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James T. Liu

Publications and source records attributed to James T. Liu.

155 records · Page 9Linked to original sources
arXiv1995

Eleven Dimensional Origin of String/String Duality: A One Loop Test

Membrane/fivebrane duality in D=11 implies Type IIA string/Type IIA fivebrane duality in D=10, which in turn implies Type IIA string/heterotic string duality in D=6. To test the conjecture, we reproduce the corrections to the 3-form field equations of the D=10 Type IIA string (a mixture of tree-level and one-loop effects) starting from the Chern-Simons corrections to the 7-form Bianchi identities of the D=11 fivebrane (a purely tree-level effect). K3 compactification of the latter then yields the familiar gauge and Lorentz Chern-Simons corrections to 3-form Bianchi identities of the heterotic string. We note that the absence of a dilaton in the D=11 theory allows us to fix both the gravitational constant and the fivebrane tension in terms of the membrane tension. We also comment on an apparent conflict between fundamental and solitonic heterotic strings and on the puzzle of a fivebrane origin of S-duality.

hep-th↗
arXiv1995

The decay $b\to sγ$ in the 3-3-1 model

The 3-3-1 model, based on the gauge group $SU(3)_c\times SU(3)_L\times U(1)_X$, makes a natural prediction of three generations based on anomaly cancellation. Since this is accomplished by incorporating the third family of quarks differently from the other two, it leads to potentially large flavor changing neutral currents. A sensitive place to look for such effects is the flavor changing $b\to sγ$ decay, which has recently been measured at CLEO. We compute this decay rate in the 3-3-1 model and compare it with that of the two-Higgs-doublet model, a subset of the full 3-3-1 model. We find that the additional 3-3-1 physics weakens the bound on the charged Higgs mass from $M_{H^+}>290$~GeV to $M_{H^+}\agt120$~GeV.

hep-ph↗
arXiv1994

Lepton flavor changing processes and CP violation in the 331 model

By extending the electroweak gauge group to $SU(3)_L\times U(1)_Y$, the 331 model incorporates dilepton gauge bosons $Y$ which do not respect individual lepton family number. We point out that, in addition to family diagonal couplings such as $Y$--$e$--$e$ that change lepton family number by two units, dileptons may also have family non-diagonal couplings such as $Y$--$μ$--$e$. The latter coupling violates lepton family number by a single unit and manifests itself via lepton flavor changing decays such as $μ\to3e$ and $μ\to eγ$. The family non-diagonal interaction can be CP violating and typically generates extremely large leptonic electric dipole moments. We demonstrate a natural mechanism for eliminating both single unit lepton flavor violation and large leptonic CP violation. Although we focus on the 331 model, our results are applicable to other dilepton models as well, including $SU(15)$ grand unification.

hep-ph↗
arXiv1993

Generation non-universality and flavor changing neutral currents in the 331 model

The 331 model, an extension of the standard electroweak theory to $SU(3)_L\times U(1)_X$, naturally predicts three families of quarks and leptons via the requirement of anomaly cancellation. This is accomplished by making one of the quark families transform differently from the other two, thus leading to flavor changing neutral currents. Using experimental input on neutral meson mixing, we show that the third family must be the one that is singled out, at least up to small family mixing. We additionally describe a convenient way to parametrize the new mixing matrix that plays a role in the gauge interactions of the ordinary quarks with the new 331 quarks.

hep-ph↗
arXiv1993

Spectrum and Thermodynamics of the one-dimensional supersymmetric t-J model with $1/r^2$ exchange and hopping

We derive the spectrum and the thermodynamics of the one-dimensional supersymmetric t-J model with long range hopping and spin exchange using a set of maximal-spin eigenstates. This spectrum confirms the recent conjecture that the asymptotic Bethe-ansatz spectrum is exact. By empirical determining the spinon degeneracies of each state, we are able to explicitly construct the free energy.

cond-mat↗
arXiv1993

SSC Phenomenology of the 331 Model of Flavor

The 331 model offers an explanation of flavor by anomaly cancellation between three families. It predicts three exotic quarks, $Q=D$, $S$, $T$, and five extra gauge bosons comprising an additional neutral $Z_2$ and four charged dileptonic gauge bosons $(Y^{--},Y^-)$, $(Y^{++},Y^+)$. Production of $Q\overline{Q}$, $QY$, $YY$ and $Z_2$ at the SSC is calculated, and signatures are discussed.

hep-ph↗
arXiv1992

Magnetic Monopoles in String Theory

Magnetic monopole solutions to heterotic string theory are discussed in toroidal compactifications to four spacetime dimensions. Particular emphasis is placed on the relation to previously studied fivebrane solutions in ten dimensions and on the possibility of constructing exact monopole solutions related to symmetric fivebranes.

hep-th↗
arXiv1992

Heterotic Parafermionic Superstring

Superstrings have been postulated based on parafermionic partition functions which permit spacetime supersymmetry by generalized Jacobi identities. A comprehensive search finds new such identities. Quadrilateral anomaly cancellation gives constraints on allowed chiral fermions. Bosonic left-movers and $Z_4$ parafermionic right-movers combine in a new heterotic superstring, more constrained than the old one, yet equally applicable to physics.

hep-th↗
arXiv1992

Running Gauge Couplings and Thresholds in the Type II Superstring

A distinctive feature of string unification is the possibility of unification by a non-simply-laced group. This occurs most naturally in four dimensional type~II string models where the gauge symmetry is realized by Kac-Moody algebras at different levels. We investigate the running coupling constants and the one-loop thresholds for such general models. As a specific case, we examine a $\rm SU(3)\times U(1)\times U(1)$ model and find that the threshold corrections lead to a small $6\%$ increase in the unification scale.

hep-th↗