Littlest Higgs Model With T-parity Research Articles

Top Quark Polarization and Spin Correlation in the Littlest Higgs Model with T-Parity at the ILC

In the framework of the littlest Higgs model with T-parity (LHT), we study the top quark spin correlation and polarization at the International Linear Collider (ILC). We find that the top quark polarization asymmetry δPt and the left-right asymmetry δALR can respectively reach −35% and −37.5% for √s = 500 GeV and √s = 1000 GeV via e+e− collision, which can reach the observable level at the ILC. By contrast, the spin correlation δC is smaller. The correlation behaviors of these observables at the e+e− collision and the γγ collision will be helpful to distinguish different models and test the LHT model at the ILC.

Flavor-Changing Bottom-Strange Associated in the Littlest Higgs Model with T-parity at the ILC

In the littlest Higgs model with T-parity (LHT) the mirror quarks induce the special flavor structures and some new flavor-changing couplings, which could greatly enhance the production rates of the flavor-changing processes. We in this paper study some bottom and anti-strange production processes in the LHT model at the International Linear Collider (ILC), i.e., e+e− → bs̄ and γγ → bs̄. The results show that the production rates of these processes are sizeable for the favorable values of the parameters. Therefore, it is quite possible to test the LHT model or make some constraints on the relevant parameters of the LHT through the detection of these processes at the ILC.

Contribution of the LHT Model to Zcc̄ Coupling

In the littlest Higgs model with T-parity (LHT), some new particles, such as the T-odd mirror quarks and goldstone bosons, can contribute to various observables. We calculate their contribution to Zcc̄ coupling. Some observables are related to Zcc̄ coupling, for example, the effective vector and axial-vector Zcc̄ coupling constants (gVc, gAc) and c-quark forward-backward asymmetry (AcFB). We give our predictions about (gVc, gAc) in the LHT model and show the allowed regions of the mirror quark masses based on the experimental data of gVc − gAc. Then, we present an explanation of AcFB.

Flavor-changing top-charm associated productions at the ILC in the littlest Higgs model withTparity

The littlest Higgs model with T-parity (LHT) has new flavor-changing (FC) couplings with the Standard Model (SM) quarks, which do not suffer strong constraints from electroweak precision data. So these FC interactions may enhance the cross sections of some flavor-changing neutral-current (FCNC) processes. In this work, we study the FC top-charm associated productions via $e^{-}\gamma$ collision at the ILC. We find that the cross sections are sensitive to the mirror quark masses. With reasonable values of the parameters, the cross sections may reach the detectable level and provide useful information about the relevant parameters in the LHT model, especially setting an upper limit on the mirror quark masses.

Tau and muon lepton flavor violations in the littlest Higgs model withTparity

Lepton flavor violation in $\ensuremath{\tau}$ and $\ensuremath{\mu}$ processes is studied in the littlest Higgs model with $T$ parity. We consider various asymmetries defined in polarized $\ensuremath{\tau}$ and $\ensuremath{\mu}$ decays. Correlations among branching ratios and asymmetries are shown in the following lepton flavor violation processes: ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma}$, ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}{e}^{+}{e}^{\ensuremath{-}}$, ${\ensuremath{\mu}}^{\ensuremath{-}}A\ensuremath{\rightarrow}{e}^{\ensuremath{-}}A$ ($A=\mathrm{Al}$, Ti, Au, and Pb), ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}\ensuremath{\gamma}$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{e}^{+}{e}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}P$ ($P={\ensuremath{\pi}}^{0}$, $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$), ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}V$ ($V={\ensuremath{\rho}}^{0}$, $\ensuremath{\omega}$ and $\ensuremath{\phi}$), ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma}$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}{e}^{+}{e}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}P$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}V$, ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{+}{e}^{\ensuremath{-}}$ and ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}{e}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. It is shown that large parity asymmetries and time-reversal asymmetries are allowed in ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}{e}^{+}{e}^{\ensuremath{-}}$. For $\ensuremath{\tau}$ lepton flavor violation processes, sizable asymmetries are possible reflecting characteristic chirality structure of lepton flavor violating interactions in this model.

Top quark rare three-body decays in the littlest Higgs model withTparity

In the littlest Higgs model with T-parity (LHT), the mirror quarks have flavor structures and will contribute to the top quark flavor changing neutral current. In this work, we perform an extensive investigation of the top quark rare three-body decays $t\to cVV (V=\gamma,Z,g)$ and $t\to cf\bar{f} (f=b,\tau,\mu,e)$ at one-loop level. Our results show that the branching ratios of $t\to cgg$ and $t\to cb\bar{b}$ could reach $\mathcal {O}(10^{-3})$ in the favorite parameter space of the littlest Higgs model with T-parity, which implies that these decays may be detectable at the LHC or ILC, while for the other decays, their rates are too small to be observable at the present or future colliders.

