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Chuan-Hung Chen

Publications and source records attributed to Chuan-Hung Chen.

At least 73 records · Page 4Linked to original sources
arXiv2011

$Δm_D$ and $ΔΓ_D$ revisted

The lifetime difference ($y_D=ΔΓ_D/2Γ_D$) and mass difference ($x_D=Δm_D/Γ_D$) of neutral $D$ meson have been measured with $y_D=(0.80\pm 0.13)%$ and $x_D=(0.59 \pm 0.20)%$, respectively. Intriguingly, in contrast with the cases of $K$ and $B_q$ systems, the current data indicate that $y_D/x_D \sim 1$ and $y_D$ favors to be larger than $x_D$. For explaining the experimental indication, we here study the $D-\bar D$ oscillation in the framework of unparticle physics. We demonstrate that {\it the peculiar phase appearing in off-shell unparticle propagator} could play an important role on $x_D$ and $y_D$.

hep-ph↗
arXiv2011

Study of the Radivative Pion Decay

We study the radiative pion decay of $π^{+} \to e^{+}ν_{e}γ$ in the chiral perturbation theory (ChPT) and light front quark model (LFQM). The vector and axial-vector hadronic form factors ($F_{V,A}$) for the $π\toγ$ transition are evaluated in the whole allowed momentum transfer. In terms of these momentum dependent form factors, we calculate the decay branching ratio and compare our results with the experimental data and other theoretical predictions in the literature. We also constrain the possible size of the tensor interaction in the LFQM.

hep-ph↗
arXiv2011

Axigluon on like-sign charge asymmetry ${\cal A}^b_{s\ell}$, FCNCs and CP asymmetries in B decays

A non-universal axigluon in generalized chiral color models leads to flavor changing neutral currents (FCNCs) at tree level. We analyze phenomenologically the new contributions to $B_{q}$ (q=d, s) mixing and the related CP asymmetries (CPAs) that are generated by axigluon exchange. We find that although $Δm_{B_q}$ can give a strict constraint on the parameters of $b\to q$ transition, the precise measurement of $\sin2β_{J/ΨK^0}$ can further exclude the parameter space of $b\to d$ transition. The axigluon-mediated effects can enhance the like-sign dimuon charge asymmetry ${\cal A}^{b}_{s\ell}$ by one order of magnitude larger than the standard model prediction. Accordingly, large CPA $\sin2β^{J/Ψϕ}_s$ and CPA difference $\sin2β_{JΨK^0}-\sin2β_{ϕK^0}$ are achieved.

hep-ph↗
arXiv2010

Charge and CP asymmetries of $B_q$ meson in unparticle physics

Recently the DØ Collaboration reported an observation of like-sign charge asymmetry (CA), which is about $3.2 σ$ deviation from the standard model (SM) prediction. Inspired by the observation we investigate the scalar unparticle effects, under the color charge of $SU(3)_c$ symmetry, in the CP violation in neutral B meson oscillations as well as the dispersive and absorptive parts of $\bar B_q\leftrightarrow B_q$ transition, which can be related to the CA directly. In order to illustrate the peculiar properties of unparticle, our analysis is carried out in two scenarios for the right-handed section: (I) $λ_R=λ_L$ and $U_D^R=U_D^L$, where $λ_{L,R}$ and $U_D^{L,R}$ are the couplings and flavor mixing matrix of left- and right-handed section, respectively; (II) $λ_R >> λ_L$ and $U_D^R$ is completely a free parameter. In scenario I we found that the wrong- and like-sign CA cannot be changed significantly for a SM-like CP violating source because of the strong constraint of $Δm_{B_d}$. Contrarily, in scenario II we can figure out the parameter space in which the CA can be enhanced to the value observed by DØ with the constraint of $Δm_{B_s}$ due to the enhancement of $Γ^s_{12}$. In the parameter space we obtained, the correlation between $ΔΓ^s$ and $ϕ_s$ is consistent with the current CDF and DØ results.

