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  2. Friendly number - Wikipedia

    en.wikipedia.org/wiki/Friendly_number

    A number that is not part of any friendly pair is called solitary. The abundancy index of n is the rational number σ(n) / n, in which σ denotes the sum of divisors function. A number n is a friendly number if there exists m ≠ n such that σ(m) / m = σ(n) / n. Abundancy is not the same as abundance, which is defined as σ(n) − 2n.

  3. List of quantum-mechanical systems with analytical solutions

    en.wikipedia.org/wiki/List_of_quantum-mechanical...

    which is an eigenvalue equation. Very often, only numerical solutions to the Schrödinger equation can be found for a given physical system and its associated potential energy. However, there exists a subset of physical systems for which the form of the eigenfunctions and their associated energies, or eigenvalues, can be found.

  4. Bogoliubov transformation - Wikipedia

    en.wikipedia.org/wiki/Bogoliubov_transformation

    The Bogoliubov transformation is often used to diagonalize Hamiltonians, which yields the stationary solutions of the corresponding Schrödinger equation. The Bogoliubov transformation is also important for understanding the Unruh effect , Hawking radiation , Davies-Fulling radiation (moving mirror model), pairing effects in nuclear physics ...

  5. Mathematical formulation of the Standard Model - Wikipedia

    en.wikipedia.org/wiki/Mathematical_formulation...

    Similarly, the muons and their neutrinos are assigned a muon number of +1 and the tau leptons are assigned a tau lepton number of +1. The Standard Model predicts that each of these three numbers should be conserved separately in a manner similar to the way baryon number is conserved. These numbers are collectively known as lepton family numbers ...

  6. Gauss circle problem - Wikipedia

    en.wikipedia.org/wiki/Gauss_circle_problem

    Another generalization is to calculate the number of coprime integer solutions , to the inequality m 2 + n 2 ≤ r 2 . {\displaystyle m^{2}+n^{2}\leq r^{2}.\,} This problem is known as the primitive circle problem , as it involves searching for primitive solutions to the original circle problem. [ 9 ]

  7. Einstein–Podolsky–Rosen paradox - Wikipedia

    en.wikipedia.org/wiki/Einstein–Podolsky–Rosen...

    In these "true" states, the positron going to Bob always has spin values opposite to the electron going to Alice, but the values are otherwise completely random. For example, the first pair emitted by the source might be "(+z, −x) to Alice and (−z, +x) to Bob", the next pair "(−z, −x) to Alice and (+z, +x) to Bob", and so forth ...

  8. Maxwell's equations - Wikipedia

    en.wikipedia.org/wiki/Maxwell's_equations

    These all form a set of coupled partial differential equations which are often very difficult to solve: the solutions encompass all the diverse phenomena of classical electromagnetism. Some general remarks follow. As for any differential equation, boundary conditions [19] [20] [21] and initial conditions [22] are necessary for a unique solution.

  9. Wick's theorem - Wikipedia

    en.wikipedia.org/wiki/Wick's_theorem

    Wick's theorem is a method of reducing high-order derivatives to a combinatorics problem. [1] It is named after Italian physicist Gian Carlo Wick. [2] It is used extensively in quantum field theory to reduce arbitrary products of creation and annihilation operators to sums of products of pairs of these operators.