arXiv subjects

K. Haris

Publications and source records attributed to K. Haris.

At least 19 recordsLinked to original sources

arXiv2025

Testing general relativity with gravitational waves -- improving and extending Modified Dispersion Relation tests

Searching for a modified dispersion relation is one of the general relativity tests performed by the LIGO-Virgo-KAGRA collaboration with each new cumulative Gravitational Wave Transient Catalog (GWTC). It considers classes of theories that modify the dispersion of gravitational waves by introducing a massive graviton or breaking Lorentz invariance. The symmetry breaking is parameterized phenomenologically by a momentum power law term $p^\alpha$ added to the dispersion relation, with the test placing constraints on the amplitude $A_\alpha$ of the introduced deviation. In this work, we implement improvements to the test, chief among them group velocity parametrization, a better sampling procedure, and extension to negative exponents $\alpha$ of $p$. We then reanalyze the events from the third catalog, GWTC-3, with our improved method. Compared with GWTC-3 results, we find significant improvement, mostly from the improved sampling method, in the posteriors obtained by analyzing individual event and more modest improvements in the combined bounds on amplitude parameters $A_\alpha$ -- on average, we observe 19% shrinking of posterior width. The 90% upper bound on the graviton mass changes from $2.42 \times 10^{-11}$ peV to $2.21 \times 10^{-11}$ peV. For the extension of our test to $\alpha \in \{-1, -2, -3\}$, we find no evidence in favor of general relativity violation.

gr-qc↗

arXiv2025

Strong gravitational-wave lensing posterior odds

Like light, gravitational waves are gravitationally lensed by intervening massive astrophysical objects, such as galaxies, clusters, black holes, and stars, resulting in a variety of potentially observable gravitational-wave lensing signatures. Searches for gravitational-wave lensing by the LIGO-Virgo-KAGRA (LVK) collaboration have begun. One common method focuses on strong gravitational-wave lensing, which produces multiple "images": repeated copies of the same gravitational wave that differ only in amplitude, arrival time, and overall "Morse phase." The literature identifies two separate approaches to identifying such repeated gravitational-wave events based on frequentist and Bayesian approaches. Several works have discussed selection effects and identified challenges similar to the well-known "birthday problem", namely, the rapidly increasing likelihood of false alarms in an ever-growing catalogue of event pairs. Here, we discuss these problems, unify the different approaches in Bayesian language, and derive the posterior odds for strong lensing. In particular, the Bayes factor and prior odds are sensitive to the number of gravitational-wave events in the data, but the posterior odds are insensitive to it once strong lensing time delays are accounted for. We confirm the Lo et al. (2023) finding that selection effects enter the Bayes factor as an overall normalisation constant. However, this factor cancels out in the posterior odds and does not affect frequentist approaches to strong lensing detection.

astro-ph.HE↗

arXiv2025

Spectrum of five-times ionized krypton: Kr VI

This work describes the spectral analysis of five-times ionized krypton ion (Kr VI) using a high-resolution spectrogram recorded on a 3 m normal incidence vacuum spectrograph in the wavelength 230--2075~\AA~region. For spectral excitation, a gas-puff triggered spark source was used. This work thoroughly examined all previously reported spectroscopic analyses for Kr VI. Many missing and new levels were added to the list of known energy levels with the help of several supportive transitions. The present experimental findings were theoretically supported within the pseudo-relativistic Hartree-Fock (HFR) formalism implemented in the Cowan suite of codes. A total of 52 (including eight new) energy levels were established with the help of 169 unique observed spectral lines (31 are new) assigned to 175 (6 doubly assigned) transitions. All observed and Ritz wavelengths were reported with their uncertainties, modeled intensities, and other evaluated radiative transition parameters such as transition probabilities and cancellation factors.

physics.atom-ph↗

arXiv2023

Relative binning for complete gravitational-wave parameter estimation with higher-order modes and precession, and applications to lensing and third-generation detectors

