arXiv subjects
Publications and source records attributed to Henri Cohen.
After recalling basic formulas concerning modular forms of half-integral weight, Gegenbauer polynomials, and Rankin--Cohen brackets, we give four versions of the Shimura lift and several applications to Hilbert modular forms associated to real quadratic fields. We claim no originality, but wanted to collect all the formulas in a single paper.
After giving a number of properties of continued fractions of polynomial type, in particular focusing on convergence properties and Bauer-Muir-Ap\'ery acceleration techniques, we give a large list of continued fractions, both for specific real numbers, and for special functions, some extracted from a number of different sources, but most others being probably new. In addition to providing such a list, one of our main additions is to include the exact speed of convergence of these continued fractions (sometimes only up to a multiplicative constant), which is almost always omitted in the literature.
We give a completely explicit Lerch, Chowla--Selberg formula without absolute values of the Dedekind eta function, and give some applications, in particular to the argument of individual CM values of the eta function. We also give precise conjectures on these CM values and a large table supporting them.
Apéry's remarkable discovery of rapidly converging continued fractions with small coefficients for $ζ(2)$ and $ζ(3)$ has led to a flurry of important activity in an incredible variety of different directions. Our purpose is to show that modifications of Apéry's continued fractions can give interesting results including new rapidly convergent continued fractions for certain interesting constants.
We give 39 rapidly convergent continued fractions for Chowla--Selberg gamma quotients, and deduce good irrationality measures for 20 of them, including for $\operatorname{CS}(-3)=(\Gamma(1/3)/\Gamma(2/3))^3$, for $a^{1/4}\operatorname{CS}(-4)=a^{1/4}(\Gamma(1/4)/\Gamma(3/4))^2$ with $a=12$ and $a=1/5$, and for $\operatorname{CS}(-7)=\Gamma(1/7)\Gamma(2/7)\Gamma(4/7)/(\Gamma(3/7)\Gamma(5/7)\Gamma(6/7))$. These appear to be the first proved and reasonable irrationality measures for gamma quotients.
Our main result is that any real cubic algebraic number has a continued fraction expansion with polynomial coefficients. Some generalizations are mentioned.
We describe a database of 1883 continued fractions with polynomial coefficients, of which more than 1600 are new, both for interesting constants and for transcendental functions, and provide the database inside the \TeX\ source of the paper. Look in particular at the section ``Table of Contents''.
We explain in detail how to accelerate continued fractions (for constants as well as for functions) using the method used by R.~Apéry in his proof of the irrationality of $ζ(3)$. We show in particular that this can be applied to a large number of continued fractions which can be found in the literature, thus providing a large number of new continued fractions. As examples, we give a new continued fraction for $\log(2)$ and for $ζ(3)$, as well as a simple proof of one due to Ramanujan.
We give an extensive list of parametrized families of polynomial continued fractions of smallest possible degrees for $π^2$ and $ζ(3)$, and mention similar results for other constants.
We show how to obtain infinitely many continued fractions for certain Z-linear combinations of zeta and L values. The methods are completely elementary.
We show that the most standard Eisenstein series such as $E_4(τ)$ or $2E_2(2τ)-E_2(τ)$, and also the function $θ^2(τ)$, are in a natural way the product of two conjugate Eisenstein series of half their weight and double their level, as well as a number of similar elementary identities for $E_6$ and Eisenstein series of levels $2$, $3$, and $4$.
We give a simple unified proof for all existing rational hypergeometric Ramanujan identities for $1/π$, and give a complete survey (without proof) of several generalizations: rational hypergeometric identities for $1/π^c$, Taylor expansions, upside-down formulas, and supercongruences.
We survey a number of different methods for computing $L(χ,1-k)$ for a Dirichlet character $χ$, with particular emphasis on quadratic characters. The main conclusion is that when $k$ is not too large (for instance $k\le100$) the best method comes from the use of Eisenstein series of half-integral weight, while when $k$ is large the best method is the use of the complete functional equation, unless the conductor of $χ$ is really large, in which case the previous method again prevails.
After defining in detail the Lambert $W$-function branches, we give a large number of exact identities involving (infinite) symmetric functions of these branches, as well as geometrically convergent series for all the branches. In doing so, we introduce a family of polynomials which may be of independent interest.
We give theoretical and practical information on the Pari/GP modular forms package available since the spring of 2018. Thanks to the use of products of two Eisenstein series, this package is the first which can compute Fourier expansions at any cusps, evaluate modular forms near the real axis, evaluate L-functions of non-eigenforms, and compute general Petersson scalar products.
We give a number of theoretical and practical methods related to the computation of L-functions, both in the local case (counting points on varieties over finite fields, involving in particular a detailed study of Gauss and Jacobi sums), and in the global case (for instance Dirichlet L-functions, involving in particular the study of inverse Mellin transforms); we also give a number of little-known but very useful numerical methods, usually but not always related to the computation of L-functions.
In this course we introduce the main notions relative to the classical theory of modular forms. A complete treatise in a similar style can be found in the author's book joint with F. Str{ö}mberg [1].
We begin by explaining how to compute Fourier expansions at all cusps of any modular form of integral or half-integral weight thanks to a theorem of Borisov-Gunnells and explicit expansions of Eisenstein series at all cusps. Using this, we then give a number of methods for computing arbitrary Petersson products. All this is available in the current release of the Pari/GP package.