arXiv subjects

Suprit Singh

Publications and source records attributed to Suprit Singh.

At least 19 recordsLinked to original sources

arXiv2026

The Fleeting Laboratory: An Experimental Guide for Total Solar Eclipses

Since times immemorial, total solar eclipses have inspired awe and wonder. In the modern scientific era, they have transformed into exclusive natural laboratories, offering fleeting but invaluable opportunities to study the Sun's faint outer atmosphere that is otherwise obscured by the intense glare of the photosphere. This unique vantage point has enabled revolutionary discoveries, from the identification of the element Helium and the first empirical validation of Einstein's General Relativity, to deciphering the corona's surprisingly high temperature. Today, ground-based eclipse experiments provide crucial data that complements and calibrates our space-based solar observatories, and offer high-resolution capabilities in the spatial, temporal as well as spectral domains. This chapter serves as a comprehensive guide detailing how to leverage modern observing equipments, detectors, and advanced computational techniques in image and data processing to conduct meaningful scientific investigations, bridging the gap between historical precedent and cutting-edge research.

astro-ph.SR↗

arXiv2025

Backreaction inclusive Schwinger effect in flat and de Sitter spacetimes via a self consistent Maxwell Schrodinger semiclassical dynamics

We employ a self consistent framework to study the backreaction effects of particle creation in the coupled semiclassical dynamics of a quantum complex scalar field and a classical electric field in both (1 + 1) and (1 + 3) dimensional Minkowski and de Sitter spacetimes. Using a general Gaussian state formalism in the Schrodinger picture, we solve the resulting nonlinear equations with Gaussian initial data, obtaining a self consistent semiclassical evolution that incorporates nonperturbative backreaction. We compute the time-dependent instantaneous particle content, current density, and electric field, defined through instantaneous eigenstates of the field modes. Comparing scenarios with and without backreaction, we find that backreaction strongly modifies the electric field and current, producing immediate plasma like oscillations and driving pronounced oscillations in the instantaneous mode occupations through nonadiabatic squeezing and quantum interference. These oscillations do not imply additional irreversible particle production the time averaged particle number remains essentially constant but they reveal the rich nonperturbative real-time dynamics captured by our self-consistent semiclassical approach across dimensions and in both Minkowski and de Sitter backgrounds.

hep-th↗

arXiv2025

Unveiling Electron Density Profile in Nearby Galaxies using SDSS MaNGA

Most observational studies of galactic-scale magnetic fields using Faraday rotation rely on estimates of thermal electron densities in galaxies and their radial variations. However, the spatial distribution of electrons in the interstellar medium (ISM) is not clearly known. In this study, we propose and utilize collision-excited doublet emission line ratios of [S II] $\lambda\lambda$ 6716, 6731 $\r{A}$ to estimate the electron densities ($n_e$). To map their distribution in the galaxies, we employ IFU spectroscopic observations from the SDSS MaNGA survey, utilising data products from both the MaNGA Data Analysis Pipeline (DAP). We present a spatially resolved analysis of $66$ face-on galaxies (inclination, $i \leq 15^\circ$), including $46$ star-forming galaxies (SFGs) and $20$ Non-SFGs. Azimuthally averaged radial profiles of $n_e$ are obtained. We found that both SFGs and Non-SFGs exhibit $n_e$ gradients, with higher densities of $n_e$(S II) = $52.87 \pm 8.32$ cm$^{-3}$ and $99.39 \pm 24.37$ cm$^{-3}$, respectively, in the inner disk region (r/R$_e$ $\leq$ 1.5), which decreases to $n_e$(S II) = $20.92 \pm 4.2$ cm$^{-3}$ in SFGs and $34.64 \pm 11.24$ cm$^{-3}$ in Non-SFGs, in the outer disk region (r/R$_e$ $>$ 1.5). We have also analysed these sources with Pipe3D fluxes. We translated $n_e$ to electron column densities ($N_e$) by assuming a typical disk of thickness 1 kpc and note that $N_e \sim 10^{22}$ cm$^{-2}$ at $\sim$14 kpc in the disk outer region. We have also discussed the profiles obtained using [O II] $\lambda\lambda$ 3726, 3729 $\r{A}$ doublet. These electron density estimates at different radii provide valuable insights for resolving ambiguities in current and future studies of magnetic fields in galaxies.

