Mirror Fermion Model Research Articles

On the gauge-invariant path-integral measure for the overlap Weyl fermions in 16 of SO(10)

AbstractWe consider the lattice formulation of SO(10) chiral gauge theory with left-handed Weyl fermions in the 16-dimensional spinor representation ($\underline{16}$) within the framework of the overlap fermion/Ginsparg–Wilson relation. We define a manifestly gauge-invariant path-integral measure for the left-handed Weyl field using all the components of the Dirac field, but the right-handed part of it is just saturated completely by inserting a suitable product of the SO(10)-invariant ’t Hooft vertices in terms of the right-handed field. The definition of the measure applies to all possible topological sectors of admissible link fields. The measure possesses all required transformation properties under lattice symmetries and the induced effective action is CP invariant. The global U(1) symmetry of the left-handed field is anomalous due to the non-trivial transformation of the measure, while that of the right-handed field is explicitly broken by the ’t Hooft vertices. There remains the issue of smoothness and locality in the gauge-field dependence of the Weyl fermion measure, but the question is well defined and the necessary and sufficient condition for this property is formulated in terms of the correlation functions of the right-handed auxiliary fields. In the weak gauge-coupling limit at least, all the auxiliary fields have short-range correlations and the question can be addressed further by Monte Carlo methods without encountering the sign problem. We also discuss the relations of our formulation to other approaches/proposals to decouple the species doubling/mirror degrees of freedom. These include the Eichten–Preskill model, the mirror-fermion model with overlap fermions, the domain-wall fermion model with the boundary Eichten–Preskill term, 4D topological insulator/superconductor with a gapped boundary phase, and the recent studies on the PMS phase/“mass without symmetry breaking”. We clarify the similarities and differences in the technical details and show that our proposal is a unified and well defined testing ground for that basic question.

Muon-to-electron conversion in mirror fermion model with electroweak scale non-sterile right-handed neutrinos

The muon-to-electron conversion in aluminum, titanium and gold nuclei is studied in the context of a class of mirror fermion model with non-sterile right-handed neutrinos having masses at the electroweak scale. We show that the electric and magnetic dipole operators from the photon exchange diagrams provide the dominant contributions, which enables us to derive a simple formula to relate the conversion rate with the on-shell radiative decay rate of muon into electron at the limit of zero momentum transfer and large mirror lepton masses. Current experimental limits (SINDRUM II) and projected sensitivities (Mu2e, COMET and PRISM) for the muon-to-electron conversion rates in various nuclei and latest limit from MEG for the radiative decay rate of muon into electron are used to put constraints on the parameter space of the model. Sensitivities to the new Yukawa couplings can reach the range of one tenth to one hundred-thousandth, depending on the mixing scenarios and mirror fermion masses in the model as well as the nuclei targets used in future experiments.

Electron electric dipole moment in mirror fermion model with electroweak scale non-sterile right-handed neutrinos

The electric dipole moment of the electron is studied in detail in an extended mirror fermion model with the following unique features of (a) right-handed neutrinos are non-sterile and have masses at the electroweak scale, and (b) a horizontal symmetry of the tetrahedral group is used in the lepton and scalar sectors. We study the constraint on the parameter space of the model imposed by the latest ACME experimental limit on electron electric dipole moment. Other low energy experimental observables such as the anomalous magnetic dipole moment of the muon, charged lepton flavor violating processes like muon decays into electron plus photon and muon-to-electron conversion in titanium, gold and lead are also considered in our analysis for comparison. In addition to the well-known CP violating Dirac and Majorana phases in the neutrino mixing matrix, the dependence of additional phases of the new Yukawa couplings in the model is studied in detail for all these low energy observables.

Top quark rare decays via loop-induced FCNC interactions in extended mirror fermion model

Flavor changing neutral current (FCNC) interactions for a top quark t decays into Xq with X represents a neutral gauge or Higgs boson, and q a up- or charm-quark are highly suppressed in the Standard Model (SM) due to the Glashow–Iliopoulos–Miami mechanism. Whilst current limits on the branching ratios of these processes have been established at the order of 10−4 from the Large Hadron Collider experiments, SM predictions are at least nine orders of magnitude below. In this work, we study some of these FCNC processes in the context of an extended mirror fermion model, originally proposed to implement the electroweak scale seesaw mechanism for non-sterile right-handed neutrinos. We show that one can probe the process t→Zc for a wide range of parameter space with branching ratios varying from 10−6 to 10−8, comparable with various new physics models including the general two Higgs doublet model with or without flavor violations at tree level, minimal supersymmetric standard model with or without R-parity, and extra dimension model.

Lepton flavor violating decays of neutral higgses in extended mirror fermion model

We investigate the one-loop induced charged lepton flavor violating decays of the neutral Higgses in an extended mirror fermion model with non-sterile electroweak-scale right-handed neutrinos and a horizontal A4 symmetry in the lepton sector. It is demonstrated that for the 125 GeV scalar h there is tension between the recent LHC result B(h→τμ)∼1% and the stringent limits on the rare processes μ→eγ and τ→(μ/e)γ as well as the muon anomalous magnetic dipole moment Δaμ from low energy experiments.

