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Biswajyoti Saha

Publications and source records attributed to Biswajyoti Saha.

16 recordsLinked to original sources
arXiv2026

On additive convolution sum of arithmetic functions and related questions

Ingham studied two types of convolution sums of the divisor function, the shifted convolution sum $\sum_{n \le N} d(n) d(n+h)$ and the additive convolution sum $\sum_{n < N} d(n) d(N-n)$ for integers $N, h$ and derived their asymptotic formulas as $N \to \infty$. There have been numerous works extending Ingham's result on the shifted convolution sum, but only little has been done towards the additive convolution sum. In this article, we extend the classical result of Ingham to derive an asymptotic formula with an error term of the sub-sum $\sum_{n < M} d(n) d(N-n)$ for certain integers $M \le N$. This involves careful choice of an applicable range of $M$. We also study the convolution sum $\sum_{n < M} f(n) g(N-n)$ for certain arithmetic functions $f$ and $g$ with absolutely convergent Ramanujan expansions, which in turn leads us to a well-established prediction of Ramanujan.

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arXiv2026

Triple convolution sums of the generalised divisor functions and related sums over primes

We study the triple convolution sum of the generalised divisor functions $$\sum_{n\leq x} d_k(n+h)d_l(n)d_m(n-h),$$ where $h \le x^{1-ε}$ for any $ε>0$ and $d_k(n)$ denotes the generalised divisor function which counts the number of ways $n$ can be written as a product of $k$ many positive integers. The purpose of this paper is three-fold. Firstly, we note a predicted asymptotic estimate for the above sum, where the constant appearing in the estimate can be obtained from the theory of Dirichlet series of several complex variables and also using some probabilistic arguments. Then we show that a lower bound of the correct order can be derived using the several variable Tauberian theorems, where, more importantly, the constant in the predicted asymptotic can be recovered. Lastly, in the spirit of the Titchmarsh divisor problem, we consider this triple convolution sum over the prime numbers, which essentially leads to a shifted convolution sum. We use the Tauberian theory of multiple Dirichlet series along with the Bombieri-Vinogradov theorem to derive an explicit lower bound of this.

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arXiv2026

Laurent type expansion of multiple polylogarithms at integer points

In this article, we study the local behaviour of the multiple polylogarithm functions at integer points, in the $s$-aspect. This is done by writing a Laurent type expansion at integer points, involving certain power series and rational functions. The coefficients of these power series are the regularised values of the multiple polylogarithm functions at certain related integer points.

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arXiv2026

Ramaswami Type translation formulae for the polylogarithm functions

In 1934, Ramaswami proved a number of curious translation formulae satisfied by the Riemann zeta function. Such translation formulae, in turn give the meromorphic extension of the Riemann zeta function. In 1954, Apostol extended those identities to establish a family of such similar translation formulae. In this article, we establish many such Ramaswami and Apostol type translation formulae for the Dirichlet series defining the polylogarithm functions. This extended set up has many interesting applications, for example, it allows us to also find some (seemingly new) recurrence relations between the Bernoulli numbers, and use them to deduce some congruence properties of the tangent numbers.

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arXiv2025

Multiple polylogarithms, a regularisation process and an admissible open domain of convergence

In this article, we study the analytic properties of the multiple polylogarithms in the $s$-aspect. Although the domain of absolute convergence of the series defining the multiple polylogarithms is well-known, the study towards a larger open domain of (conditional) convergence has been limited, particularly when the depth is $\ge 2$. Here, we exhibit a larger open domain of (conditional) convergence for this series by writing certain translation formulas satisfied by them. The series moreover defines a holomorphic function in this open set. We then introduce a regularisation process for the multiple polylogarithms, extending an earlier work of the second author. This regularisation process requires a generalisation of the Euler-Boole summation formula that we derive in the appendix of this article. The regularisation process leads to a larger open domain, where the series (conditionally) converges at integer points. The holomorphicity at such points is a more delicate question and this regularisation process is to be used to study the local behaviour of the multiple polylogarithms around such points.

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arXiv2025

A triple convolution sum of the divisor function

We study the triple convolution sum of the divisor function given by $$\sum_{n\leq x} d(n)d(n-h)d(n+h)$$ for $h\neq 0$ and $d(n)$ denotes the number of positive divisors of $n$. Based on algebraic and geometric considerations, Browning conjectured that the above sum is asymptotic to $c_hx(\log x)^3$, for a suitable constant $c_h\neq 0$, as $x\to \infty$. This conjecture is still unproved. Using sieve-theoretic results of Wolke and Nair (respectively), it is possible to derive the exact order of the sum. The lower bound of the correct order of magnitude can also be derived by very elementary arguments. In this paper, using the Tauberian theory for multiple Dirichlet series, we prove an explicit lower bound and provide a new theoretical framework to predict Browning's conjectured constant $c_h$.

