We study the scalar curvature of the Fisher information metric on the microscopic coupling-parameter manifold of lattice spin models at criticality. For a
d-dimensional lattice with periodic boundary conditions and
n=Ld sites, the Fisher manifold has
m=d⋅n dimensions (one per bond), and we find
∣R(Jc)∣∼ndR with
dR=(dν+2η)/(dν+η), where
ν and
η are the correlation-length and anomalous-dimension critical exponents. For 2D Ising (
ν=1,
η=1/4), this predicts
dR=10/9, confirmed by exact transfer-matrix computations (
L=6--
9:
dR=1.1115±0.0002) and multi-seed MCMC through
L=24. For 3D Ising (
ν=0.630,
η=0.0363), the prediction
dR=1.019 is consistent with MCMC on
L3 tori up to
L=10 (power-law fit:
dR=1.040). For 2D Potts
q=3 (predicted
33/29≈1.138), FFT-MCMC through
L=40 shows
deff oscillating non-monotonically around
∼1.20, consistent with
O(1/(lnL)2) logarithmic corrections. For
q=4 (predicted
22/19), effective exponents oscillate with strong logarithmic corrections. The Ricci decomposition identity
R3=−R1/2,
R4=−R2/2 holds to 5--6 digits for all models. This exponent is distinct from Ruppeiner thermodynamic curvature and reflects the collective geometry of the growing Fisher manifold. We provide falsification criteria and predictions for additional universality classes.
The corrections to finite-size scaling in the critical two-point correlation function G(r) of 2D Ising model on a square lattice have been studied numerically by means of exact transfer-matrix algorithms. The systems of square geometry with periodic boundaries oriented either along <10> or along <11> direction have been considered, including up to 800 spins. The calculation of G(r) at a distance r equal to the half of the system size L shows the existence of an amplitude correction proportional to 1/L^2. A nontrivial correction proportional to 1/L^0.25 of a very small magnitude also has been detected in agreement with predictions of our recently developed GFD (grouping of Feynman diagrams) theory. A refined analysis of the recent MC data for 3D Ising, phi^4, and XY lattice models has been performed. It includes an analysis of the partition function zeros of 3D Ising model, an estimation of the correction-to-scaling exponent omega from the Binder cumulant data near criticality, as well as a study of the effective critical exponent eta and the effective amplitudes in the asymptotic expansion of susceptibility at the critical point. In all cases a refined analysis is consistent with our (GFD) asymptotic values of the critical exponents (nu=2/3, omega=1/2, eta=1/8 for 3D Ising model and omega=5/9 for 3D XY model), while the actually accepted "conventional" exponents are, in fact, effective exponents which are valid for approximation of the finite--size scaling behavior of not too large systems.