hep-ph↗
arXiv2010

Z-mediated charge and CP asymmetries and FCNCs in $B_{d,s}$ processes

We show model-independently that the negative like-sign charge asymmetry $(-A^b_{s\ell})$ is less than $ 3.16\times 10^{-3}$ when the constraints from the $B_q-\bar B_q$ mixings and the time-dependent CP asymmetries (CPAs) for $B_q\to J/ΨM_q$ with $M_q=K,ϕ$ and $q=d,s$ are taken into account. Although the result is smaller than the measured value by the DØ Collaboration at Fermilab, there is still plenty of room to have new physics, which is sensitive to new CP violating effects, as the standard model (SM) prediction is $(2.3_{-0.5}^{+0.6})\times 10^{-4}$. To illustrate the potential large $|A^{b}_{s\ell}|$, we show the influence of new $SU(2)_L$ singlet exotic quarks in the vector-like quark model, where the $Z$-mediated flavor changing neutral currents (FCNCs) are generated at tree level. In particular, we demonstrate that (a) the like-sign charge asymmetry could be enhanced by a factor of two in magnitude; (b) the CPA of $\sin2β^{J/Ψϕ}_s$ could reach to $-15%$; (c) the CPA of $\sin2β_{ϕK_S}$ could be higher than $\sin2β_{J/ΨK_S}$ when $|A^b_{s\ell}|$ is larger than the SM prediction; and (d) the branching ratio for $B_s\to μ^+ μ^-$ could be as large as $0.6\times 10^{-8}$.

hep-ph↗
arXiv2010

Forward-backward asymmetry of top quark in unparticle physics

The updated CDF measurement of the forward-backward asymmetry (FBA) in the top quark production p{bar p} -> t{bar t} at Tevatron (with the CMS energy 1.96 TeV) shows a deviation of 2*sigma from the value predicted by the Standard QCD Model. We present calculation of this quantity in the scenario where colored unparticle physics contributes to the s-channel of the process, and obtain the regions in the plane of the unparticle parameters lambda and dU which give the values of the FBA and of the total t{bar t} production cross section compatible with the present measurements.

hep-ph↗
arXiv2010

Forward-backward asymmetry of top quark in diquark models

Motivated by the recent unexpected large forward-backward asymmetry (FBA) of the top quark observed by D$Ø$ and CDF at the Tevatron, we investigate a possible explanation for the anomaly within the framework of diquark models. Unlike other mechanisms induced by s-channel or t-channel, the top-quark pair production in the diquark models is dictated by the u-channel diagram. We find that the color-triplet diquark can generate the FBA of 20% when the constraint from the cross section of the top-quark pair production is taken into account.

hep-ph↗
arXiv2010

Lepton flavor violating tau decays in type-III seesaw mechanism

In this paper, the lepton flavor violating $τ\to \ell P(V)$ ($P,V= π^0, η, η^{\prime}, ρ^0, ω, ϕ$) and $τ\to 3\ell$ ($\ell = e, μ$) decays are studied in the framework of the type-III seesaw model, in which new triplet fermions with a zero hypercharge (Y=0) interact with ordinary lepton doublets via Yukawa couplings, and affect tree-level leptonic Z-boson couplings. We investigate the experimental bound from the leptonic Z decay to get contraint on the exsiting parameters space. We predict that the upper limits on the branching ratios of $τ\to \ell P(V)$ and $τ\to 3\ell$ can reach the experimental current limits.

hep-ph↗
arXiv2010

New charged Higgs effects on $Γ_{K_{e2}}/Γ_{K_{μ2}}$, $f_{D_s}$ and ${\cal B}(B^+\to τ^+ ν)$ in the Two-Higgs-Doublet model

A new scheme for Yukawa matrices is proposed for free of flavor changing neutral currents (FCNCs) at tree level in general two-Higgs-doublet model (THDM) without imposing symmetry. We find that the new type couplings of charged Higgs to fermions not only depend on the flavors, but also can be ascribed by new CP violating phases. Unlike conventional THDM, the resulted new charged Higgs effects could have the specialties: (a) the influence on $Γ(K^\pm_{e 2})/Γ(K^\pm_{μ2})$ cannot be eliminated, (b) the decay constant of $D_s$ could be enhanced, and (c) enhancement of branching ratio for $B^+\to τ^+ ν$ could be achieved.