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arXiv2022

An abelian analogue of Schanuel's conjecture and applications

In this article we study an abelian analogue of Schanuel's conjecture. This conjecture falls in the realm of the generalised period conjecture of Y. Andr{é}. As shown by C. Bertolin, the generalised period conjecture includes Schanuel's conjecture as a special case. Extending methods of Bertolin, it can be shown that the abelian analogue of Schanuel's conjecture we consider, also follows from Andr{é}'s conjecture. C. Cheng et al. showed that the classical Schanuel's conjecture implies the algebraic independence of the values of the iterated exponential function and the values of the iterated logarithmic function, answering a question of M. Waldschmidt. We then investigate a similar question in the setup of abelian varieties.

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arXiv2022

Semi-abelian analogues of Schanuel Conjecture and applications

In this article we study Semi-abelian analogues of Schanuel conjecture. As showed by the first author, Schanuel Conjecture is equivalent to the Generalized Period Conjecture applied to 1-motives without abelian part. Extending her methods, the second, the third and the fourth authors have introduced the Abelian analogue of Schanuel Conjecture as the Generalized Period Conjecture applied to 1-motives without toric part. As a first result of this paper, we define the Semi-abelian analogue of Schanuel Conjecture as the Generalized Period Conjecture applied to 1-motives. C. Cheng et al. proved that Schanuel conjecture implies the algebraic independence of the values of the iterated exponential and the values of the iterated logarithm, answering a question of M. Waldschmidt. The second, the third and the fourth authors have investigated a similar question in the setup of abelian varieties: the Weak Abelian Schanuel conjecture implies the algebraic independence of the values of the iterated abelian exponential and the values of an iterated generalized abelian logarithm. The main result of this paper is that a Relative Semi-abelian conjecture implies the algebraic independence of the values of the iterated semi-abelian exponential and the values of an iterated generalized semi-abelian logarithm.

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arXiv2019

Multiple Stieltjes constants and Laurent type expansion of the multiple zeta functions at integer points

In this article, we study the local behaviour of the multiple zeta functions at integer points and write down a Laurent type expansion of the multiple zeta functions around these points. Such an expansion involves a convergent power series whose coefficients are obtained by a regularisation process, similar to the one used in defining the classical Stieltjes constants for the Riemann zeta function. We therefore call these coefficients {\it multiple Stieltjes constants}. The remaining part of the above mentioned Laurent type expansion is then expressed in terms of the multiple Stieltjes constants arising in smaller depths.

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arXiv2017

A conjecture about multiple $t$-values

For positive integers $a_1,\ldots,a_r$ with $a_1 \ge 2$, the multiple $t$-value $t(a_1,\ldots,a_r)$ is defined by the series $\sum\limits_{n_1 > \ldots > n_r > 0 \atop n_i \text{ odd}} n_1^{-a_1} \cdots n_r^{-a_r}$. For an integer $k \ge 2$, the dimension of the $\mathbb Q$-vector space generated by all the multiple $t$-values of weight $k$ has been predicted by Hoffman to be the $k$-th Fibonacci number. In this short note we give a conjectural basis of this vector space.

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arXiv2017

Multiple Lerch zeta functions and an idea of Ramanujan

In this article, we derive meromorphic continuation of multiple Lerch zeta functions by generalising an elegant identity of Ramanujan. Further, we describe the set of all possible singularities of these functions. Finally, for the multiple Hurwitz zeta functions, we list the exact set of singularities.

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arXiv2017

Multiple Dirichlet series associated to additive and Dirichlet characters

In this article we study analytic properties of the multiple Dirichlet series associated to additive and Dirichlet characters. For the multiple Dirichlet series associated to additive characters, the meromorphic continuation is established via obtaining translation formulas satisfied by these multiple Dirichlet series. While it seems difficult to obtain such a translation formula for the multiple Dirichlet series associated to Dirichlet characters, we rely on their intrinsic connection with the multiple Dirichlet series associated to additive characters in order to investigate their analytic characteristics. We are also able to determine the exact set of singularities of the multiple Dirichlet series associated to additive characters.

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arXiv2015

On the error term in a Parseval type formula in the theory of Ramanujan expansions II

For two arithmetical functions $f$ and $g$ with absolutely convergent Ramanujan expansions, Murty and Saha have recently derived asymptotic formulas with error term for the convolution sum $\sum_{n \le N} f(n) g(n+h)$ under some suitable conditions (see http://arxiv.org/abs/1506.01945). In this follow up article we improve these results with a weakened hypothesis which is in some sense minimal.

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arXiv2015

On the error term in a Parseval type formula in the theory of Ramanujan expansions

Given two arithmetical functions $f,g$ we derive, under suitable conditions, asymptotic formulas with error term, for the convolution sums $\sum_{n \le N} f(n) g(n+h)$, building on an earlier work of Gadiyar, Murty and Padma. A key role in our method is played by the theory of Ramanujan expansions for arithmetical functions.

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arXiv2014

On the zeros of weakly holomorphic modular forms

In this article, we study the nature of zeros of weakly holomorphic modular forms. In particular, we prove results about transcendental zeros of modular forms of higher levels and for certain Fricke groups which extend a work of Kohnen. Furthermore, we investigate the algebraic independence of values of weakly holomorphic modular forms.

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