TC2 Models Research Articles

Analysis of flow and heat transfer of different miniature chambers with/and/without rectangular pin: Numerical investigation with empirical validation

A numerical analysis is conducted on flow and heat transfer of different configurations of miniature chamber with and without the rectangular pin as complex and smooth models, respectively. Five configurations of the miniature chamber are considered, and they are named for short as smooth models, including RC, HC1, TC1, HC2, and TC2, and complex models, including RC-RP, HC1-RP, TC1-RP, HC2-RP, and TC2-RP. Experiments are also carried out on a real straight case in order to validate the numerical results and create a baseline for the comparison. The working fluid is water in the laminar flow regime. It is found that the numerical results are in a good agreement with the current experimental data, whose the maximum differences are 5.3% for the heat transfer coefficient and 6.4% for the pressure drop. Depending on the studied case and Reynolds number (400 < Re < 1990), the Nusselt number and friction factor are 0.85–1.95 and 0.45–10.66 times as compared with those for the straight baseline model, leading to the performance index of 0.77–1.54. The results indicate that the complex models have better heat transfer performance with a certain pressure drop as compared to the smooth models. It can attribute to enlarging of surface area, increasing of fluid mixing, interrupting and redeveloping of boundary layers, etc. This study can provide efficient findings for thermal engineers working on microelectronic cooling systems.

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.

Flavour changing scalar couplings and tγ(Z) production at hadron colliders

We calculate the contributions of the flavour changing scalar (FCS) couplings arising from topcolour-assisted technicolour (TC2) models at the tree level to the tγ and tZ production at the Tevatron and LHC experiments. We find that the production cross sections are very small at the Tevatron with , which is smaller than 5 fb in most of the parameter space of TC2 models. However, the virtual effects of the FCS couplings on the tγ(Z) production can easily be detected at the LHC with , via the final state .

Top-pions and single top production at HERA and THERA

We study single top quark production at the HERA and THERA colliders as coming from the FCNC vertices tcγ and tcZ that appear at one loop level in topcolor-assisted technicolor models (TC2). In contrast with previous expectations, we find that the production cross section is of order 10−6 pb for HERA and 10−4 pb for THERA (even lower that the SM prediction). Therefore, none of the two colliders are capable to probe the pseudoscalar top-pion or the scalar top-Higgs predicted in TC2 models via single top production.

Non-universal Gauge Bosons Z' and the Process

We discuss the observability of the non-universal bosons Z' predicted by topcolor-assisted technicolor (TC2) models in the near future high-energy linear collider (LC) experiments via studying its contributions to the processes and . We find that the signals of the new particle Z' can be detected by measuring the relative corrections to the cross sections and the ratio of signal over square root of the background for these two processes in the LC experiments. In most of the parameter space of TC2 models, it is difficult to observe the virtual effects of the Z' exchange on the forward-backward asymmetries and .

Production of the top-pions at the THERA collider based γp collisions

In the framework of the topcolor-assisted technicolor (TC2) models, we study the production of the top-pions π0t, πt± via the processes ep→γc→π0tc and ep→γc→π±tb mediated by the anomalous top coupling tcγ. We find that the production cross section of the process ep→γc→π0tc is very small. With reasonable values of the parameters in TC2 models, the production cross section of the process ep→γc→π±tb can reach 1.2 pb. The charged top-pions π±t might be directly observed via this process at the THERA collider based γp collisions.

Non-Universal Gauge Bosons Z′ and Rare Top Decays

We study a new method for detecting non-universal gauge bosons Z′ via considering their effects on rare top decays. We calculate the contributions of the non-universal gauge bosons Z′ predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models on the rare top decays t → cV (V = g,γ,Z) and t → clilj (li,lj = τ,μ, or e). We show that the branching ratios of these processes can be significantly enhanced. Over a sizeable region of the parameter space, we have Br (t → cg) ~ 10-5 and Br (t → cττ) ~ 10-7, which may approach the observable threshold of near future experiments. Non-universal gauge bosons Z′ may be detected via the rare top decay processes at the top-quark factories such as the CERN LHC.

The process e+e− → νν̄γ in topcolour-assisted technicolour models

In the context of topcolour-assisted technicolour (TC2) models, we consider the process e+e− → νν̄γ and calculate the cross section of this process at leading order. It is shown that the extra U(1) gauge boson Z′ predicted by TC2 models can give significant contributions to the process e+e− → ντν̄τγ, which may be detected in the future high energy linear e+e− collider (LC) experiments.

Top-Higgs and the Process **The project supported by National Natural Science Foundation of China (9203005) and Foundation of Henan Educational Committee

In the context of topcolor-assisted technicolor (TC2) models, we calculate the s-channel contributions of the top-Higgs to the process . We find that, for reasonable ranges of the parameters, can give significant contributions to this process. When the top-Higgs mass approximately equals to the center-of-mass energy and the free parameter , the cross section can reach 161 fb, which may be detected in the γγ collisions based on the future e+e− colliders. Thus, the process may be used to probe the top-Higgs and further test TC2 models in γγ collisions.

Lepton flavor violating processes [formula omitted] in topcolor-assisted technicolor models

We study the lepton flavor violating (LFV) processes li→ljνlν̄l in the context of the topcolor-assisted technicolor (TC2) models. We find that the branching ratios Br(τ→ljντν̄τ) are larger than the branching ratios Br(τ→ljνlν̄l) in all of the parameter space. Over a wide range of parameter space, we have Br(τ→ljντν̄τ)∼10−6 and Br(τ→ljνlν̄l)∼10−9 (l=μ or e). Taking into account the bounds given by the experimental upper limit Brexp(μ→3e)⩽1×10−12 on the free parameters of TC2 models, we further give the upper limits of the LFV processes li→ljνlν̄l. We hope that the results may be useful to partly explain the data of the neutrino oscillations and the future neutrino experimental data might be used to test TC2 models.

