Methods in Field TheoryDownloaded from www.worldscientific.com by UNIVERSITY OF BIRMINGHAM LIBRARY -INFORMATION SERVICES on 03/22/15. For personal use only. Contents 1. Introduction 331 2. Landau theory 332 2.1. Consequences for uniform situations 333 2.2. Correlation functions 337 2.3. Conclusion 340 3. Scaling and universality 340 3.1. Role of the dimension of space 340 3.2. Role of n 341 3.3. Universality 341 3.4. Scaling properties 342 4. Corrections to Landau theory : difficulties for dimensions smaller than four 343 4.1. Tree approximation 345 4.2. One-loop corrections 348 4.3. Higher number of loops 350 5. The renormalization group approach 350 5.1. The renormalization group strategy 351 5.2. Scaling of the correlation functions at Tc353 5.3. Scaling laws above Tc 357 5.4. Scaling laws in a field, and below the critical temperature 359 5.5 Conclusion 363 6. Stability of the fixed points; corrections to scaling 365 6.1.0 (n) symmetric fixed point 365 6.2. Gradient flow 366 6.3. Stability and instability of the 0 (n) symmetric fixed point 367 7. Dipolar Ising ferromagnets : a decisive experiment 371 7.1. Uniaxial dipolar ferromagnets in three dimensions 371 7.2. Divergence of the specific heat 372 7.3. Comparison with experiment 376 8. The zero and the infinite 377 8.1. Large n limit : expansion around the spherical model 377 8.2. n = 0 : the excluded volume problem 380 9. Applications of the operator product expansion 384 References 386 R. Balian and J. Zinn-Justin, eds., Les Houches, Session XXVIII, 1975 -Methodes en theories des champs / Methods in field theory © North-Holland Publishing Company, 1976 Methods in Field Theory Downloaded from www.worldscientific.com by UNIVERSITY OF BIRMINGHAM LIBRARY -INFORMATION SERVICES on 03/22/15. For personal use only.