astro-ph.GA↗

arXiv2025

Non-local correlations of a test quantum field in gravitational collapse

Quantum correlations across the horizon could be pivotal in unveiling the puzzles surrounding quantum aspects of black holes and Hawking radiation. The peaks in the equal time correlation function are typically attributed to the entangled particle excitations. In this work, we have investigated the evolution of the correlations of a test quantum field on a dynamical background spacetime undergoing gravitational collapse. In the case of super-critical collapse, as the black hole and its horizon forms, correlated peaks are seen to appear across the horizon, representing an entangled Hawking pair. The outside peak moves away from the horizon as the system evolves, possibly representing outgoing Hawking flux. The implications of these non-local correlations are discussed in light of information paradox, quantum atmosphere and analogue black holes.

gr-qc↗

arXiv2024

Thermodynamics of Gravity in Local Frames

We probe the thermodynamic structure of gravity at local scales. In any general curved spacetime, it is possible to transform to a local inertial frame at any point such that the metric is flat up to quadratic order where the curvature at that point comes in when the metric is written in Riemann normal coordinates. We consider local Rindler observers in that patch and hence the local Rindler horizon. In doing so, we find that the local horizons are also hot provided the $aL>>1$ which can always be satisfied.

gr-qc↗

arXiv2024

Investigation of the Radial Profile of Galactic Magnetic Fields using Rotation Measure of Background Quasars

Probing magnetic fields in high-redshift galactic systems is crucial to investigate galactic dynamics and evolution. Utilizing the rotation measure of the background quasars, we have developed a radial profile of the magnetic field in a typical high-$z$ galaxy. We have compiled a catalog of 59 confirmed quasar sightlines, having one intervening Mg \rom{2} absorber in the redshift range $0.372\leq z_{\text{abs}} \leq 0.8$. The presence of the foreground galaxy is ensured by comparing the photometric and spectroscopic redshifts within $3 σ_{z-\text{photo}}$ and visual checks. These quasar line-of-sights (LoS) pass through various impact parameters (D) up to $160$ kpc, covering the circumgalactic medium of a typical Milky-Way type galaxy. Utilizing the residual rotation measure (RRM) of these sightlines, we estimated the excess in RRM dispersion, $σ_{\text{ex}}^{\text{RRM}}$. We found $σ_{\text{ex}}^{\text{RRM}}$ decreases with increasing D. We translated $σ_{\text{ex}}^{\text{RRM}}$ to average LoS magnetic field strength, $\langle B_{\|}\rangle$ by considering a typical electron column density. Consequently, the decreasing trend is sustained in the magnetic field. In particular for sightlines with $\text{D} \leq 50$ kpc and $\text{D} > 50$ kpc, $\langle B_{\|}\rangle$ is found to be $2.39 \pm 0.7 \ μ$G and $1.67 \pm 0.38 \ μ$G, respectively. This suggests a clear indication of varying magnetic field from the disk to the circumgalactic medium. This work provides a methodology that, when applied to ongoing and future radio polarisation surveys such as LOFAR and SKA, promises to significantly enhance our understanding of magnetic field mapping in galactic systems.

astro-ph.GA↗

arXiv2022

Dynamics and entanglement in quantum and quantum-classical systems: lessons for gravity

Motivated by quantum gravity, semi-classical theory, and quantum theory on curved spacetimes, we study the system of an oscillator coupled to two spin-1/2 particles. This model provides a prototype for comparing three types of dynamics: the full quantum theory, the classical oscillator with spin backreaction, and spins propagating on a fixed oscillator background. From nonperturbative calculations of oscillator and entanglement entropy dynamics, we find that entangled tripartite states produce novel oscillator trajectories, and that the three systems give equivalent dynamics for sufficiently weak oscillator-spin couplings, but deviate significantly for intermediate couplings. These results suggest that semiclassical dynamics with back reaction does not provide a suitable intermediate regime between quantum gravity and quantum theory on curved spacetime.

