Searcharxiv⌕ Search

arXiv subjects

Gongru Lu

Publications and source records attributed to Gongru Lu.

At least 37 records · Page 2Linked to original sources
arXiv2010

Technicolor corrections to b\bar{b} -> W^{\pm}π^{\mp}_t 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\bar{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 \rightarrow b\bar{b} -> W^{\pm}π_t^{\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 -> b\bar{b} -> W^{\pm}H^{\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 -> W^{\pm}π_t^{\mp}.

hep-ph↗
arXiv2010

Associated production of a neutral top-Higgs with a heavy-quark pair in the γγcollisions 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 γγcollisions at the International Linear Collider (ILC). We find that the cross section for t\bar{t}h_t in γγcollisions is at the level of a few fb with the c.m. energy \sqrt{s}=1000 GeV, which is consistent with the results of the cross section of t\bar{t}H in the standard model and the cross section of t\bar{t}h in the minimal supersymmetric standard modeland the little Higgs models. It should be distinct that hundreds of to thousands of h_t per year can be produced at the ILC, this process of γγ\to t\bar{t}h_t is really interesting in testing the standard model and searching the signs of technicolor.

hep-ph↗
arXiv2009

Testing the Littlest Higgs Model with T-parity in Bottom Quark Pair Production at High Energy Photon Colliders

We have calculated the cross section of the process e^+e^- \to γγ\to b\bar{b} in the littlest Higgs model with T parity (LHT). We find that, for the favorable parameters, the total cross section σ(e^+e^- \to γγ\to b\bar{b}) is sensitive to the breaking scale f, mixing parameter x_L, the masses of the mirror quarks m_{Hi}, and the relative correction of the LHT model is a few percent to dozens of percent. The cross section is significantly larger than the corresponding results in the standard model and in the other typical new physics models. Therefore the prediction in the LHT model is quite different from the predictions in other new physics models and such a process is really interesting in searching for the signs of the LHT model.

hep-ph↗
arXiv2009

Top quark three-body decays in the R-parity violating MSSM

In the minimal supersymmetric standard model the R-parity violating interactions can trigger various exotic three-body decays for the top quark, which may be accessible at the LHC. In this work we examine the R-violating decays t-> c X_1 X_2, which include the tree-level processes t-> c l^-_i l^+_j (l_i=e, mu, tau) and t->c d_i \bar{d}_j (d_i=d, s, b), as well as the loop induced processes t->c g X (X=g, γ, Z, h). We find that the hereto weakly constrained R-violating couplings can render the decay branching ratios quite sizable, some of which already reach the sensitivity of the Tevatron collider and can be expored at the LHC with better sensitivity.

hep-ph↗
arXiv2007

Probing R-parity Violating Interactions from Top Quark Polarization at LHC

In minimal supersymmetric standard model the R-parity violating interactions can induce anomalous top pair productions at the LHC through the t-channel process d_R \bar d_R -> t_L \bar t_L by exchanging a slepton or u-channel process d_R \bar d_R -> t_R \bar t_R by exchanging a squark. Such top pair productions with certain chirality cause top quark polarization in the top pair events. We found that at the LHC, due to the large statistics, the statistical significance of the polarization observable and thus the probing ability for the corresponding R-parity violating couplings are much higher than at the Tevatron upgrade.

hep-ph↗
arXiv2004

Charmless $\bar{B}_s\to VV$ Decays in QCD Factorization

The two body charmless decays of $B_s$ meson to light vector mesons are analyzed within the framework of QCD factorization. This approach implies that the nonfactorizable corrections to different helicity amplitudes are not the same. The effective parameters $a_i^h$ for helicity $h=0,+,-$ states receive different nonfactorizable contributions and hence are helicity dependent, contrary to naive factorization approach where $a_i^h$ are universal and polarization independent. The branching ratios for $\bar{B}_s\to VV$ decays are calculated and we find that branching ratios of some channels are of order $10^{-5}$, which are measurable at future experiments. The transverse to total decay rate $Γ_T/Γ$ is also evaluated and found to be very small for most decay modes, so, in charmless $\bar{B}_s\to VV$ decays, both light vector mesons tend to have zero helicity.

hep-ph↗
arXiv2003

The Rare Radiative Annihilation Decays $\bar{B}^0_{s,d} \to J/ψγ$

We investigate the physics potential of the annihilation decays $\bar{B}^0_{s,d} \to J/ψ$ $γ$ in the Standard Model and beyond. In naive factorization approach, the branching ratios are estimated to be $\mathcal{B}(\bar{B}^0_s \to J/ψγ)=1.40\times 10^{-6}$ and $\mathcal{B}(\bar{B}^0_d \to J/ψγ)=5.29\times 10^{-8}$. In the framework of QCD factorization, we compute the non-factorizable corrections and get $\mathcal{B}(\bar{B}^0_s \to J/ψγ) = 2.11\times10^{-7}$, $\mathcal{B}(\bar{B}^0_d \to J/ψγ) =7.65\times10^{-9}$. Future measurements of these decays would be useful for testing the factorization frameworks. The smallness of these decays in the SM make them sensitive probes of New Physics. As an example, we will consider the possible admixture of (V+A) charge current to the standard (V-A) current. This admixture will give significant contributions to the decays.

