arXiv subjects

Yi Liao

Publications and source records attributed to Yi Liao.

150 records · Page 9Linked to original sources

arXiv1999

Vanishing Contribution to Quark Electric Dipole Moment in the 2HD Model with CKM CP Violation

In the standard model (SM) of electroweak interactions, CP noninvariance arises from the nonzero phase in the CKM matrix. Its contribution to the quark electric dipole moment (EDM) vanishes surprisingly at two loop order. This makes the quark EDM extremely small in the SM. In this paper, we consider the two Higgs doublet extension of the SM and assume that CP noninvariance is still encoded in the CKM matrix. We calculate the charged Higgs boson contribution to the quark EDM which naively should be of order $eG_F^2\tildeδ(4π)^{-4}m_{u(d)}m_t^2m_b^2m_H^{-2}$ for the up (down) quark with possible enhancement factors of $\tan^2β$. Here $\tildeδ$ is the rephasing invariant of CP violation. However, contrary to the above naive expectation, we find that the charged Higgs boson contribution vanishes strictly at two loop order. We show explicitly how this comes about and explains how it is related to the general form of Yukawa couplings in a spontaneously broken gauge theory.

hep-ph↗

arXiv1997

Production of neutral scalar Higgs bosons at $eγ$ colliders

We study the production of neutral scalar (CP even) Higgs bosons in the process $eγ\to e h$ by including supersymmetric corrections to the dominant $t$-channel photon exchange amplitude. In addition to the standard model $W^{\pm}$ and fermion loops, there are substantial contributions from chargino loops. For some cases, these contributions can exceed those of the $W$'s and ordinary fermions. The cross sections in this channel are generally one or two orders of magnitude larger than those in the related channel $e\bar{e}\toγh$.

hep-ph↗

arXiv1996

$O(α^2 G_F m^2_t)$ Contributions to $H\toγγ$

The rare decay $H\to γγ$ is a promising detection channel for an intermediate mass Higgs boson. We compute its two-loop $O(α^2 G_F m_t^2)$ correction in the standard model and find that the relative correction to the decay rate runs between $0.7%$ and $0.5%$ for $M_H=80-150$ GeV. The analogous correction to the amplitude for $gg\to H$ is recovered as a special case. The generalization of our result to other models is also briefly indicated.

hep-ph↗

arXiv1995

Heavy Fermion Screening Effects and Gauge Invariance

We show that the naively expected large virtual heavy fermion effects in low energy processes may be screened if the process under consideration contains external gauge bosons constrained by gauge invariance. We illustrate this by a typical example of the process $γγ\to b \bar{b}$. Phenomenological implications are also briefly indicated.

hep-ph↗

arXiv1995

Axial Vector Couplings of the Nucleon in Chiral Quark Model Incorporating $ U(1)_A$ Anomaly Effects

Renormalization of the axial vector currents due to Goldstone loops is studied in a simple extension of Manohar - Georgi chiral quark model which incorporates $U(1)_A$ anomaly effects. The polarized strage quark sea in the polarized nucleon results from different renormalization of the flavor singlet and octet currents and is in reasonable agreement with the experiment.

hep-ph↗

arXiv1994

Renormalization of the Electroweak Theory in the Background Field Method

The applicability of the background field method in spontaneously broken gauge theories is examined with new features emphasized. An explicit one loop analysis in the electroweak theory shows that the method can be consistently implemented in the on-shell renormalization scheme, and that the choice of the background gauge cannot be arbitrary and must be fixed in the Landau gauge if one calculates scattering amplitudes involving unphysical Goldstone bosons. Some possible applications are also briefly indicated.

hep-ph↗