quant-ph↗

arXiv2021

The Life and Science of Thanu Padmanabhan

Thanu Padmanabhan was a renowned Indian theoretical physicist known for his research in general relativity, cosmology, and quantum gravity. In an extraordinary career spanning forty-two years, he published more than three hundred research articles, wrote ten highly successful technical and popular books, and mentored nearly thirty graduate students and post-doctoral fellows. He is best known for his deep work investigating gravitation as an emergent thermodynamic phenomenon. He was an outstanding teacher, and an indefatigable populariser of science, who travelled very widely to motivate and inspire young students. Paddy, as he was affectionately known, was also a close friend to his students and collaborators, treating them as part of his extended academic family. On September 17, 2021 Paddy passed away very unexpectedly, at the age of sixty-four and at the height of his research career, while serving as a Distinguished Professor at the Inter-University Centre for Astronomy and Astrophysics, Pune. His untimely demise has come as a shock to his family and friends and colleagues. In this article, several of them have come together to pay their tributes and share their fond memories of Paddy.

physics.hist-ph↗

arXiv2021

Quantum backreaction on a classical universe

We study a first-order formulation for the coupled evolution of a quantum scalar field and a classical Friedmann universe. The model is defined by a state dependent hamiltonian constraint and the time dependent Schrödinger equation for the scalar field. We solve the resulting non-linear equations numerically for initial data consisting of a Gaussian scalar field state and gravity phase space variables. This gives a self-consistent semiclassical evolution that includes non-perturbative ``backreaction" due to particle production. We compare the results with the evolution of a quantum scalar field on a fixed background, and find that the backreaction modifies both particle production and cosmological expansion, and that these effects remain bounded.

gr-qc↗

arXiv2021

Schwinger Effect in Compact Space

We consider a theory of scalar QED on a spatially compact 1+1-dimensional spacetime. By considering a constant electric field pointing down the compact dimension, we compute the quantum effective action by integrating out the scalar degrees of freedom in the Euclidean sector. Working in the saddle-point approximation we uncover two novel branches/physical regimes upon analytically continuing back to real time and discover a new result, hitherto unreported in previous literature. Implications of our results are discussed.

hep-th↗

arXiv2020

Matter-Geometry entanglement in quantum cosmology

We present a study of the evolution of entanglement entropy of matter and geometry in quantum cosmology. For a variety of Gaussian initial states and their linear combinations, and with evolution defined with respect to a relational time, we show numerically that (i) entanglement entropy increases rapidly at very early times, and subsequently saturates to a constant non-zero value, and (ii) that the saturation value of this entropy is a linear function of the energy associated to the quantum state: $S_{\text{ent}}^ψ= γ\langle \hat{H} \rangle_ψ$. These results suggest a remnant of quantum entanglement in the macroscopic Universe from the era of the Big Bang, independent of the initial state parameters, and a "First Law" associated with matter-gravity entanglement entropy in quantum gravity.

gr-qc↗

arXiv2018

Semiclassical cosmology with back reaction: the Friedmann-Schrodinger equation and inflation

We propose and study a semi-classical cosmological system akin to the Newton-Schrödinger equation where matter field evolution is determined by time dependent Schrödinger equation. The resulting dynamics is one where the scale factor self-consistently informs the quantum evolution of the scalar field wave function via the Friedmann equation. We study various potentials, and show that for each case, inflation arises naturally, without fine-tuning, for arbitrary initial wave functions for the scalar field. Furthermore, due to zero-point quantum fluctuations of the scalar field, the equation of state $P=-ρ$ arises dynamically at late times for all initial states and potentials.

gr-qc↗

arXiv2018

Does quantum gravity relate the constants of nature?

The central equation of quantum gravity is the Wheeler-DeWitt equation. We give an argument suggesting that exact solutions of this equation give a surface in the space of coupling constants. This provides a mechanism for determining the cosmological constant as a function of the gravitational and other interaction constants. We demonstrate the idea by computing one such surface in a cosmological model.

gr-qc↗

arXiv2018

Schwinger Pair Production in Hot Anti-de Sitter Space

We consider particle production in $1+1$ dimensional thermal Anti-de Sitter space under the influence of a constant electric field. The vacuum-persistence amplitude is given by a non-relativistic tunnelling instanton once we interpret the system as being governed by an "equivalent" non-relativistic Schrödinger equation. Working in the WKB approximation, we calculate the tunnelling rate in anti de Sitter space at finite temperature and observe that the particle production rate is enhanced. Additionally, it is observed that there is a critical temperature beyond which the production rate is affected by the thermal environment. We claim this to be a new result for Anti-de Sitter space in the semi-classical approximation.

