Description: I Basic Models.- 1 Electron Interactions in Solids.- 2 Spin Exchange.- 3 The Hubbard Model and Its Descendants.- II Wave Functions and Correlations.- 4 Ground States of the Hubbard Model.- 5 Ground States of the Heisenberg Model.- 6 Disorder in Low Dimensions.- 7 Spin Representations.- 8 Variational Wave Functions and Parent Hamiltonians.- 9 From Ground States to Excitations.- III Path Integral Approximations.- 10 The Spin Path Integral.- 11 Spin Wave Theory.- 12 The Continuum Approximation.- 13 Nonlinear Sigma Model: Weak Coupling.- 14 The Nonlinear Sigma Model: Large N.- 15 Quantum Antiferromagnets: Continuum Results.- 16 SU(N) Heisenberg Models.- 17 The Large N Expansion.- 18 Schwinger Bosons Mean Field Theory.- 19 The Semiclassical Theory of the t -- J Model.- IV Mathematical Appendices.- Appendix A Second Quantization.- A.1 Fock States.- A.2 Normal Bilinear Operators.- A.3 Noninteracting Hamiltonians.- A.4 Exercises.- Appendix B Linear Response and Generating Functionals.- B.1 Spin Response Function.- B.2 Fluctuations and Dissipation.- B.3 The Generating Functional.- Appendix C Bose and Fermi Coherent States.- C.1 Complex Integration.- C.2 Grassmann Variables.- C.3 Coherent States.- C.4 Exercises.- Appendix D Coherent State Path Integrals.- D.1 Constructing the Path Integral.- D.2 Normal Bilinear Hamiltonians.- D.3 Matsubara Representation.- D.4 Matsubara Sums.- D.5 Exercises.- Appendix E The Method of Steepest Descents.

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