36560824
Origin of the Immirzi parameter
Using quadratic spinor techniques we demonstrate that the Immirzi parameter can be expressed as ratio between scalar and pseudoscalar contributions in the theory and can be interpreted as a measure of how Einstein gravity differs from a generally constructed covariant theory for gravity. This interpretation is independent of how gravity is quantized. One of the important advantage of deriving the Immirzi parameter using the quadratic spinor techniques is to allow the introduction of renormalization scale associated with the Immirzi parameter through the expectation value of the spinor field upon quantization.
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.
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}.
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.
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.
119123919
Fermion Mass Hierarchy and Proton Stability from Non-anomalous U(1)(F) in SUSY SU(5)
We present a realistic supersymmetric SU(5) model combined with a nonanomalous U(1){sub F} symmetry. We find a set of U(1){sub F} charges which automatically lead to the realistic mass hierarchy and mixing patterns for quarks, leptons, and neutrinos. All gauge anomalies, including the [U(1){sub F}]{sup 3} anomaly, are canceled in our model without invoking the Green-Schwarz mechanism or having exotic fields. Proton decay mediated by dimension-5 operators is automatically suppressed in our model, because the scale set by the largest right-handed neutrino mass is much less than the GUT scale.
121187481
A test of the glueball theory for the ξ(2230)
Abstract The possibility that the ξ(2230) is considered as a glueball is discussed in the framework of a nonrelativistic potential model [D. Robson, Nucl. Phys. B 130 (1977) 328] of the glueball with massive constituent gluons by using the experimental data from the Mark III Collaboration. The ratios of the helicity amplitude are calculated. The results are that the theoretical values cannot be consistent with the data if the ξ(2230) is a 2 ++ glueball in a pure S wave and the theoretical values are in excellent agreement with the data if the ξ(2230) is a 2 ++ glueball in a mixture between the S wave and two D waves or a 4 ++ glueball in a pure D wave.
17177636
Quantum Gravity and Astrophysics: The Microwave Background and Other Thermal Sources
The problem of formulating a fully consistent quantum gravity theory (QGT) has not yet been solved. Even before we are able to work out the details of a complete theory, however, we do know some important qualitative features to be expected in any quantum theory. Fluctuations of the metric, for example, are expected and are associated with fluctuations of the lightcone. Lightcone fluctuations affect the arrival time of signals from distant sources in potentially measurable ways, broadening the spectra. In this paper, we start with a thermal spectrum and derive the form of spectral changes expected in a wide class of QGTs. We apply these results, valid for any thermal spectrum, to the cosmic microwave background (CMB). The CMB offers two advantages: (1) deviations from a thermal spectrum are well constrained, and (2) the radiation emanates from the most distant source of light, the surface of last scattering. We use existing CMB data to derive an upper bound on the value of $\Delta t,$ the mean spread in arrival times due to metric fluctuations: ${\Delta t} < 2.1 \times 10^{-14}$ s at the 95% confidence limit. This limit applies to a wide range of QGTs, and falsifies those predicting a larger spread in arrival times. We find this limit rules out at least one QGT, the 5-dimensional theory in which the "extra" dimension is flat. Tests of other models may also be possible, depending on the results of calculations to predict values of \Delta t,$ and also a second time scale, $\tau_c,$ the correlation time, which is the characteristic time scale of the metric fluctuations. We show that stronger limits on the value of $\Delta t,$ hence on lightcone fluctuations, can likely be derived through observations of of higher-T sources, e.g., in the X-ray and gamma-ray regimes.
119682398
Relationship between Hawking radiation from black holes and spontaneous excitation of atoms
Using the formalism that separates the contributions of vacuum fluctuations and radiation reaction to the rate of change of the mean atomic energy, we show that a two-level atom in interaction with a quantum massless scalar field both in the Hartle-Hawking and Unruh vacuum in a $1+1$ dimensional black hole background spontaneously excites as if there is thermal radiation at the Hawking temperature emanating from the black hole. Our calculation, therefore, ties the existence of Hawking radiation to the spontaneous excitation of a two-level atom placed in vacuum in the exterior of a black hole and shows pleasing consistence of two different physical phenomena, the Hawking radiation and the spontaneous excitation of atoms, which are quite prominent in their own right.
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.