Number of Magic Squares From Parallel Tempering Monte Carlo

There are 880 magic squares of size 4 by 4, and 275,305,224 of size 5 by 5. It seems very difficult if not impossible to count exactly the number of higher order magic squares. We propose a method to estimate these numbers by Monte Carlo simulating magic squares at finite temperature. One is led to perform low temperature simulations of a system with many ground states that are separated by energy barriers. The Parallel Tempering Monte Carlo method turns out to be of great help here. Our estimate for the number of 6 by 6 magic squares is 0.17745(16) times 10**20.Comment: 8 pages, no figure

Improved actions, the perfect action, and scaling by perturbation theory in Wilsons renormalization group: the two dimensional O(N)O(N)-invariant non linear σ\sigma-model in the hierarchical approximation

We propose a method using perturbation theory in the running coupling constant and the idea of scaling to determine improved actions for lattice field theories combining Wilson's renormalization group with Symanzik's improvement program . The method is based on the analysis of a single renormalization group transformation. We test it on the hierarchical $O(N)$ invariant $\sigma$ model in two dimensions.Comment: 13 pages in LaTeX, 5 uuencoded PS figures included with epsfig.sty (including of ps-files fixed

The Hierarchical ϕ4\phi^4 - Trajectory by Perturbation Theory in a Running Coupling and its Logarithm

We compute the hierarchical $\phi^4$-trajectory in terms of perturbation theory in a running coupling. In the three dimensional case we resolve a singularity due to resonance of power counting factors in terms of logarithms of the running coupling. Numerical data is presented and the limits of validity explored. We also compute moving eigenvalues and eigenvectors on the trajectory as well as their fusion rules.Comment: 24 pages, 9 pictures included, uuencoded compressed postscript fil

The renormalized ϕ44\phi^4_4-trajectory by perturbation theory in a running coupling II: the continuous renormalization group

The renormalized trajectory of massless $\phi^4$-theory on four dimensional Euclidean space-time is investigated as a renormalization group invariant curve in the center manifold of the trivial fixed point, tangent to the $\phi^4$-interaction. We use an exact functional differential equation for its dependence on the running $\phi^4$-coupling. It is solved by means of perturbation theory. The expansion is proved to be finite to all orders. The proof includes a large momentum bound on amputated connected momentum space Green's functions.Comment: 26 pages LaTeX2

Canonical Demon Monte Carlo Renormalization Group

We describe a new method to compute renormalized coupling constants in a Monte Carlo renormalization group calculation. The method can be used for a general class of models, e.g., lattice spin or gauge models. The basic idea is to simulate a joint system of block spins and canonical demons. In contrast to the Microcanonical Renormalization Group invented by Creutz et al. our method does not suffer from systematical errors stemming from a simultaneous use of two different ensembles. We present numerical results for the $O(3)$ nonlinear $\sigma$-model.Comment: LaTeX file, 7 pages, preprints CERN TH.7330/94, MS-TPI-

Running coupling expansion for the renormalized ϕ44\phi^4_4-trajectory from renormalization invariance

We formulate a renormalized running coupling expansion for the $\beta$--function and the potential of the renormalized $\phi^4$--trajectory on four dimensional Euclidean space-time. Renormalization invariance is used as a first principle. No reference is made to bare quantities. The expansion is proved to be finite to all orders of perturbation theory. The proof includes a large momentum bound on the connected free propagator amputated vertices.Comment: 14 pages LaTeX2e, typos and references correcte