arXiv subjects

Rahul Kumar Singh

Publications and source records attributed to Rahul Kumar Singh.

17 recordsLinked to original sources

arXiv2026

Spectral and Logarithmic Atiyah Classes for Higgs Bundles

For a regular semisimple Higgs bundle with a smooth spectral curve, we prove that, over the \etale\ locus, the Atiyah class of the underlying bundle is induced by the Atiyah class of the spectral line bundle and takes values in the centralizer of the Higgs field. Further, when the discriminant is reduced, we construct a logarithmic refinement across the branch divisor: the Atiyah class extends as a class with logarithmic poles and values in a natural regularized centralizer sheaf.

math.AG↗

arXiv2026

Decompositions of ZMC Graphs and Euler-Ramanujan type identities

In this paper, we study finite and infinite decomposition formulas for zero mean curvature (ZMC) graphs in Euclidean, Lorentz--Minkowski, and isotropic (3)-spaces. We first derive new Euler--Ramanujan-type identities that decompose the conjugate of Scherk's first minimal surface into dilated catenoids. Using Weierstrass factorisation and power series methods, we then obtain infinite decompositions for a broad class of isotropic ZMC graphs into helicoids, logarithmoids of revolution, and Enneper surfaces. These results are extended to wider families of ZMC surfaces arising from the L\'opez--Ros transformation, Bonnet rotation, and a one-parameter family of metric deformations. We also establish finite decomposition formulas, including analogues of Scherk tower decompositions in Euclidean and isotropic settings, and prove a characterisation theorem for finite decompositions of isotropic minimal surfaces. Finally, we discuss applications to lamellar structures.

math.DG↗

arXiv2026

Geometry, elasticity, and activity in the transport of self-propelled filaments in turbulence

We investigate the transport of elastic active filaments in two-dimensional turbulence, focusing on how propulsion geometry and elasticity determine vortex trapping and transport. Using a bead-spring model with activity applied at the filament head, we compare propulsion that follows the instantaneous filament conformation with propulsion imposed along a fixed external direction. We find that activity does not generically enhance transport: when propulsion remains coupled to the filament backbone, vortex trapping remains dominant and motion stays effectively diffusive, whereas fixed-direction propulsion enables persistent excursions across flow structures and leads to superdiffusive transport. In both cases, activity shifts filament conformations toward more extended states, effectively opposing elastic relaxation without eliminating preferential sampling of coherent vortical regions. At low Weissenberg number, this conformational change is amplified: activity cooperates with elasticity to enhance preferential sampling of vortical regions and strengthen vortex trapping. Transport therefore emerges from a competition between activity, elasticity, and flow-induced deformation, with elasticity determining how effectively activity-induced extensions can persist against turbulent trapping. These results establish propulsion geometry as the key control parameter for transport, with elasticity and activity acting cooperatively rather than independently to shape filament dynamics in turbulent flows.

physics.flu-dyn↗

arXiv2025

Decompositions of Scherk-Type Zero Mean Curvature Surfaces

In this paper, by using a special Euler-Ramanujan identity and the idea of Wick rotation, we show that a one-parameter family of solutions to the zero mean curvature equation in Lorentz-Minkowski $3$-space $\mathbb E_1^3$, namely Scherk-type zero mean curvature surfaces, can be expressed as an infinite superposition of dilated helicoids. Further, we also obtain different finite decompositions for these surfaces. We end this paper with an application of these decompositions to formulate maximal codimension 2 surfaces into finite and infinite "sums" of weakly untrapped and *-surfaces in Lorentz-Minkowski 4-space.

