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Ramesh Sreekantan

Publications and source records attributed to Ramesh Sreekantan.

At least 19 recordsLinked to original sources
arXiv2026

Algebraic cycles and values of Green's functions -- Products of Elliptic Curves

Gross and Zagier defined certain `higher Green's functions' on products of modular curves and conjectured that the value of these functions at complex multiplication points should be logarithms of algebraic numbers. This is now a theorem of Li and Bruinier-Li-Yang. We relate this conjecture to the existence of motivic cycles in the universal family of products of elliptic curves along the lines of Mellit and Zhang. Using this we are able to prove Zagier's conjecture in some cases when the two CM points have the same discriminant. This is originally a theorem of Viazovska. Li, Bruinier-Li-Yang, Bruinier-Ehlen-Yang, Viazovska and others relate this conjecture to Borcherds' lifts of weakly holomorphic modular forms. Their works, coupled with ours, suggest that there should be a link between motivic cycles in the universal family on the one hand and Borcherds lifts on the other. We explain why this is the case. This suggests a motivic interpretation of weakly holomorphic modular forms. In the special case we look at we show that indeed this is true.

math.AG↗
arXiv2026

Torsion cycles on Fermat varieties

A theorem of Manin and Drinfeld states that any divisor of degree $0$ on the cusps of a modular curve is torsion in the Jacobian. An elegant proof of this result was provided by Elkik using mixed Hodge theory. Rohrlich proved a generalization of this to Fermat curves. In this note we reprove his results along the lines of the work of Elkik. We then use the same methods to generalize it to higher codimensional null-homologous cycles as well as higher Chow cycles on Fermat varieties.

math.AG↗
arXiv2025

Equations defining Jacobians with Real Multiplication

If $C:y^2=x(x-1)(x-a_1)(x-a_2)(x-a_3)$ is genus $2$ curve a natural question to ask is: Under what conditions on $a_1,a_2,a_3$ does the Jacobian $J(C)$ have real multiplication by $\mathbb{Z}[\sqrtΔ]$ for some $Δ>0$. Over a hundred years ago Humbert gave an answer to this question for $Δ=5$ and $Δ=8$. In this paper we use work of Birkenhake and Wilhelm along with some classical results in enumerative geometry to generalize this to all discriminants, in principle. We also work it out explicitly in a few more cases.

math.NT↗
arXiv2024

Indecomposable motivic cycles on K3 surfaces of degree 2

In this paper we construct new indecomposable motivic cycles in the group $H^3_{\mathcal M}(X,{\mathbb Q}(2))$ where X is a degree 2 K3 surface. This generalizes our construction in [Sre22] for Kummer surfaces of Abelian surfaces as well as the recent work of Ma and Sato [MS23] on degree 2 K3 surfaces.

math.AG↗
arXiv2024

Motivic cycles on K3 double covers of del Pezzo surfaces

We construct motivic cohomology cycles in the group $H^3_{\mathcal M}(Z,{\mathbb Q}(2))$ where $Z$ is a K3 surface obtained as a double cover of a del Pezzo surface $X$ branched at a curve in $|-2K_X|$. The construction uses (-1) curves on the del Pezzo and is a generalization of a recent pre-print of Ken Sato arXiv: 2408.09102 where he considers the case of fourfold covers of ${\mathbb P}^2$ branched at a quartic curve.

math.AG↗
arXiv2024

Singularities of Feynman Integrals

In this paper, we study the singularities of Feynman integrals using homological techniques. We analyse the Feynman integrals by compactifying the integration domain as well as the ambient space by embedding them in higher-dimensional space. In this compactified space the singularities occur due to the meeting of compactified propagators at non-general position. The present analysis, which had been previously used only for the singularities of second-type, is used to study other kinds of singularities viz threshold, pseudo-threshold and anomalous threshold singularities. We study various one-loop and two-loop examples and obtain their singularities. We also present observations based on results obtained, that allow us to determine whether the singularities lie on the physical sheet or not for some simple cases. Thus this work at the frontier of our knowledge of Feynman integral calculus sheds insight into the analytic structure.

hep-th↗
arXiv2023

Old and new motivic cycles on Abelian surfaces

Collino \cite{colo} discovered indecomposable motivic cycles in the group $H^{2g-1}_{\mathcal M}(J(C),{\mathds Z}(g))$. In an earlier paper we described the construction of some new motivic cycles which can be viewed as a generalization of Collino's cycle when $g=2$. In this paper we show that our new cycles are in fact related to Collino's cycles of higher genus. On one hand this suggests that new cycles are hard to find. On the other, it suggests that the tools developed to study Collino's cycle can be applied to our cycles.

math.AG↗
arXiv2022

The fundamental group and extensions of motives of Jacobians of curves

In this paper we construct extensions of mixed Hodge structures coming from the mixed Hodge structure on the graded quotients of the group ring of the fundamental group of a smooth, projective, pointed curve. These extensions correspond to the regulators of certain motivic cycles in the Jacobian of the curve which were constructed by Beilinson and Bloch. This leads to a new iterated integral expression for the regulator. This is a generalisation of a theorem of Colombo where she constructed the extension corresponding to Collino's cycles in the Jacobian of a hyperelliptic curve.

math.AG↗
arXiv2022

Abelian surfaces and the non-Archimedean Hodge D-conjecture -- the semi-stable case

