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F. Antonuccio

Publications and source records attributed to F. Antonuccio.

At least 19 recordsLinked to original sources
arXiv1999

Supersymmetry and DLCQ

In this talk we describe the application of discrete light cone quantization (DLCQ) to supersymmetric field theories. We find that it is possible to formulate DLCQ so that supersymmetry is exactly preserved in the discrete approximation and call this formulation of DLCQ, SDLCQ. It combines the power of DLCQ with all of the beauty of supersymmetry. We have applied SDLCQ to several interesting supersymmetric theories and discussed zero modes, vacuum degeneracy, massless states, mass gaps, and theories in higher dimensions. Most recently we have used it to discuss the Maldacena conjecture.

hep-th↗
arXiv1999

The Perils of `Soft' SUSY Breaking

We consider a two dimensional SU(N) gauge theory coupled to an adjoint Majorana fermion, which is known to be supersymmetric for a particular value of fermion mass. We investigate the `soft' supersymmetry breaking of the discrete light cone quantization (DLCQ) of this theory. There are several DLCQ formulations of this theory currently in the literature and they naively appear to behave differently under `soft' supersymmetry breaking at finite resolution. We show that all these formulations nevertheless yield identical bound state masses in the decompactification limit of the light-like circle. Moreover, we are able to show that the supersymmetry-inspired version of DLCQ (so called `SDLCQ') provides the best rate of convergence of DLCQ bound state masses towards the actual continuum values, except possibly near or at the critical fermion mass. In this last case, we discuss improved extrapolation schemes that must supplement the DLCQ algorithm in order to obtain correct continuum bound state masses. Interestingly, when we truncate the Fock space to two particles, the SDLCQ prescription presented here provides a scheme for improving the rate of convergence of the massive t'Hooft model. Thus the supersymmetry-inspired SDLCQ prescription is applicable to theories without supersymmetry.

hep-th↗
arXiv1999

Two-Loop Calculations in phi^4 Light-Front Field Theory

We perform a two-loop calculation in light-front phi^4 theory to determine the effective mass renormalization of the light-front Hamiltonian. The renormalization scheme adopted here is manifestly boost invariant, and yields results that are in perfect agreement with the explicitly covariant Feynman diagram approach.

hep-th↗
arXiv1998

The Light-Cone Vacuum in 1+1 Dimensional Super-Yang-Mills Theory

The Discrete Light-Cone Quantization (DLCQ) of a supersymmetric SU(N) gauge theory in 1+1 dimensions is discussed, with particular emphasis given to the inclusion of all dynamical zero modes. Interestingly, the notorious `zero-mode problem' is now tractable because of special supersymmetric cancellations. In particular, we show that anomalous zero-mode contributions to the currents are absent, in contrast to what is observed in the non-supersymmetric case. We find that the supersymmetric partner of the gauge zero mode is the diagonal component of the fermion zero mode. An analysis of the vacuum structure is provided and it is shown that the inclusion of zero modes is crucial for probing the phase properties of the vacua. In particular, we find that the ground state energy is zero and N-fold degenerate, and thus consistent with unbroken supersymmetry. We also show that the inclusion of zero modes for the light-cone supercharges leaves the supersymmetry algebra unchanged. Finally, we remark that the dependence of the light-cone Fock vacuum in terms of the gauge zero is unchanged in the presence of matter fields.

hep-th↗
arXiv1998

A Comment on the Light-Cone Vacuum in 1+1 Dimensional Super-Yang-Mills Theory

The Discrete Light-Cone Quantization (DLCQ) of a supersymmetric gauge theory in 1+1 dimensions is discussed, with particular attention given to the inclusion of the gauge zero mode. Interestingly, the notorious `zero-mode' problem is now tractable because of special supersymmetric cancellations. In particular, we show that anomalous zero-mode contributions to the currents are absent, in contrast to what is observed in the non-supersymmetric case. An analysis of the vacuum structure is provided by deriving the effective quantum mechanical Hamiltonian of the gauge zero mode. It is shown that the inclusion of the zero modes of the adjoint scalars and fermions is crucial for probing the phase properties of the vacua. We find that the ground state energy is zero and thus consistent with unbroken supersymmetry, and conclude that the light-cone Fock vacuum is unchanged with or without the presence of matter fields.

