# Mordell conjecture

A conjecture on the finiteness of the set of rational points on an algebraic curve of genus . Advanced by L.J. Mordell [1] for the case when the ground field is the field of rational numbers. At present (1982) Mordell's conjecture is taken to be the assertion of the finiteness of the set of rational points of an irreducible algebraic curve of genus defined over a field of finite type over the field of rational numbers in any finite extension . A reduction of Mordell's conjecture to the most difficult case when is an algebraic number field has been obtained (see [3]). A number of special results related to Mordell's conjecture are known. Thus, it has been proved [2] that is finite if the rank of the group of -automorphisms from into an elliptic curve is larger than the rank of the group . The finiteness of has been established, [7], for the broad class of modular curves (cf. Modular curve) and their fields of definition . An estimate for the growth of the height,

of the rational points has been found, [8], showing that they are situated more "sparsely" than on the curves of genus . It has also been proved that Mordell's conjecture is a consequence of Shafarevich's conjecture on the finiteness of the number of algebraic curves having a given genus , a given field of definition (a finite extension of ) and a given set of points of bad reduction (see [4], and also Siegel theorem on integer points).

The geometric analogue of Mordell's conjecture is the assertion of the finiteness of the number of sections of a bundle

where is a non-singular projective surface, is a curve and the general fibre of is an irreducible curve of genus . This assertion is true if the bundle is non-constant, that is, if it is not a direct product after a certain covering of the base , and if the characteristic of the ground field is equal to zero (see [3], [6]). For constant bundles it is possible only to assert the finiteness of the number of classes consisting of sections that are algebraically equivalent as curves on . If the characteristic of is positive, the geometric analogue of Mordell's conjecture is false [4].

#### References

 [1] L.J. Mordell, "On the rational solutions of the indeterminate equation of the third and fourth degrees" Proc. Cambridge Philos. Soc. , 21 (1922) pp. 179–192 [2] V.A. Dem'yanenko, "Rational points of a class of algebraic curves" Izv. Akad. Nauk SSSR Ser. Mat. , 30 : 6 (1966) pp. 1373–1396 (In Russian) Zbl 0162.24502 [3] Yu.I. Manin, "Rational points of algebraic curves over function fields" Transl. Amer. Math. Soc. (2) , 50 (1966) pp. 189–234 Izv. Akad. Nauk SSSR Ser. Mat. , 27 : 6 (1963) pp. 1395–1440 Zbl 0178.55102 [4] A.N. Parshin, "Quelques conjectures de finitude en géométrie diophantienne" , Proc. Internat. Congress Mathematicians (Nice, 1970) , 1 , Gauthier-Villars (1971) pp. 467–471 [5] H. Grauert, "Modell's Vermutung über rationale Punkte auf algebraischen Kurven und Funktionenkörpern" Publ. Math. IHES : 25 (1965) pp. 131–149 [6] S. Lang, "Diophantine geometry" , Interscience (1962) MR0142550 Zbl 0115.38701 [7] B. Mazur, "Rational points on modular curves" J.-P. Serre (ed.) P. Deligne (ed.) W. Kuyk (ed.) , Modular functions of one variable. 5 , Lect. notes in math. , 601 , Springer (1977) pp. 107–148 MR0450283 Zbl 0357.14005 [8] D. Mumford, "A remark on Mordell's conjecture" Amer. J. Math. , 87 : 4 (1965) pp. 1007–1016 MR186624