Topcolor-assisted Technicolor Model Research Articles

Associated Production of a Neutral Top-Higgs with Top Quark Pairs at the LHC within the TC2 model

Within the context of the topcolor-assisted technicolor (TC2) model we investigate the associated production of the neutral top-higgs ht0 with a pair of top quarks, i.e. pp → tt̄ht0 at the Large Hadron Collider (LHC), which proceeds through the partonic processes qq̄ → tt̄ht0 and gg → tt̄ht0. We calculate the production rate and show the distributions of the transverse momenta of ht0. It is found that the cross section of pp → tt̄ht0 can reach a few hundred fb in the most part of the allowed parameter space and even a few tens of pb for the light top-higgs. Due to the large cross section of tt̄ht0 production and the top-charm decay mode of ht0 for mht0 < 2mt, the process pp → tt̄ht0 can play an important role in the probe of neutral top-higgs and the test of the TC2 model.

Top-Higgs and top-pion phenomenology in the top triangle moose model

We discuss the deconstructed version of a topcolor-assisted technicolor model wherein the mechanism of top quark mass generation is separated from the rest of electroweak symmetry breaking. The minimal deconstructed version of this scenario is a "triangle moose" model, where the top quark gets its mass from coupling to a top-Higgs field, while the gauge boson masses are generated from a Higgsless sector. The spectrum of the model includes scalar (top-Higgs) and pseudoscalar (top-pion) states. In this paper, we study the properties of these particles, discuss their production mechanisms and decay modes, and suggest how best to search for them at the LHC.

One-Loop Effects of Non-Universal Gauge Boson Z′ in Top Quark Pair Production at LHC in TC2 Model

The top color-assisted technicolor model (TC2) predicts a non-universal Z′ gauge boson, which couples to the third generation fermions with enhanced strength. We study the effects of this non-universal gauge boson on the cross section and spin correlation of top quark pair production through the process gg → tt̄ at the LHC. We find that the total cross section and the spin correlation can be reduced by −4.7% and −1.4% respectively in the allowed parameter space.

Single top or bottom production associated with a scalar inγpcollision as a probe of topcolor-assisted technicolor

In the framework of the topcolor-assisted technicolor (TC2) models, we study the productions of a single top or bottom quark associated with a scalar in \gamma-p collision, which proceed via the subprocesses c\gamma -> t\pi_t^0, c\gamma -> t h_t^0 and c\gamma -> b\pi^+_t mediated by the anomalous top or bottom coupling tc\pi_t^0, tch_t^0 and bc\pi_t^+. These productions, while extremely suppressed in the Standard Model, are found to be significantly enhanced in the large part of the TC2 parameter space, especially the production via c\gamma -> b\pi^+ can have a cross section of 100 fb, which may be accessible and allow for a test of the TC2 models.

The lepton flavor violating signal of the extra gauge boson Z′ in photon-photon collision at the ILC

The hitherto unconstrained lepton flavor mixings, induced by the new gauge boson Z′, which are the prediction of many new physics models, such as topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models, may lead to the lepton flavor violating productions of τ $$ \bar \mu $$ , τ $$ \bar e $$ and µ $$ \bar e $$ in photon-photon collision at the proposed International Linear Collider (ILC). Through a comparative analysis of these processes, we find that the better channel to probe the new physics models is the production of τ $$ \bar \mu $$ or τ $$ \bar e $$ which occurs at a much higher rate than µ $$ \bar e $$ production due to the large mixing angle and the large flavor changing coupling, and may reach the detectable level of the ILC for a large part of the parameter space. Since the rates predicted by the Standard Model are far below the detectable level, these processes may serve as a sensitive probe for such new physics models.

Associated production of a neutral top-Higgs with a heavy-quark pair in the γγ collisions at ILC

We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in γγ collisions at the International Linear Collider (ILC). We find that the cross section for tt̄ht in γγ collisions is at the level of a few fb with the am. energy √s = 1000 GeV, which is consistent with the results of the cross section of tt̄H in the standard model and the cross section of tth in the minimal supersymmetric standard model. It should be clear that hundreds of to thousands of ht per year can be produced at the ILC. This process of γγ → tt̄ht is really interesting in testing the standard model and searching the signs of technicolor.

Charged Top-Pion Production at e+e− and γγ Colliders

We study the charged top-pion in the topcolor assisted technicolor model(TC2), and calculate the production of charged top-pion at e+e− and γγ colliders. At an e+e− collider, charged top-pion can be produced via the processes e+e− → tbb̄π−t(t̄bπ+t). At a γγ collider, it can be produced via the processes γγ → tb̄π−t(t̄bπ+t). The cross section can reach to a few of fb depending on the mass of the charged top-pion.

