arXiv subjects

Susmita Jana

Publications and source records attributed to Susmita Jana.

10 recordsLinked to original sources

arXiv2026

Integrated cosmological memory: A dark-siren method to probe dark energy

Gravitational-wave (GW) cosmology is currently bottlenecked by the scarcity of electromagnetic counterparts for bright sirens and the systematic uncertainties of galaxy catalogs for dark sirens. We propose a purely gravitational resolution using the Integrated Cosmological Memory (ICM)-the cumulative GW strain encoded in the spacetime geometry of an expanding Universe. While the GW transient emitted by the source provides the luminosity distance, the ICM accumulates a mathematically distinct integral of the cosmic expansion history. We demonstrate that extracting both observables from a single binary merger completely breaks the distance-redshift degeneracy within the gravitational sector. This establishes a novel, catalog-free dark siren framework for third-generation GW detector networks. Crucially, the resulting constraints on late-time dark energy are only weakly sensitive to the local expansion rate, providing a robust cosmological probe that can potentially mitigate the impact of the H0 tension.

astro-ph.CO↗

arXiv2026

Quantum Resistance in Multilayer Graphene-BiFeO3 Memristor for Brain-Inspired Computing

In the era of big data and the Internet of Things, quantum-level control of conductance states offers a promising route toward high-density data storage and brain-inspired neuromorphic computing. Although quantum conductance (QC) phenomena have been demonstrated in various metal oxide memristors, achieving reliable and precise control over quantized states remains in its infancy. Here, we demonstrate bidirectional quantum conductance states in multifunctional BiFeO3 (BFO) perovskite memristors integrated with multilayer-graphene contacts, enabling higher-order tunability and revealing the potential of perovskite-2D heterostructures for quantum-engineered memory and computing devices. XPS analysis provides detailed insights into oxygen vacancy dynamics in BFO, whereas first-principles density functional theory calculations clearly reveal a strong localized electric field at the graphene-BFO interface. Our devices exhibit current-controlled higher-order QC transitions facilitated by quantum point contact formation, giving rise to quantized conductance states during both SET and RESET processes. Time-lag correlation maps quantify the stochastic evolution of QC states under dynamic voltage-pulse tuning schemes. Notably, the quantized conductance states effectively emulate synaptic potentiation and depression, enabling precise weight modulation for high-accuracy image and digit recognition in convolutional neural networks. These findings establish perovskite-2D heterostructures as promising candidates for QC-driven resistive switching and demonstrate their potential for developing controllable quantum memristors.

cond-mat.mes-hall↗

arXiv2025

Abelian and non-Abelian mimetic black holes

We investigate black hole solutions in the mimetic extension of the Einstein-Yang-Mills system, in which the Yang-Mills term is constrained to be constant. In the Abelian U(1) case, we find a static spherically symmetric solution that includes the Schwarzschild and Reissner-Nordstrom black holes as special cases. Moreover, we identify a stealth Schwarzschild solution with an electric hair. We show that it is impossible to have magnetic hair in the U(1) gauge case, while, in contrast, the non-Abelian SU(2) stealth solutions can sustain both electric and magnetic hair. Unlike the conventional SU(2) Einstein-Yang-Mills black hole, which requires a unit magnetic parameter to exhibit nontrivial non-Abelian contributions, the stealth mimetic SU(2) solution admits genuinely non-Abelian configurations with arbitrary integer magnetic parameter.

gr-qc↗

arXiv2025

Signatures of asymmetry: Gravitational wave memory and the parity violation

Einstein's equivalence principle suggests a deep connection between matter and spacetime, prompting the question: if matter violates parity, must gravity? This letter explores the detection of parity violation in gravity using gravitational wave (GW) memory. Gravitational parity violation could be observable through GW amplitude birefringence and large-scale structure correlations. With improved sensitivity, next-generation GW detectors offer unprecedented opportunities to probe these effects. We propose that the integrated cosmological memory (ICM) of GWs, amplified over cosmological distances, can enhance faint parity-violating signatures. Specifically, if GWs from astrophysical events have differing polarization amplitudes, as in Chern-Simons gravity, ICM significantly amplifies this disparity. ICM uniquely and independently allows us to test fundamental symmetries, constrain gravity parameters, and gain insights into the interplay of particle physics, cosmology and gravity.

