arXiv subjects

Guey-Lin Lin

Publications and source records attributed to Guey-Lin Lin.

65 records · Page 4Linked to original sources

arXiv1999

Gauge Independent Effective Potential and the Higgs Mass Bound

We introduce the Vilkovisky-DeWitt formalism for deriving the lower bound of the Higgs boson mass. We illustrate the formalism with a simplified version of the Standard Electroweak Model, where all charged boson fields as well as the bottom-quark field are disregarded. The effective potential obtained in this approach is gauge independent. We derive from the effective potential the mass bound of the Higgs boson. The result is compared to its counterpart obtained from the ordinary effective potential.

hep-ph↗

arXiv1998

$B \to η' X_s$ in the Standard Model

We study $B \to η' X_s$ within the framework of the Standard Model. Several mechanisms such as $b \to η' s g$ from the QCD anomaly, and $b \to η's $ and $B\to η' s \bar q$ from four-quark operators are treated simultaneously. We find that the first mechanism give a significant contribution to the branching ratio for $B\to η' X_s$, while the other two mechanisms account for about 15% of the experimental value. The Standard Model prediction for $B\to η' X_s$ is consistent with the CLEO data.

hep-ph↗

arXiv1998

Vilkovisky-DeWitt Effective Potential and the Higgs-Mass Bound

We compute the Vilkovisky-DeWitt effective potential of a simplified version of the Standard Electroweak Model, where all charged boson fields as well as the bottom-quark field are neglected. The effective potential obtained in this formalism is gauge-independent. We derive from the effective potential the mass bound of the Higgs boson. The result is compared to its counterpart obtained from the ordinary effective potential.

hep-ph↗

arXiv1997

QCD Corrections to $b\to sγγ$ and Exclusive $B_s\to γγ$ Decay

The short distance QCD corrections to $b\to sγγ$ are calculated in the leading logarithmic approximation. The equivalence of operator basis reduction for S-matrix elements by using the equations of motion or by proving a low energy theorem is discussed. We apply the above results to the exclusive $B_s\to γγ$ decay. The branching ratio of this decay is found to be $5\times 10^{-7}$ in the Standard Model. We also found that QCD corrections modify considerably the ratio between CP-even and CP-odd two-photon amplitudes.

hep-ph↗

arXiv1997

Like Sign Top Pair Production at LHC

Having a mass comparable to the weak scale, the top quark may have a sizable flavor changing couplings to Higgs bosons. We show that such couplings can be probed at the LHC through the parton subprocess $c(\bar c)g \to t (\bar t)A^0$, where the pseudoscalar $A^0$ subsequently decays into $t \bar c$ or ${\bar t} c$, giving rise to the intriguing final state of like sign top quark pairs. We also discuss major backgrounds to the above signal, in particular the QCD-Weak process $q\bar q' \to W^+(W^-) t \bar t$. The issue of background reduction is briefly discussed.

hep-ph↗

arXiv1997

Probing Flavor Changing Neutral Higgs Couplings at LHC

Uniquely heavy with mass at the weak scale, the top quark may have large flavor changing couplings to Higgs bosons that are as yet unexplored. We show that such couplings can be directly probed at the LHC through the parton subprocess $c(\bar c)g \to t (\bar t)A^0$, where the pseudoscalar $A^0$ subsequently decays into $t \bar c$ or ${\bar t} c$, giving rise to the intriguing final state of like sign top quark pairs. After demanding $\ell^\pm\ell^\pm$, missing energy and two $b$-jets, the major background turns out to be $q\bar q' \to Wt \bar t$, which can be partially suppressed by jet counting. The signal can then manifest itself in the asymmetry of numbers of $\ell^+\ell^+$ and $\ell^-\ell^-$ events. To further improve the signal over background, efficient $t$ vs. $\bar t$ tagging methods should be developed.

