arXiv subjects

S. Ghosh

Publications and source records attributed to S. Ghosh.

At least 73 records · Page 4Linked to original sources

arXiv2023

Transient RFI environment of LOFAR-LBA at 72-75 MHz: Impact on ultra-widefield AARTFAAC Cosmic Explorer observations of the redshifted 21-cm signal

Measurement of the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn (CD) and Epoch of Reionisation (EoR) promises to unveil a wealth of information about the astrophysical processes during the first billion years of evolution of the universe. The AARTFAAC Cosmic Explorer (ACE) utilises the AARTFAAC wide-field imager of LOFAR to measure the power spectrum of the intensity fluctuations of the redshifted 21-cm signal from the CD at z~18. The RFI from various sources contaminates the observed data and it is crucial to exclude the RFI-affected data in the analysis for reliable detection. In this work, we investigate the impact of non-ground-based transient RFI using cross-power spectra and cross-coherence metrics to assess the correlation of RFI over time and investigate the level of impact of transient RFI on the ACE 21-cm power spectrum estimation. We detected moving sky-based transient RFI sources that cross the field of view within a few minutes and appear to be mainly from aeroplane communication beacons at the location of the LOFAR core in the 72-75 MHz band, by inspecting filtered images. This transient RFI is mostly uncorrelated over time and is only expected to dominate over the thermal noise for an extremely deep integration time of 3000 hours or more with a hypothetical instrument that is sky temperature dominated at 75 MHz. We find no visible correlation over different k-modes in Fourier space in the presence of noise for realistic thermal noise scenarios. We conclude that the sky-based transient RFI from aeroplanes, satellites and meteorites at present does not pose a significant concern for the ACE analyses at the current level of sensitivity and after integrating over the available 500 hours of observed data. However, it is crucial to mitigate or filter such transient RFI for more sensitive experiments aiming for significantly deeper integration.

astro-ph.CO↗

arXiv2023

Cosmogenic background simulations for the DARWIN observatory at different underground locations

Xenon dual-phase time projections chambers (TPCs) have proven to be a successful technology in studying physical phenomena that require low-background conditions. With 40t of liquid xenon (LXe) in the TPC baseline design, DARWIN will have a high sensitivity for the detection of particle dark matter, neutrinoless double beta decay ($0νββ$), and axion-like particles (ALPs). Although cosmic muons are a source of background that cannot be entirely eliminated, they may be greatly diminished by placing the detector deep underground. In this study, we used Monte Carlo simulations to model the cosmogenic background expected for the DARWIN observatory at four underground laboratories: Laboratori Nazionali del Gran Sasso (LNGS), Sanford Underground Research Facility (SURF), Laboratoire Souterrain de Modane (LSM) and SNOLAB. We determine the production rates of unstable xenon isotopes and tritium due to muon-included neutron fluxes and muon-induced spallation. These are expected to represent the dominant contributions to cosmogenic backgrounds and thus the most relevant for site selection.

physics.ins-det↗

arXiv2023

Crystal structure and magnetic properties of spin-$1/2$ frustrated two-leg ladder compounds (C$_4$H$_{14}$N$_2$)Cu$_2X_6$ ($X$= Cl and Br)

We have successfully synthesized single crystals, solved the crystal structure, and studied the magnetic properties of a new family of copper halides (C$_4$H$_{14}$N$_2$)Cu$_2X_6$ ($X$= Cl, Br). These compounds crystallize in an orthorhombic crystal structure with space group $Pnma$. The crystal structure features Cu$^{2+}$ dimers arranged parallel to each other that makes a zig-zag two-leg ladder-like structure. Further, there exists a diagonal interaction between two adjacent dimers which generates inter-dimer frustration. Both the compounds manifest a singlet ground state with a large gap in the excitation spectrum. Magnetic susceptibility is analyzed in terms of both interacting spin-$1/2$ dimer and two-leg ladder models followed by exact diagonalization calculations. Our theoretical calculations in conjunction with the experimental magnetic susceptibility establish that the spin-lattice can be described well by a frustrated two-leg ladder model with strong rung coupling ($J_0/k_{\rm B} \simeq 116$ K and 300 K), weak leg coupling ($J^{\prime\prime}/k_{\rm B} \simeq 18.6$ K and 105 K), and equally weak diagonal coupling ($J^{\prime }/k_{\rm B} \simeq 23.2$ K and 90 K) for Cl and Br compounds, respectively. These exchange couplings set the critical fields very high, making them experimentally inaccessible. The correlation function decays exponentially as expected for a gapped spin system. The structural aspects of both the compounds are correlated with their magnetic properties. The calculation of entanglement witness divulges strong entanglement in both the compounds which persists upto high temperatures, even beyond 370~K for the Br compound.

