Universality of random knotting

Knotting probability [P-K(N)] is defined by the probability of an N-noded random polygon being topologically equivalent to a given knot K. For several nontrivial knots we numerically evaluate the knotting probabilities for Gaussian and rod-bead models. We find that they are well approximated by the following formula: P-K(N)=C(K)[(N) over tilde/N(K)](m(K))exp[-(N) over tilde/N(K)] where (N) over tilde=N-N-ini(K), and that the fitting parameters C(K); N(K), and N-ini(K) are model dependent, while m(K) is not. We suggest that given a knot K, the exponent m(K) should be universal: it is independent of models of random polygon and is determined only by the knot K.