hep-ph↗
arXiv2003

The rare $\bar{B}^0_{d} \to ϕγ$ decays in Standard Model and as a probe of R-parity violation

We present the first study of the rare annihilation decay $\bar{B}^0_d \to ϕγ$ in the Standard Model. Using QCD factorization formalism, we find ${\cal B}(\bar{B}^0_d \toϕγ)=3.6\times 10^{-12}$. The smallness of the decay rate in the Standard Model make the decay a sensitive probe of new physics contributions. As an example, we calculate the effects of R-parity violating couplings. Within the available upper bounds for $|λ^{''}_{i23}λ^{''}_{i12}|$ and $|λ^{'}_{i32}λ^{'*}_{i12}|$, ${\cal B}(\bar{B}^0_d \toϕγ)$ could be enhanced to order of $10^{-9}\sim 10^{-8}$, which might be accessible at LHCB, B-TeV and the planning super high luminosity B factories at KEK and SLAC.

hep-ph↗
arXiv2003

The rare top quark decays $t\to cV$ in the topcolor-assisted technicolor model

We consider the rare top quark decays in the framework of topcolor-assisted technicolor (TC2) model. We find that the contributions of top-pions and top-Higgs predicted by the TC2 model can enhance the SM branching ratios by as much as 6-9 orders of magnitude. i.e., in the most case, the orders of magnitude of branching ratios are $Br(t\to c g)\sim 10^{-5}$, $Br(t\to c Z)\sim 10^{-5}$, $Br(t\to c γ)\sim 10^{-7}$. With the reasonable values of the parameters in TC2 model, such rare top quark decays may be testable in the future experiments. So, rare top quark decays provide us a unique way to test TC2 model.

hep-ph↗
arXiv2001

The rare top decay $t\to c g$ in topcolor assisted technicolor models

In the framework of topcolor-assisted technicolor(TC2) models, we calculate the contributions of flavor changing scalar couplings involved the neutral top-pion $π_{t}^{0}$ and top-Higgs $h_{t}^{0}$ to the branching ratio $B_{r}(t\longrightarrow cg)$. We find that the value of $B_{r}(t\longrightarrow cg)$ can reach $ 1\times10^{-3}$ with reasonable values of the parameters in TC2 models, which may be testable in the future experiments.

hep-ph↗
arXiv2001

The $B -> X_s gamma gamma$ decay in the standard model and the general two-Higgs-doublet model

Based on the low-energy effective Hamiltonian, we calculate the new physics corrections to the branching ratio and the differential distributions of the rare decay $B \to X_s γγ$ induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs-doublet model with the restriction $λ_{ij}^{U,D}=0$ for $i\neq j$. Within the considered parameter space, we see the following: (a) the standard model predictions of ${\cal B}(B \to X_s γγ)$ and $A_{FB}$ have a moderate $m_s$ dependence; (b) in model III, the prediction of the branching ratio ${\cal B}(B \to X_s γγ)$ ranges from one third to three times of the standard model prediction, but is highly correlated with that of ${\cal}(B \to X_s γ)$; (c) the new physics enhancement to the branching ratio ${\cal B}(B \to X_s γγ)$ in model II can be as large as $(30-50)%$; (d) the contribution from 1PR diagrams is dominant and hence four normalized differential distributions are insensitive to the variation of scale $μ$ and possible new physics corrections; (e) due to the smallness of its decay rate and the long-distance background, the $B \to X_s γγ$ decay is not a better process in detecting new physics than the $B \to X_s γ$ decay.

hep-ph↗
arXiv2001

$\etap K$ puzzle of B meson decays and new physics effects in the TC2 model

Using the low energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to $B \to π^+ π^-, K π$ and $K \etap$ in the Topcolor-assisted-Technicolor(TC2) model, and compare the results with the available data. By using $F_0^{\rm Bπ}(0)=0.20\pm 0.04$ preferred by the CLEO data of $B \to π^+ π^-$ decay, we find that the new physics enhancements to $B \to K \etap$ decays are significant in size, $\sim 50%$ with respect to the standard model predictions, insensitive to the variations of input parameters and hence provide a simple and plausible new physics interpretation for the observed unexpectedly large $B\to K \etap$ decay rates.

hep-ph↗
arXiv2001

The flavor-changing rare top decays $t\to c V V$ in topcolor-assisted technicolor theory

In the framework of topcolor-assisted technicolor (TC2) theory, we calculate the contributions of the scalars(the neutral top-pion $π_{t}^{0}$ and the top-Higgs $h_{t}^{0}$) to the flavor-changing rare top decays $t\to c V V$(V= W, g, $γ$ or Z). Our results show that $h_{t}^{0}$ can enhance the standard model $B_{r}^{SM}(t\longrightarrow cWW)$ by several orders of magnitude for most of the parameter space. The peak of the branching ratio resonance emerges when the top-Higgs mass is between $2m_{W}$ and $m_{t}$. The branching ratio $ B_{r}(t\to c W W)$ can reach $ 10^{-3}$ in the narrow range.

