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  2. Non-linear sigma model - Wikipedia

    en.wikipedia.org/wiki/Non-linear_sigma_model

    In quantum field theory, a nonlinear σ model describes a field Σ that takes on values in a nonlinear manifold called the target manifold T.The non-linear σ-model was introduced by Gell-Mann & Lévy (1960, §6), who named it after a field corresponding to a spinless meson called σ in their model. [1]

  3. Sigma model - Wikipedia

    en.wikipedia.org/wiki/Sigma_model

    When the sigma field is coupled to a gauge field, the resulting model is described by Ginzburg–Landau theory. This article is primarily devoted to the classical field theory of the sigma model; the corresponding quantized theory is presented in the article titled "non-linear sigma model".

  4. List of quantum field theories - Wikipedia

    en.wikipedia.org/wiki/List_of_quantum_field_theories

    5 Sigma models. 6 Supersymmetric quantum field theories. ... Non-linear sigma model; Wess–Zumino–Witten model; Supersymmetric quantum field theories

  5. Skyrmion - Wikipedia

    en.wikipedia.org/wiki/Skyrmion

    In particle theory, the skyrmion (/ ˈ s k ɜːr m i. ɒ n /) is a topologically stable field configuration of a certain class of non-linear sigma models.It was originally proposed as a model of the nucleon by (and named after) Tony Skyrme in 1961.

  6. Chiral model - Wikipedia

    en.wikipedia.org/wiki/Chiral_model

    It is a nonlinear sigma model with the principal homogeneous space of a Lie group as its target manifold. When the model was originally introduced, this Lie group was the SU, where N is the number of quark flavors.

  7. Sigmoid function - Wikipedia

    en.wikipedia.org/wiki/Sigmoid_function

    Step function – Linear combination of indicator functions of real intervals; Sign function – Mathematical function returning -1, 0 or 1; Heaviside step function – Indicator function of positive numbers

  8. Activation function - Wikipedia

    en.wikipedia.org/wiki/Activation_function

    Nonlinear When the activation function is non-linear, then a two-layer neural network can be proven to be a universal function approximator. [6] This is known as the Universal Approximation Theorem. The identity activation function does not satisfy this property.

  9. Nonlinear sigma models - Wikipedia

    en.wikipedia.org/?title=Nonlinear_sigma_models&...

    Pages for logged out editors learn more. Contributions; Talk; Nonlinear sigma models