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.
121750634
Topological gravity with minimal matter
Abstract Topological minimal matter, obtained by twisting the minimal N = 2 superconformal field theory, is coupled to two-dimensional topological gravity. The free field formulation of the coupled system allows explicit representations of BRST charge, physical operators and their correlation functions. The contact terms of the physical operators may be evaluated by extending the argument used in a recent solution of topological gravity without matter. The consitency of the contact terms in correlation functions implies recursion relations which coincide with the Virasoro constraints derived from the multi-matrix models. Topological gravity with minimal matter thus provides the field theoretic description for the multi-matrix models of two-dimensional quantum gravity.
121812692
Remarks on local discrete symmetry
Abstract It is pointed out that discrete symmetries left unbroken after a spontaneous Higgs condensation remain as global symmetries in the low-energy effective theory. The global nature of these discrete symmetries makes the associated charges physical so that they may become “quantum hair” for black holes as has been suggested recently. It is also emphasized that to obtain a theory with a local discrete symmetry G, one must not only introduce sectors in the Hilbert space corresponding to G-twisted boundary conditions, but should also project out G non-invariant states in each sector to preserve the local G gauge invariance. Explicit examples discussed here include a Z N model with two scalars and the SO(3) → O(2) model with Alice strings.
120126783
Aspects of anomaly structures in W gravity
The authors give a brief review of some of the recent developments in W gravity coupled to matter theories. They then extend the discussion to the case of minimal W conformal field theory, realized in terms of free bosons with background charges, and use this action to investigate some aspects of the anomaly structure and the covariantization of W gravity.
121144435
Character-valued index theorems in supersymmetric string theories
By using (1+1)-dimensional supersymmetric sigma models, the local expressions for various G*U(1) character-valued topological indices in closed supersymmetric string theories are constructed explicitly, where U(1) is the group of constant rotations along the closed string and G is the non-trivial automorphism group of the vector bundle or the tangent bundle over which the string sigma model is defined.
121326193
Construction of topological W3 gravity
Topological W_3 gravity is constructed in detail from its definition as topological Yang-Mills theory in two dimensions with the gauge group being a contraction of SL(3, R). The gauge transformation of the Yang-Mills gauge field can be rewritten to resemble that of the spin-2 and -3 gauge fields describing W_3 gravity. This fact provides a local parametrization of the moduli space of the flat connections in terms of spin-2 and -3 Beltrami differentials on Riemann surfaces. The variations of the action with respect to the moduli give the stress tensor and the spin-3 W current, and the BRST charge can be expressed in terms of these currents in a way similar to that of W_3 gravity. The physical content of the model is briefly discussed.
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.
45165928
Self-consistent solutions for vacuum currents around a magnetic flux string.
We consider the feedback effects of the vacuum currents induced by a magnetic flux string in 2+1 dimensions. Self-consistent induced charge and current densities that satisfy both the Dirac and Maxwell equations are given for the dimensionless coupling constant [ital g]==[ital e][sup 2]/[ital m][r arrow]0 and [ital g][r arrow][infinity]. These quantities for arbitrary [ital g] are inferred from the results of the two limiting cases, and also studied numerically.
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])].
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.
38608728
Comment on "Role of g2 in relating the Schwinger and Gerasimov-Drell-Hearn sum rules"