gr-qc↗

arXiv2024

Non-minimally coupled electromagnetic fields and observable implications for primordial black holes

General relativity (GR) postulates have been verified with high precision, yet our understanding of how gravity interacts with matter fields remains incomplete. Various modifications to GR have been proposed in both classical and quantum realms to address these interactions within the strong gravity regime. One such approach is non-minimal coupling (NMC), where the space-time curvature (scalar and tensor) interacts with matter fields, resulting in matter fields not following the geodesics. To probe the astrophysical implications of NMC, in this work, we investigate non-minimally coupled electromagnetic (EM) fields in the presence of black holes. Specifically, we show that primordial black holes (PBHs) provide a possible tool to constrain the NMC parameter. PBHs represent an intriguing cosmological black hole class that does not conform to the no-hair theorem. We model the PBH as a Sultana--Dyer black hole and compare it with Schwarzschild. We examine observables such as the radius of the photon sphere, critical impact parameter, and total deflection angles for non-minimally coupled photons for Schwarzschild and Sultana--Dyer black holes. Both the black hole space-times lead to similar constraints on the NMC parameter. For a PBH of mass $M=10^{-5} M_{\odot}$, the photon sphere will not be formed for one mode. Hence, the photons forming the photon sphere will be highly polarized, potentially leading to observable implications.

gr-qc↗

arXiv2024

Prospects for cosmological constraints using gravitational wave memory

The {\Lambda}CDM model has long served as a robust and predictive framework for cosmology, successfully explaining a wide range of observations, including the accelerated expansion of the Universe. However, discrepancies in cosmological parameter estimates and recent findings, such as those from DESI, hint at potential deviations from {\Lambda}CDM. Gravitational wave (GW) observations offer an independent method to probe the nature of dark energy, leveraging GWs from compact binary mergers as standard candles. In this study, we demonstrate that the integrated GW memory over cosmological distances encodes a unique imprint of the background spacetime. Unlike previous analyses, our approach captures non-linear dependencies on cosmological quantities, resulting in an enhancement of the integrated GW memory by a factor of 100 for high-redshift sources well within the sensitivity range of next-generation detectors like Cosmic Explorer and the Einstein Telescope. We find that despite the diminishing strength of individual GWs at high redshifts, their cumulative effect leads to a significant amplification, akin to the integrated Sachs-Wolfe effect, offering a potential new avenue for cosmological studies. By examining a range of dark energy models, we reveal that GW memory is potentially highly sensitive to the underlying cosmological framework, making it a promising probe of dark energy. This novel approach presents the possibility of a fresh perspective to address persistent cosmological tensions, and the nature of dark energy.

gr-qc↗

arXiv2024

Transient electromagnetic sources can detect solitary black holes in Milky Way galaxy

The Milky Way galaxy is estimated to host up to a billion stellar-mass solitary black holes (BHs). The number and distribution of BH masses can provide crucial information about the processes involved in BH formation, the existence of primordial BHs, and the interpretation of gravitational wave (GW) signals detected in LIGO-VIRGO-KAGRA. {Sahu et al. recently confirmed one solitary stellar-mass BH in our galaxy using astrometric microlensing}. This work proposes a novel mechanism to identify such BH by analyzing the frequency and damping of the quasi-normal modes of GW generated from the interaction of the BH and EM wave originating from a transient electromagnetic (TEM) source. The incoming EM waves distort the curvature of a BH, releasing GWs as it returns to a steady state. Using the covariant semi-tetrad formalism, we quantify the generated GWs via the \emph{Regge-Wheeler tensor} and relate the GW amplitude to the energy of the TEM. We demonstrate that isolated BHs at a distance of 50 pc from Earth can be detected by LIGO A+ and 100 pc by Cosmic Explorer/Einstein Telescope. Additionally, we discuss the observational implications for orphan afterglows associated with GRBs, highlighting the potential for further discoveries.