STRATEGY TOWARDS MIRROR-FERMION SIGNATURES

The existence of mirror fermions interacting strongly under a new gauge group and having masses near the electroweak scale has been recently proposed as a viable alternative to the standard-model Higgs mechanism. The main purpose of this work is to investigate which specific experimental signals are needed to clearly differentiate the mirror-fermion model from other new-physics models. In particular, the case is made for a future large lepton collider with c.o.m. energies of roughly 4 TeV or higher.

Exotic heavy quark contribution in hadron-hadron production of W+W- pairs.

In this paper we study the contribution of new possible heavy quarks to the process $\mathrm{h}\mathrm{a}\mathrm{d}\mathrm{r}\mathrm{o}\mathrm{n}\ensuremath{-}\mathrm{h}\mathrm{a}\mathrm{d}\mathrm{r}\mathrm{o}\mathrm{n}\ensuremath{\rightarrow}{W}^{+}{W}^{\ensuremath{-}}X$. We consider new exotic quarks as proposed in three extended electroweak models: the vector singlet model (VSM), the vector doublet model (VDM), and the fermion---mirror-fermion model (FMFM). We discuss the high energy unitarity behavior for the elementary process and their implications. We present the predictions of the exotic quark contribution for the CERN Large Hadron Collider (LHC). We present some distributions that can separate the standard model contribution from the new exotic quark contribution.

Lattice study of the decoupling of heavy fermions

According to one-loop perturbation theory, fermions whose masses are totally generated from Yukawa couplings do not decouple in the heavy mass limit. We have investigated this issue nonperturbatively in the strong coupling regime of the chiral U (1) mirror-fermion model in four dimensions. Our numerical results indicate nondecoupling of heavy fermion and mirror-fermion, thus supporting the one-loop picture. We also study this issue in a simpler, but vector-like Z 2 scalar-fermion model. Preliminary results at intermediate and strong Yukawa couplings on 8 4 and 12 4 lattices suggest the nondecoupling of fermions as well.

Nondecoupling of heavy mirror-fermion

According to one-loop perturbation theory, fermions whose masses are totally generated from Yukawa couplings do not decouple in the heavy mass limit. We investigate this issue nonperturbatively in the strong coupling regime of the chiral U(1) mirror-fermion model in four dimensions. Our numerical results, obtained on 6 3·16, 6 3·24 and 8 3·16 lattices, indicate nondecoupling of heavy fermion and mirror-fermion, thus supporting the one-loop picture.

Grand unification for mirror fermions

The possibility of grand unification of the standard model (SM) with fermion spectrum extended to include mirror fermions is examined. SM gauge couplings do not automatically unify. SO(10) grand unification is studied with one intermediate scale. Renormalization group equations (RGE) for fermion Yukawa couplings and the scalar self-coupling are studied numerically at one and two loop level. Strong restrictions for mirror fermion masses are obtained assuming perturbative unification. Mirror masses much smaller than the tree unitarity bounds are required. In particular mirror leptons have to be around 50 GeV. Consistency of the mirror fermion model with LEP precision data is established. A direct search for single production of mirror neutrinos at LEP could exclude or confirm the GUT version of the mirror fermion model.

Mirror fermions and LEP precision data

The three-generation mirror fermion model is compared with LEP precision and low energy data. While for zero mixing of ordinary and mirror fermions the model is not favoured, for non-zero mixing very low χ 2 fits have been obtained, in particular when right-handed leptonic mixings are small and left-handed leptonic mixings are large (of the order of 0.1 radians).

On Gauge invariant chiral theories on a lattice

Gauge invariant formulations of chiral theories on a lattice are discussed: models with the Wilson-Yukawa coupling, with mirror fermions, and also their variants without fundamental scalar fields. We argue that all the models without mirror fermions that are reducible to those bilinear in fermion variables are potentially nonunitary. The Nambu-Jona-Lasinio mechanism in a mirror fermion model is briefly discussed.

Fermions in models with strong Wilson-Yukawa interactions

A theory with two different types of Wilson-Yukawa couplings is discussed. The spectrum contains free fermions or fermions which couple to the gauge fields as vectors in different regions of the phase diagrams. With the two couplings equal, both types of fermions exist, and the theory is conjectured to be equivalent to a special case of the mirror fermion model.

Neutrinoless double beta decay and the limits to the right-handed currents

We consider the neutrinoless double beta decay within two extended electroweak gauge models with right-handed weak interactions, the left-right symmetric model and the mirror fermion model. We show that if the two electron-like neutrinos with opposite chiralities appearing in these models are lighter than a few MeV, the double beta decay data do not restrict the magnitude of right-handed currents.

Mirror fermions, universality and the beam dump experiment

The electron deficiency observed in beam dump experiments is discussed within the mirror fermion model. We make a general study of the leptonic weak universality and show that only a 4% change in thee/μ-ratio due to non-universal vector/axial vector charged couplings is allowed. In the mirror fermion model this corresponds to the possibility that the electron-like mirror neutrinoNe is very heavy. IfNe is light enough to be produced, oscillation ofve into sterileNe is possible. IfNe is lighter than about 1 MeV, only a 6.5% decrease in thee/μ ratio is allowed, due to the constraints from reactor neutrino experiments. However, if\(m_{N_e } \) is between a couple of MeV's and 45 MeV, only one loose bound exists, allowing thee/μ ratio to decrease by 11%.