arXiv subjects

Xinmin Zhang

Publications and source records attributed to Xinmin Zhang.

189 records · Page 11Linked to original sources

arXiv1999

Bounds On Anomalous Magnetic And Electric Moments Of Tau Lepton From LEP And Lepton Flavor Violation

The most stringent bounds on the anomalous magnetic and electric dipole moments of the tau lepton was derived by Escribano and Massó[6] from the Z width at LEP in an effective lagrangian approach to the new physics. In this paper we point out that the higher dimensional operators introduced by Escribano and Massó not only modify the neutral currents of the tau lepton to Z gauge boson and the photon, but also induce lepton flavor violation (LFV). The size of the LFV effect depends crucially on the dynamics of the lepton mass generation. Assuming the lepton mass matrices in the form of an Fritzsch ansatz, we point out that the experimental limit on $μ\to e γ$ will push the anomalous magnetic and electric dipole moments of the tau lepton down to $10^{-11}$ and $10^{-25} e cm$ respectively.

hep-ph↗

arXiv1998

Anomalous Global Strings and Primordial Magnetic Fields

We propose a new mechanism for the generation of primordial magnetic fields, making use of the magnetic fields which are induced by anomalous global strings which couple to electromagnetism via Wess-Zumino type interactions. This mechanism can be realized in QCD by utilizing pion strings, global vortices which appear in the linear sigma model which describes physics below the QCD confinement scale. During the chiral symmetry breaking phase transition, pion strings can be produced, thus leading to primordial magnetic fields. We calculate the magnitude and coherence length of these fields. They are seen to depend on the string dynamics. With optimistic assumptions, both the magnitude and coherence scale of the induced magnetic fields can be large enough to explain the seed magnetic fields of greater than $10^{-23}$ Gauss necessary to produce the observed galactic magnetic fields via the galactic dynamo mechanism.

hep-ph↗

arXiv1998

Probing anomalous top quark couplings at eγcolliders

We study in the effective Lagrangian approach the possibility of probing anomalous top quark charged current couplings in the single top production at a high energy eγcollider. We analyzed all possible dimension-six CP-conserving operators which can give rise to an anomalous Wtb coupling which represent new physics effect generated at a higher energy scale. For those operators which also give rise to anomalous Zbb_bar or right-handed Wtb couplings, we find that they are strongly constrained by the existing R_b and b->sγdata. As a result, a collider with a luminosity of the order of 100 fb^{-1} is required to observe the anomalous effects. For other operators which currently subject to no strong constraints, the high energy eγcollider can probe their couplings effectively because of the clean environment of such a collider.

hep-ph↗

arXiv1998

Effective CP-violating operators of the tau lepton and some of their phenomenologies

The dimension-six CP-violating SU_L(2)\times U_Y(1) invariant operators involving the tau lepton are studied. The constraints from the available experimental data on tau dipole moments are derived. Under the current constraints, the induced CP-violating effects could possibly be observed in tau -> 3πν_τ at the future tau-charm factory.

hep-ph↗

arXiv1997

Pion and Eta Strings

In this paper we construct a string-like classical solution, the pion-string, in the linear sigma model. We then study the stability of the pion-string, and find that it is unstable in the parameter space allowed experimentally. We also speculate on the existance of an unstable eta-string, associated with spontaneous breakdown of the anomalous $U_A(1)$ symmetry in QCD at high temperatures. The implications of the pion and eta strings for cosmology and heavy ion collisions are briefly mentioned.

hep-ph↗

arXiv1995

Top Quark As A Topological Color Soliton

In this paper I propose an scenario for the top quark as a topological color soliton. I illustrate some features of the top quark as a soliton in a toy model based on nonlinear realization of the $SU(3)_L \times SU(3)_R / SU(3)_{L+R}$, with $SU(3)_{L+R}$ being the color gauge group.

hep-ph↗

arXiv1995

Electroweak Sphaleron For Effective Theory In The Limit Of Large Higgs Boson Mass

Theoretical arguments suggest that the Higgs sector of the standard model is an effective theory. We parametrize the new physics by means of an effective Lagrangian technique and study its effect on the energy of the electroweak sphaleron. We found that in the presence of a certain class of higher dimension operators the sphaleron energy becomes arbitrarily large as the Higgs boson mass increases. The physical meaning of this result and its implications to the electroweak baryogenesis in the dynamical models are discussed.

hep-ph↗

arXiv1994

Z -> b\bar{b} Versus Dynamical Electroweak Symmetry Breaking involving the Top Quark

In models of dynamical electroweak symmetry breaking which sensitively involve the third generation, such as top quark condensation, the effects of the new dynamics can show up experimentally in Z->b\bar{b}. We compare the sensitivity of Z->b\bar{b} and top quark production at the Tevatron to models of the new physics. Z->b\bar{b} is a relatively more sensitive probe to new strongly coupled U(1) gauge bosons, while it is generally less sensitive a probe to new physics involving color octet gauge bosons as is top quark production itself. Nonetheless, to accomodate a significant excess in Z->b\bar{b} requires choosing model parameters that may be ruled out within run I(b) at the Tevatron.

hep-ph↗

arXiv1993

Electroweak Sphaleron in Large Higgs Boson Mass Limit

Since the TRIVIALITY argument of the Higgs sector requires the existence of new physics beyond the standard model, there should exist a cutoff $Λ$ beyond which the standard model will breakdown. The cutoff can be determined from the position of the Landau pole. We study the effects of this cutoff on the energy of the electroweak sphaleron, $E^{spha}$, in the large Higgs boson mass limit. We found that $E^{spha}$ becomes arbitrarily large as the Higgs boson mass increases. This is in contrast to the well-known result, which is held in the standard model and a wide class of its extensions, that $E^{spha}$ is stable against the variation of the {\it bare} Higgs boson mass. The physical meaning of this result is discussed.

hep-ph↗