17940028
Perturbative QCD analysis of B meson decays.
The resummation of large QCD radiative corrections, including leading and next-to-leading logarithms, in the pion electromagnetic form factor is reviewed. A similar formalism is applied to exclusive processes involving heavy mesons, and leads to Sudakov suppression for the semileptonic decay {ital B}{r_arrow}{pi}{ital l}{nu}. It is found that, with the inclusion of Sudakov effects, a perturbative QCD analysis of this decay is reliable for the energy fraction of the pion above 0.4. Combining predictions from soft pion theorems we estimate that the upper limit of the matrix element {parallel}{ital V}{sub {ital ub}}{parallel} is 2.8{endash}4.8{times}10{sup {minus}3} from different models of the {ital B} meson wave function. {copyright} {ital 1996 The American Physical Society.}
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.
121958607
Infrared finiteness of the two-loop correction to the Chern–Simons term in the Yang–Mills–Chern–Simons theory
We show that the two-loop contribution to the coefficient of the Chern–Simons term in the effective action of the Yang–Mills–Chern–Simons theory is infrared finite in the background field Landau gauge. We also discuss the difficulties in verifying the conjecture, due to topological considerations, that there are no more quantum corrections to the Chern–Simons term other than the well-known one-loop shift of the coefficient.
5428879
Origin of the $k_{T}$ smearing in direct photon production
We show that the Sudakov factor from the resummation of double logarithms $\ln(s/k_T^2)$ contained in the distribution functions is responsible for the $k_T$ smearing mechanism employed in the next-to-leading-order QCD ($\alpha\alpha_s^2$) calculations of direct photon production. $s$ is the center-of-mass energy, and $k_T$ the transverse momentum carried by a parton in a colliding hadron. This factor exhibits the appropriate $s$-dependent Gaussian width in $k_T$, such that our predictions are in good agreement with experimental data.
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.
124014107
Extraction of V(ub) from decay B ---> pi lepton neutrino
37936938
Extracting Energy from Accretion into a Kerr Black Hole.
The highest efficiency of converting rest mass into energy by accreting matter into a Kerr black hole is approximately 31% (Thorne 1974). We propose a new process in which periods of accretion from a thin disk, and the associated spin-up of the black hole, alternate with the periods of no accretion and magnetic transfer of energy from the black hole to the disk. These cycles can repeat indefinitely, at least in principle, with the black hole mass increasing by approximately 66% per cycle and up to approximately 43% of accreted rest mass radiated away by the disk.
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.
28317308
Coplanar and noncoplanar nucleon-nucleon bremsstrahlung calculation: A study of pseudoscalar and pseudovector pi N couplings.
The {ital pp}{gamma} and {ital np}{gamma} processes have been used to study pseudoscalar (ps) and pseudovector (pv) {pi}{ital N} couplings. We calculate both coplanar and noncoplanar cross sections using a realistic one-boson exchange model in the energy region between 100 and 300 MeV. We find that the difference in cross sections calculated using the two couplings increases as the nucleon scattering angles decrease. Furthermore, this difference becomes greater with increasing incident energy. We show for the {ital pp}{gamma} case that this difference will be significantly increased upon the inclusion of electromagnetic form factors. For {ital pp}{gamma} with large proton scattering angles ({ge}30{degree}), cross sections (both ps and pv) calculated using an on-shell {ital p}{gamma}{ital p} vertex are in very good agreement with the data, and they are also extremely close to a recent soft-photon calculation at 157 MeV using the two-{ital u}-two-{ital t} special amplitude. The ps and pv calculations are both in good agreement with the TRIUMF data at 200 and 280 MeV. More accurate data are required to differentiate between these two couplings. Agreement with sparsely available {ital np}{gamma} data is good for most cases, but discrepancies do exist for some data points. For large nucleon scattering angles,more » noncoplanar cross sections for both {ital np}{gamma} and {ital pp}{gamma} change rapidly with the noncoplanar angle. However, the respective shapes of the noncoplanar {ital np}{gamma} and {ital pp}{gamma} curves are very different.« less
12610818
eta photoproduction of nucleons and the structure of the resonance S11(1535) in the quark model.
In this paper, we present our study on {eta} photoproduction based on the chiral quark model. We find that the quark model provides a very good description of {eta} production with far fewer parameters, and the threshold region is not a reliable source to determine the {eta}{ital NN} coupling constant due to its strong dependence on the properties of the resonance {ital S}{sub 11}(1535). We suggest that the systematic data in {ital E}{sub lab}=1.2--1.4 GeV region may help us to determine the {eta}{ital NN} coupling constant more precisely. The structure of the resonance {ital S}{sub 11}(1535) is discussed; we find that the recent data from Mainz group bring the helicity amplitude much closer to the quark model prediction. However, more studies need to be done to understand the large {eta}{ital N} branching ratio of the resonance {ital S}{sub 11}(1535). Our results show that the quark model is a very good approach to studying the underlying structure of baryon resonances from the meson photoproduction data.
10326293
New light on time machines: Against the chronology protection conjecture.
I construct a spacetime with closed timelike curves and without closed causal geodesics. There is a noncompactly generated Cauchy horizon separating the region with closed timelike curves from that without closed causal curves. This spacetime might be stable against the vacuum fluctuation of matter fields. Whether such a spacetime is stable against the vacuum fluctuation of a gravitational field is an open question.