The study of the contribution of the LHT model to [formula omitted] coupling

In the framework of the Littlest Higgs model with T-parity (LHT), we study the contributions of the new particles to Z b b ¯ couplings at one-loop level. Based on these results, we further study the branching ratio R b and the unpolarized forward–backward asymmetry A FB b . We find that the correction of the new particles to Z b b ¯ couplings is mainly on the left-handed coupling and has small part of the parameter space to alleviate the deviation between theoretical predictions and experimental values. The precision measurement value of R b can give severe constraints on the relevant parameters. The constraints from the precision measurement value of A FB b are very weak.

Dilepton and four-lepton signals at the LHC in the Littlest Higgs model with T-parity violation

In the presence of the T-parity violating Wess-Zumino-Witten (WZW) anomaly term, the otherwise stable heavy photon A_H in the Littlest Higgs model with T-parity (LHT) decays to either Standard Model (SM) gauge boson pairs, or to SM fermions via loop diagrams. We make a detailed study of the collider signatures where the A_H can be reconstructed from invariant mass peaks in the opposite sign same flavor dilepton or the four-lepton channels. This enables us to obtain information about the fundamental symmetry breaking scale f in the LHT and thereby the low-lying mass spectrum of the theory. In addition, indication of the presence of the WZW term gives us hints of the possible UV completion of the LHT via strong dynamics. The crucial observation is that the sum of all production processes of heavy T-odd quark pairs has a sizeable cross-section at the LHC and these T-odd particles eventually all cascade decay down to the heavy photon A_H. We show that for certain regions of the parameter space with either a small f of around 500 GeV or relatively light T-odd quarks with a mass of around 400 GeV, one can reconstruct the A_H even at the early LHC run with \sqrt{s}=10 TeV and a modest integrated luminosity of 200 pb^{-1}. At \sqrt{s} = 14 TeV and with an integrated luminosity of 30 fb^{-1}, it is possible to cover a large part of the typical parameter space of the LHT, with the scale f up to 1.5 TeV and with T-odd quark masses almost up to 1 TeV. In this region of the parameter space, the mass of the reconstructed A_H ranges from 66 GeV to 230 GeV.

Littlest Higgs model withTparity and top quark pair production at LHC

We consider the top-quark pair production at the upcoming LHC and investigate the contributions of the new particles to the related observables within the framework of the littlest Higgs model with T-parity(LHT). It is found that the LHT model can generate significant corrections to the tt production cross section and their spin correlations.

The impossibility of heavy neutrino dark matter in the Littlest Higgs Model with T-parity: Constraints from direct search

We consider the Littlest Higgs Model with T-parity (LHT), in the parameter region where a heavy neutrino is the lightest T-odd particle (LTP). Having emphasized that this corresponds to a sizable region in the parameter space of the theory, we show that both the Cryogenic Dark Matter Search (CDMS) and Xenon10 experiments disallow the entire region where the masses of the new particles in LHT can lie within several TeV. Therefore, any observation of the signals of a heavy neutrino LTP is likely to seriously reopen the issue of cold dark matter in the universe.

Study of the top reconstruction in top-partner events at the LHC

In the Littlest Higgs model with T-parity (LHT), top-partners (T−) are produced in pairs at the Large Hadron Collider (LHC). Each top-partner decays into a top quark (t) and the lightest T-odd gauge partner AH. We demonstrate reconstruction of the t system decaying hadronically, and measurement of the top-partner mass from the mT2 distribution. A top quark from a T− decay is polarized, and we discuss the effect of this polarization on the decay distributions. Because the events consist of highly collinear jets which occasionally overlap each other, we compare distributions using different jet reconstruction algorithms (Snowmass cone, kt, Cambridge, SISCone). We find clustering algorithms are advantageous for studying top polarization effects.

Lepton flavour violating decays in the littlest Higgs model with t-parity

We present the results of an extensive analysis of lepton flavour violating decays in the Littlest Higgs model with T-parity (LHT). As lepton flavour violation is highly suppressed in the Standard Model by small neutrino masses, the LHT effects turn out to be naturally huge and could be seen in the near future experiments.

LHC signals ofT-odd heavy quarks in the Littlest Higgs model

Recently proposed Little Higgs models present a viable solution to the naturalness problem of the Standard Model. An additional discrete symmetry, called T-parity, has been included in the simplest Little Higgs models to evade the constraints arising from electroweak precision data. The Littlest Higgs model with T-parity (LHT) not only predicts a set of new fermions in addition to the heavy gauge bosons of the original Little Higgs model, but also provides a new candidate for dark matter. In this paper, we study two particularly interesting signatures of T-odd fermion pair production at the LHC, namely, (a) jj + l^+ l^- + missing E_T and (b) jj + b \bar b + l^\pm + missing E_T. Using a parton level Monte Carlo event generator, we evaluate both the signal as well as the standard model background profile for a selected set of model parameters thereby developing a good discriminator. Finally, we scan the parameter space and delineate the possible discovery region in the same.