Technicolor corrections tobb¯→W±πt∓at the CERN Large Hadron Collider

In this paper we calculate the technicolor correction to the production of a charged top pion in association with a $W$ boson via $b\overline{b}$ annihilation at the CERN Large Hadron Collider in the context of the topcolor assisted technicolor model. We find that the cross section of $pp\ensuremath{\rightarrow}b\overline{b}\ensuremath{\rightarrow}{W}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}_{t}^{\ensuremath{\mp}}$ at the tree level can reach a few hundred femtobarns for reasonable ranges of the parameters, roughly corresponding to the result of the process $pp\ensuremath{\rightarrow}b\overline{b}\ensuremath{\rightarrow}{W}^{\ifmmode\pm\else\textpm\fi{}}{H}^{\ensuremath{\mp}}$ in the minimal supersymmetric standard model; the relative corrections arising from the one-loop diagrams are about a few percent to two dozen percent, and they will increase the cross section at the tree level. As a comparison, we also discuss the size of the hadron cross section via the other subprocess $gg\ensuremath{\rightarrow}{W}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}_{t}^{\ensuremath{\mp}}$.

Lepton flavor violation decays τ −→μ − P 1 P 2 in the topcolor-assisted technicolor model and the littlest Higgs model with T-parity

The new particles predicted by the topcolor-assisted technicolor ($TC2$) model and the littlest Higgs model with T-parity (called $LHT$ model) can induce the lepton flavor violation ($LFV$) couplings at tree level or one loop level, which might generate large contributions to some $LFV$ processes. Taking into account the constraints of the experimental data on the relevant free parameters, we calculate the branching ratios of the $LFV$ decay processes $\tau^-\to\mu^- P_1 P_2 $ with $P_1 P_2$ = $\pi^+\pi^-$, $K^+K^-$ and $K^0\bar{K^0}$ in the context of these two kinds of new physics models. We find that the $TC2$ model and the $LHT$ model can indeed produce significant contributions to some of these $LFV$ decay processes.

Flavor-Changing Neutral-Current Production of tc̄ in Association with a Neutral Top-Higgs at LHC in the Topcolor-Assisted Technicolor Model

In the framework of the topcolor-assisted technicolor (TC2) model we investigate the flavor-changing neutral-current production pp → tc̄h0t at the Large Hadron Collider (LHC), which proceeds through the parton-level processes gg → tc̄h0t, uū → tc̄h0t and dd → tc̄h0t. We calculate the production rate and present the distributions of the transverse momenta and the invarient mass of the neutral top-higgs. It is found that the cross section of pp → tc̄h0t can reach a few hundreds of fb in a large part of the allowed parameter space. Considering the main decay mode of top-higgs for mht < 2mt, we find that such a production may provide copious events. In the case of unobservation, the LHC can set meaningful constraints on the TC2 model.

Rare decays [formula omitted] in the TC2 model and the LHT model

In the framework of the topcolor-assisted technicolor ( TC2) model and the littlest Higgs model with T-parity ( LHT model), we consider the rare B decays B → M ν ν ¯ with M = π , K , ρ , or K * . We find that the contributions of the TC2 model to the branching ratios of these decay processes are larger than those for the LHT model. The experimental upper limits for some branching ratios can give severe constraints on the free parameters of the TC2 model.

Charged Top-Pion Production at Hadron Colliders

We studied the charged top-pion in the topcolor assisted technicolor model (TC2). If the charged top-pions are heavy, mπt > mt + mb, they will decay mainly via the channel πt+ → tb̄. We also calculated the production of charged top-pion at the Tevatron and LHC. The cross section can reach to 100 fb at the Tevatron and dozens of pb at the LHC depending on the mass of the top-pion.

Top Quark Decay t → cbb̄ in Topcolor-Assisted Technicolor Models

The topcolor-assisted technicolor (TC2) model predicts the existence of the top-pions and the CP-even top-Higgs with large flavor-changing couplings to the top quark, which at tree-level can mediate the top quark three-body decay t → cbb̄. We study this decay, show the dependence of the decay rate on the relevant TC2 parameters and compare the results with the predictions in the minimal supersymmetric model. We find that the decay rate in the TC2 model is much larger than that in the minimal supersymmetric model if the new particles are not too heavy. However, in consideration of the CDF and the LEP experiment limits, the top-pion mass is greater than 340 GeV in a more realistic parameter space, so the decay width of the channel t → cbb̄ intermediated by top-pions will be depressed greatly and difficult to be detected at the future collider. Thus, to observe this channel at the future collider, considering the top-higgs contribution may be the possible way when the masses of the top-pions and the top-higgs are not degenerate.

Production of the neutral top-pion π0t in association with a high pT jet at the LHC

In the framework of the topcolor-assisted technicolor (TC2) model, we study the production of the neutral top-pion π0t in association with a high-pT jet at the LHC, which proceeds via the partonic processes gg → π0tg, gq → π0tq, qq̄ → π0tg, gb(b̄) → π0tb(b̄), and bb̄ → π0tg. We find that it is very challenging to detect the neutral top-pion π0t via the process pp → π0t + jet + X → tt̄ + jet + X, while the possible signatures of π0t might be detected via the process pp → π0t + jet + X → (t̄c + tc̄)+jet + X at the LHC.

