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M. C. B. Abdalla

Publications and source records attributed to M. C. B. Abdalla.

52 records · Page 3Linked to original sources
arXiv1995

Massive Two-Dimensional Quantum Chromodynamics

In this work we study the zero-charge sector of massive two-dimensional Quantum Chromodynamics in the decoupled formulation. We find that some general features of the massless theory, concerning the constraints and the right- and left-moving character of the corresponding BRST currents, survive in the massive case. The implications for the integrability properties previously valid in the massless case, and the structure of the Hilbert space are discussed.

hep-th↗
arXiv1995

Gravitational Interactions of integrable models

We couple non-linear $σ$-models to Liouville gravity, showing that integrability properties of symmetric space models still hold for the matter sector. Using similar arguments for the fermionic counterpart, namely Gross--Neveu-type models, we verify that such conclusions must also hold for them, as recently suggested.

hep-th↗
arXiv1995

Loop scattering in two-dimensional QCD

Using the integrability conditions that we recently obtained in QCD$_2$ with massless fermions, we arrive at a sufficient number of conservation laws to be able to fix the scattering amplitudes involving a local version of the Wilson loop operator.

hep-th↗
arXiv1995

Updating QCD$_2$

We review two-dimensional QCD. The report contains: 1. Introduction. 2. QCD$_2$ as a field theory 2.1 The 1/N expansion and spectrum, 2.2 Ambiguity in the self-energy of the quark, 2.3 Polyakov--Wiegmann formula and gauge interactions, 2.4 Strong coupling analysis, 2.5 A Lagrangian realization of the coset construction, 2.6 Chiral interactions. 3. Pure QDC$_2$ and string theory, 3.1 Introduction, 3.2 Wilson loop average and large-N limit, 3.3 String interpretation, 3.4 Collective coordinates approach, 3.5 Phase structure of QCD$_2$, 4. Generalized QCD$_2$ and adjoint-matter coupling, 4.1 Introduction and motivation, 4.2 Scalar and fermionic matter coupling; quantization 4.3 The Hagedorn transition; supersymmetry 4.4 Landau--Ginzburg description; spectrum and string theory 5. Algebraic aspects of QCD$_2$ and integrability 5.1 $W_\infty$ algebras for colourless bilinears 5.2 Integrability and duality 5.3 Constraint structure of the theory 5.4 Spectrum and comparison with the 1/N expansion 5.5 Integrability conditions and Calogero-type models 5.6 QCD at high energies and two-dimensional field theory 6. Conclusions, 3 appendices.

hep-th↗
arXiv1994

Higher algebras and mesonic spectrum in two-dimensional QCD

We construct composite operators in two-dimensional bosonized QCD, which obey a $W_\infty$ algebra, and discuss their relation to analogous objects recently obtained in the fermionic language. A complex algebraic structure is unravelled, supporting the idea that the model is integrable. For singlets we find a mass spectrum obeying the Regge behavior.

hep-th↗
arXiv1994

Integrability and duality in two-dimensional QCD

We consider bosonized $QCD_2$, and prove that after rewritting the theory in terms of gauge invariant fields, there exists an integrability condition valid for the quantum theory as well. Furthermore, performing a duality type transformation we obtain an appropriate action for the description of the strong coupling limit, which is still integrable. We also prove that the model displays a complicated set of constraints, restricting the dynamics of part of the theory, but which are necessary to maintain the positive metric Hilbert space.

hep-th↗
arXiv1993

Exact S matrices and extended supersymmetry

In this revised version we correct some mistakes, realizing the supersymmetry algebra on the exact S matrix, taking into account several phase factros. We study the constraint imposed by supersymmetry on the exact $S$-matrix of $\Complex P^{n-1}$ model, and compute a non-trivial phase factor in the relation between the $S$-matrix and one of the supersymmetry generators. We discuss several features connected with the physical interpretation of the result. The supersymmetry current is studied in such context as well, and we find some operators appearing in the conservation equation of the supersymmetry current that might be connected with such phase factors. The relation with the literature on the subject is also discussed. hep-th/yymmnnn

hep-th↗
arXiv1993

The Algebra of Non-Local Charges in Non-Linear Sigma Models

We obtain the exact Dirac algebra obeyed by the conserved non-local charges in bosonic non-linear sigma models. Part of the computation is specialized for a symmetry group $O(N)$. As it turns out the algebra corresponds to a cubic deformation of the Kac-Moody algebra. The non-linear terms are computed in closed form. In each Dirac bracket we only find highest order terms (as explained in the paper), defining a saturated algebra. We generalize the results for the presence of a Wess-Zumino term. The algebra is very similar to the previous one, containing now a calculable correction of order one unit lower.