hep-th↗
arXiv1998

On Exact Supersymmetry in DLCQ

In recent years a supersymmetric form of discrete light-cone quantization (hereafter `SDLCQ') has emerged as a very powerful tool for solving supersymmetric field theories. In this scheme, one calculates the light-cone supercharge with respect to a discretized light-cone Fock basis, instead of working with the light-cone Hamiltonian. This procedure has the advantage of preserving supersymmetry even in the discretized theory, and eliminates the need for explicit renormalizations in 1+1 dimensions. In order to compare the usual DLCQ prescription with the supersymmetric prescription, we consider two dimensional SU(N) Yang-Mills theory coupled to a massive adjoint Majorana fermion, which is known to be supersymmetric at a particular value of the fermion mass. After studying how singular-valued amplitudes and intermediate zero momentum modes are regularized in both schemes, we are able to establish a precise connection between conventional DLCQ and its supersymmetric extension, SDLCQ. In particular, we derive the explicit form of the (irrelevant) interaction that renders the DLCQ formulation of the theory exactly supersymmetric for any light-cone compactification. We check our analytical results via a numerical procedure, and discuss the relevance of this interaction when supersymmetry is explicitly broken.

hep-th↗
arXiv1998

DLCQ Bound States of N =(2,2) Super-Yang-Mills at Finite and Large N

We consider the 1+1 dimensional N = (2,2) supersymmetric matrix model which is obtained by dimensionally reducing N = 1 super Yang-Mills from four to two dimensions. The gauge groups we consider are U(Nc) and SU(Nc), where Nc is finite but arbitrary. We adopt light-cone coordinates, and choose to work in the light-cone gauge. Quantizing this theory via Discretized Light-Cone Quantization (DLCQ) introduces an integer, K, which restricts the light-cone momentum-fraction of constituent quanta to be integer multiples of 1/K. Solutions to the DLCQ bound state equations are obtained for K=2,3,...,6 by discretizing the light-cone supercharges, which results in a supersymmetric spectrum. Our numerical results imply the existence of normalizable massless states in the continuum limit K -> infinity, and therefore the absence of a mass gap. The low energy spectrum is dominated by string-like (or many parton) states. Our results are consistent with the claim that the theory is in a screening phase.

hep-th↗
arXiv1998

The DLCQ Spectrum of N=(8,8) Super Yang-Mills

We consider the 1+1 dimensional N = (8,8) supersymmetric matrix field theory obtained from a dimensional reduction of ten dimensional N = 1 super Yang-Mills. The gauge groups we consider are U(N) and SU(N), where N is finite but arbitrary. We adopt light-cone coordinates, and choose to work in the light-cone gauge. Quantizing this theory via Discretized Light-Cone Quantization (DLCQ) introduces an integer, K, which restricts the light-cone momentum-fraction of constituent quanta to be integer multiples of 1/K. Solutions to the DLCQ bound state equations are obtained for K=2,3 and 4 by discretizing the light-cone super charges, which preserves supersymmetry manifestly. We discuss degeneracies in the massive spectrum that appear to be independent of the light-cone compactification, and are therefore expected to be present in the decompactified limit K -> infinity. Our numerical results also support the claim that the SU(N) theory has a mass gap.

hep-th↗
arXiv1998

On the Transition from Confinement to Screening in QCD_{1+1} Coupled to Adjoint Fermions at Finite N

We consider SU(N) QCD_{1+1} coupled to massless adjoint Majorana fermions, where N is finite but arbitrary. We examine the spectrum for various values of N, paying particular attention to the formation of multi-particle states, which were recently identified by Gross, Hashimoto and Klebanov in the N -> infinity limit of the theory. It is believed that in the limit of vanishing fermion mass, there is a transition from confinement to screening in which string-like states made out of adjoint fermion bits dissociate into stable constituent ``single particles''. In this work, we provide numerical evidence that such a transition into stable constituent particles occurs not only at large N, but for any finite value of N. In addition, we discuss certain issues concerning the ``topological'' properties exhibited by the DLCQ spectrum.

hep-th↗
arXiv1998

Non-Perturbative Spectrum of Two Dimensional (1,1) Super Yang-Mills at Finite and Large N

We consider the dimensional reduction of N = 1 SYM_{2+1} to 1+1 dimensions, which has (1,1) supersymmetry. The gauge groups we consider are U(N) and SU(N), where N is a finite variable. We implement Discrete Light-Cone Quantization to determine non-perturbatively the bound states in this theory. A careful analysis of the spectrum is performed at various values of N, including the case where N is large (but finite), allowing a precise measurement of the 1/N effects in the quantum theory. The low energy sector of the theory is shown to be dominated by string-like states. The techniques developed here may be applied to any two dimensional field theory with or without supersymmetry.

