Solving some gauge systems at infinite N

After summarizing briefly some numerical results for four-dimensional supersymmetric SU(2) Yang-Mills quantum mechanics, we review a recent study of systems with an infinite number of colours. We study in detail a particular supersymmetric matrix model which exhibits a phase transition, strong-weak duality, and a rich structure of supersymmetric vacua. In the planar and strong coupling limits, this field theoretical system is equivalent to a one-dimensional XXZ Heisenberg chain and, at the same time, to a gas of $q$-bosons. This not only reveals a hidden supersymmetry in these well-studied models; it also maps the intricate pattern of our supersymmetic vacua into that of the now-popular ground states of the XXZ chain.Comment: 23 pages, 7 figures; lecture given at the XLVI Cracow School of Theoretical Physics; some typos and references correcte

Recent progress in supersymmetric Yang-Mills quantum mechanics in various dimensions

We review the last year progress in understanding supersymmetric SU(2) Yang-Mills quantum mechanics in four and ten space-time dimensions. The four dimensional system is now well under control and the precise spectrum is obtained in all channels. In D=10 some new results are also available.Comment: 19 pages, 4 figures, presented at the Workshop on Random Geometry, Krakow, May 15 - 17, 200

Large N, Supersymmetry ... and QCD

This paper consists of two (still only vaguely) related parts: in the first, we briefly review work done in the past three years on the ``planar equivalence" between a class of non-supersymmetric theories (including limiting cases of QCD) and their corresponding supersymmetric "parents"; in the second, we present details of a new formulation of planar quantum mechanics and illustrate its effectiveness in an intriguing supersymmetric example.Comment: A contribution to the A. Di Giacomo Festschrift: Physics and Beauty, 21 pages, 8 figure

Quantum systems in a cut Fock space

Standard quantum mechanics is viewed as a limit of a cut system with artificially restricted dimension of a Hilbert space. Exact spectrum of cut momentum and coordinate operators is derived and the limiting transition to the infinite dimensional Hilbert space is studied in detail. The difference between systems with discrete and continuous energy spectra is emphasized. In particular a new scaling law, characteristic for nonlocalized, states is found. Some applications for supersymmetric quantum mechanics are briefly outlined.Comment: 10 page

Lattice study of the simplified model of M-theory for larger gauge groups

Lattice discretization of the supersymmetric Yang-Mills quantum mechanics is dis cussed. First results of the quenched Monte Carlo simulations, for D=4 and with higher g auge groups (3 <= N <= 8), are presented. We confirm an earlier (N=2) evidence tha t the system reveals different behaviours at low and high temperatures separated by a narrow transiti on region. These two regimes may correspond to a black hole and elementary excitations phases conjectured in the M-theory. Dependence of the "transition temperature" on N is consistent with 't Hooft scaling and shows a smooth saturation of lattice results towards the large N limit. Is not yet resolved if the observed change between the two regimes corresponds to a genuine phase transition or to a gentle crossover . A new, noncompact formulation of the lattice model is also proposed and its advantages are briefly discussed.Comment: 10 pages, 2 figures, Invited talk presented at the Sixth Workshop on Non-Perturbative QCD, American University of Paris, Paris, June, 200

Planar Quantum Mechanics: an Intriguing Supersymmetric Example

After setting up a Hamiltonian formulation of planar (matrix) quantum mechanics, we illustrate its effectiveness in a non-trivial supersymmetric example. The numerical and analytical study of two sectors of the model, as a function of 't Hooft's coupling $\lambda$, reveals both a phase transition at $\lambda=1$ (disappearence of the mass gap and discontinuous jump in Witten's index) and a new form of strong-weak duality for $\lambda \to 1/\lambda$.Comment: 14 pages, 3 .eps figures (1 figure, 2 acknowledgements added, typos corrected

Supersymmetry and Combinatorics

We show how a recently proposed supersymmetric quantum mechanics model leads to non-trivial results/conjectures on the combinatorics of binary necklaces and linear-feedback shift-registers. Pauli's exclusion principle plays a crucial role: by projecting out certain states/necklaces, it allows to represent the supersymmetry algebra in the resulting subspace. Some of our results can be rephrased in terms of generalizations of the well-known Witten index.Comment: 14 pages, 3 figures, text expanded, references adde