Topcolor-assisted Technicolor Model Research Articles

Search for heavy resonances decaying to tau lepton pairs in proton-proton collisions at sqrt{s}=13 TeV

A search for heavy resonances that decay to tau lepton pairs is performed using proton-proton collisions at sqrt{s}=13 TeV. The data were collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 2.2 fb−1. The observations are in agreement with standard model predictions. An upper limit at 95% confidence level on the product of the production cross section and branching fraction into tau lepton pairs is calculated as a function of the resonance mass. For the sequential standard model, the presence of Z′ bosons decaying into tau lepton pairs is excluded for Z′ masses below 2.1 TeV, extending previous limits for this final state. For the topcolor-assisted technicolor model, which predicts Z′ bosons that preferentially couple to third-generation fermions, Z′ masses below 1.7 TeV are excluded, representing the most stringent limit to date.

750 GeV diphoton excess confronted with a top-pion in the TTM model

The latest LHC data suggest an intriguing excess at [Formula: see text] which apparently requires an explanation from the beyond standard model physics. In this paper, we explore the possibility for this signal to arise from a top-pion in the Top Triangle Moose model which can be viewed as a dimensional-deconstruction version of the top-color assisted technicolor model. We demonstrate that the observed excess can be accommodated by and has important implications for this interesting model.

Analysis of the semileptonicΛb→Λℓ+ℓ−transition in the topcolor-assisted technicolor model

We comparatively analyze the flavor changing neutral current process of the $\Lambda_b \rightarrow \Lambda \ell^+ \ell^-$ in the standard model as well as topcolor-assisted technicolor model using the form factors calculated via light cone QCD sum rules in full theory. In particular, we calculate the decay width, branching ratio and lepton forward-backward asymmetry related to this decay channel. We compare the results of the topcolor-assisted technicolor model with those of the standard model and debate how the results of the topcolor-assisted technicolor model depart from the standard model predictions. We also compare our results on the differential branching ratio with recent experimental data provided by CDF and LHCb Collaborations.

The single neutral top-higgs production at LHC and ILC in the Topcolor-Assisted Technicolor Model

In this paper, we study the single neutral top-higgs (ht0) production processes at the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). At the LHC, the production rates of processes pp → Z(W)ht0 are too small to detect ht0. However, with the reasonable parameter values, the cross sections can reach the level of 102 fb for qq → qqht0 process and 103 fb for top quark associated production process pp → tht0 + X, respectively. At the ILC, we study the single top-higgs production processes e−γ → νeW−ht0 and γγ → W+W−ht0 in e−γ and γγ collisions. It is found that the production cross sections can reach the level of a few fb with reasonable parameter values. Furthermore, such processes with the flavor-changing decay mode \(h_t^0 \to t\bar c\) might provide typical signatures to detected the top-higgs. Therefore, it is hopeful to find the signal of top-higgs at the LHC and ILC experiments via theses processes and test the TC2 model directly.

Photoproduction of the Charged Top-Pions at the LHeC

The top triangle moose (TTM) model, which can be seen as the deconstructed version of the topcolor-assisted technicolor (TC2) model, predicts the existence of the charged top-pions πt± in low energy spectrum. In the context of this model, we consider photoproduction of πt± via the subprocesses γb → tπt− and at the large hadron-electron collider (LHeC), in which high energy photon beams are generated by using the Compton backscatting method. We find that, as long as the charged top-pions are not too heavy, they can be abundantly produced via 76 collision.

Probing topcolor-assisted technicolor from top charge asymmetry and triple-top production at the LHC

In a topcolor-assisted technicolor model (TC2) with large FCNC top quark couplings, we study its correlated contributions to the top quark forward–backward asymmetry (AFB) at the Tevatron, the top charge asymmetry (AC) and the triple-top production at the LHC. Under current constraints on the top quark from the LHC and Tevatron (such as the total and differential production rates), we scan the parameter space of such a TC2 model. We find that in the allowed parameter space the TC2 model can explain the Tevatron measured AFB at 2σ level, but meanwhile significantly enhance AC at the LHC. Such enhanced AC, albeit currently allowed by the LHC measurement at 2σ level, will serve as a test of TC2 with the improvement of measurement precision at the LHC. Then with all the constraints (including the requirement to explain AFB at 2σ level and satisfying the current LHC measurement of AC at 2σ level), we find that the TC2 model can induce sizable triple-top production at the 14 TeV LHC (the production rate can maximally reach 16 pb). Due to the low SM backgrounds, the triple-top production can also be a good probe for TC2 model, complementary to AC.

PGB pair production at LHC and ILC as a probe of the topcolor-assisted technicolor models

The topcolor-assisted technicolor (TC2) model predicts some light pseudo goldstone bosons (PGBs), which may be accessible at the LHC or ILC. In this work we study the pair productions of the charged or neutral PGBs at the LHC and ILC. For the productions at the LHC we consider the processes proceeding through gluon-gluon fusion and quark-antiquark annihilation, while for the productions at the ILC we consider both the electron-positron collision and the photon-photon collision. We find that in a large part of parameter space the production cross sections at both colliders can be quite large compared with the low standard model backgrounds. Therefore, in future experiments these productions may be detectable and allow for probing TC2 model.

