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Prime numbers, diophantine equations, diophantine approximations, analytic or algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions

3 votes

Forms over finite fields and Chevalley's theorem

Perhaps it is obvious to most readers, but about a year ago I spent several days trying to determine for which pairs (d,n) there existed an anisotropic degree d form in n variables over a finite field …
Pete L. Clark's user avatar
7 votes

Diophantine equation of first degree

It sounds to me like the OP is asking about the Diophantine Problem of Frobenius. This is as follows: let $(a_1,\ldots,a_n)$ be positive integers which generate the unit ideal (i.e., their setwise gc …
Pete L. Clark's user avatar
10 votes

prime ideal factorization in an extension field

The best explicit criterion that I know is the criterion of Kummer-Dedekind, which involves writing $K = \mathbb{Q}[t]/(P(t))$ and factoring $P(t)$ modulo the prime $p$. Then the factorization of $(p …
Pete L. Clark's user avatar
12 votes
Accepted

Fermat over Number Fields

This is mostly an amplification of Kevin Buzzard's comment. You ask about points on the Fermat curve $F_n: X^n + Y^n = Z^n$ with values in a number field $K$. First note that since the equation is …
Pete L. Clark's user avatar
6 votes

Question on the abel map and modular parametrization

This is an answer to the question A. Pacetti asked in his comment to Emerton's answer. The modular variety $A_f$ does not have to be geometrically simple. William Stein and I computed many examples …
Pete L. Clark's user avatar
5 votes
Accepted

Nonnegative polynomial in two variables

The following theorem of Artin -- his solution of Hilbert's 17th problem, but in a stronger form than Hilbert himself asked for -- answers the question. Theorem (Artin, 1927): Let $F$ be a subfield o …
Pete L. Clark's user avatar
15 votes

Primes P such that ((P-1)/2)!=1 mod P

The following is a relevant classical paper: Mordell, L. J. The congruence $(p-1/2)!\equiv ±1$ $({\rm mod}$ $p)$. Amer. Math. Monthly 68 1961 145--146. http://alpha.math.uga.edu/~pete/Mordell61.pdf …
Pete L. Clark's user avatar
14 votes
Accepted

Is there a standard way to read the Legendre symbol?

I say "a on b" for the Legendre/Jacobi/Kronecker symbol. This works because, as an American, I say "a over b" for an ordinary fraction.
Pete L. Clark's user avatar
9 votes
Accepted

Do finite places of a number field also correspond to embeddings?

The Archimedean places of a number field K do not quite correspond to the embeddings of K into $\mathbb{C}$: there are exactly $d = [K:\mathbb{Q}]$ of the latter, whereas there are $r_1 + r_2$ Archim …
Pete L. Clark's user avatar
29 votes
Accepted

Number fields with same discriminant and regulator?

Yes, see e.g. the paper "Arithmetically equivalent number fields of small degree" (Google for it) by Bosma and de Smit. In brief: two number fields $K$ and $K'$ are said to be arithmetically equiva …
Pete L. Clark's user avatar
6 votes

Maximal subfields in a division algebra over a local field

To address 2.: for any central simple algebra $A$ over a field $k$, there is a well-developed theory describing the relations between finite splitting fields $l/k$ for $A$ and fields which are sub-$k$ …
Pete L. Clark's user avatar
18 votes

What objects do the cusps of Modular curve classify?

Yes, the moduli problem extends to the cusps by way of generalized elliptic curves, i.e., certain semistable curves of arithmetic genus one. For instance, with no level structure there is one point a …
Pete L. Clark's user avatar
12 votes

Complete discrete valuation rings with residue field ℤ/p

The classification of CDVRs with residue field any given perfect field k is discussed in Chapter 2 of Serre's Local Fields. In particular: Theorem II.2: Let R be a CDVR with residue field k. Suppos …
Pete L. Clark's user avatar
10 votes

CM of elliptic curves

Allow me to say something which is not so much an answer to this question as to a (very natural) question that I sense is coming in the future. There are two possible pitfalls in the definition of "h …
Pete L. Clark's user avatar
9 votes
Accepted

remark in milne's class field theory notes

The point is that it is one thing to show that two mathematical objects are isomorphic; it is another (stronger) thing to give a particular isomorphism between them. A rather concrete instance of thi …
Pete L. Clark's user avatar

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