Once a gravitational wave signal is detected, the measurement of its source parameters is important to achieve various scientific goals. This is done through Bayesian inference, where the analysis cost increases with the model complexity and the signal duration. For typical binary black hole signals with precession and higher-order modes, one has 15 model parameters. With standard methods, such analyses require at least a few days. For strong gravitational wave lensing, where multiple images of the same signal are produced, the joint analysis of two data streams requires 19 parameters, further increasing the complexity and run time. Moreover, for third generation detectors, due to the lowered minimum sensitive frequency, the signal duration increases, leading to even longer analysis times. With the increased detection rate, such analyses can then become intractable. In this work, we present a fast and precise parameter estimation method relying on relative binning and capable of including higher-order modes and precession. We also extend the method to perform joint Bayesian inference for lensed gravitational wave signals. Then, we compare its accuracy and speed to those of state-of-the-art parameter estimation routines by analyzing a set of simulated signals for the current and third generation of interferometers. Additionally, for the first time, we analyze some real events known to contain higher-order modes with relative binning. For binary black hole systems with a total mass larger than $50\, M_{\odot}$, our method is about 2.5 times faster than current techniques. This speed-up increases for lower masses, with the analysis time being reduced by a factor of 10 on average. In all cases, the recovered posterior probability distributions for the parameters match those found with traditional techniques.

gr-qc↗

arXiv2023

How well can modified gravitational wave propagation be constrained with strong lensing?

Strong gravitational lensing produces multiple images of a gravitational wave (GW) signal, which can be observed by detectors as time-separated copies of the same event. It has been shown that under favourable circumstances, by combining information from a quadruply lensed GW with electromagnetic observations of lensed galaxies, it is possible to identify the host galaxy of a binary black hole coalescence. Comparing the luminosity distance obtained through electromagnetic means with the effective luminosity distance inferred from the lensed GW signal would then enable us to constrain alternative theories of gravity that allow for modified GW propagation. Here we analyze models including large extra spatial dimensions, a running Planck mass, and a model that captures propagation effects occurring in a variety of alternative theories to general relativity. We consider a plausible population of lenses and binary black holes and use Bayesian inference on simulated GW signals as seen in current detectors at design sensitivity, to arrive at a realistic assessment of the bounds that could be placed. We find that, due to the fact that the sources of lensed events will typically be at much larger redshifts, this method can improve over bounds from GW170817 and its electromagnetic counterpart by a factor of $\sim 5$ to $\mathcal{O}(10^2)$, depending on the alternative gravity model.

gr-qc↗

arXiv2023

Follow-up Analyses to the O3 LIGO-Virgo-KAGRA Lensing Searches

Along their path from source to observer, gravitational waves may be gravitationally lensed by massive objects. This results in distortions of the observed signal which can be used to extract new information about fundamental physics, astrophysics, and cosmology. Searches for these distortions amongst the observed signals from the current detector network have already been carried out, though there have as yet been no confident detections. However, predictions of the observation rate of lensing suggest detection in the future is a realistic possibility. Therefore, preparations need to be made to thoroughly investigate the candidate lensed signals. In this work, we present some of the follow-up analyses and strategies that could be applied to assess the significance of such events and ascertain what information may be extracted about the lens-source system from such candidate signals by applying them to a number of O3 candidate events, even if these signals did not yield a high significance for any of the lensing hypotheses. For strongly-lensed candidates, we verify their significance using a background of simulated unlensed events and statistics computed from lensing catalogs. We also look for potential electromagnetic counterparts. In addition, we analyse in detail a candidate for a strongly-lensed sub-threshold counterpart that is identified by a new method. For microlensing candidates, we perform model selection using a number of lens models to investigate our ability to determine the mass density profile of the lens and constrain the lens parameters. We also look for millilensing signatures in one of the lensed candidates. Applying these additional analyses does not lead to any additional evidence for lensing in the candidates that have been examined. However, it does provide important insight into potential avenues to deal with high-significance candidates in future observations.