hep-ph↗

arXiv1995

Like Sign Top Quark Pair Production at Linear Colliders

In the general two Higgs doublet model with flavor changing neutral Higgs couplings, neutral Higgs bosons may decay dominantly via $t\bar c$ or $\bar tc$ final states. At the linear collider, $e^+e^- \to h^0A^0$ or $H^0A^0$ production processes may result in $b\bar bt\bar c$, $W^+W^-t\bar c$ or $tt\bar c\bar c$ (or $\bar t\bar tcc$) final states. The process $γγ\to h^0,\ A^0 \to t\bar c$ is also promising, but $e^+e^- \to (h^0,\ H^0) Z^0 \to t\bar c Z^0$ is relatively suppressed. The possibility of observing like sign lepton pairs, usually the hallmark for neutral meson mixing, is quite interesting since $T^0$ mesons do not even form.

hep-ph↗

arXiv1994

Heavy Quark Effective Theory on the Light Front

The light-front heavy quark effective theory is derived to all orders in $1/m_Q$. In the limit $m_Q\rightarrow \infty$, the theory exhibits the familiar heavy quark spin-flavor symmetry. This new formalism permits a straightforward canonical quantization to all orders in $1/m_Q$; moreover, higher order terms have rather simple operator structures. The light-front heavy quark effective theory can serve as an useful framework for the study of non-perturbative QCD dynamics of heavy hadron bound states.

hep-ph↗

arXiv1994

Effective Lagrangian Approach to Weak Radiative Decays of Heavy Hadrons

Motivated by the observation of the decay $\bar{B}\to \bar{K}^*γ$ by CLEO, we have systematically analyzed the two-body weak radiative decays of bottom and charmed hadrons. There exist two types of weak radiative decays: One proceeds through the short-distance $b\to sγ$ transition and the other occurs through $W$-exchange accompanied by a photon emission. Effective Lagrangians are derived for the $W$-exchange bremsstrahlung processes at the quark level and then applied to various weak electromagnetic decays of heavy hadrons. Predictions for the branching ratios of $\bar{B}^0\to D^{*0} γ,~Λ_b^0\toΣ_c^0γ,~Ξ_b^0\to Ξ_c^0γ$ and $Ξ_b^0\to\xip_c^0γ$ are given. In particular, we found ${\cal B}(\bar{B}^0 \to D^{*0}γ)\approx 0.9\times 10^{-6}$. Order of magnitude estimates for the weak radiative decays of charmed hadrons: $~D^0\to \bar{K}^{*0}γ,~Λ_c^+\toΣ^+γ$ and $Ξ_c^0\toΞ^0γ$ are also presented. Within this approach, the decay asymmetry for antitriplet to antitriplet heavy baryon weak radiative transitions is uniquely predicted by heavy quark symmetry. The electromagnetic penguin contribution to $Λ_b^0\toΛγ$ is estimated by two different methods and its branching ratio is found to be of order $1\times 10^{-5}$. We conclude that weak radiative decays of bottom hadrons are dominated by the short-distance $b\to sγ$ mechanism.

hep-ph↗

arXiv1994

Corrections to Chiral Dynamics of Heavy Hadrons: SU(3) Symmetry Breaking, (with some minor corrections)

In previous publications we have analyzed the strong and electromagnetic decays of heavy mesons and heavy baryons in a formalism which incorporates heavy-quark and chiral symmetries. There are two possible symmetry-breaking effects on the chiral dynamics of heavy hadrons: the finite-mass effects from light quarks and the $1/ m_Q$ corrections from heavy quarks. In the present paper, chiral-symmetry-breaking effects are studied and applications to various strong and radiative decays of heavy hadrons are illustrated. SU(3) violations induced by chiral loops in the radiative decays of charmed mesons and charmed baryons are compared with those predicted by the constituent quark model. In particular, available data for $D^*$ decays favor values of the parameters in chiral perturbation theory which give predictions for $D^*$ decays close to the quark model results except for the $D^{*+}_s$. Implications are discussed.

hep-ph↗

arXiv1993

Subleading Corrections to Semileptonic Lambda_c Decays

The semileptonic decay $Λ_c \to Λ\ell ν$ is considered in the framework of heavy quark effective theory beyond the leading order in the $1/m_c$ expansion. According to our estimate the polarization variable will receive only very small corrections such that $α_{Λ_c} \le -0.95$.

hep-ph↗