hep-ph↗
arXiv2000

Charmless decays B -> PP, PV, and effects of new strong and electroweak penguins in Topcolor-assisted Technicolor model

Based on the low energy effective Hamiltonian with generalized factorization, we calculate the new physics contributions to the branching ratios and CP-violating asymmetries of the two-body charmless hadronic decays $B \to PP, PV$ from the new strong and electroweak penguin diagrams in the TC2 model. The top-pion penguins dominate the new physics corrections, and both new gluonic and electroweak penguins contribute effectively to most decay modes. For tree-dominated decay modes $B \to ππ, ρπ, etc,$ the new physics corrections are less than 10%. For decays $B \to K^{(*)} π$, $K^{(*)} η$, $etc$, the new physics enhancements can be rather large (from $- 70%$ to $\sim 200%$) and are insensitive to the variations of $N_c^{eff}$, $k^2$, $η$ and $m_{\tildeπ}$ within the reasonable ranges. For decays $B^0 \to ϕπ$, $ϕη^{(')}$, $K^* \bar{K}^0$ and $ρ^+ K^0$, $δ{\cal B}$ is strongly $N_c^{eff}-$dependent: varying from -90% to $\sim 1680%$ in the range of $N_c^{eff}=2-\infty$. The new physics corrections to the CP-violating asymmetries ${\cal A}_{CP}$ vary greatly for different B decay channels. For five measured CP asymmetries of $B \to K π, K η', ωπ$ decays, $δ{\cal A}_{CP}$ is only about 20% and will be masked by large theoretical uncertainties. The new physics enhancements to interesting $B \to K η'$ decays are significant in size ($\sim 50%$), insensitive to the variations of input parameters and hence lead to a plausible interpretation for the unexpectedly large $B \to K η'$ decay rates. The TC2 model predictions for branching ratios and CP-violating asymmteries of all fifty seven $B \to PP, PV$ decay modes are consistent with the available data within one or two standard deviations.

hep-ph↗
arXiv2000

Neutral top-pion and top-charm production in high energy $e^{+}e^{-}$ collisions

We calculate the contributions of the neutral top-pion, predicted by topcolor-assisted technicolor (TC2) theory, to top-charm production via the processes $γγ\longrightarrow\bar{t}c$ and $e^{+}e^{-}\longrightarrow γγ\longrightarrow \bar{t}c$ at the high energy linear $e^{+}e^{-}$ collider (LC) experiments. The cross section is of order $10^{-2}pb$ in most of the parameter space of TC2 theory, which may be detected at the LC experiments. So the process $e^{+}e^{-}\longrightarrow \bar{t}c$ can be used to detect the signature of TC2 theory.

hep-ph↗
arXiv1999

Inclusive $η'$ production in B decays and the Enhancement due to charged technipions

The new contributions to the charmless B decay $B \to X_{s}η^{\prime}$ from the unit-charged technipions $P^{\pm}$ and $P^{\pm}_{8}$ are estimated. The technipions can provide a large enhancement to the inclusive branching ratio: $Br(B \to X_{s}η^{\prime}) \sim 7\times 10^{-4}$ for $m_{p1}=100GeV$ and $m_{p8}=250 \sim 350 GeV$ when the effect of QCD gluon anomaly is also taken into account. The new physics effect is essential to interpret the CLEO data.

hep-ph↗
arXiv1999

The rare K-decays in the Multiscale Walking Technicolor Model

We calculate the one-loop $Z^0$-penguin contributions to the rare K-decays, $K^+ \to π^+ ν\bar ν$, $K_L \to π^0 ν\bar ν$ and $K_L \to μ^+ μ^-$, from the unit-charged technipions $π_1$ and $π_8$ in the framework of the Multiscale Walking Technicolor Model. We find that: (a) the $π_1$ and $π_8$ can provide one to two orders enhancements to the branching ratios of the rare K-decays; (b) by comparing the experimental data of $Br(K^+ \to π^+ ν\bar ν)$ with the theoretical prediction one finds the lower mass bounds, $m_{p8} \geq 249 GeV$ for $F_Q=40GeV$ and $m_{p1}=100 GeV$; (c) by comparing the experimental data of $Br(K_L \to μ^+ μ^-)$ with the theoretical predictions one finds the lower bounds on $m_{p1}$ and $m_{p8}$, $m_{p1} \geq 210 GeV$ if only the contribution from $π_1$ is taken into account, and $m_{p8} \geq 580 GeV$ for $m_{p1}=210 GeV$, assuming $F_Q=40GeV$; (d) the assumed ranges of the masses $m_{p1}$ and $m_{p8}$ in the Multiscale Walking Technicolor Model are excluded by the rare K-decay data.

hep-ph↗