examine the possibility that, by the strong four-Fermi interaction, massive vectorlike fields undergo condensation and break electroweak symmetry. The model becomes almost the same as the standard model at a low energy scale and predicts a heavy Higgs boson. Moreover, we discuss a model in which the four-Fermi interaction can be induced by massive gauge boson exchange. In this model, the masses of ordinary matter fermions (quark and lepton) are enhanced.

Low energy properties of the heavy vector fermions and electroweak symmetry breaking.

We discuss the properties of the heavy vector fermions with bare Dirac mass terms and an SU(2)[times]SU(2) global symmetry in the Yukawa interaction Lagrangian. Using the heat kernel expansion method we calculate their contributions to the low energy observables. We argue that these heavy fermions may be responsible for a soft dynamical symmetry breaking through their condensation. We also discuss the possibility of considering ordinary fermions as one part of the vector fermions within our model.

B → sγ and [formula omitted] in technicolor with scalars

We consider the radiative decay b → sγ, and the correction to the Zb b vertex in technicolor models with scalars. In these models, the scalar develops a vacuum expectation value when the technifermions condense, and the ordinary fermions develop masses via Yukawa couplings. Since the symmetry breaking sector involves both a fundamental scalar doublet and an isotriplet of composite scalars (the technipions), the phenomenology associated with the charged scalars is similar to that found in a type-I two-Higgs doublet model. We show that the correction to the Zb b vertex is small over the allowed parameter space of the model in the two limits that we consider, and that there can be large, potentially observable, contributions to the b → sγ branching fraction.

Model-independent determination of Z′ couplings at LEP 200

All couplings of a new heavy gauge boson to ordinary fermions can be determined in a model-independent way at a large e + e − collider for large enough statistics. No such determination is possible at LEP 200, however, because its design integrated luminosity is too low for existing and forthcoming limits on Z′ interactions. At any rate, it should be possible to distinguish between models for Z′ masses < 1 TeV, or to set limits of this order on Z′ masses for definite models. These are (preliminary) 1σ limits. We neglect systematic errors and assume an integrated luminosity of 0.5 fb −1

A q-analogue of the supersymmetric oscillator and its q-supercoherent states

A q-analogue of the supersymmetric oscillator is constructed out of q-boson and ordinary fermion creation and annihilation operators. q-supercoherent states are explicitly obtained for the q-deformed supersymmetric oscillator. They are shown to be eigenstates of both q-boson and fermion annihilation operators and to satisfy a completeness relation. The representation of the q-deformed superalgebra in super Bargmann-Fock space is also discussed by means of the q-supercoherent states.

A possible origin of the Wilson lattice fermion

Considering relevant and irrelevant high-dimension operators for ordinary and mirror fermions respectively, we show that the Wilson lattice fermion can originate from a spontaneous symmetry breaking phenomenon. Ward identities, due to symmetries at the cutoff, guarantee the cancellation of mirror-fermion contributions and the infrared limit can be achieved. The Wilson parameter turns out to be fixed at r ⋍ 0.18, where the vacuum energy of the system is minimized.

THERMODYNAMICS OF A FREE q-FERMION GAS

We study the thermodynamics of a q-fermion gas for complex values of q on the unit circle. Special emphasis is given to the study of the virial coefficients and the specific heat of this gas. In particular, it is shown that if any state can accommodate up to p q-fermions, then the first p virial coefficients of such a gas are the same as that of a gas of free bosons. Explicit expressions for the deviation of higher virial coefficients from the corresponding values for a Bose gas are obtained. Further, as for ordinary fermions, it is shown that the specific heat of a q-fermion gas at low temperature is proportional to T. Numerical computations show that the derivative of the specific heat as a function of T has no discontinuity.

New fermions at e+e? colliders II. Signals and backgrounds

We discuss the production, at high--energy e$^+$e$^-$ linear colliders, of new heavy fermions predicted by extensions of the Standard Model. We analyze in great details the various signals and the corresponding backgrounds for both pair production and single production in association with ordinary fermions. Concentrating on new leptons, we use a model detector for e$^+$e$^-$ collisions at a center of mass energy of 500 GeV, to illustrate the discovery potential of the Next Linear Colliders.