Mirror Fermions Research Articles

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.

Spontaneous mirror left-right symmetry breaking for leptogenesis parametrized by Majorana neutrino mass matrix

We introduce a mirror copy of the ordinary fermions and Higgs scalars for embedding the SU(2)L × U(1)Y electroweak gauge symmetry into an SU(2)L × SU(2)R × U(1)B−L left-right gauge symmetry. We then show the spontaneous left-right symmetry breaking can automatically break the parity symmetry motivated by solving the strong CP problem. Through the SU(2)R gauge interactions, a mirror Majorana neutrino can decay into a mirror charged lepton and two mirror quarks. Consequently we can obtain a lepton asymmetry stored in the mirror charged leptons. The Yukawa couplings of the mirror and ordinary charged fermions to a dark matter scalar then can transfer the mirror lepton asymmetry to an ordinary lepton asymmetry which provides a solution to the cosmic baryon asymmetry in association with the SU(2)L sphaleron processes. In this scenario, the baryon asymmetry can be well described by the neutrino mass matrix up to an overall factor.

Low scale left-right-right-left symmetry

We propose an effective left-right-right-left model with a parity breaking scale around a few TeV. One of the main achievements of the model is that the mirror fermions as well as the mirror gauge sector simultaneously could be at TeV scale. It is shown that the most dangerous quadratic divergence of the SM Higgs boson involving the top quark in the loop is naturally suppressed, and begins at three loop. The model postpones the fine-tuning of the mass of the SM Higgs boson up to a sufficiently high scale. The model explains the smallness of the neutrino masses whether they are Dirac or Majorana. Furthermore, the strong $CP$ phase is zero in this model.

Search for electroweak-scale right-handed neutrinos and mirror charged leptons through like-sign dilepton signals

The existence of tiny neutrino masses at a scale more than a million times smaller than the lightest charged fermion mass, namely the electron, and their mixings can not be explained within the framework of the exceptionally successful Standard Model. There are four ideas that has been proposed to explain the tiny neutrino masses. These include the see-saw mechanism with a right handed neutrino at the GUT scale, and this is the most elegant mechanism. The other mechanisms are radiatively generated neutrino masses, the neutrino mass arising from a 2nd Higgs doublet having a tiny VEV and coupling only to the neutrinos, and finally the mirror model or simply the EW-scale $\nu_R$ model. The mirror model has new quarks and leptons of opposite chirality at the electroweak scale (for the same Standard Model gauge symmetry $SU(2)_W \times U(1)_Y$) compared to what we have for the Standard Model. With suitable modification of the Higgs sector, the EW-scale $\nu_R$ model satisfies the electroweak precision test and also the constraints coming from the observed 125-GeV Higgs scalar. Since in this model, the mirror fermions are required to be in the EW scale, these can be produced at the LHC giving final states with a very low background from the SM. One such final state is the same sign dileptons with large missing $p_T$ for the events. In this work, we explore the constraint provided by the $8$ TeV data, and prospect of observing this signal in the $13$ TeV runs at the LHC. Additional signals will be the presence of displaced vertices depending on the smallness of the Yukawa couplings of the mirror leptons with the ordinary leptons and the singlet Higgs present in the model. Of particular importance to the EW-scale $\nu_R$ model is the production of $\nu_R$ which will be a direct test of the seesaw mechanism at collider energies.

Strongly-interacting mirror fermions at the LHC

The introduction of mirror fermions corresponding to an interchange of leftwith right-handed fermion quantum numbers of the Standard Model can lead to a model according to which the BEH mechanism is just an effective manifestation of a more fundamental theory while the recently-discovered Higgs-like particle is composite. This is achieved by a non-abelian gauge symmetry encompassing three mirror-fermion families strongly coupled at energies near 1 TeV. The corresponding non-perturbative dynamics lead to dynamical mirror-fermion masses between 0.14 - 1.2 TeV. Furthermore, one expects the formation of composite states, i.e. “mirror mesons”, with masses between 0.1 and 3 TeV. The number and properties of the resulting new degrees of freedom lead to a rich and interesting phenomenology, part of which is analyzed in the present work.