B s → ϕl + l − decays in the topcolor-assisted technicolor model

Using the updated form factors within the light-cone QCD sum rule approach, we calculate the new physics contributions to rare semileptonic $ \overline B {\text{s}} $ → ϕμ + μ − , ϕτ + τ − decays from the new particles appearing in the topcolor-assisted technicolor (TC2) model. In our evaluations, we find that: (i) the branching ratio, normalized forward-backward asymmetry and lepton polarization asymmetries show highly sensitivity to charged toppions contributions and little sensitivity to Z ′ contributions. The TC2 enhancements to the branching ratios of these decays can reach a factor of ~ 2; (ii) the NP enhancement to the forward-backward asymmetry of the decay B s → ϕμ + μ − is in the range −13 % to 3 %, but −9 % to −6 % for decay B s → ϕτ + τ − compared to the SM predictions; (iii) the TC2 model provide an enhancement of about 12 % to the longitudinal polarization asymmetry P L for decay B s → ϕμ + μ −, but a decrease of about 10 % to the transverse polarization asymmetry P T for the decay B s → ϕτ + τ −.

Radiative Dileptonic Decays Bs → l+l−γ in the TC2 Model

We investigate the radiative dileptonic decays Bs → l+l−γ (l = e, μ and τ) in the framework of the topcolor-assisted technicolor (TC2) model. The contributions of the new particles predicted by this model to the branching ratios and the forward-backward asymmetry (AFB) of these decays are considered. It is found that the values of their branching ratios are greater than the standard model (SM) predictions by several times up to one order of magnitude and |AFB| can also be enhanced by several times in a wide range of the parameter space.

SINGLE CHARGED TOP-PION PRODUCTION AT THE LHeC IN γp COLLISION

In the context of the topcolor-assisted technicolor (TC2) model, we study the productions of the charged top-pion associated with single top, charm or bottom quark in γp collision, which proceed via the subprocesses [Formula: see text], [Formula: see text] and [Formula: see text]. With the electron energy Ee = 50 GeV and photon energy Ep = 7 TeV , we find that the production rates can reach the level of several tens fb for [Formula: see text] production, and hundreds of fb for [Formula: see text] (or [Formula: see text]) productions. So one can expect that enough signals could be produced in the large part of the parameter space. Furthermore, these flavor-changing (FC) productions are extremely suppressed in the standard model (SM). With a large number of events and the clean background, the charged top-pion should be observable at the Large Hadron electron Collider (LHeC) based γp colliders. Thus, such charged top-pion production processes may offer a useful way to test the TC2 model.

Production of a neutral scalar associated with a photon at the LHC in the topcolor-assisted technicolor model

In the context of the topcolor-assisted technicolor (TC2) model, we consider the production of the neutral scalar S(π0t or h0t) associated with a photon at the LHC and compare our results with those given by the minimal supersymmetric extension of the Standard Model (MSSM). We find that its production cross section is larger or smaller than that of the scalar particle predicted by the MSSM model, depending on the values of the relevant free parameters.

Search for resonant production oftt¯decaying to jets inpp¯collisions ats=1.96 TeV

This Letter reports a search for non standard model topquark resonances, $Z'$, decaying to $t\bar{t} \rightarrow W^+b W^-\bar{b}$ %\rightarrow qq'b qq' \bar{b}$, where both $W$ decay to quarks. We examine the top-antitop quark invariant mass spectrum for the presence of narrow resonant states. The search uses a data sample of $\ppb$ collisions at a center of mass energy of 1.96 TeV collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of 2.8 fb$^{-1}$. No evidence for top-antitop quark resonant production is found. We place upper limits on the production cross section times branching ratio for a specific topcolor assisted technicolor model with width of $\Gamma_{Z'} = 0.012 M_{Z'}$. Within this model, we exclude $Z'$ boson with masses below 805 GeV$/c^2$ at the 95% confidence level.

The anomalous top quark coupling tqg and tW production at the LHC

Many new physics models beyond the standard model (SM) can give rise to the large anomalous top couplings tqg (q=u and c). We focus our attention on these couplings induced by the topcolor-assisted technicolor (TC2) model and the littlest Higgs model with T-parity (called LHT model), and consider their contributions to the production cross section and the charge asymmetry for tW production at the LHC. We find that the anomalous top coupling tqg induced by these two kinds of new physics models can indeed generate sizable charge asymmetry. The correction effects of the LHT model on the production cross sections of the processes pp→tW−+X and pp→t¯W++X are significant large, which might be detected at the LHC.