hep-th↗
arXiv1993

On the Dirac Quantization of two Dimensional Gravity

We discuss the Dirac quantization of two dimensional gravity with bosonic matter fields. After defining the extended Hamiltonian it is possible to fix the gauge completely. The commutators can all be obtained in closed form; nevertheless, the results are not particularly simple.

hep-th↗
arXiv1993

Off critical current algebras

We discuss the infinite dimensional algebras appearing in integrable perturbations of conformally invariant theories, with special emphasis in the structure of the consequent non-abelian infinite dimensional algebra generalizing $W_\infty$ to the case of a non abelian group. We prove that the pure left-symmetry as well as the pure right-sector of the thus obtained algebra coincides with the conformally invariant case. The mixed sector is more involved, although the general structure seems to be near to be unraveled. We also find some subalgebras that correspond to Kac-Moody algebras. The constraints imposed by the algebras are very strong, and in the case of the massive deformation of a non-abelian fermionic model, the symmetry alone is enough to fix the 2- and 3-point functions of the theory.

hep-th↗
arXiv1993

Current Algebra of Super WZNW Models

We derive the current algebra of supersymmetric principal chiral models with a Wess-Zumino term. At the critical point one obtains two commuting super Kac-Moody algebra as expected, but in general there are intertwining fields connecting both right and left sectors, analogously to the bosonic case. Moreover, in the present supersymmetric extension we have a quadratic algebra, rather than an affine Lie algebra, due to the mixing between bosonic and fermionic fields since the purely fermionic sector displays a Lie algebra as well.

hep-th↗
arXiv1992

On the amplitudes for non-critical n=2 supuerstrings

We compute correlation functions in $N=2$ non critical superstrings on the sphere. Our calculations are restrained to the ($s=0$) bulk amplitudes. We show that the four point function factorizes as a consequence of the non-critical kinematics, but differently from the $N=0,1$ cases no extra discrete state appears in the $\hat c\to 1^-$ limit.

hep-th↗
arXiv1992

Correlation Functions in non critical (super) string theory

We consider the correlation functions of the tachyon vertex operator of the super Liouville theory coupled to matter fields in the super Coulomb gas formulation, on world sheets with spherical topology. After integrating over the zero mode and assuming that the $s$ parameter takes an integer value, we subsequently continue it to an arbitrary real number and compute the correlators in a closed form. We also included an arbitrary number of screening charges and, as a result, after renormalizing them, as well as the external legs and the cosmological constant, the form of the final amplitudes do not modify. The result is remarkably parallel to the bosonic case. For completeness, we discussed the calculation of bosonic correlators including arbitrary screening charges.

hep-th↗
arXiv1991

General Neveu-Schwarz Correlators in Super Liouville Theory

In this paper we compute the N-point correlation functions of the tachyon operator from the Neveu Schwarz sector of super Liouville theory coupled to matter fields (with $\hat c\le 1$) in the super Coulomb gas formulation, on world sheets with spherical topology. We first integrate over the zero mode assuming that the $s$ parameter takes an integer value, subsequently we continue the parameter to an arbitrary real number. We included an arbitrary number of screening charges (s.c.) and as a result, after renormalizing the s.c., the external legs and the cosmological constant, the form of the final amplitudes do not modify. Remarkably, the result is completely parallel to the bosonic case. We also completed a discussion on the calculation of bosonic correlators including arbitrary screening charges.

hep-th↗
arXiv1991

Correlation functions in super Liouville theory

We calculate three- and four-point functions in super Liouville theory coupled to super Coulomb gas on world sheets with spherical topology. We first integrate over the zero mode and assume that a parameter takes an integer value. After calculating the amplitudes, we formally continue the parameter to an arbitrary real number. Remarkably the result is completely parallel to the bosonic case, the amplitudes being of the same form as those of the bosonic case.

hep-th↗