gr-qc↗

arXiv2023

Critically Evaluated Atomic Data for Au IV Spectrum

The spectral investigation of the triply ionized gold (Au IV) has been carried out in the wavelength region of 500--2106 {\AA}. The gold spectra were photographed at the National Institute of Standards and Technology (NIST, USA) on a 10.7-m normal incidence vacuum spectrograph (NIVS) using a sliding spark source as well as on a 3-m NIVS at the Antigonish laboratory in Canada with a triggered spark source. Our analysis is theoretically supported by the pseudo-relativistic Hartree-Fock (HFR) formalism with superposition of configuration interactions implemented in Cowan's suite of codes. Radiative transition parameters are also calculated using HFR+CPOL (core-polarization effects) model and multiconfiguration Dirac-Hartree-Fock (MCDHF) approach, and their comparisons are used to evaluate the transition rate data. All the previously reported levels of the $5d^{8}$, $5d^{7}6s$, and $5d^{7}6p$ configurations are confirmed, except one and three are newly established. The missing $^{1}S_{0}$ level of $5d^{8}$ is now established at 55277.8 cm$^{-1}$. A total of 981 observed lines (E1-type) classified to 1031 transitions, including 133 newly identified, enabled us to optimize 139 energy levels. Several astrophysically important transitions, forbidden (M1- and E2-types) lines of $5d^{8}$ and $5d^{7}6s$, are provided with their Ritz wavelengths and radiative parameters. A critically evaluated set of energy levels, observed and Ritz wavelengths along with their uncertainties, transition rates, and uniformly-scaled intensities of Au IV lines have been presented. Also, large scale atomic data to compute opacity of Au IV in the kilonova ejecta have been supplemented in this work.

physics.atom-ph↗

arXiv2023

The Return of GOLUM: Improving Distributed Joint Parameter Estimation for Strongly-Lensed Gravitational Waves

Owing to the forecasted improved sensitivity of ground-based gravitational-wave detectors, new research avenues will become accessible. This is the case for gravitational-wave strong lensing, predicted with a non-negligible observation rate in the coming years. However, because one needs to investigate all the event pairs in the data, searches for strongly-lensed gravitational waves are often computationally heavy, and one faces high false-alarm rates. In this paper, we present upgrades made to the \GOLUM software, making it more reliable while increasing its speed by re-casting the look-up table, imposing a sample control, and implementing symmetric runs on the two lensed images. We show how the recovered posteriors have improved coverage of the parameter space and how we increase the pipeline's stability. Finally, we show the results obtained by performing a joint analysis of all the events reported until the GWTC-3 catalog, finding similar conclusions to the ones presented in the literature.

gr-qc↗

arXiv2022

Critically Evaluated Spectral Data for Singly Ionized Carbon (C II)

All available experimental data on the spectrum of singly ionized carbon have been critically analyzed. Measurement uncertainties of all published studies have been re-assessed. The scope of observational data includes laboratory emission spectra of arcs, sparks, electrodeless discharges, and hollow cathode lamps recorded with grating and Fourier transform spectrometers, laboratory photoabsorption spectra, and emission spectra of planetary nebulae. The total number of observed spectral lines included in this compilation is 597. These lines participate in 972 transitions. From this list of identified transitions, we have derived a set of 414 energy levels, which are optimized using a least-squares fitting procedure. The identifications are supported by parametric calculations with Cowan's codes. The existing tables of critically evaluated transition probabilities have been extended with our newly calculated data. The ionization energy has been derived from the newly optimized energy levels with improved precision. Data on isotope shifts and hyperfine structure have also been compiled.

physics.atom-ph↗

arXiv2022

GOLUM: A fast and precise methodology to search for, and analyze, strongly lensed gravitational-wave events

