9459591
Applicability of perturbative QCD to B-->D decays.
We examine the applicability of perturbative QCD to {ital B} meson decays into {ital D} mesons. We find that the perturbative QCD formalism, which includes Sudakov effects at intermediate energy scales, is applicable to the semileptonic decay {ital B}{r_arrow}{ital Dl}{nu}, when the {ital D} meson recoils fast. Following this conclusion, we analyze the two-body nonleptonic decays {ital B}{r_arrow}{ital D}{pi} and {ital B}{r_arrow}{ital DD}{sub {ital s}}. By comparing our predictions with experimental data, we extract the matrix element {vert_bar}{ital V}{sub {ital c}{ital b}}{vert_bar}=0.044.
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.
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.
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.
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.
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
14522537
Effects of the quantity sigma TS on the spin structure functions of nucleons in the resonance region.
In this paper, we investigate the effects of the quantity {sigma}{sub {ital TS}} on the spin structure functions of nucleons in the resonance region. The Schwinger sum rule for the spin structure function {ital g}{sub 2}({ital x},{ital Q}{sup 2}) at the real photon limit is derived for the nucleon treated as a composite system, and it provides a crucial constraint on the longitudinal transition operator which has not been treated consistently in the literature. The longitudinal amplitude {ital S}{sub 1/2} is evaluated in the quark model with the transition operator that generates the Schwinger sum rule. The numerical results of the quantity {sigma}{sub {ital TS}} are presented for both spin structure functions {ital g}{sub 1}({ital x},{ital Q}{sup 2}) and {ital g}{sub 2}({ital x},{ital Q}{sup 2}) in the resonance region. Our results show that this quantity plays an important role in the low {ital Q}{sup 2} region, which can be tested in future experiments at CEBAF. {copyright} {ital 1996 The American Physical Society.}
2293560
Kaon photoproduction on the neutron using deuterium.
The three processes \ensuremath{\gamma}+d\ensuremath{\rightarrow}${\mathrm{\ensuremath{\Lambda}}}^{0}$(${\mathrm{\ensuremath{\Sigma}}}^{0}$)+${\mathit{K}}^{0}$+p and \ensuremath{\gamma}+d\ensuremath{\rightarrow}${\mathrm{\ensuremath{\Sigma}}}^{\mathrm{\ensuremath{-}}}$+${\mathit{K}}^{+}$+p are investigated in the framework of the impulse approximation. The exclusive reactions d(\ensuremath{\gamma},Kp)Y where the proton is detected in coincidence with the ${\mathit{K}}^{0}$ or ${\mathit{K}}^{+}$ should provide unique signatures for each of the processes. In most kinematic situations the final-state Yp interaction is insignificant and the elementary process cross section for \ensuremath{\gamma}+n\ensuremath{\rightarrow}Y+K can be reliably extracted. Cross-section estimates are given for several models of the basic production operator.
31943448
Extracting Energy from a Black Hole through Its Disk.
When some magnetic field lines connect a Kerr black hole with a disk rotating around it, energy and angular momentum are transferred between them. If the black hole rotates faster than the disk, ca&solm0;GMH>0.36 for a thin Keplerian disk, then energy and angular momentum are extracted from the black hole and transferred to the disk (MH is the mass and aMH is the angular momentum of the black hole). This way, the energy originating in the black hole may be radiated away by the disk. The total amount of energy that can be extracted from the black hole spun down from ca&solm0;GMH=0.998 to ca&solm0;GMH=0.36 by a thin Keplerian disk is approximately 0.15MHc2. This is larger than approximately 0.09MHc2, which can be extracted by the Blandford-Znajek mechanism.
18101899
Role of short distance behavior in off-shell open-string field theory.
A recent proposal for a background-independent open-string field theory is studied in detail for a class of backgrounds that correspond to general quadratic boundary interactions on the world sheet. A short distance cutoff is introduced to formulate the theory with a finite number of local and potentially unrenormalizable boundary couplings. It is shown that renormalization of the boundary couplings makes both the world-sheet partition function and the string field action finite and cutoff independent, although the resulting string field action has an unpalatable dependence on the leading unrenormalizable coupling.