Correlations between ε′/ε and rareKdecays in the Littlest Higgs model with T-parity

We calculate the CP-violating ratio epsilon'/epsilon in the Littlest Higgs model with T-parity (LHT) and investigate its correlations with the branching ratios for K_L -> pi^0 nu {bar nu}, K_L -> pi^0 l^+ l^- and K^+ -> pi^+ nu {bar nu}. The resulting correlations are rather strong in the case of K_L decays, but less pronounced in the case of K^+ -> pi^+ nu {bar nu}. Unfortunately, they are subject to large hadronic uncertainties present in epsilon'/epsilon, whose theoretical prediction in the Standard Model (SM) is reviewed and updated here. With the matrix elements of Q_6 (gluon penguin) and Q_8 (electroweak penguin) evaluated in the large-N limit and m_s^MS(2 GeV) = 100 MeV from lattice QCD, (epsilon'/epsilon)_SM turns out to be close to the data so that significant departures of Br(K_L -> pi^0 nu {bar nu}) and Br(K_L -> pi^0 l^+ l^-) from the SM expectations are unlikely, while Br(K^+ -> pi^+ nu {bar nu}) can be enhanced even by a factor 5. On the other hand, modest departures of the relevant hadronic matrix elements from their large-N values allow for a consistent description of epsilon'/epsilon within the LHT model accompanied by large enhancements of Br(K_L -> pi^0 nu {bar nu}) and Br(K_L -> pi^0 l^+ l^-), but only modest enhancements of Br(K^+ -> pi^+ nu {bar nu}).

Charged lepton flavour violation and(g−2)μin the Littlest Higgs model with T-Parity: a clear distinction from Supersymmetry

We calculate the rates for the charged lepton flavour violating decays l_i -> l_j gamma, tau -> l pi, tau -> l eta, tau -> l eta', mu^- -> e^- e^+ e^-, the six three body leptonic decays tau^- -> l_i^- l_j^+ l_k^- and the rate for mu-e conversion in nuclei in the Littlest Higgs model with T-Parity (LHT). We also calculate the rates for K_{L,S} -> mu e, K_{L,S} -> pi^0 mu e and B_{d,s} -> l_i l_j. We find that the relative effects of mirror leptons in these transitions are by many orders of magnitude larger than analogous mirror quark effects in rare K and B decays analyzed recently. In particular, in order to suppress the mu -> e gamma and mu^- -> e^- e^+ e^- decay rates and the mu-e conversion rate below the experimental upper bounds, the relevant mixing matrix in the mirror lepton sector V_Hl must be rather hierarchical, unless the spectrum of mirror leptons is quasi-degenerate. We find that the pattern of the LFV branching ratios in the LHT model differs significantly from the one encountered in the MSSM, allowing in a transparent manner to distinguish these two models with the help of LFV processes. We also calculate (g-2)_mu and find the new contributions to a_mu below 10^{-10} and consequently negligible. We compare our results with those present in the literature.

Another look at the flavour structure of the Littlest Higgs model with T-parity

Abstract We discuss the mixing matrix V H d that describes the charged and neutral current interactions between ordinary down-quarks and up- and down-mirror quarks in the Littlest Higgs model with T-parity (LHT). We point out that this matrix in addition to three mixing angles contains three physical complex phases and not only one as used in the present literature. We explain the reason for the presence of two additional phases, propose a new standard parameterization of V H d and briefly comment on the relevance of these new phases for the phenomenology of FCNC processes in the LHT model. In a separate paper we present a detailed numerical analysis, including these new phases, of K and B physics, with particular attention to the most interesting rare decays.

Particle-antiparticle mixing,εK, ΔΓq, ASLq, ACP(Bd→ψKS), ACP(Bs→ψphi) and B→Xs,dγ in the Littlest Higgs model with T-parity

We calculate a number of observables related to particle-antiparticle mixing in the Littlest Higgs model with T-parity (LHT). The resulting effective Hamiltonian for Delta F=2 transitions agrees with the one of Hubisz et al., but our phenomenological analysis goes far beyond the one of these authors. In particular, we point out that the presence of mirror fermions with new flavour and CP-violating interactions allows to remove the possible Standard Model (SM) discrepancy between the CP asymmetry S_{psi K_S} and large values of |V_ub| and to obtain for the mass difference Delta M_s < (Delta M_s)_SM as suggested by the recent result by the CDF collaboration. We also identify a scenario in which simultaneously significant enhancements of the CP asymmetries S_{phi psi} and A_SL^q relative to the SM are possible, while satisfying all existing constraints, in particular from the B -> X_s gamma decay and A_CP(B -> X_s gamma) that are presented in the LHT model here for the first time. In another scenario the second, non-SM, value for the angle gamma=-(109+-6) from tree level decays, although unlikely, can be made consistent with all existing data with the help of mirror fermions. We present a number of correlations between the observables in question and study the implications of our results for the mass spectrum and the weak mixing matrix of mirror fermions. In the most interesting scenarios, the latter one turns out to have a hierarchical structure that differs significantly from the CKM one.