Like light, gravitational waves can be gravitationally lensed by massive objects along their travel path. Strong lensing produces several images from the same binary coalescence and is forecasted to have a promising rate in ground-based gravitational detectors. To search for this effect in the data, one would, in principle, have to analyze all the possible combinations of the individual detected events, whose number will be ever-increasing. To keep up with the rising computational cost, we propose a fast and precise methodology to analyze strongly-lensed gravitational wave events. The method works by effectively using the posterior of the first image as prior for the second image. Thanks to its increased speed tractability, this method enables the joint analysis of more than two images. In addition, it opens the door to new strong lensing studies where a large number of injections is required.

gr-qc↗

arXiv2021

Constraints on compact dark matter from gravitational wave microlensing

If a significant fraction of dark matter is in the form of compact objects, they will cause microlensing effects in the gravitational wave (GW) signals observable by LIGO and Virgo. From the non-observation of microlensing signatures in the binary black hole events from the first two observing runs and the first half of the third observing run, we constrain the fraction of compact dark matter in the mass range $10^2-10^5~{M_\odot}$ to be less than $\simeq 50-80\%$ (details depend on the assumed source population properties and the Bayesian priors). These modest constraints will be significantly improved in the next few years with the expected detection of thousands of binary black hole events, providing a new avenue to probe the nature of dark matter.

gr-qc↗

arXiv2020

Testing the nature of gravitational-wave polarizations using strongly lensed signals

Gravitational-wave (GW) observations by a network of ground-based laser interferometric detectors allow us to probe the nature of GW polarizations. This would be an interesting test of general relativity (GR), since GR predicts only two polarization modes while there are theories of gravity that predict up to six polarization modes. The ability of GW observations to probe the nature of polarizations is limited by the available number of linearly independent detectors in the network. (To extract all polarization modes, there should be at least as many detectors as the polarization modes.) Strong gravitational lensing of GWs offers a possibility to significantly increase the effective number of detectors in the network. Due to strong lensing (e.g., by galaxies), multiple copies of the same signal can be observed with time delays of several minutes to weeks. Owing to the rotation of the earth, observation of the multiple copies of the same GW signal would allow the network to measure different combinations of the same polarizations. This effectively multiplies the number of detectors in the network. Focusing on strongly lensed signals from binary black hole mergers that produce two observable "images", using Bayesian model selection and assuming simple polarization models, we show that our ability to distinguish between polarization models is significantly improved.

gr-qc↗

arXiv2020

Critically Evaluated Energy Levels, Wavelengths, Transition Probabilities, and Intensities of Six-Times Ionized Cesium: Cs VII

Previously reported works on the spectrum of Cs VII are critically studied using supplementary spectrograms recorded on a 3 m normal incidence vacuum spectrograph in the wavelength region 300-1240 A at the Antigonish laboratory (Canada). We confirmed the results of the earlier work of Gayasov and Joshi on this spectrum. Our analysis is supported by extended calculations with the pseudo-relativistic Hartree-Fock (HFR) method with superposition of configuration interactions implemented in Cowan's suite of codes. In this critical evaluation, in addition to the accurate energy levels of Cs VII with their uncertainties, observed and Ritz wavelengths with uncertainties and transition probabilities, the uniformly-scaled intensities of Cs VII lines are also presented. A total of 196 lines attributed to 197 transitions enabled us to optimize the energy values of 72 levels in Cs VII spectrum. Furthermore, Ritz wavelengths of 141 possibly observable lines are provided along with their transition probabilities.

physics.atom-ph↗

arXiv2019

Search for gravitational lensing signatures in LIGO-Virgo binary black hole events

We search for signatures of gravitational lensing in the binary black hole events detected by Advanced LIGO and Virgo during their first two observational runs. In particular, we look for three effects: 1) evidence of lensing magnification in the individual signals due to galaxy lenses, 2) evidence of multiple images due to strong lensing by galaxies, 3) evidence of wave optics effects due to point-mass lenses. We find no compelling evidence of any of these signatures in the observed gravitational wave signals. However, as the sensitivities of gravitational wave detectors improve in the future, detecting lensed events may become quite likely.