cond-mat.mtrl-sci↗

arXiv2023

Snowmass2021 Cosmic Frontier: The landscape of low-threshold dark matter direct detection in the next decade

The search for particle-like dark matter with meV-to-GeV masses has developed rapidly in the past few years. We summarize the science case for these searches, the recent progress, and the exciting upcoming opportunities. Funding for Research and Development and a portfolio of small dark matter projects will allow the community to capitalize on the substantial recent advances in theory and experiment and probe vast regions of unexplored dark-matter parameter space in the coming decade.

hep-ph↗

arXiv2023

Axion Dark Matter

Axions are well-motivated dark matter candidates with simple cosmological production mechanisms. They were originally introduced to solve the strong CP problem, but also arise in a wide range of extensions to the Standard Model. This Snowmass white paper summarizes axion phenomenology and outlines next-generation laboratory experiments proposed to detect axion dark matter. There are vibrant synergies with astrophysical searches and advances in instrumentation including quantum-enabled readout, high-Q resonators and cavities and large high-field magnets. This white paper outlines a clear roadmap to discovery, and shows that the US is well-positioned to be at the forefront of the search for axion dark matter in the coming decade.

hep-ex↗

arXiv2023

Neutrino magnetohydrodynamic instabilities in presence of two-flavor oscillations

The influence of neutrino flavor oscillations on the propagation of magnetohydrodynamic (MHD) waves and instabilities is studied in neutrino-beam driven magnetoplasmas. Using the neutrino MHD model, a general dispersion relation is derived which manifests the resonant interactions of MHD waves, not only with the neutrino beam, but also with the neutrino flavor oscillations. It is found that the latter contribute to the wave dispersion and enhance the magnitude of the instability of oblique magnetosonic waves. However, the shear-Alfv{é}n wave remains unaffected by the neutrino beam and neutrino flavor oscillations. Such an enhancement of the magnitude of the instability of magnetosonic waves can be significant for relatively long-wavelength perturbations in the regimes of high neutrino number density and/or strong magnetic field, giving a convincing mechanism for type-II core-collapse supernova explosion.

physics.plasm-ph↗

arXiv2023

Endowing networks with desired symmetries and modular behavior

Symmetries in a network regulate its organization into functional clustered states. Given a generic ensemble of nodes and a desirable cluster (or group of clusters), we exploit the direct connection between the elements of the eigenvector centrality and the graph symmetries to generate a network equipped with the desired cluster(s), with such a synthetical structure being furthermore perfectly reflected in the modular organization of the network's functioning. Our results solve a relevant problem of reverse engineering, and are of generic application in all cases where a desired parallel functioning needs to be blueprinted.

nlin.AO↗

arXiv2022

Colossal piezoresistance in narrow-gap Eu5In2Sb6

Piezoresistance, the change of a material's electrical resistance ($R$) in response to an applied mechanical stress ($σ$), is the driving principle of electromechanical devices such as strain gauges, accelerometers, and cantilever force sensors. Enhanced piezoresistance has been traditionally observed in two classes of uncorrelated materials: nonmagnetic semiconductors and composite structures. We report the discovery of a remarkably large piezoresistance in Eu$_5$In$_2$Sb$_6$ single crystals, wherein anisotropic metallic clusters naturally form within a semiconducting matrix due to electronic interactions. Eu$_5$In$_2$Sb$_6$ shows a highly anisotropic piezoresistance, and uniaxial pressure along [001] of only 0.4~GPa leads to a resistivity drop of more than 99.95\% that results in a colossal piezoresistance factor of $5000\times10^{-11}$Pa$^{-1}$. Our result not only reveals the role of interactions and phase separation in the realization of colossal piezoresistance, but it also highlights a novel route to multi-functional devices with large responses to both pressure and magnetic field.