gr-qc↗

arXiv2023

A test of Einstein's equivalence principle in future VLBI observations

We show that very-long-baseline-interferometry (VLBI) observations of supermassive black holes will allow us to test the fundamental principles of General Relativity (GR). GR is based on the universality of gravity and Einstein's equivalence principle (EEP). However, EEP is not a basic principle of physics but an empirical fact. Non-minimal coupling (NMC) of electromagnetic fields violates EEP, and their effects manifest in the strong-gravity regime. Hence, VLBI observations of black holes provide an opportunity to test NMC in the strong-gravity regime. To the leading order in the spin parameter, we explicitly show that the NMC of the electromagnetic field introduces observable modifications to the black hole image. In addition, we find that the size of the photon rings varies by $\sim 3 r_H$, which corresponds to $\sim 30 μas$ for Sagittarius $A^*$ and $\sim 23 μas$ for M87. VLBI telescopes are expected to attain a resolution of $\sim 5 μas$ in the near future. However, direct detection of photon ring will require the resolution of $\sim 1 μas$ for M87, which can potentially be probed by the space-based Event Horizon Explorer.

gr-qc↗

arXiv2023

Electronic structure and optoelectronic properties of halide double perovskites: Fundamental insights and design of a theoretical workflow

Like single perovskites, halide double perovskites (HDP) have truly emerged as efficient optoelectronic materials since they display superior stability and are free of toxicity. However, challenges still exist due to either wide and indirect bandgaps or parity-forbidden transitions in many of them. The lack of understanding in chemical bonding and the formation of parity-driven valence and conduction band edge states have hindered the design of optoelectronically efficient HDPs. In this study, we have developed a theoretical workflow using a multi-integrated approach involving ab-initio density functional theory (DFT) calculations, model Hamiltonian studies, and molecular orbital picture leading to momentum matrix element (MME) estimation. This workflow gives us detailed insight into chemical bonding and parity-driven optical transition between edge states. In the process, we have developed a band-projected molecular orbital picture (B-MOP) connecting free atomic orbital states obtained at the Hartree-Fock level and orbital-resolved DFT bands. From the B-MOP, we show that the nearest neighbor cation-anion interaction determines the position of atom-resolved band states, while the second neighbor cation-cation interactions determine the shape and width of band dispersion and, thereby, MME. The latter is critical to quantify the optical absorption coefficient. Considering both B-MOP and MME, we demonstrate a mechanism of tailoring bandgap and optical absorptions through chemical doping at the cation sites. Furthermore, the cause of bandgap bowing, a common occurrence in doped HDPs, is explained by ascribing it to chemical effect and structural distortion.

cond-mat.mtrl-sci↗

arXiv2023

Electromagnetic memory in arbitrary curved space-times

The gravitational memory effect and its electromagnetic (EM) analog are potential probes in the strong gravity regime. In the literature, this effect is derived for static observers at asymptotic infinity. While this is a physically consistent approach, it restricts the space-time geometries for which one can obtain the EM memory effect. To circumvent this, we evaluate the EM memory effect for comoving observers (defined by the 4-velocity $u_μ$) in arbitrary curved space-times. Using the covariant approach, we split Maxwell's equations into two parts -- projected parallel to the 4-velocity $u_μ$ and into the 3-space orthogonal to $u_μ$. Further splitting the equations into $1+1+2$-form, we obtain \emph{master equation} for the EM memory in an arbitrary curved space-time. We provide a geometrical understanding of the contributions to the memory effect. We then obtain EM memory for specific space-time geometries and discuss the salient features.

gr-qc↗