If $X$ is a smooth projective variety over ${\mathbb R}$, the Hodge ${\mathcal D}$-conjecture of Beilinson asserts the surjectivity of the regulator map to Deligne cohomology with real coefficients. It is known to be false in general but is true in some special cases like Abelian surfaces and $K3$-surfaces - and still expected to be true when the variety is defined over a number field. We prove an analogue of this for Abelian surfaces at a non-Archimedean place where the surface has bad reduction. Here the Deligne cohomology is replaced by a certain Chow group of the special fibre. The case of good reduction is harder and was first studied by Spiess in the case of products of elliptic curve and by me in general.

math.AG↗
arXiv2022

Algebraic Cycles and values of Green's functions

We construct indecomposable cycles in the motivic cohomology group $H^3_{\mathcal M}(A,{\mathbb Q}(2))$ where $A$ is an Abelian surface over a number field or the function field of a base. When $A$ is the self product of the universal elliptic curve over a modular curve, these cycles can be used to prove algebraicity results for values of higher Green's functions, similar to a conjecture of Gross, Kohnen and Zagier. We formulate a conjecture which relates our work with the recent work of Bruinier-Ehlen-Yang on the conjecture of Gross-Kohnen-Zagier.

math.NT↗
arXiv2017

Extensions of Motives and the Fundamental Group

In this paper we construct extensions of the Mixed Hodge structure on the fundamental group of a pointed algebraic curve. These extensions correspond to the regulator of certain explicit motivic cohomology cycles in the self product of the curve which were first constructed by Bloch and Beilinson. This leads to a new iterated integral expression for the regulator. Our result is a generalization of a result of Colombo's where she constructs the extension corresponding to a motivic cycle class in the Jacobian of a hyperelliptic curve constructed by Collino. This is to appear in the Mathematical Proceedings of the Indian Academy of Sciences.

math.AG↗
arXiv2013

Higher Chow Cycles on an Abelian Surface and a non-Archimedean analogue of the Hodge-D-conjecture

We construct new indecomposable elements in the higher Chow group CH2(A,1) of a principally polarized Abelian surface over a non Archimedean local field, which generalize an element constructed by Collino. These elements are constructed using a generalization, due to Birkenhake and Wilhelm, of a classical construction of Humbert, along with some recent work of Bogomolov, Hassett and Tschinkel on deformations of rational curves on a K3 surface. They can be used to prove the non-Archimedean Hodge-D-conjecture - namely, the surjectivity of the boundary map in the localization sequence - in the case when the Abelian surface has good and ordinary reduction. This is a revised and updated version of an earlier preprint with the name `Abelian surfaces, Kummer surfaces and the non-Archimedean Hodge-D-conjecture.'

math.NT↗
arXiv2009

Higher order modular forms and mixed Hodge theory

In this paper we introduce a certain space of higher order modular forms of weight 0 and show that it has a Hodge structure coming from the geometry of the fundamental group of a modular curve. This generalizes the usual structure on classical weight 2 forms coming from the cohomology of the modular curve. Further we construct some higher order Poincare series to get higher order higher weight forms and using them we define a space of higher weight, higher order forms which has a mixed Hodge structure as well.

math.NT↗
arXiv2009

K_1 of products of Drinfeld modular curves and special values of L-functions

Beilinson obtained a formula relating the special value of the L-function of H^2 of a product of modular curves to the regulator of an element of a motivic cohomology group - thus providing evidence for his general conjectures on special values of L-functions. In this paper we prove a similar formula for the L-function of the product of two Drinfeld modular curves providing evidence for an analogous conjecture in the case of function fields.

math.NT↗
arXiv2008

Iterated Integrals and higher order automorphic forms

Higher order automorphic forms have recently been introduced to study important questions in number theory and mathematical physics. We investigate the connection between these functions and Chen's iterated integrals. Then using Chen's theory, we prove a structure theorem for automorphic forms of all orders. This allows us to define an analogue of a mixed Hodge structure on a space of higher order automorphic forms.

math.NT↗
arXiv2008

A non-Archimedean analogue of the Hodge-D-conjecture for products of elliptic curves

In this paper we show that the map % $$\partial:CH^2(E_1 \times E_2,1)\otimes \Q \longrightarrow PCH^1(\XX_v)$$ % is surjective, where $E_1$ and $E_2$ are two non-isogenous semistable elliptic curves over a local field, $CH^2(E_1 \times E_2,1)$ is one of Bloch's higher Chow groups and $PCH^1(\XX_v)$ is a certain subquotient of a Chow group of the special fibre $\XX_{v}$ of a semi-stable model $\XX$ of $E_1 \times E_2$. On one hand, this can be viewed as a non-Archimedean analogue of the Hodge-$\D$-conjecture of Beilinson - which is known to be true in this case by the work of Chen and Lewis \cite{lech}, and on the other, an analogue of the works of Speiß \cite{spie}, Mildenhall \cite{mild} and Flach \cite{flac} in the case when the elliptic curves have split multiplicative reduction.

math.NT↗
arXiv2003

Non-Archimedean regulator maps and special values of L-functions

We define an analogue of the `Real' Deligne cohomology group at a prime of semi-stable or good reduction of a variety. We also define regulator maps to this group and formulate a conjecture about the image. This allows us to formulate a non-Archimedian version of Beilinson's Hodge-D-conjecture, S-integral and function field versions of Beilinson's global conjectures as well as a precise special value conjecture in the function field case. Finally we give a few examples where these conjectures are known to be true.

math.NT↗