- Source: Variational perturbation theory
In mathematics, variational perturbation theory (VPT) is a mathematical method to convert divergent power series in a small expansion parameter, say
s
=
∑
n
=
0
∞
a
n
g
n
{\displaystyle s=\sum _{n=0}^{\infty }a_{n}g^{n}}
,
into a convergent series in powers
s
=
∑
n
=
0
∞
b
n
/
(
g
ω
)
n
{\displaystyle s=\sum _{n=0}^{\infty }b_{n}/(g^{\omega })^{n}}
,
where
ω
{\displaystyle \omega }
is a critical exponent (the so-called index of "approach to scaling" introduced by Franz Wegner). This is possible with the help of variational parameters, which are determined by optimization order by order in
g
{\displaystyle g}
. The partial sums are converted to convergent partial sums by a method developed in 1992.
Most perturbation expansions in quantum mechanics are divergent for any small coupling strength
g
{\displaystyle g}
. They can be made convergent by VPT (for details see the first textbook cited below). The convergence is exponentially fast.
After its success in quantum mechanics, VPT has been developed further to become an important mathematical tool in quantum field theory with its anomalous dimensions. Applications focus on the theory of critical phenomena. It has led to the most accurate predictions of critical exponents.
More details can be read here.
References
External links
Kleinert H., Path Integrals in Quantum Mechanics, Statistics, Polymer Physics, and Financial Markets, 3. Auflage, World Scientific (Singapore, 2004) (readable online here) (see Chapter 5)
Kleinert H. and Verena Schulte-Frohlinde, Critical Properties of φ4-Theories, World Scientific (Singapur, 2001); Paperback ISBN 981-02-4658-7 (readable online here) (see Chapter 19)
Feynman, R. P.; Kleinert, H. (1986). "Effective classical partition functions" (PDF). Physical Review A. 34 (6): 5080–5084. Bibcode:1986PhRvA..34.5080F. doi:10.1103/PhysRevA.34.5080. PMID 9897894.
Kata Kunci Pencarian:
- Variational perturbation theory
- Perturbation theory
- Perturbation theory (quantum mechanics)
- Richard Feynman
- Molecular orbital theory
- Critical phenomena
- Møller–Plesset perturbation theory
- Perturbation (astronomy)
- Hagen Kleinert
- Theory
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