math.DG↗

arXiv2025

Modular Surfaces in Lorentz-Minkowski 3-Space: Curvature and Applications

In this paper, we study the relation of the sign of the Gaussian and mean curvature of modular surfaces in Lorentz-Minkowski $3$-space to the zeroes of the associated complex analytic functions and its derivatives. Further, we completely classify zero Gaussian curvature modular surfaces. Next we show non-existence of non-planar maximal modular surfaces, characterize CMC modular surfaces, analyze asymptotic behaviour of Gaussian curvature of complete modular graphs and the Hessian of their height functions and lastly as application, demonstrate how modular surfaces can be realised as integral surfaces of some conformal field theories and non-linear sigma models.

math.DG↗

arXiv2025

Timelike minimal surface in $\mathbb{E}^3_1$ with arbitrary ends

In this paper, we show the existence of a timelike minimal surface with an arbitrary number of weak complete ends. Then, we discuss the asymptotic behaviour of the simple ends and the topology of the singularity set of the constructed timelike minimal surface.

math.DG↗

arXiv2024

Interpolation by maximal and minimal surfaces

In this article, we use the inverse function theorem for Banach spaces to interpolate a given real analytic spacelike curve $a$ in Lorentz-Minkowski space $\mathbb{L}^3$ to another real analytic spacelike curve $c$, which is ``close" enough to $a$ in a certain sense by constructing a maximal surface containing them. Next we apply the same method to interpolate two given real analytic curve $a$ in Euclidean space $\mathbb{E}^3$ and a real analytic curve $c$, which is also ``close" enough to ``a" in a certain sense with a minimal surface. Throughout this study, the Björling problem and Schwarz's solution to it play pivotal roles.

math.DG↗

arXiv2024

CMC surfaces of revolution, Elliptic curves, Weierstrass-$\wp$ functions, and Algebraicity

This paper establishes an interesting connection between the family of CMC surfaces of revolution in $\mathbb E_1^3$ and some specific families of elliptic curves. As a consequence of this connection, we show in the class of spacelike CMC surfaces of revolution in the $\mathbb E_1^3$, only spacelike cylinders and standard hyperboloids are algebraic. We also show that a similar connection exists between CMC surfaces of revolution in $\mathbb E^3$ and elliptic curves. Further, we use this to reestablish the fact that the only CMC algebraic surfaces of revolution in $\mathbb E^3$ are spheres and right circular cylinders.

math.DG↗

arXiv2021

Local interpolation for minimal surfaces

Let $a: I\to \mathbb{R}^3 $ be a real analytic curve satisfying some conditions. In this article, we show that for any real analytic curve $l:I\to \mathbb R^3$ close to $a$ (in a sense which is precisely defined in the paper) there exists a translation of $l$, and a minimal surface which contains both $ a $ and the translated $l$.

math.DG↗

arXiv2020

On seat allocation problem with multiple merit lists

In this note, we present a simpler algorithm for joint seat allocation problem in case there are two or more merit lists. In case of two lists (the current situation for Engineering seats in India), the running time of the algorithm is proportional to sum of running time for two separate (delinked) allocations. The algorithm is straight forward and natural and is not (at least directly) based on deferred acceptance algorithm of Gale and Shapley. Each person can only move higher in his or her preference list. Thus, all steps of the algorithm can be made public. This will improve transparency and trust in the system.

cs.DS↗

arXiv2020

Rational Cuspidal Curves in a moving family of $\mathbb{P}^2$

In this paper we obtain a formula for the number of rational degree d curves in $\mathbb{P}^3$ having a cusp, whose image lies in a $\mathbb{P}^2$ and that passes through $r$ lines and $s$ points (where $r + 2s = 3d + 1$). This problem can be viewed as a family version of the classical question of counting rational cuspidal curves in $\mathbb{P}^2$, which has been studied earlier by Z. Ran, R. Pandharipande and A. Zinger. We obtain this number by computing the Euler class of a relevant bundle and then finding out the corresponding degenerate contribution to the Euler class. The method we use is closely based on the method followed by A. Zinger and I. Biswas, S. D'Mello, R. Mukherjee and V. Pingali. We also verify that our answer for the characteristic numbers of rational cuspidal planar cubics and quartics is consistent with the answer obtained by N. Das and the first author, where they compute the characteristic number of $\delta$-nodal planar curves in $\mathbb{P}^3$ with one cusp (for $\delta \leq 2$).

