padic analysis
In mathematics, padic analysis is a branch of number theory that deals with the mathematical analysis of functions of padic numbers.
The theory of complexvalued numerical functions on the padic numbers is part of the theory of locally compact groups. The usual meaning taken for padic analysis is the theory of padicvalued functions on spaces of interest.
Applications of padic analysis have mainly been in number theory, where it has a significant role in diophantine geometry and diophantine approximation. Some applications have required the development of padic functional analysis and spectral theory. In many ways padic analysis is less subtle than classical analysis, since the ultrametric inequality means, for example, that convergence of infinite series of padic numbers is much simpler. Topological vector spaces over padic fields show distinctive features; for example aspects relating to convexity and the Hahn–Banach theorem are different.
Contents
Important results
Ostrowski's theorem
Ostrowski's theorem, due to Alexander Ostrowski (1916), states that every nontrivial absolute value on the rational numbers Q is equivalent to either the usual real absolute value or a padic absolute value.^{[1]}
Mahler's theorem
Mahler's theorem, introduced by Kurt Mahler,^{[2]} expresses continuous padic functions in terms of polynomials.
In any field, one has the following result. Let
be the forward difference operator. Then for polynomial functions f we have the Newton series:
where
is the kth binomial coefficient polynomial.
Over the field of real numbers, the assumption that the function f is a polynomial can be weakened, but it cannot be weakened all the way down to mere continuity.
Mahler proved the following result:
Mahler's theorem: If f is a continuous padicvalued function on the padic integers then the same identity holds.
Hensel's lemma
Hensel's lemma, also known as Hensel's lifting lemma, named after Kurt Hensel, is a result in modular arithmetic, stating that if a polynomial equation has a simple root modulo a prime number p, then this root corresponds to a unique root of the same equation modulo any higher power of p, which can be found by iteratively "lifting" the solution modulo successive powers of p. More generally it is used as a generic name for analogues for complete commutative rings (including padic fields in particular) of the Newton method for solving equations. Since padic analysis is in some ways simpler than real analysis, there are relatively easy criteria guaranteeing a root of a polynomial.
To state the result, let be a polynomial with integer (or padic integer) coefficients, and let m,k be positive integers such that m ≤ k. If r is an integer such that
 and
then there exists an integer s such that
 and
Furthermore, this s is unique modulo p^{k+m}, and can be computed explicitly as
 where
Applications
Padic quantum mechanics
Padic quantum mechanics is a relatively recent approach to understanding the nature of fundamental physics. It is the application of padic analysis to quantum mechanics. The padic numbers are a counterintuitive arithmetic system that was discovered by the German mathematician Kurt Hensel in about 1899. The closely related adeles and ideles were introduced in the 1930s by Claude Chevalley and André Weil. Their study has now transformed into a major branch of mathematics. They were occasionally applied to the physical sciences, but it wasn't until a publication by the Russian mathematician Volovich in 1987 that the subject was taken seriously in the physics world.^{[3]} There are now hundreds of research articles on the subject,^{[4]}^{[5]} along with international journals as well.
There are two main approaches to the subject.^{[6]}^{[7]} The first considers particles in a padic potential well, and the goal is to find solutions with smoothly varying complexvalued wavefunctions. Here the solutions to have a certain amount of familiarity from ordinary life. The second considers particles in padic potential wells, and the goal is to find padic valued wavefunctions. In this case, the physical interpretation is more difficult. Yet the math often exhibits striking characteristics, therefore people continue to explore it. The situation was summed up in 2005 by one scientist as follows: "I simply cannot think of all this as a sequence of amusing accidents and dismiss it as a 'toy model'. I think more work on this is both needed and worthwhile."^{[8]}
Local–global principle
Helmut Hasse's local–global principle, also known as the Hasse principle, is the idea that one can find an integer solution to an equation by using the Chinese remainder theorem to piece together solutions modulo powers of each different prime number. This is handled by examining the equation in the completions of the rational numbers: the real numbers and the padic numbers. A more formal version of the Hasse principle states that certain types of equations have a rational solution if and only if they have a solution in the real numbers and in the padic numbers for each prime p.
See also
References

^ Koblitz, Neal (1984). Padic numbers, padic analysis, and zetafunctions (2nd ed.). New York: SpringerVerlag. p. 3. ISBN 9780387960173. Retrieved 24 August 2012.
Theorem 1 (Ostrowski). Every nontrivial norm ‖ ‖ on ℚ is equivalent to  _{p} for some prime p or for p = ∞.
 ^ Mahler, K. (1958), "An interpolation series for continuous functions of a padic variable", Journal für die reine und angewandte Mathematik, 199: 23–34, ISSN 00754102, MR 0095821
 ^ I.V.Volovich, Number theory as the ultimate theory, CERN preprint, CERNTH.4791/87
 ^ V. S. Vladimirov, I.V. Volovich, and E.I. Zelenov Padic Analyisis and Mathematical Physics, (World Scientific, Singapore 1994)
 ^ L. Brekke and P. G. O. Freund, Padic numbers in physics, Phys. Rep. 233, 166(1993)
 ^ Branko Dragovich, Adeles in Mathematical Physics (2007), https://arxiv.org/abs/0707.3876
 ^ page 3, second paragraph, Goran S. Djordjevic and Branko Dragovich, pAdic and Adelic Harmonic Oscillator with TimeDependent Frequency, https://arxiv.org/abs/quantph/0005027
 ^ Peter G.O. Freund, padic Strings and their Applications, https://arxiv.org/abs/hepth/0510192
Further reading
 Koblitz, Neal (1980). padic analysis: a short course on recent work. London Mathematical Society Lecture Note Series. 46. Cambridge University Press. ISBN 0521280605. Zbl 0439.12011.
 Cassels, J.W.S. (1986). Local Fields. London Mathematical Society Student Texts. 3. Cambridge University Press. ISBN 0521315255. Zbl 0595.12006.
 Chistov,Alexander and Karpinski, Marek: Complexity of Deciding Solvability of Polynomial Equations over padic Integers, Univ. of Bonn CS reports 85183 (1997)
 Karpinski, Marek; van der Poorten, Alf; Shparlinski, Igor (2000). "Zero testing of padic and modular polynomials". Theoretical Computer Science. 233: 309–317. doi:10.1016/S03043975(99)001334. (preprint)
 A course in padic analysis, Alain Robert, Springer, 2000, ISBN 9780387986692
 Ultrametric Calculus: An Introduction to PAdic Analysis, W. H. Schikhof, Cambridge University Press, 2007, ISBN 9780521032872
 Padic Differential Equations, Kiran S. Kedlaya, Cambridge University Press, 2010, ISBN 9780521768795