Griffiths's take on degenerate perturbation theory
103579
Why are the zeroth order terms in degenerate perturbation theory the eigenstates of the perturbing Hamiltonian?
129827
Product of invertibles in $\Bbb Z_n$ [Wilson's Theorem generalization]
112987
Exponential of ladder operators acting on a Fock state
100004
Differentiating $e^x$ from first principles using limits.
54668
Proof for the completeness of eigenfunctions of a self-adjoint operator
15035
An operator on the other side of the Schrödinger equation
148914
Total Variation and indefinite integrals
150830
Path integral measure in Coleman's "Aspects of symmetry"
136849
Mathematical rigorous introduction to solid state physics
112398
Proof that the effective/proper action is the generating functional of one-particle-irreducible (1PI) correlation functions
88971
An approximate eigenvalue for $ T \in B(X) $.
132129
Derivation of derangement with inclusion-exclusion
3201
Landau & Lifshitz's Approach (contour method) on the WKB connection formulas
126425
Consistent, complete, and generalized description of the quantum harmonic oscillator
27812
Understanding the differential $dx$ when doing $u$-substitution
92455
Orthonormalization of non-hermitian matrix eigenvectors
59235
Finding eigenvalues of a differential operator