NLO Corrections of HTCΠ0 and Π+Π− Pair Production at ILC in TC2 Model

As well known, if the Higgs boson were not observed at LHC, the technicolor model would be the most favorable candidate responsible for the symmetry breaking. To overcome some defects in the previous model, some extended versions have been proposed. In the TC2 model typical signature is existence of heavy HTC and technipion Π. A direct proof of validity of the model is to produce them at accelerator. Thus we study the production rates of e+e− → HTCΠ0 and e+e− → Π+Π− at ILC in the topcolor-assisted technicolor (TC2) model. In fact, there is a flood of models belonging to new physics, which can result in products with characteristics similar to HTC + Π of the TC2 model. Therefore to distinguish this model from others one may need to investigate some details by calculating the cross section to NLO. We indeed find that the NLO corrections are significant, namely the ratio δ = (σNLO – σLO)/σLO in e+e− → HTCΠ0 exceeds 100% within a plausible parameter space.

Production of Top-Pions Associated with W Boson at Next Generation γγ Colliders

In the context of topcolor-assisted technicolor (TC2) model, we study the charged and neutral top-pions production process γ γ → W+Π−tΠt0t. We find that the production cross section is larger than that of the process γγ → W+H− H in the minimal supersymmetric standard model. With reasonable values of the parameters in the TC2 model, the cross section can reach the level of a few fb. Furthermore, the flavor-changing (FC) decay mode Π0t → tc̄ is the best channel to detect the neutral top-pion due to the clean SM background. With a large number of events and the clean background, the neutral top-pion should be observable at future linear colliders operating in γγ mode at the TeV energy scale.

The top-quark decay vertex in standard model extensions

New physics interactions can affect the strength and structure of the tbW vertex. We investigate the magnitudes and phases of “anomalous” contributions to this vertex in a two-Higgs doublet and the minimal supersymmetric extension of the standard model, and in a top-color assisted technicolor (TC2) model. While the magnitudes of the anomalous couplings remain below 1 percent in the first two models, TC2 interactions can reduce the left-chiral coupling f L by several percent.

Rare decaysBs→l+l−andB→Kl+l−in the topcolor-assisted technicolor model

We examine the rare decays ${B}_{s}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ and $B\ensuremath{\rightarrow}K{l}^{+}{l}^{\ensuremath{-}}$ in the framework of the topcolor-assisted technicolor ($TC2$) model. The contributions of the new particles predicted by this model to these rare decay processes are evaluated. We find that the values of their branching ratios are larger than the standard model predictions by one order of magnitude in wide range of the parameter space. The longitudinal polarization asymmetry of leptons in ${B}_{s}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ can approach $\mathcal{O}({10}^{\ensuremath{-}2})$. The forward-backward asymmetry of leptons in $B\ensuremath{\rightarrow}K{l}^{+}{l}^{\ensuremath{-}}$ is not large enough to be measured in future experiments. We also give some discussions about the branching ratios and the asymmetry observables related to these rare decay processes in the littlest Higgs model with T-parity.

Electroweak chiral Lagrangian from a natural topcolor-assisted technicolor model

Based on previous studies on computing coefficients of the electroweak chiral Lagrangian from C. T. Hill's schematic topcolor-assisted technicolor model, we generalize the calculation to K. Lane's prototype natural topcolor-assisted technicolor model. We find that typical features of the model are qualitatively similar to those of Hill's, but Lane's model prefers a smaller technicolor group and the ${Z}^{\ensuremath{'}}$ mass must be smaller than 400 GeV. Furthermore, the $S$ parameter is around the order of $+1$, mainly due to the existence of three doublets of techniquarks. We obtain the values for all coefficients of the electroweak chiral Lagrangian up to the order ${p}^{4}$. Apart from large negative four-fermion coupling values, the extended technicolor impacts on the electroweak chiral Lagrangian coefficients are small, since the techniquark self energy, which determines these coefficients, in general receives almost no influence from the extended technicolor induced four-fermion interactions except for its large momentum tail.

Bottom quark pair production in γγ collision

We study the Yukawa corrections to the γγ→b cross section in the topcolor assisted technicolor models at the photon-photon colliders. We find that, for the favorable parameters, the relative corrections from pseudo-Goldstone bosons give out a 3.17%—5.90% decrement of the cross section from the tree level when /{s/}2=500 GeV, the total relative corrections are significantly larger than the corresponding corrections in the standard model, the general two Higgs doublet model and the minimal supersymmetric standard model. So the observation of the correction to the γγ→b process at the International Linear Colliders is certainly the clue to the standard model and new physics.