cond-mat.str-el↗

arXiv2022

Exploring the effects of Delta Baryons in magnetars

Strong magnetic fields can modify the microscopic composition of matter with consequences on stellar macroscopic properties. Within this context, we study, for the first time, the possibility of the appearance of spin-3/2 $Δ$ baryons in magnetars. We make use of two different relativistic models for the equation of state of dense matter under the influence of strong magnetic fields considering the effects of Landau levels and the anomalous magnetic moment (AMM) proportional to the spin of all baryons and leptons. In particular, we analyze the effects of the AMM of $Δ$ baryons in dense matter for the first time. {We also obtain global properties corresponding to the EoS models numerically and study the corresponding role of the $Δ$ baryons.} We find that they are favored over hyperons, which causes an increase in isopin asymmetry and a decrease in spin polarization. We also find that, contrary to what generally occurs when new degrees of freedom are introduced, the $Δ$s do not make the EoS significantly softer and magnetars less massive. Finally, the magnetic field distribution inside a given star is not affected by the presence of $Δ$s.

astro-ph.HE↗

arXiv2022

Spatial properties of entangled two-photon absorption

We experimentally study entangled two-photon absorption in Rhodamine 6G as a function of the spatial properties of a high flux of broadband entangled photon pairs. We first demonstrate a key signature dependence of the entangled two-photon absorption rate on the type of entangled pair flux attenuation: linear, when the laser pump power is attenuated, and quadratic, when the pair flux itself experiences linear loss. We then perform a fluorescence-based Z-scan measurement to study the influence of beam waist size on the entangled two-photon absorption process and compare this to classical single- and two-photon absorption processes. We demonstrate that the entangled two-photon absorption shares a beam waist dependence similar to that of classical two-photon absorption. This result presents an additional argument for the wide range of contrasting values of quoted entangled two-photon absorption cross-sections of dyes in literature.

quant-ph↗

arXiv2022

Host galaxy magnitude of OJ 287 from its colours at minimum light

OJ 287 is a BL Lacertae type quasar in which the active galactic nucleus (AGN) outshines the host galaxy by an order of magnitude. The only exception to this may be at minimum light when the AGN activity is so low that the host galaxy may make quite a considerable contribution to the photometric intensity of the source. Such a dip or a fade in the intensity of OJ 287 occurred in November 2017, when its brightness was about 1.75 magnitudes lower than the recent mean level. We compare the observations of this fade with similar fades in OJ 287 observed earlier in 1989, 1999, and 2010. It appears that there is a relatively strong reddening of the B$-$V colours of OJ 287 when its V-band brightness drops below magnitude 17. Similar changes are also seen V$-$R, V$-$I, and R$-$I colours during these deep fades. These data support the conclusion that the total magnitude of the host galaxy is $V=18.0 \pm 0.3$, corresponding to $M_{K}=-26.5 \pm 0.3$ in the K-band. This is in agreement with the results, obtained using the integrated surface brightness method, from recent surface photometry of the host. These results should encourage us to use the colour separation method also in other host galaxies with strongly variable AGN nuclei. In the case of OJ 287, both the host galaxy and its central black hole are among the biggest known, and its position in the black hole mass-galaxy mass diagram lies close to the mean correlation.

astro-ph.GA↗

arXiv2022

Horizons: Nuclear Astrophysics in the 2020s and Beyond

Nuclear Astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities.

nucl-ex↗

arXiv2022

Neutral Bremsstrahlung emission in xenon unveiled

We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White TPC and a dedicated setup. Detailed comparison with first-principle calculations allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that has been postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about 10$^{-2}$ photon/e$^{-}$ cm$^{-1}$ bar$^{-1}$ at pressure-reduced electric field values of 50 V cm$^{-1}$ bar$^{-1}$ to above 3$\times$10$^{-1}$ photon/e$^{-}$ cm$^{-1}$ bar$^{-1}$ at 500 V cm$^{-1}$ bar$^{-1}$. Above 1.5 kV cm$^{-1}$ bar$^{-1}$, values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around 1 photon/e$^{-}$ cm$^{-1}$ bar$^{-1}$, which is about two orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the "buffer" and "veto" regions, where keeping the electric field below the electroluminescence (EL) threshold will not suffice to extinguish secondary scintillation. The electric field in these regions should be chosen carefully to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path towards obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to 20-50 photons/e$^{-}$ cm$^{-1}$.