hep-ph↗
arXiv2010

Sommerfeld Enhancement from Unparticle Exchange for Dark Matter Annihilation

We investigate the implication of unparticle exchange for the possible Sommerfeld enhancement in dark matter annihilation process. Assuming the unparticle exchange during WIMP collision, we solve the Schr\rm\ddot{o}dinger equation for the effective potential, and find that the Sommerfeld enhancement factor is dictated by the scale dimension of unparticle as 1/v^{3-2d_{\UP}}. Numerically the Sommerfeld enhancement could be {\cal O}(10-10^{3}).

hep-ph↗
arXiv2010

Double Neutral Higgs production in the Two-Higgs doublet model at the LHC

In this work we study the production and decay of two CP-even Higgs bosons in the general CP-conserving two-Higgs doublet model at the LHC. We also study the limiting case of the decoupling scenario. For each Yukawa version of the model, we look for the region of the parameter space where a signal would be seen at the LHC. Taking into account theoretical and experimental constraints on the two Higgs doublet model parameters, we show that the cross section can be two orders of magnitude above the corresponding Standard Model cross section. We have also studied in detail the decay profile of the Higgs bosons and showed that interesting signatures may emerge for some particular values of the parameters. In some scenarios, specific triple Higgs could be measured.

hep-ph↗
arXiv2010

$|V_{ub}|$ and $B\toη^{(')}$ Form Factors in Covariant Light Front Approach

$B\to (π, η, η')$ transition form factors are investigated in the covariant light-front approach. With theoretical uncertainties, we find that $B\to (π, η, η')$ form factors at $q^2=0$ are $f^{(π, η, η')}_{+}(0)=(0.245^{+0.000}_{-0.001}\pm 0.011, 0.220 \pm 0.009\pm0.009, 0.180\pm 0.008^{+0.008}_{-0.007})$ for vector current and $f^{(π, η, η')}_{T}(0)=(0.239^{+0.002+0.020}_{-0.003-0.018}, 0.211\pm 0.009^{+0.017}_{-0.015}, 0.173\pm 0.007^{+0.014}_{-0.013})$ for tensor current, respectively. With the obtained $q^2$-dependent $f^π_{+}(q^2)$ and observed branching ratio (BR) for $\bar B_d\to π^+ \ell \bar ν_{\ell}$, the $V_{ub}$ is found as $|V_{ub}|_{LF}= (3.99 \pm 0.13)\times 10^{-3}$. As a result, the predicted BRs for $\bar B\to (η, η') \ell \barν_{\ell}$ decays with $\ell=e,μ$ are given by $(0.49^{+0.02+0.10}_{-0.04- 0.07}, 0.24^{+0.01+0.04}_{-0.02-0.03})\times 10^{-4}$, while the BRs for $D^-\to (η,η')\ell\barν_{\ell}$ are $(11.1^{+0.5+0.9}_{-0.6-0.9}, 1.79^{+0.07+0.12}_{-0.08-0.12})\times 10^{-4}$. In addition, we also study the integrated lepton angular asymmetries for $\bar B\to (π,η,η')τ\barν_τ$:$(0.277^{+0.001+0.005}_{-0.001-0.007},0.290^{+0.002+0.003}_{-0.000-0.003},0.312^{+0.004+0.005}_{-0.000-0.006})$.

hep-ph↗
arXiv2009

CP phase of nonuniversal $Z'$ on $\sinϕ^{J/Ψϕ}_s$ and T-odd observables of $\bar B_{q}\to V_{q} \ell^{+} \ell^{-}$

The evidence of a large CP phase has been shown by CDF and DØ collaborations in the time-dependent CP asymmetry (CPA) of $B_s\to J/Ψϕ$ decay, where the nonvanished CPA clearly implies the existence of a non-Kobayashi-Maskawa phase in $b\to s$ transition. We study the new phases originated by the extra family dependent $U(1)'$ model and examine their impact on $\hat{T}$ or CP violating observables in $\bar B_q\to V_q \ell^{+} \ell^{-}$ decays with $V_q=K^* (ϕ)$. Adopting the constraints from the current data of $Δm_s$ and the branching ratios for $\bar B_s\to μ^+ μ^-$ and $\bar B_q\to V_q\ell^+ \ell^-$, we find that $ϕ^{J/Ψϕ}_s=-(0.26\pm 0.22)$ and the T-odd observables of above 10% in the decay chain $\bar B_q\to V_q(\to Kπ[KK]) \ell^+ \ell^-$ can be achieved. In addition, we demonstrate that the longitudinal and transverse polarizations of $K^*$ and the up-down asymmetry of $K$ in the same decay chain are also sensitive to the $Z'$-mediated effects.

