Английская Википедия:Bernstein–Sato polynomial

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Шаблон:Short description In mathematics, the Bernstein–Sato polynomial is a polynomial related to differential operators, introduced independently by Шаблон:Harvs and Шаблон:Harvs, Шаблон:Harvtxt. It is also known as the b-function, the b-polynomial, and the Bernstein polynomial, though it is not related to the Bernstein polynomials used in approximation theory. It has applications to singularity theory, monodromy theory, and quantum field theory.

Шаблон:Harvs gives an elementary introduction, while Шаблон:Harvs and Шаблон:Harvs give more advanced accounts.

Definition and properties

If <math>f(x)</math> is a polynomial in several variables, then there is a non-zero polynomial <math>b(s)</math> and a differential operator <math>P(s)</math> with polynomial coefficients such that

<math>P(s)f(x)^{s+1} = b(s)f(x)^s.</math>

The Bernstein–Sato polynomial is the monic polynomial of smallest degree amongst such polynomials <math>b(s)</math>. Its existence can be shown using the notion of holonomic D-modules.

Шаблон:Harvtxt proved that all roots of the Bernstein–Sato polynomial are negative rational numbers.

The Bernstein–Sato polynomial can also be defined for products of powers of several polynomials Шаблон:Harv. In this case it is a product of linear factors with rational coefficients.Шаблон:Citation needed

Шаблон:Harvs generalized the Bernstein–Sato polynomial to arbitrary varieties.

Note, that the Bernstein–Sato polynomial can be computed algorithmically. However, such computations are hard in general. There are implementations of related algorithms in computer algebra systems RISA/Asir, Macaulay2, and SINGULAR.

Шаблон:Harvs presented algorithms to compute the Bernstein–Sato polynomial of an affine variety together with an implementation in the computer algebra system SINGULAR.

Шаблон:Harvs described some of the algorithms for computing Bernstein–Sato polynomials by computer.

Examples

  • If <math>f(x)=x_1^2+\cdots+x_n^2 \, </math> then
<math>\sum_{i=1}^n \partial_i^2 f(x)^{s+1} = 4(s+1)\left(s+\frac{n}{2}\right)f(x)^s</math>
so the Bernstein–Sato polynomial is
<math>b(s)=(s+1)\left(s+\frac{n}{2}\right).</math>
  • If <math> f(x)=x_1^{n_1}x_2^{n_2}\cdots x_r^{n_r}</math> then
<math>\prod_{j=1}^r\partial_{x_j}^{n_j}\quad f(x)^{s+1}

=\prod_{j=1}^r\prod_{i=1}^{n_j}(n_js+i)\quad f(x)^s</math>

so
<math>b(s)=\prod_{j=1}^r\prod_{i=1}^{n_j}\left(s+\frac{i}{n_j}\right).</math>
  • The Bernstein–Sato polynomial of x2 + y3 is
<math>(s+1)\left(s+\frac{5}{6}\right)\left(s+\frac{7}{6}\right).</math>
  • If tij are n2 variables, then the Bernstein–Sato polynomial of det(tij) is given by
<math>(s+1)(s+2)\cdots(s+n)</math>
which follows from
<math>\Omega(\det(t_{ij})^s) = s(s+1)\cdots(s+n-1)\det(t_{ij})^{s-1}</math>
where Ω is Cayley's omega process, which in turn follows from the Capelli identity.

Applications

<math>f(x)^s={1\over b(s)} P(s)f(x)^{s+1}.</math>
It may have poles whenever b(s + n) is zero for a non-negative integer n.
  • If f(x) is a polynomial, not identically zero, then it has an inverse g that is a distribution;[lower-alpha 1] in other words, f g = 1 as distributions. If f(x) is non-negative the inverse can be constructed using the Bernstein–Sato polynomial by taking the constant term of the Laurent expansion of f(x)s at s = −1. For arbitrary f(x) just take <math>\bar f(x)</math> times the inverse of <math>\bar f(x)f(x).</math>
  • The Malgrange–Ehrenpreis theorem states that every differential operator with constant coefficients has a Green's function. By taking Fourier transforms this follows from the fact that every polynomial has a distributional inverse, which is proved in the paragraph above.
  • Шаблон:Harvs showed how to use the Bernstein polynomial to define dimensional regularization rigorously, in the massive Euclidean case.
  • The Bernstein-Sato functional equation is used in computations of some of the more complex kinds of singular integrals occurring in quantum field theory Шаблон:Harvs. Such computations are needed for precision measurements in elementary particle physics as practiced for instance at CERN (see the papers citing Шаблон:Harv). However, the most interesting cases require a simple generalization of the Bernstein-Sato functional equation to the product of two polynomials <math>(f_1(x))^{s_1}(f_2(x))^{s_2}</math>, with x having 2-6 scalar components, and the pair of polynomials having orders 2 and 3. Unfortunately, a brute force determination of the corresponding differential operators <math>P(s_1,s_2)</math> and <math>b(s_1,s_2)</math> for such cases has so far proved prohibitively cumbersome. Devising ways to bypass the combinatorial explosion of the brute force algorithm would be of great value in such applications.

Notes

Шаблон:Notelist

References

Партнерские ресурсы
Криптовалюты
Магазины
Хостинг
Разное


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