120093276
CONSISTENT FACTORIZATION AND TWIST-3 CONTRIBUTIONS TO THE POLARIZED NUCLEON STRUCTURE FUNCTION g2(x,Q2)
Quark mass effects are clarified in the parton model approach to the transversely polarized nucleon structure function. The special propagator technique is employed to obtain manifestly gauge invariant results and extract the buried short-distance contributions inside the soft part after momentum factorization in the collinear expansion approach. A generalized massive special propagator for a massive quark is constructed. We identify the corresponding matrix elements of the transversely polarized structure function in deep inelastic scattering by the massive special propagator technique.
10063732
Effective Lagrangian approach to weak radiative decays of heavy hadrons.
Motivated by the observation of the decay B\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}K${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}^{\mathrm{*}}$\ensuremath{\gamma} by the CLEO Collaboration, we have systematically analyzed the two-body weak radiative decays of bottom and charmed hadrons. There exist two types of weak radiative decays: One proceeds through the short-distance b\ensuremath{\rightarrow}s\ensuremath{\gamma} transition and the other occurs through W exchange accompanied by a photon emission. Effective Lagrangians are derived for the W-exchange bremsstrahlung processes at the quark level and then applied to various weak electromagnetic decays of heavy hadrons. Predictions for the branching ratios of B${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}^{0}$\ensuremath{\rightarrow}${\mathit{D}}^{\mathrm{*}0}$\ensuremath{\gamma}, ${\mathrm{\ensuremath{\Lambda}}}_{\mathit{b}}^{0}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\Sigma}}}_{\mathit{c}}^{0}$\ensuremath{\gamma}, ${\mathrm{\ensuremath{\Xi}}}_{\mathit{b}}^{0}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\Xi}}}_{\mathit{c}}^{0}$\ensuremath{\gamma}, and ${\mathrm{\ensuremath{\Xi}}}_{\mathit{b}}^{0}$\ensuremath{\rightarrow}\ensuremath{\Xi}${\mathcal{'}}_{\mathit{b}}^{0}$\ensuremath{\gamma} are given. In particular, we find scrB(B${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}^{0}$\ensuremath{\rightarrow}${\mathit{D}}^{\mathrm{*}0}$\ensuremath{\gamma})\ensuremath{\approxeq}0.9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$. Order of magnitude estimates for the weak radiative decays of charmed hadrons, ${\mathit{D}}^{0}$\ensuremath{\rightarrow}K${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}^{\mathrm{*}0}$\ensuremath{\gamma}, ${\mathrm{\ensuremath{\Lambda}}}_{\mathit{c}}^{+}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\Sigma}}}^{+}$\ensuremath{\gamma}, and ${\mathrm{\ensuremath{\Xi}}}_{\mathit{c}}^{0}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\Xi}}}^{0}$\ensuremath{\gamma}, are also presented. Within this approach, the decay asymmetry for antitriplet to antitriplet heavy baryon weak radiative transitions is uniquely predicted by heavy quark symmetry. The electromagnetic penguin contribution to ${\mathrm{\ensuremath{\Lambda}}}_{\mathit{b}}^{0}$\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma} is estimated by two different methods and its branching ratio is found to be of the order of 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$. We conclude that weak radiative decays of bottom hadrons are dominated by the short-distance b\ensuremath{\rightarrow}s\ensuremath{\gamma} mechanism.
34810684
Restudy of the open-superstring tree amplitudes by looking at their field-theoretical limits.
We carry out complete computations of some open- and closed-superstring tree amplitudes by using the bosonized covariant vertices. Some open-superstring amplitudes so obtained are shown to be different from those obtained in the light-cone gauge approach by some numerical factors. The low-energy limits of our five open-superstring amplitudes are then shown to match the five super Yang-Mills field amplitudes while the five light-cone gauge open-superstring amplitudes fail to do so.
43012116
Are there really no experimental limits on a light Higgs boson from kaon decay?
We reexamine the theoretical estimates of the decay {ital K}{r arrow}{pi}{ital H} and the experimental constraints on the existence of a light Higgs boson from this process. We find that (i) pole diagrams generated from the Higgs-boson--gluon coupling via a loop of heavy quarks do contribute to {ital K}{r arrow}{pi}{ital H}, (ii) there is an additional contribution to the {ital K}{r arrow}{pi}{ital H} amplitude coming from the effective {ital KHW} and {pi}{ital HW} couplings, (iii) even if {ital B}, the unknown parameter in the chiral-Lagrangian description of {ital K}{endash}{pi}{ital H} transitions, is nonzero and even if the real part of the {ital K}{r arrow}{pi}{ital H} amplitude is canceled accidentally, the imaginary contribution alone suffices to rule out a Higgs boson lighter than 2{ital m}{sub {pi}}, and (iv) whether Higgs bosons in the mass range 2{ital m}{sub {pi}}{lt}m{sub H}{lt}350 MeV are excluded by the imaginary part of the {ital K}{r arrow}{pi}{ital H} amplitude depends on the branching ratio of {ital H}{r arrow}{mu}{sup +}{mu}{sup {minus}} and the top-quark mass. Decay modes {ital K}{sub {ital L}}{r arrow}{pi}{sup +}{pi}{sup {minus}}H and {ital K}{sup +}{r arrow}l{sup +}{nu}H are briefly discussed.
