arXiv subjects

Harsh

Publications and source records attributed to Harsh.

6 recordsLinked to original sources

arXiv2026

Quantum Reservoir Computing with Physics-Informed Correction for Reduced-Order PDE Forecasting

We study a hybrid proposal--correction architecture for reduced-order PDE forecasting in which a pure-state quantum reservoir computer (QRC) predicts latent coefficient dynamics and a PINN-based physics-informed corrector (PIC) refines local rollout windows. The method is evaluated on Burgers and Kuramoto--Sivashinsky (KS), with KS as the primary chaotic benchmark. On KS, QRC+PIC consistently improves over QRC alone in RMSE, NRMSE, and PDE residual, while Burgers highlights a regime in which simple baselines remain strong. These results suggest that QRC proposals with local physics-informed correction are a viable benchmark-dependent reduced-order forecasting strategy.

quant-ph↗

arXiv2026

Octupolar Gravitational Radiation in de Sitter Spacetime

We derive the gravitational radiation generated by a localised matter source in de Sitter spacetime at octupolar order in the multipolar expansion, working in generalised harmonic gauge in the future Poincar\'e patch. The scalar, vector, and tensor perturbation equations are solved explicitly, taking into account the cosmological tail. This constitutes the first extension of the de Sitter multipolar expansion beyond quadrupolar order. A key technical ingredient is a universal multipole moment differentiation identity, which unifies the relations between multipole moments into a single recursive formula and enables a controlled extension to higher multipoles. Using the symmetric trace-free tensor formalism of Blanchet, Damour, and Iyer, we further develop a systematic translation of the radiative solution into a spherical harmonic basis, and apply it to both the quadrupolar and octupolar metric perturbations. This representation renders the angular structure of the radiation manifest, simplifies the verification of the linearised field equations, and facilitates direct comparison with Bondi-gauge and other perturbative treatments of de Sitter spacetime. Our results constitute a step toward a systematic ``multipolar post-de Sitter formalism''.

gr-qc↗

arXiv2026

Consistent Truncation of Linearized gravitational waves in de Sitter space-time

An important step in using observations of gravitational waves from bounded sources is to relate the observed waveforms far away from a source to the local dynamics and environment of the source. To isolate and identify different features of the source, multipole expansion of both the radiation field and the source distribution are crucial. At a practical level, these expansions are truncated at some finite multipole order and a consistency issue arises. This was flagged in \cite{CHK} as the emergence of disallowed $\log(r)$ terms in certain asymptotic forms and a particular quadrupolar truncation was proposed which was consistent with the source conservation. In \cite{NKD80}, it was noted (incorrectly) that the particular solution does not satisfy the generalized harmonic gauge condition and this may be the source of appearance of the log(r) terms. In this work the consistency issue is analyzed by explicitly integrating the gauge conditions and the source conservation equations over the conformal time. This gives a general procedure for a consistent truncation. The procedure is verified in generalized harmonic gauge in conformal chart and in the Bondi gauge in Bondi chart.

gr-qc↗

arXiv2025

Towards the Parametric Renormalization of the S-matrix -- I

Zimmermann's forest formula is the corner stone of perturbative renormalization in QFT. By renormalizing individual Feynman graphs, it generates the UV finite S-matrix. This approach to renormalization makes the graph and all its forests center pieces in the theory of renormalization. On the other hand the positive geometry program delegate the role of Feynman graphs as secondary to the amplitude itself, which are generated by canonical forms associated to positive geometries. State of the art in this program is the convergence of S-matrix theory in local QFTs and string theory as the scattering amplitudes in QFT arise as integrals over certain moduli spaces. These integrals are known as curve integrals. For theories such as $\textrm{Tr}(\Phi^{3})$ theory with massive colored scalars, these integrals are divergent in the UV and have to be regularized. It is then natural to ask if there is a ``forest-like formula'' for these integrals which produce a renormalized amplitude without needing to explicitly invoke the forests associated to divergent subgraphs. In this paper, we initiate such a program by deriving forest-like formula for planar massive $\textrm{Tr}(\Phi^{3})$ amplitudes in $D = 4$ dimensions. Our analysis relies on the insightful manifestation of the forest formula derived by Brown and Kreimer in \cite{Brown:2011pj}, that lead us to a definition of ``tropical counter-term'' for the bare amplitude.

hep-th↗

arXiv2024

de Sitter Teukolsky waves

We present de Sitter Teukolsky waves -- linearised quadrupolar gravitational waves in the transverse-traceless gauge in de Sitter spacetime. In the cosmological constant $\Lambda$ going to zero limit, our solutions match to Teukolsky solutions. For non-zero $\Lambda$, we compare our solutions to the wider literature, where different authors have constructed linearised gravitational perturbations in de Sitter spacetime with varied motivations. For de Sitter Teukolsky waves, we compute the energy flux across future timelike infinity $\mathcal{I}^{+}$ and show that it is manifestly positive.

gr-qc↗

arXiv2021

Single Particle Detection System for Strong-Field QED Experiments

Measuring signatures of strong-field quantum electrodynamics (SF-QED) processes in an intense laser field is an experimental challenge: it requires detectors to be highly sensitive to single electrons and positrons in the presence of the typically very strong x-ray and $\gamma$-photon background levels. In this paper, we describe a particle detector capable of diagnosing single leptons from SF-QED interactions and discuss the background level simulations for the upcoming Experiment-320 at FACET-II (SLAC National Accelerator Laboratory). The single particle detection system described here combines pixelated scintillation LYSO screens and a Cherenkov calorimeter. We detail the performance of the system using simulations and a calibration of the Cherenkov detector at the ELBE accelerator. Single 3 GeV leptons are expected to produce approximately 537 detectable photons in a single calorimeter channel. This signal is compared to Monte-Carlo simulations of the experiment. A signal-to-noise ratio of 18 in a single Cherenkov calorimeter detector is expected and a spectral resolution of 2% is achieved using the pixelated LYSO screens.

hep-ex↗