38207022
Complete screening of a magnetic flux string by vacuum polarization in 3+1 dimensions.
The feedback effects of the vacuum current induced by a magnetic flux string in 3 + 1 dimensions are studied. It is found that the induced magnetic field cancels the applied one completely; i.e., a magnetic flux string does not exist in 3 + 1 dimensions.
108240
Fat penguins and imaginary penguins in perturbative QCD
Abstract We evaluate B → Kπ decay amplitudes in perturbative QCD picture. It is found that penguin contributions are dynamically enhanced by nearly 50% compared to those assumed in the factorization approximation. It is also shown that annihilation diagrams are not negligible, and give large strong phases. Our results for branching ratios of B → Kπ decays for a representative parameter set are consistent with data.
124014107
Extraction of V(ub) from decay B ---> pi lepton neutrino
7999949
Factorization theorems, effective field theory, and nonleptonic heavy meson decays
The nonleptonic heavy meson decays B → D (∗) π(ρ), J/ψK (∗) and D → K (∗) π are studied based on the three-scale perturbative QCD factorization theorem developed recently. In this formalism the Bauer-Stech-Wirbel parameters a1 and a2 are treated as the Wilson coefficients, whose evolution from the W boson mass down to the characteristic scale of the decay processes is determined by effective field theory. The evolution from the characteristic scale to a lower hadronic scale is formulated by the Sudakov resummation. The scale-setting ambiguity, which exists in the conventional approach to nonleptonic heavy meson decays, is moderated. Nonfactorizable and nonspectator contributions are taken into account as part of the hard decay subamplitudes. Our formalism is applicable to both bottom and charm decays, and predictions, including those for the ratios R and RL associated with the B → J/ψK (∗) decays, are consistent with experimental data.
119010824
Resolution to the B ---> pi K puzzle
We calculate the important next-to-leading-order contributions to the B -> pi K, pi pi decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD approach. It is found that the latter two reduce the leading-order penguin amplitudes by about 10%, and modify only the B -> pi K branching ratios. The main effect of the vertex corrections is to increase the small color-suppressed tree amplitude by a factor of 3, which then resolves the large difference between the direct CP asymmetries of the B^0 -> pi^\mp K^\pm and B^\pm -> pi^0 K^\pm modes. The puzzle from the large B^0 -> pi^0 pi^0 branching ratio still remains.
16486400
The resummation approach to evolution equations
We derive the evolution equations of parton distribution functions appropriate in different kinematic regions in a unified and simple way using the resummation technique. They include the Gribov-Lipatov-Altarelli-Parisi equation for large momentum transfer $Q$, the Balitskii-Fadin-Kuraev-Lipatov equation for a small Bjorken variable $x$, and the Ciafaloni-Catani-Fiorani-Marchesini equation which unifies the above two equations. We propose a modified Balitskii-Fadin-Kuraev-Lipatov equation from the view point of the resummation. This modified version possesses an intrinsic $Q$ dependence and its predictions for the structure function $F_2(x,Q^2)$ are consistent with the HERA data.
27837585
Screw Instability and the Blandford-Znajek Mechanism.
When magnetic field lines thread a rotating black hole's horizon and connect with remote astrophysical loads, the rotational energy of the black hole can be extracted through the Blandford-Znajek mechanism. Due to the rotation of the black hole, the magnetic field lines are twisted and toroidal components are generated. Thus, poloidal electric currents are induced and the black hole's rotational energy is transported to the astrophysical loads through Poynting flux. The Blandford-Znajek mechanism has been considered to be a possible process for powering extragalactic jets. In this Letter, we show that because of the screw instability of the magnetic field, the toroidal components of the magnetic field, and thus the poloidal currents, cannot exceed the limits given by the Kruskal-Shafranov criterion. This significantly lowers the power of the Blandford-Znajek mechanism when the loads are far from the black hole. So the Blandford-Znajek mechanism can only work efficiently within the neighborhood of the black hole. The implications of the results for the scenario of extragalactic jets powered by the Blandford-Znajek mechanism are discussed.
38711007
Hybrid baryons via QCD sum rules.
Hybrid baryons, consisting of the three light quarks and a gluon, are investigated using the QCD sum rule method. We find that the mixed condensate 〈0\ensuremath{\Vert}\ensuremath{\psi}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\sigma}G\ensuremath{\psi}\ensuremath{\Vert}0〉=${\mathit{m}}_{0}^{2}$〈0\ensuremath{\Vert}\ensuremath{\psi}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\psi}\ensuremath{\Vert}0〉 plays a dominant role in hybrid baryons in contrast with the quark condensate in the nucleon case. For the standard value of ${\mathit{m}}_{0}^{2}$=0.8 ${\mathrm{GeV}}^{2}$, the mass of the lowest hybrid state is found to be approximately 1.5 GeV, about the observed mass of the Roper resonance.
20647092
Anomalous but consistent gravity in two dimensions.
Two-dimensional gravity coupled to chiral fermions possesses a Lorentz anomaly, but it can be made consistent by allowing the gauge degree of freedom to be physical at the quantum level. The theory has massless excitations or a ghost particle depending on the sign of a counterterm. The possibility of adding the Wess-Zumino term in order to cancel the anomaly is also discussed.
32917384
Analytic calculation of the vacuum wave function for (2+1)-dimensional SU(2) lattice gauge theory.
The long wavelength vacuum wave function of (2+1)-dimensional SU(2) lattice gauge theory is calculated by the method of truncated eigenvalue equation. Third order results are consistent with Monte Carlo measurement and display a good scaling behavior extending to the deep weak coupling region.
18117055
Threshold pion photoproduction of nucleons in the chiral quark model.
In this paper, we show that the low energy theorem (LET) of threshold pion photoproduction can be fully recovered in the quark model. An essential result of this investigation is that the quark-pion operators are obtained from the effective chiral Lagrangian, and the low energy theorem does not require constraints on the internal structures of the nucleon. Changing from pseudovector to pseudoscalar quark-pion couplings generates an additional term at order [mu]=[ital m][sub [pi]]/[ital M] only in the isospin amplitude [ital A][sup ([minus])]. The role of the transitions between the nucleon and the resonance [ital P][sub 33](1232) or [ital P]-wave baryons is also discussed; we find that the leading contributions to the isospin amplitudes at [ital O]([mu][sup 2]) are from the transition between the [ital P]-wave baryons and the nucleon, and from the charge radius of the nucleon. The leading contribution from the [ital P]-wave baryons only affects neutral pion production, and improves the agreement with data significantly. The transition between the resonance [ital P][sub 33](1232) and the nucleon only gives an order [mu][sup 3] correction to [ital A][sup ([minus])].