13594754
Heavy-flavor-conserving nonleptonic weak decays of heavy baryons.
The heavy-flavor-conserving nonleptonic weak decays of heavy baryons are studied in a formalism that incorporates both heavy-quark symmetry and chiral symmetry. The phenomenological {Delta}{ital S}=1 nonleptonic weak chiral Lagrangian for these transitions contains two independent coupling constants that describe the transitions between two flavor-SU(3) antitriplet heavy baryons, and the transitions between two flavor-SU(3) sextet heavy baryons. In the MIT bag model and the diquark model, only transitions between antitriplets are allowed. The coupling constants for these transitions are calculated in both models. The result is applied to specific nonleptonic decays such as {Xi}{sub {ital c}}{r arrow}{Lambda}{sub {ital c}}{pi}, and the branching ratios are found to be of the order of 10{sup {minus}4}. An example of a nonleptonic decay due to symmetry breaking is provided by {Omega}{sub {ital c}}{r arrow}{Xi}{sub {ital c}}{sup {prime}}{pi}, which is estimated to have a smaller branching ratio, of the order of 10{sup {minus}5}.
36067168
Dimensional regularization and perturbative solution of the chiral Schwinger model.
The anomalous chiral Schwinger model is regulated by the method of dimensional regularization and is solved by diagrammatic perturbative expansion. It is shown that there is a regulation ambiguity in the solution. The result disagrees with Das's assertion and agrees with that of Jackiw, Rajaraman, and others.
16163396
Lightcone fluctuations in quantum gravity and extra dimensions
Abstract We discuss how compactified extra dimensions may have potentially observable effects which grow as the compactification scale decreases. This arises because of lightcone fluctuations in the uncompactified dimensions which can result in the broadening of the spectral lines from distant sources. We analyze this effect in a five dimensional model, and argue that data from gamma ray burst sources require the compactification length to be greater than about 105 cm in this model.
118405912
Spontaneous excitation of a static multilevel atom coupled with electromagnetic vacuum fluctuations in Schwarzschild spacetime
We study the spontaneous excitation of a radially polarized static multilevel atom outside a spherically symmetric black hole in multipolar interaction with quantum electromagnetic fluctuations in the Boulware, Unruh and Hartle–Hawking vacuum states. We find that spontaneous excitation does not occur in the Boulware vacuum, and, in contrast to the scalar field case, the spontaneous emission rate is not well behaved at the event horizon as a result of the blow-up of the proper acceleration of the static atom. However, spontaneous excitation can take place both in the Unruh and the Hartle–Hawking vacua as if there were thermal radiation from the black hole. Distinctive features in contrast to the scalar field case are the existence of a term proportional to the proper acceleration squared in the rate of change of the mean atomic energy in the Unruh and the Hartle–Hawking vacua and the structural similarity in the spontaneous excitation rate between the static atoms outside a black hole and uniformly accelerated ones in a flat space with a reflecting boundary, which is particularly dramatic at the event horizon where a complete equivalence exists.
14974262
Quantum states with negative energy density in the Dirac field and quantum inequalities
Abstract Energy densities of the quantum states that are superposition of two multi-electron–positron states are examined. It is shown that the energy densities can be negative when two multi-particle states have the same number of electrons and positrons or when one state has one more electron–positron pair than the other. In the cases in which negative energy could arise, we find that the energy is that of a positive constant plus a propagating part which oscillates between positive and negative, and the energy can dip to negative at some places for a certain period of time if the quantum states are properly manipulated. It is demonstrated that the negative energy densities satisfy the quantum inequality. Our results also reveal that for a given particle content, the detection of negative energy is an operation that depends on the frame where any measurement is to be performed. This suggests that the sign of energy density for a quantum state may be a coordinate-dependent quantity in quantum theory.
119198751
Minimal flavor violation in the lepton sector of the Randall–Sundrum model
Abstract We propose a realization of Minimal Flavor Violation in the lepton sector of the Randall–Sundrum model. With the MFV assumption, the only source of flavor violation are the 5 D Yukawa couplings, and the usual two independent sources of flavor violation are related. In the limit of massless neutrinos, the bulk mass matrices and 5 D Yukawa matrices are simultaneously diagonalized, and hence the absence of FCNCs. In the case of massive neutrinos, the contributions to FCNCs in the charged lepton sector are highly suppressed, due to the smallness of neutrino masses. In addition, the MFV assumption also allows suppressing one-loop charged current contributions to flavor changing processes by reducing the size of the Yukawa couplings, which is not possible in the generic anarchical case. We found that the first KK mass scale as low as ∼ 3 TeV can be allowed. In both cases, we present a set of numerical results that give rise to realistic lepton masses and mixing angles. Mild hierarchy in the 5 D Yukawa matrix of O ( 25 ) in our numerical example is required to be consistent with two large and one small mixing angles. This tuning could be improved by having a more thorough search of the parameter space.
18519588
On the mass relation of a meson nonet
It is pointed out that the omission of the effects of the transition between quarkonia or the assumption that the transition between quarkonia is flavor-independent would result in the inconsistent results for the pseudoscalar meson nonet. It is emphasized that the mass relation of the non-ideal mixing meson nonets should incorporate the effects of the flavor-dependent transition between quarkonia. The new mass relations of a meson nonet axe presented.