Hasse principle

One of the central principles of Diophantine geometry, which reduces the problem of the existence of rational points on an algebraic variety over a global field to the analogous problem over local fields.

Let $M$ be a class of algebraic varieties over a global field $K$. The Hasse principle holds in $M$ if for any $X$ in $M$ such that for all non-trivial absolute valuations $\nu$ on $KK$ the set of $K_\nu$-rational points $X(K_\nu)$ of $X$ is non-empty, the set of $K$-rational points $X(K)$ is also not empty (where $K_\nu$ is the completion of $K$ relative to $\nu$). In particular, if $K$ is the field $\Q$ of rational numbers, then if the set of real points $X(\R)$ and the set of $p$-adic points $\Q_p$, for all primes $p$, are not empty, it follows that the set of rational points $X(\Q)$ is also not empty. The Hasse principle holds for quadrics [2], and so it is valid for algebraic curves of genus 0 (see [3]). For quadrics over a number field the Hasse principle was stated and proved by H. Hasse in [1]. For cubic hypersurfaces the Hasse principle is not true, in general (see [3], [4]); a counterexample (over $\Q$) is the projective curve $3x^3+4y^3+5z^3 = 0$ or the projective surface $5x^3+12y^3+9z^3+10t^3=0$.

Let $G$ be an algebraic group over $K$ and let $M(G)$ be the class of algebraic varieties consisting of all principal homogeneous spaces over $G$ (see Galois cohomology; Weil–Châtelet group, and also [2], [3], [5]). One says that the Hasse principle holds for $G$ if it holds for $M(G)$. The Hasse principle holds for simply-connected and adjoint semi-simple algebraic groups over number fields ([5], [6]). If $G$ is an Abelian variety, then the Hasse principle holds for $G$ if and only if the Shafarevich–Tate group (cf. Galois cohomology) of $G$ vanishes (see the examples in [7], [8]).

References

[1]	H. Hasse, "Darstellbarkeit von Zahlen durch quadratische Formen in einem beliebigen algebraischen Zahlkörper" J. Reine Angew. Math. , 153 (1924) pp. 113–130
[2]	J.W.S. Cassels (ed.) A. Fröhlich (ed.) , Algebraic number theory , Acad. Press (1967)
[3]	J.W.S. Cassels, "Diophantine equations with special reference to elliptic curves" J. London Math. Soc. , 41 (1966) pp. 193–291
[4]	Yu.I. Manin, "Cubic forms. Algebra, geometry, arithmetic" , North-Holland (1974) (Translated from Russian)
[5]	J.-P. Serre, "Cohomologie Galoisienne" , Springer (1964)
[6]	V. Chernusov, "The Hasse principle for groups of type $E_8$" , Minsk (1988) (In Russian)
[7]	K. Rubin, "Tate–Shafarevich groups and $L$-functions of elliptic curves with complex multiplication" Invent. Math. , 89 (1987) pp. 527–560
[8]	V. Kolyvagin, "The Mordell–Weil groups and the Shafarevich–Tate groups of Weil's elliptic curves" Izv. Akad. Nauk. SSSR Ser. Mat. , 52 : 6 (1988)