Detection of mirror-meson decays at CERN

The existence of mirror partners (katoptrons) of Standard-Model fermions offers a viable alternative to a fundamental BEH mechanism, with the coupling corresponding to the mirror generation gauge symmetry becoming strong at around 1 TeV. The resulting non-perturbative processes produce dynamical katoptron masses and create mirror mesons with masses ranging approximately from 0.1 to 2.8 TeV. Since the corresponding phenomenology expected at the LHC is particularly rich, some relevant detection methods of mirror mesons are explored in order to obtain a deeper understanding of strongly-interacting mirror fermions.

Chiral solution to the Ginsparg-Wilson equation

We present a chiral solution of the Ginsparg-Wilson equation. This work is motivated by our recent proposal for nonperturbatively regulating chiral gauge theories, where five-dimensional domain wall fermions couple to a four-dimensional gauge field that is extended into the extra dimension as the solution to a gradient flow equation. Mirror fermions at the far surface decouple from the gauge field as if they have form factors that become infinitely soft as the distance between the two surfaces is increased. In the limit of an infinite extra dimension we derive an effective four-dimensional chiral overlap operator which is shown to obey the Ginsparg-Wilson equation, and which correctly reproduces a number of properties expected of chiral gauge theories in the continuum.

Fermion number anomaly with the fluffy mirror fermion

Quite recently, Grabowska and Kaplan presented a 4-dimensional lattice formulation of chiral gauge theories based on the chiral overlap operator. We study this formulation from the perspective of the fermion number anomaly and possible associated phenomenology. A simple argument shows that the consistency of the formulation implies that the fermion with the opposite chirality to the physical one, the "fluffy mirror fermion" or "fluff", suffers from the fermion number anomaly in the same magnitude (with the opposite sign) as the physical fermion. This immediately shows that if at least one of the fluff quarks is massless, the formulation provides a simple viable solution to the strong CP problem. Also, if the fluff interacts with gravity essentially in the same way as the physical fermion, the formulation can realize the asymmetric dark matter scenario.

The decay h→µτ in the Littlest Higgs Model with T-parity

We calculate the one loop contributions to h→µτ decay in the littlest Higgs model with T-parity. We include mirror fermions and odd gauge bosons loops. We find that for a special choice of the mixing matrix of mirror fermion kii = 0.2 and kii = 0.45, the branching fraction is the order 10-3 — 10-2 and 10-2 — 10-1, respectively, with an energy scale ƒ = 0.5 — 2TeV. However, our results are a function of the square of the product of mixing matrices |V†HμVHτ|2.

Wick rotation and fermion doubling in noncommutative geometry

In this paper, we discuss two features of the noncommmutative geometry and spectral action approach to the Standard Model: the fact that the model is inherently Euclidean, and that it requires a quadrupling of the fermionic degrees of freedom. We show how the two issues are intimately related. We give a precise prescription for the Wick rotation from the Euclidean theory to the Lorentzian one, eliminating the extra degrees of freedom. This requires not only projecting out mirror fermions, as has been done so far, and which leads to the correct Pfaffian, but also the elimination of the remaining extra degrees of freedom. The remaining doubling has to be removed in order to recover the correct Fock space of the physical (Lorentzian) theory. In order to get a Spin(1,3) invariant Lorentzian theory from a Spin(4) invariant Euclidean theory such an elimination must be performed after the Wick rotation. Differences between the Euclidean and Lorentzian case are described in detail, in a pedagogical way.

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.