Searching for a neutral top-Higgs in association with top-quark pairs at an e+e− collider in the TC2 model

We investigate the associated production of the neutral top-Higgs h0t with a pair of top-quarks in the context of the topcolor-assisted technicolor (TC2) model at the future e+e− Linear Colliders (LC) i.e. e+e− → tt̄h0t. We calculate the production rate and present the distributions of the transverse momenta of top-Higgs and top-quarks. The results show that the total cross section is typically of the order of 1.0–7.5 fb in the energy range between 1000 GeV and 2000 GeV of the LC for the whole top-Higgs mass region of interest. It should be distinctly possible that hundreds or even thousands of h0t signals can be produced per year at the LC given the luminosity .

Searches for the technicolor signatures via gg → W±πt∓ at the Large Hadron Collider

In this paper, we calculate the production of a charged top pion in association with a W boson via gg fusion at CERN's Large Hadron Collider in the context of the topcolor assisted technicolor model. We find that the total cross section of pp → gg → W±πt∓ is several dozen femtobarns with reasonable values of the parameters, and the total cross section of pp → W±πt∓ can reach a few hundred femtobarns when we consider the sum of the contributions of these two parton subprocesses, gg → W±πt∓ and bb̄ → W±πt∓.

Charged top-pion production associated with the bottom quark pair as a probe of the topcolor-assisted technicolor model at the LHC

The topcolor-assisted technicolor (TC2) model predicts the existence of the charged top-pions ($\pi_t^\pm$), whose large couplings with the third generation fermions will induce the charged top-pion production associated with the bottom and anti-bottom quark pair at the CERN Large Hadron Collider (LHC) through the parton processes $c\bar b \to \pi_t^+ b \bar b$ and $u\bar d(c\bar s) \to \pi_t^+ b \bar b$. In this paper we examine these productions and find that, due to the small Standard Model backgrounds, their production rates can exceed the $3\sigma$ sensitivity of the LHC in a large part of parameter space, so these processes may serve as a good probe for the TC2 model.

Electroweak chiral Lagrangian from the topcolor-assisted technicolor model with nontrivial technicolor fermion condensation and walking

The electroweak chiral Lagrangian for the topcolor assisted technicolor model proposed by K. Lane, which uses nontrivial patterns of techniquark condensation and walking, was investigated in this study. We found that the features of the model are qualitatively similar to those of Lane's previous natural TC2 prototype model, but there is no limit on the upper bound of the Z' mass. We discuss the phase structure and possible walking behavior of the model. We obtained the values of all coefficients of the electroweak chiral Lagrangian up to an order of p4. We show that although the walking effect reduces the S parameter to half its original value, it maintains an order of 2. Moreover, a special hyper-charge arrangement is needed to achieve further reductions in its value.

PAIR PRODUCTION OF CHARGED TOP-PIONS ASSOCIATED WITH Z GAUGE BOSON IN THE TOPCOLOR-ASSISTED TECHNICOLOR MODEL AT THE ILC

The top-pions [Formula: see text] are the three additional typical particles predicted by the topcolor-assisted technicolor (TC2) model and the observation of these particles can be regarded as the direct evidence of the TC2 model. In this paper, we investigate the production of a pair of charged top-pions associated with Z gauge boson at the International Linear Collider (ILC), i.e. [Formula: see text] and [Formula: see text]. We calculate the production rate of the process [Formula: see text] and present the distributions of the transverse momenta of Z gauge boson and charged top-pion [Formula: see text]. We find that the cross-section of the process [Formula: see text] can reach 1 fb with reasonable parameter space of the TC2 model. Considering the main decay mode of charged top-pion, we find that such a production may provide copious events. While the cross-section of the process [Formula: see text] is below 1 fb, hence the process [Formula: see text] will play an important role in the test of the TC2 model at the ILC when compared with the process [Formula: see text].

Probing Topcolor-Assisted Technicolor Models from Like-Sign τ Pair Production in eγ Collisions

We consider the contributions of the extra gauge boson Z′ to the like sign τ production processes e−γ → e+(μ+)τ−τ−, induced by the tree-level flavor changing interactions. Since these rare production are far below the observable level in the Standard Model and other popular new physics models such as the minimal supersymmetric model, we find that, in the topcolor-assisted technicolor models, the Z′ can give significant contributions to these processes, and with reasonable values of the parameters, the cross section σ can reach several tens of fb and may be detected at the eγ collisions.

THE SINGLE NEUTRAL TOP-HIGGS PRODUCTION AT ILC IN THE TC2 MODEL

In the framework of the topcolor-assisted technicolor (TC2) model, we study the neutral top-Higgs [Formula: see text] production processes [Formula: see text], [Formula: see text] and [Formula: see text]. The results show that the production rates can reach the level of a few fb with reasonable parameter values. With the clean background of the flavor-changing [Formula: see text] channel, the top-Higgs events can possibly be detected at the International Linear Collider (ILC) experiments. Therefore, such neutral top-Higgs production processes offer a useful way to probe for neutral top-Higgs and test the TC2 model directly.