hep-ph↗
arXiv2009

Impact of colored scalars on $D^0-\bar D^0$ mixing in diquark models

Inspired by the recent observation of the $D^0-\bar D^0$ mixing, we explore the effects of colored scalars on the $ΔC=2$ process in diquark models. As an illustration, we investigate the diquarks with the quantum numbers of (6, 1, 1/3) and (6, 1, 4/3) under $SU(3)_C\times SU(2)_L\times U(1)_Y$ gauge symmetries, which contribute to the process at one-loop and tree levels, respectively. We show that $Δm_D$ gives the strongest constraint on the free parameters. In addition, we find that the small couplings can be naturally interpreted by the suppressed flavor mixings if the diquark of (6, 1, 4/3) only couples to the third generation.

hep-ph↗
arXiv2009

$B_{s,d}-\bar B_{s,d}$ mixings and $b\to q (\ga, \ell \bar \ell)$ decays in private Higgs model

We study the low energy phenomena induced by the lightest charged Higgs in the private Higgs (PH) model, in which each quark flavor is associated with a Higgs doublet. We show that the couplings of the charged Higgs scalars to fermions are fixed and the unknown parameters are only the masses and mixing elements of the charged Higgs scalars. As the charged Higgs masses satisfy with $M_b<M_{c}\ll M_{s} \ll M_{d,u}$, processes involving $B$-meson are expected to be the ideal places to test the PH model. In particular, we explore the constraints on the model from experimental data in $B$ physics, such as the branching ratio (BR) and CP asymmetry (CPA) of $B\to X_s \ga$, $B_{d,s}-\bar B_{d,s}$ mixings and the BR for $B\to K^* \ell^{+} \ell^{-}$. We illustrate that the sign of the Wilson coefficient for $B\to X_s \ga$ can be different from that in the standard model, while this flipped sign can be displayed by the forward-backward asymmetry of $B\to V \ell^{+} \ell^{-}$ with $V$ a vector meson. We also demonstrate that $B_{d,s}-\bar B_{d,s}$ mixings and their time-dependent CPAs are negligible small and the BR of $B\to K^* \ell^{+} \ell^{-}$ can have a more strict bound than that of $B\to X_s \ga$.

hep-ph↗
arXiv2009

Neutrino Masses, Leptogenesis and Decaying Dark Matter

We study a simple extension of the standard model to simultaneously explain neutrino masses, dark matter and the matter-antimatter asymmetry of the Universe. In our model, the baryon asymmetry is achieved by the leptogenesis mechanism, while the decaying dark matter with the lifetime of O(10^26 s) provides a natural solution to the electron and positron excesses in Fermi and PAMELA satellite experiments. In particular, we emphasize that our model is sensitive to the structure at the endpoint around 1 TeV of the Fermi data. In addition, some of new particles proposed in the model are within the reach at the near future colliders, such as the Large Hadron Collider.

hep-ph↗
arXiv2009

Resolution to neutrino masses, baryon asymmetry in leptogenesis and cosmic-ray anomalies

By extending the lepton sector of standard model to include one sterile neutrino and two sets of new Higgs doublets and right-handed neutrinos, denoted by $(η_1, N_1, N_3)$ and $(η_2, N_2, N_4)$, with two $Z_2$ symmetries, the puzzles of neutrino masses, matter-antimatter asymmetry and cosmic-ray excess observed by Fermi-LAT and PAMELA can be resolved simultaneously. The characters of the model are: (a) neutrino masses arise from type-I and radiative seesaw mechanisms; (b) leptogenesis leading to baryon asymmetry at the energy scale of $O(1- 10\rm TeV)$ could be realized through soft $Z_2$ symmetry breaking effects; and (c) the conditions of small couplings for a long-lived dark matter could be achieved naturally through loop corrections due to the same soft symmetry breaking effects. The candidate for dark matter in leptophilic decays could fit the Fermi-LAT and PAMELA data well.

hep-ph↗