Clifford Algebraic Unification of Conformal Gravity with an Extended Standard Model

A Clifford \({ Cl( 5, C ) }\) unified gauge field theory formulation of conformal gravity and \({ U (4) \times U (4) \times U(4) }\) Yang–Mills in \({4D}\) is elaborated further. It is shown how the \({ Cl( 5, C ) }\) group has for physically relevant subgroup the one given by \({ SU (2, 2) \times SU (4)_C \times SU (4)_L \times SU (4)_R}\), and which is compatible with the Coleman–Mandula theorem (in the absence of a mass gap). The proposals presented here for a Clifford algebraic unification of conformal gravity with an extended standard model deal mainly with models of four generations of fermions. Mirror fermions can be incorporated as well. Whether these mirror fermions are dark matter candidates is an open question. There are also residual \({U(1)}\) groups within this Clifford group unification scheme that should play an important role in cosmology in connection to dark matter particles coupled to gravity via a bimetric extension of general relativity. Other four generation scenarios based on \({ Cl(6, R), Cl(8, R) }\) algebras, supersymmetric field theories and quaternions are discussed.

Nonperturbative Regulator for Chiral Gauge Theories?

We propose a nonperturbative gauge-invariant regulator for d-dimensional chiral gauge theories on the lattice. The method involves simulating domain wall fermions in d+1 dimensions with quantum gauge fields that reside on one d-dimensional surface and are extended into the bulk via gradient flow. The result is a theory of gauged fermions plus mirror fermions, where the mirror fermions couple to the gauge fields via a form factor that becomes exponentially soft with the separation between domain walls. The resultant theory has a local d-dimensional interpretation only if the chiral fermion representation is anomaly free. A physical realization of this construction would imply the existence of mirror fermions in the standard model that are invisible except for interactions induced by vacuum topology, and which could gravitate differently than conventional matter.

On unification of gravity and gauge interactions

Considering a higher dimensional Lorentz group as the tangent symmetry, we unify gravity and gauge interactions in a natural way. The spin connection of the gauged Lorentz group is then responsible for both gravity and gauge fields, and the action for the gauged fields becomes part of the spin curvature squared. The realistic group which unifies all known particles and interactions is the $SO(1,13)$ Lorentz group whose gauge part leads to $SO(10)$ grand unified theory and contains double the number of required fermions in the fundamental spinor representation. Mirror fermions could acquire mass utilizing a mechanism employed for topological superconductors. Family unification could be achieved by considering the $SO(1,21)$ Lorentz group.

Masses and mixings of neutrinos in extended models

In the framework of a left-right model containing mirror fermions (LRMM) with gauge group SU(3)C⊗SU(2)L⊗SU(2)R⊗U(1)Y′, we estimate the neutrino masses, which are found to be consistent with their experimental bounds and hierarchy. We also estimate the decay rates of heavy Majorana neutrinos in the channels N→W±l∓, N→Zνl and N→Hνl, which are roughly equal for large values of the heavy neutrino mass. Starting from the most general Majorana neutrino mass matrix, the smallness of active neutrino masses turns out from the interplay of the hierarchy of the involved scales and the double application of seesaw mechanism. An appropriate ansatz on the structure of the neutrino mass matrix imposing a symmetric mixing of electron neutrino with muon and tau neutrinos leads to tribimaximal mixing matrix for light neutrinos.

An extended standard model and its Higgs geometry from the matrix model

We find a simple brane configuration in the IKKT matrix model which resembles the standard model at low energies, with a second Higgs doublet and right-handed neutrinos. The electroweak sector is realized geometrically in terms of two minimal fuzzy ellipsoids, which can be interpreted in terms of four point-branes in the extra dimensions. The electroweak Higgs connects these branes and is an indispensable part of the geometry. Fermionic would-be zero modes arise at the intersections with two larger branes, leading precisely to the correct chiral matter fields at low energy, along with right-handed neutrinos which can acquire a Majorana mass due to a Higgs singlet. The larger branes give rise to $SU(3)_c$, extended by $U(1)_B$ and another $U(1)$ which are anomalous at low energies and expected to disappear. At higher energies, mirror fermions and additional fields arise, completing the full ${\cal N}=4$ supersymmetry. The brane configuration is a solution of the model, assuming a suitable effective potential and a non-linear stabilization of the singlet Higgs. The basic results can be carried over to ${\cal N}=4$ $SU(N)$ super-Yang-Mills on ordinary Minkowski space with sufficiently large $N$.

