arXiv subjects

Sharang Rajesh Iyer

Publications and source records attributed to Sharang Rajesh Iyer.

5 recordsLinked to original sources

arXiv2026

Scattering of Null strings - Flipped Vacuum & CHY

We investigate the scattering of null tensionless strings. Classical null strings, given by the ILST action, give rise to three distinct quantum theories built on different vacua and representations of the underlying 2d Conformal Carroll algebra (CCA) which form the residual gauge symmetries on the null worldsheet. In this paper, we are interested in the quantum theory built out of the so-called "flipped" vacuum which realises the highest weight representation of the 2d CCA. By considering a novel class of vertex operators, intimately connected to the compactified null string, we build scattering amplitudes of the theory. We show that one naturally obtains the Cachazo-He-Yuan (CHY) formulae when one considers scattering of massless states in the null ``flipped'' string.

hep-th↗

arXiv2026

Double Copy from the Flipped Null String

We study the double-copy structure of tree amplitudes of the bosonic null string in the flipped vacuum. We show that its level-one vector correlator supplies the Cachazo-He-Yuan (CHY) kinematic half-integrand of the higher-derivative $(DF)^2$ gauge theory, while distinguished compact momentum-winding sectors generate the complementary Parke-Taylor factor. For factorized level-two states, the same Carrollian world-sheet produces two kinematic half-integrands and hence the symmetric double copy to the six-derivative Weyl-cubed graviton sector. Lattice sectors with common external momenta reproduce the Bern-Carrasco-Johansson (BCJ) ordering relation and the corresponding field-theory Kawai-Lewellen-Tye (KLT) representation. These results provide a direct Carrollian world-sheet origin of the double copy and point toward a current-algebra realization of the emergent color sector compatible with the $O(d,d)$ structure of the compact lattice.

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arXiv2026

Black hole Near Horizons through the Looking Glass

We show that the near horizon of a generic non-extremal black hole (BH) can be understood in terms of a Carrollian geometry with two null directions, also called a String-Carroll (SC) geometry. The base space of this fibre-bundle structure is a sphere (or a plane for a black brane) and the fibre is the two-dimensional Rindler spacetime. We launch a detailed study of probes in this geometry. We study particle geodesics and scalar fields. The first part of the paper constructs geodesics and probe scalar fields directly in the SC geometry. We then look at a wide class of examples, including the Schwarzschild BH and the Kerr BH in asymptotically flat spacetimes, the BTZ BH and the black brane in AdS spacetimes, as well as Lifshitz black holes and construct the explicit maps to the SC geometry to obtain results specific to each case. These results are reproduced by considering the probe particles and fields in the original BH background and taking the near-horizon limit of the solutions. Our encyclopedia of examples establishes the notion of SC geometries as near-horizon geometries of non-extremal black objects, paving the way for a detailed, intricate future analysis of the quantum aspects of this geometry.

hep-th↗

arXiv2026

High energy scattering and null strings

We propose an instrinsic worldsheet description of the ultra-high energy regime of string scattering based on worldsheet symmetries. At very high energies, the fundamental string becomes tensionless and in flat target spacetimes, the worldsheet becomes a null surface. Tensionless null strings thus emerge and the worldsheet symmetries morph from two copies of the Virasoro algebra to the two dimensional (2d) conformal Carroll or equivalently the 3d Bondi-van der Burgh-Metzner-Sachs (BMS) algebra. Tensionless strings have three inequivalent vacua over which they can be constructed, leading to distinct quantum theories. High energy tensile strings naturally connect to null strings built on the so-called induced vacuum. Our principle goal in this paper is the construction of scattering amplitudes for null strings in the induced vacuum. We show that these amplitudes, constructed from worldsheet methods of the null string, coincide with the high energy limit of usual string amplitudes. A crucial part of our analysis is the construction of integrated vertex operators. This achieved by relying on lessons from the parent string theory and following the tensionless limit carefully. A striking feature of the null string is the blurring of differences between open and closed strings. We see this at the level of the amplitudes as well. We then focus on four-point amplitudes and recover all expected regimes including the Gross-Mende regime and the Regge limit. We finally comment on a new class of vertex operators which arise naturally only in the zero tension string. This reproduces all our earlier analyses when put onshell but also has hints of signatures beyond the perturbative tensile string.

hep-th↗

arXiv2025

Strings near BTZ black holes: A Carrollian Chronicle

The BTZ black hole provides a tractable (2+1)-dimensional example for investigating string dynamics in curved spacetime. However, a systematic and robust analysis of the solution space of strings in the near-horizon region of BTZ black holes remains elusive in the literature. This work aims to fill this gap by employing the string-Carroll expansion. This formalism provides a natural setting for working with the near-horizon region, because near-horizon expansions for non-extremal black holes match string-Carroll expansions. Using this formalism, and expanding the string action and pullback fields in powers of an effective speed of light, we study the dynamics of closed bosonic strings in the near-horizon, non-extremal BTZ spacetime. Our approach classifies the general characteristics and further reveals some novel features of the families of string solutions.

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