hep-th↗
arXiv1997

On Matrix Strings, the Large N Limit and Discretized Light-Cone Quantization

We consider the 1+1 dimensional supersymmetric matrix field theory obtained from a dimensional reduction of ten dimensional ${\cal N} = 1$ super Yang-Mills, which is a matrix model candidate for non-perturbative Type IIA string theory. The gauge group here is U($N$), where $N$ is sent to infinity. We adopt light-cone coordinates to parametrize the string world sheet, and choose to work in the light-cone gauge. Quantizing this theory via Discretized Light-Cone Quantization (DLCQ) introduces an integer, K, which restricts the light-cone momentum-fraction of constituent quanta to be integer multiples of 1/K. We show how a double scaling limit involving the integers $K$ and $N$ implies the existence of an extra (free) parameter in the Yang-Mills theory, which plays the role of an effective string coupling constant. The formulation here provides a natural framework for studying quantitatively string dynamics and conventional Yang-Mills in a unified setting.

hep-th↗
arXiv1997

Light-Cone Wavefunctions at Small $x$

There exist an infinite number of exact small momentum fraction-$x$ boundary conditions on light-cone wavefunctions of bound states in gauge theory. They are necessary for finite expectation values of the invariant mass operator and relate components of the wavefunction from different Fock sectors. We illustrate their consequences by analyzing the small-$x$ quark Regge behavior of a heavy large-$N$ meson, finding power-law rise of unpolarized distributions. The polarized distribution changes sign and then vanishes with minus the unpolarized Regge intercept.

hep-ph↗
arXiv1997

Light-Cone Quantization and Renormalization of Large-N Scalar Matrix Models

We discuss the issue of renormalization and the derivation of effective interactions for light-cone Hamiltonians in the context of large-N scalar matrix models with $Φ^3$ interactions. For various space-time dimensions $D \geq 3$, we deduce appropriate mass, coupling constant, and wavefunction renormalizations which are necessary for finiteness of the Hamiltonian at leading order. We also outline how higher order corrections may be derived within this framework, and discuss the relevance of this approach in the light-cone quantization of gauge theories.

hep-th↗
arXiv1996

Matrix Theories from Reduced SU(N) Yang-Mills with Adjoint Fermions

We consider a dimensional reduction of 3+1 dimensional SU(N) Yang-Mills theory coupled to adjoint fermions to obtain a class of 1+1 dimensional matrix field theories. We derive the quantized light-cone Hamiltonian in the light-cone gauge A_- = 0 and large-N limit, and then solve for the masses, wavefunctions and structure functions of the color singlet ``meson-like'' and ``baryon-like'' boundstates. Among the states we study are many massless string-like states that can be solved for exactly.

hep-th↗
arXiv1995

A (1+1)-Dimensional Reduced Model of Mesons

We propose an extension of 't Hooft's large-$N_c$ light-front QCD in two dimensions to include helicity and physical gluon degrees of freedom, modelled on a classical dimensional reduction of four dimensional QCD. A non-perturbative renormalisation of the infinite set of coupled integral equations describing boundstates is performed. These equations are then solved, both analytically in a phase space wavefunction approximation and numerically by discretising momenta, for (hybrid) meson masses and (polarized) parton structure functions.

hep-th↗
arXiv1995

Glueballs from 1+1 Dimensional Gauge Theories with Transverse Degrees of Freedom

We study $1+1$-dimensional $SU(N)$ gauge theories with adjoint scalar matter representations, based on a dimensional truncation of $2+1$ and $3+1$-dimensional pure QCD, which approximate the dynamics of transversely polarized gluons. The glueballs are investigated non-perturbatively using light-front quantisation, detailed spectra and wavefunctions being obtained for the large-$N$ limit. In general there is some qualitative agreement of the spectra with lattice Monte Carlo data from the higher dimensional QCD. From the light-front wavefunctions we calculate (polarized) structure functions and interpret the gluon and spin content of glueballs. We discuss the phase structure of the reduced theories in relation to matrix models for relativistic non-critical strings.

hep-ph↗
arXiv1995

Adjoint 2D QCD and Pure 3D QCD: A Comparison of Spectra

We briefly review the 1+1-dimensional SU(N) gauge theory minimally coupled to an adjoint scalar, based upon a dimensional reduction of 2+1-dimensional pure gauge theory, which approximates the dynamics of the transversely polarized gluon. The lightest glueball states are investigated non-perturbatively using light-front quantisation in the large-N limit a la 't Hooft, and the physical meaning of the results elucidated. Comparison is made with recent lattice Monte Carlo data for 3-dimensional quenched QCD.

hep-lat↗