Top quark flavor-changing neutral-current decay to a 125 GeV Higgs boson in the littlest Higgs model withTparity

Motivated by the current observation of a 125 GeV Higgs boson, we calculate $t\rightarrow cH$ and $t\rightarrow cg(\gamma)H$ in the unitary gauge in the littlest Higgs model with T-parity(LHT). Due to the large contribution from the new mirror fermions, we find that the branching ratios of $t\rightarrow cH$ and $t\rightarrow cgH$ can be greatly enhanced in the LHT model and maximally reach $\mathcal O(10^{-5})$ in the allowed parameter space. When the mirror fermion mass $M_3 > 2(1.5)$ TeV and the cut-off scale $f=500$ GeV, the process of $pp \to t\bar{t} \to 3b +c +\ell+ \slashed E_{T}^{miss}$ can reach $3\sigma$($5\sigma$) sensitivity at 8(14) TeV LHC with luminosity $\cal{L}$ $=20(300) fb^{-1}$.

Unification with mirror fermions

We present a new framework unifying interactions in nature by introducing mirror fermions, explaining the hierarchy between the weak scale and the coupling unification scale, which is found to lie close to Planck energies. A novel process leading to the emergence of symmetry is proposed, which not only reduces the arbitrariness of the scenario proposed but is also followed by significant cosmological implications. Phenomenology includes the probability of detection of mirror fermions via the corresponding composite bosonic states and the relevant quantum corrections at the LHC.

Collider signatures of mirror fermions in the framework of a left-right mirror model

The idea of left-right symmetry with mirror fermions is very appealing from the symmetry point of view. In this picture, unlike the Standard Model, the symmetry is not only left-right symmetric, but each left handed fermion multiplet is accompanied by new right handed fermion multiplet of opposite chirality. In this work, we consider a gauge symmetry, $SU(3)_c \otimes SU(2)_L\otimes SU(2)_R \otimes U(1)_{Y^\prime}$ supplemented by a discrete $Z_2$ symmetry. Instead of having right handed multiplets for each left handed multiplets of the same fermions as in the usual left-right model, the mirror model include right handed doublets involving new fermions (called mirrors), and similarly for each right handed singlet, there are corresponding mirror singlets. Thus the gauge anomaly is naturally absent in this model, and the model also provide a solution for the strong CP problem because of parity conservation. The first stage of symmetry breaking is achieved by a doublet mirror Higgs with a vacuum expectation value $\simeq 10^7$ GeV, needed to explain the neutrino mass $\simeq 10^{-11}$ GeV. The mirror fermions can mix with the ordinary fermions via a scalar which is singlet under the gauge symmetry. In this model, only light mirror particles, having masses in the few hundred GeV range are $\hat{e}, \hat{u}, \hat{d}$ with well-defined spectrum. $\hat{u}$ and $\hat{d}$ can be pair produced at the LHC, and can be detected as ($u Z$) and ($d Z$) resonances. We discuss the signals of these mirror fermions at the LHC, and find that the reach at the LHC can be as large as $m_{\hat q}\simeq 800$ GeV.

Electroweak precision constraints on the electroweak-scale right-handed neutrino model

A model of electroweak-scale right-handed neutrino (EWνR) model was constructed five years ago in which the right-handed neutrinos are members of mirror fermion weak doublets and where the Majorana masses of the right-handed neutrinos are found to be naturally of the order of the electroweak scale. These features facilitate their searches at the LHC through signals such as like-sign dilepton events. This model contains, in addition to the mirror quarks and leptons, extra scalars transforming as weak triplets. In this paper, we study the constraints imposed on these additional particles by the electroweak precision parameters S, T, and U. These constraints are crucial in determining the viability of the electroweak νR model and the allowed parameter space needed for a detailed phenomenology of the model.