hep-th↗

arXiv2017

On the Penrose inequality in anti-deSitter space

For asymptotically flat spacetimes the Penrose inequality gives an initial data test for the weak cosmic censorship hypothesis. We give a formulation of this inequality for asymptotically anti-deSitter (AAdS) spacetimes, and show that the inequality holds for time asymmetric data in spherical symmetry. Our analysis is motivated by the constant-negative-spatial-curvature form of the AdS black hole metric.

gr-qc↗

arXiv2017

Multifaceted Schwinger effect in de Sitter space

We investigate particle production à la Schwinger mechanism in an expanding, flat de Sitter patch as is relevant for the inflationary epoch of our universe. Defining states and particle content in curved spacetime is certainly not a unique process. There being different prescriptions on how that can be done, we have used the Schrödinger formalism to define instantaneous particle content of the state etc. This allows us to go past the adiabatic regime to which the effect has been restricted in the previous studies and bring out its multifaceted nature in different settings. Each of these settings gives rise to contrasting features and behaviour as per the effect of electric field and expansion rate on the instantaneous mean particle number. We also quantify the degree of classicality of the process during its evolution using a "classicality parameter" constructed out of parameters of the Wigner function to obtain information about the quantum to classical transition in this case.

gr-qc↗

arXiv2016

From Quantum to Classical in the Sky

Inflation has by-far set itself as one of the prime ideas in the current cosmological models that seemingly has an answer for every observed phenomenon in cosmology. More importantly, it serves as a bridge between the early quantum fluctuations and the present-day classical structures. Although the transition from quantum to classical is still not completely understood till date, there are two assumptions made in the inflationary paradigm in this regard: (i) the modes (metric perturbations or fluctuations) behave classically once they are well outside the Hubble radius and, (ii) once they become classical they stay classical and hence can be described by standard perturbation theory after they re-enter the Hubble radius. We critically examine these assumptions for the tensor modes of (linear) metric perturbations in a toy three stage universe with (i) inflation, (ii) radiation-dominated and (iii) late-time accelerated phases. The quantum-to-classical transition for these modes is evident from the evolution of Wigner function in phase space and its peaking on the classical trajectory. However, a better approach to quantify the degree of classicality and study its evolution was given by Mahajan and Padmanabhan [1] using a classicality parameter constructed from the parameters of the Wigner function. We study the evolution of the classicality parameter across the three phases and it turns out that the first assumption holds true, there is emergence of classicality on Hubble exit, however the latter assumption of "once classical, always classical" seems to lie on a shaky ground.

gr-qc↗

arXiv2016

It's a dark, dark world: Background evolution of interacting $ϕ$CDM models beyond simple exponential potentials

We study the background cosmological dynamics with a three component source content: a radiation fluid, a barotropic fluid to mimic the matter sector and a single scalar field which can act as dark energy giving rise to the late-time accelerated phase. Using the well-known dimensionless variables, we cast the dynamical equations into an autonomous system of ordinary differential equations (ASODE), which are studied by computing the fixed points and the conditions for their stability. The matter fluid and the scalar field are taken to be uncoupled at first and later, we consider a coupling between the two of the form $Q = \sqrt{2/3}κβρ_m\dotϕ$ where $ρ_m$ is the barotropic fluid density. The key point of our analysis is that for the closure of ASODE, we only demand that the jerk, $Γ= V V"/V'^2$ is a function of acceleration, $z = - M_p V'/ V$, that is, $Γ= 1+ f(z)$. In this way, we are able to accommodate a large class of potentials that goes beyond the simple exponential potentials. The analysis is completely generic and \emph{independent} of the form of the potential for the scalar field. As an illustration and confirmation of the analysis, we consider $f(z)$ of the forms $μ/z^2$, $μ/z$, $(μ-z)/z^2$ and $(μ-z)$ to numerically compute the evolution of cosmological parameters with and without coupling. Implications of the approach and the results are discussed.

astro-ph.CO↗