Lepton flavour violating signals of gauge bosons Z′ at future e+e− colliders

Many models, such as topcolour-assisted technicolour (TC2) models and flavour-universal TC2 models, predict the existence of extra U(1) gauge bosons Z′, which couple preferentially to the third generation. The lepton flavour violating (LFV) signals of these new particles at the future e+e− colliders (LCs) are discussed by calculating their contributions to the LFV process e+e− → μτ. We calculate the cross section of this process and discuss its dependence on the beam polarization. The ratio of the signal over the square root of the background (S/√B) is also calculated. The results show that the LFV signals of the gauge bosons Z′ may be detected at the future LC experiments.

Rc constrains topcolour-assisted technicolour models

We consider the Z → cc̄ branching ratio Rc in the context of topcolour-assisted technicolour (TC2) models. We find that the main corrections to Rc in TC2 models come from the neutral top-pion π0t and the top-Higgs boson h0t via the flavour changing scalar (FCS) coupling φt̄c. The recent experimental value of Rc imposes a severe constraint on the FCS coupling factor Ktc.

Flavor changing Z decay [formula omitted] in topcolor-assisted technicolor models

In the context of topcolor-assisted technicolor (TC2) models, we examine the flavor changing (FC) Z decay Z→b s ̄ ( b ̄ s) and calculate the contributions of the new particles predicted by TC2 models to the branching ratio Br(Z→b s ̄ + b ̄ s) . We find that the contributions mainly come from the top-pions. In most of the parameter space, the Br(Z→b s ̄ + b ̄ s) can reach 10 −5, which may be detected in near future experiments such as Giga-Z version of the TESLA. Thus, the FC Z decay Z→b s ̄ ( b ̄ s) can be used to test TC2 models.

SIGNATURES OF THE NEUTRAL TOP-PION IN eγ COLLISIONS

We calculate the contributions of the neutral top-pion [Formula: see text] to the process [Formula: see text] in the framework of topcolor-assisted technicolor (TC2) models. Our results show that [Formula: see text] can give significant contributions to this process. With reasonable values of the parameters in TC2 models, the cross-section σ can reach 1.3 pb which may be detected at the eγ collisions based on the future high energy linear e+e- collider experiments.

Lepton–Flavor Violating Processes li → liγ in Topcolor Assisted Technicolor Models**The project supported by National Natural Science Foundation of China (19905004), the Excellent Youth Foundation of Henan Scientific Committee (9911)

We consider the lepton-flavor violating (LFV) processes li → liγ in the framework of topcolor-assisted technicolor (TC2) models. We find that the new gauge boson Z′ predicted by TC2 models can give significantly contributions to these processes via the flavor-changing couplings Z′lilj. The present experimental bound on the LFV process μ → eγ gives severe constraints on the TC2 models. Using other experimental constraints on the Z′ mass MZ, we obtain constraints on the lepton mixing factors Kτμ and Kτe. The future LFV experiments will probe into TC2 models.

Non-universal gauge bosons Z′ and lepton flavor-violating tau decays

There are many models beyond the standard model predicting the existence of non-universal gauge bosons Z′, which can give rise to very rich phenomena. We calculate the contributions of the non-universal gauge bosons Z′, predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models, to the lepton flavor-violating tau decays τ→liγ and τ→liljlk. We find that the branching ratio Br(τ→liljlk) is larger than that of the process τ→liγ in all of the parameter space. Over a sizable region of the parameter space, we have Br(τ→liljlk)∼10−8, which may be detected in the future experiments.

Electroweak limits on nonuniversalZ′bosons

Many types of physics beyond the standard model include an extended electroweak gauge group. If these extensions are associated with flavor symmetry breaking, the gauge interactions will not be flavor universal. In this paper we update the bounds placed by electroweak data on the existence of flavor nonuniversal extensions to the standard model in the context of top-color assisted technicolor (TC2), noncommuting extended technicolor (NCETC), and the ununified standard model (UUM). In the first two cases the extended gauge interactions couple to the third generation fermions differently than to the light fermions, while in the ununified standard model the gauge interactions couple differently to quarks and leptons. The extra $\mathrm{SU}(2)$ triplet of gauge bosons in NCETC and UUM models must be heavier than about 3 TeV, while the extra Z boson in TC2 models must be heavier than about 1 TeV.

Top quark associated production of the neutral top pion at high energye+e−colliders

In the context of topcolor-assisted technicolor (TC2) models, we calculate the associated production of the neutral top-pion $\pi_{t}^{0}$ with a pair of top quarks via the process $e^{+}e^{-}\longrightarrow t\bar{t}\pi_{t}^{0}$. We find that the production cross section is larger than that of the process $ e^{+}e^{-}\longrightarrow t\bar{t}H$ both in the standard model (SM) and in the minimal supersymmetric SM. With reasonable values of the parameters in TC2 models, the cross section can reach $20fb$. The neutral top-pion $\pi_{t}^{0}$ may be direct observed via this process.

Lepton flavor violating Z→ lilj in flavor-universal topcolor-assisted technicolor

In the context of flavor-universal topcolor-assisted technicolor (TC2) models, we calculate the lepton flavor violating (LFV) Z→ l i l j decays. We find that the extra U(1) gauge boson Z′ can give significant contributions to these LFV processes. With reasonable values of the parameters, the branching ratios of the processes Z→ τμ and Z→ τe can approach the experimental upper limits. The indirect bound on the process Z→ μe can give a severe constraint on the flavor-universal TC2 models.