physics.ins-det↗

arXiv2022

New Horizons: Scalar and Vector Ultralight Dark Matter

The last decade has seen unprecedented effort in dark matter model building at all mass scales coupled with the design of numerous new detection strategies. Transformative advances in quantum technologies have led to a plethora of new high-precision quantum sensors and dark matter detection strategies for ultralight ($<10\,$eV) bosonic dark matter that can be described by an oscillating classical, largely coherent field. This white paper focuses on searches for wavelike scalar and vector dark matter candidates.

hep-ex↗

arXiv2022

Evaluation of Controllers and Development of a new in-house Controller for the Teledyne HxRG Focal Plane Array for the IRSIS satellite payload

The Infrared Astronomy Group (Department of Astronomy and Astrophysics) at Tata Institute of Fundamental Research (TIFR) is presently developing controllers for the Teledyne HxRG Focal Plane Arrays (FPAs) to be used on board the Infrared Spectroscopic Imaging Survey (IRSIS) satellite payload. In this manuscript we discuss the results of our tests with different FPA controllers like the Astronomical Research Cameras (ARC) controller, Teledyne's SIDECAR ASIC as well as our new in-house designed Array controller. As part of the development phase of the IRSIS instrument, which is an optical fibre based Integral Field Unit (IFU) Near-Infrared (NIR) Spectrometer, a laboratory model with limited NIR bandwidth was built which consisted of various subsystems like a Ritchey-Chretien (RC) 30 cm telescope, optical fibre IFU, spectrometer optics, and the Teledyne H2RG detector module. We discuss the various developments during the building and testing of the IRSIS laboratory model and the technical aspects of the prototype in-house H2RG controller.

astro-ph.IM↗

arXiv2022

Exact Solutions for Solitary Waves in a Bose-Einstein Condensate under the Action of a Four-Color Optical Lattice

We address dynamics of Bose-Einstein condensates (BECs) loaded into a one-dimensional four-color optical lattice (FOL) potential with commensurate wavelengths and tunable intensities. This configuration lends system-specific symmetry properties. The analysis identifies specific multi-parameter forms of the FOL potential which admits exact solitary-wave solutions. This newly found class of potentials includes more particular species, such as frustrated double-well superlattices, and bi-chromatic and three-color lattices, which are subject to respective symmetry constraints. Our exact solutions provide options for controllable positioning of density maxima of the localized patterns, and tunable Anderson-like localization in the frustrated potential. A numerical analysis is performed to establish dynamical stability and structural stability of the obtained solutions, which makes them relevant for experimental realization. The newly found solutions offer applications to the design of schemes for quantum simulations and processing quantum information.

cond-mat.quant-gas↗

arXiv2021

Electron Captures and Stability of White Dwarfs

Electron captures by atomic nuclei in dense matter are among the most important processes governing the late evolution of stars, limiting in particular the stability of white dwarfs. Despite considerable progress in the determination of the equation of state of dense Coulomb plasmas, the threshold electron Fermi energies are still generally estimated from the corresponding $Q$ values in vacuum. Moreover, most studies have focused on nonmagnetized matter. However, some white dwarfs are endowed with magnetic fields reaching $10^9$ G. Even more extreme magnetic fields might exist in super Chandrasekhar white dwarfs, the progenitors of overluminous type Ia supernovae like SN 2006gz and SN 2009dc. The roles of the dense stellar medium and magnetic fields on the onset of electron captures and on the structure of white dwarfs are briefly reviewed. New analytical formulas are derived to evaluate the threshold density for the onset of electron captures for arbitrary magnetic fields. Their influence on the structure of white dwarfs is illustrated by simple analytical formulas and numerical calculations.

astro-ph.SR↗

arXiv2021

Magnon-polarons in van der Waals antiferromagnet FePS3

The hybridization of magnons (spin waves) with phonons, if sufficiently strong and comprising long wavelength excitations, may offer a new playground when manipulating the magnetically ordered systems with light. Applying a magnetic field to a quasi-2D antiferromagnet, FePS3, we tune the magnon-gap excitation towards coincidence with the initially lower-in-energy phonon modes. Hybrid magnon-phonon modes, the magnon polarons are unveiled with demonstration of a pronounced avoided crossing between the otherwise bare magnon and phonon excitations. The magnon polarons in FePS3 are primary traced with Raman scattering experiments, but, as we show, they also couple directly to terahertz photons, what evokes their further explorations in the domain of antiferromagnetic optospintronics.

cond-mat.mtrl-sci↗