math.AG↗

arXiv2019

On Euler-Ramanujan formula, Dirichlet series and minimal surfaces

In this paper, we rewrite two forms of an Euler-Ramanujan identity in terms of certain Dirichlet series and derive functional equation of the latter. We also use the Weierstrass-Enneper representation of minimal surfaces to obtain some identities involving these Dirichlet series and one complex parameter.

math.NT↗

arXiv2018

Enumeration of rational curves in a moving family of $\mathbb{P}^2$

We obtain a recursive formula for the number of rational degree $d$ curves in $\mathbb{P}^3$, whose image lies in a $\mathbb{P}^2$, passing through $r$ lines and $s$ points, where $r + 2s = 3d+2$. This can be viewed as a family version of the classical question of counting rational curves in $\mathbb{P}^2$. We verify that our numbers are consistent with those obtained by T. Laarakker, where he studies the parallel question of counting $\delta$-nodal degree $d$ curves in $\mathbb{P}^3$ whose image lies inside a $\mathbb{P}^2$. Our numbers give evidence to support the conjecture, that the polynomials obtained by T. Laarakker are enumerative when $d \geq 1 + [\frac{\delta}{2}]$, which is analogous to the {G}\"ottsche threshold for counting nodal curves in $\mathbb{P}^2$.

math.AG↗

arXiv2017

Wick rotations of solutions to the minimal surface equation, the zero mean curvature equation and the Born-Infeld equation

In this paper we investigate relations between solutions to the minimal surface equation in Euclidean $3$-space $\mathbb{E}^3$, the zero mean curvature equation in Lorentz-Minkowski $3$-space $\mathbb{L}^3$ and the Born-Infeld equation under Wick rotations. We prove that the existence conditions of real solutions and imaginary solutions after Wick rotations are written by symmetries of solutions, and reveal how real and imaginary solutions are transformed under Wick rotations. We also give a transformation theory for zero mean curvature surfaces containing lightlike lines with some symmetries. As an application, we give new correspondences among some solutions to the above equations by using the non-commutativity between Wick rotations and isometries in the ambient space.

math.DG↗

arXiv2017

Weierstrass-Enneper representation for Maximal Surfaces in Hodographic coordinates

We obtain the Weierstrass-Enneper representation for maximal graphs(whose Gauss map is one-one) in Lorentz-Minkowski space. For this we use the method of Barbishov and Chernikov, which they have used to find the solutions of Born-Infeld equation in hodographic coordinates. We could use their method in our case, because we realized that the maximal surface equation and Born-Infeld equation are related via a wick rotation in the first variable of the parametrising domain.

math.DG↗

arXiv2017

Existence of maximal surface containing given curve and special singularity

We give a different formulation for describing maximal surfaces in Lorentz-Minkowski space, $\mathbb{L}^3$, using the identification of $\mathbb L^3$ with $\mathbb C\times \mathbb R$. Further we give a different proof for the singular Björling problem for the case of closed real analytic null curve. As an application, we show the existence of maximal surface which contains a given curve and has a special singularity.

math.DG↗

arXiv2017

Born-Infeld solitons, Maximal surfaces and Ramanujan's identities

We show that a Born-Infeld soliton can be realised either as a spacelike minimal graph or timelike minimal graph over a timelike plane or a combination of both away from singular points. We also obtain some exact solutions of the Born-Infeld equation from already known solutions to the maximal surface equation. Further we present a method to construct a one-parameter family of complex solitons from a given one parameter family of maximal surfaces. Finally, using Ramanujan's Identities and the Weierstrass-Enneper representation of maximal surfaces, we derive further non-trivial identities.

math.DG↗