gr-qc↗

arXiv2018

Identifying strongly lensed gravitational wave signals from binary black hole mergers

Based on the rate of gravitational-wave (GW) detections by Advanced LIGO and Virgo, we expect these detectors to observe hundreds of binary black hole mergers as they achieve their design sensitivities (within a few years). A small fraction of them can undergo strong gravitational lensing by intervening galaxies, resulting in multiple images of the same signal. To a very good approximation, the lensing magnifies/de-magnifies these GW signals without affecting their frequency profiles. We develop a Bayesian inference technique to identify pairs of strongly lensed images among hundreds of binary black hole events and demonstrate its performance using simulated GW observations.

gr-qc↗

arXiv2018

Energy Level Structure of Sn$^{3+}$ Ions

Laser-produced Sn plasma sources are used to generate extreme ultraviolet (EUV) light in state-of-the-art nanolithography. An ultraviolet and optical spectrum is measured from a droplet-based laser-produced Sn plasma, with a spectrograph covering the range 200 - 800 nm. This spectrum contains hundreds of spectral lines from lowly charged tin ions Sn$^{1+}$ - Sn$^{4+}$ of which a major fraction was hitherto unidentified. We present and identify a selected class of lines belonging to the quasi-one-electron, Ag-like ([Kr]$4d^{10} nl$ electronic configuration), Sn$^{3+}$ ion, linking the optical lines to a specific charge state by means of a masking technique. These line identifications are made with iterative guidance from COWAN code calculations. Of the 53 lines attributed to Sn$^{3+}$, some 20 were identified from previously known energy levels, and 33 lines are used to determine previously unknown level energies of 13 electronic configurations, i.e., $ 7p $, $ (7,8)d $, $ (5,6)f $, $ (6-8)g $, $ (6-8)h $, $ (7,8)i $. The consistency of the level energy determination is verified by the quantum-defect scaling procedure. The ionization limit of Sn$^{3+}$ is confirmed and refined to 328908.4 cm$^{-1}$ with an uncertainty of 2.1 cm$^{-1}$. The relativistic Fock space coupled cluster (FSCC) calculation of the measured level energies are generally in good agreement with experiment, but fail to reproduce the anomalous behavior of the $5d$ $^2$D and $nf$ $^2$F terms. By combining the strengths of FSCC, COWAN code calculations, and configuration interaction many-body perturbation theory (CI+MBPT), this behavior is shown to arise from interactions with doubly-excited configurations.

physics.atom-ph↗

arXiv2018

Revision of the ionization energy of neutral carbon

This publication describes a re-analysis of previously published data on neutral carbon (C I) utilizing critically examined and improved values for the line energies of the absorption spectrum of molecular iodine to calibrate the transition energies of C I absorption lines originating from the 1s22s22p3s 3P°2) level and terminating on highly excited Rydberg states of the 1s22s22pnp 3D3 series, which converges on the first excited fine-structure level of the ionic ground configuration. Additional use of improved energy values for the 1s22s22p3s 3P°2 level, the fine-structure interval of the ionic ground state, and sophisticated modern fitting techniques lead to a new value of the ionization energy of neutral carbon with 9 times the precision of previous work, 90820.348(9) cm^{-1}, as well as a table of predicted values for the energies of not yet observed states in the series.

physics.atom-ph↗

arXiv2017

Performance of multi-detector hybrid statistic in targeted compact binary coalescence search

In this paper we compare the performance of two likelihood ratio based detection statistics namely maximum likelihood ratio statistic and {\it hybrid} statistic designed for the detection of gravitational waves from compact binary coalescence using multiple interferometric detector networks. We perform simulations with non-spinning double neutron star binary system and neutron star-black hole binary systems with spinning as well as non-spinning black hole component masses. The binary injections are distributed uniformly in volume up to 1 Gpc. We observe that, on average, the maximum likelihood ratio statistic recovers $\sim 34.45\%$, $\sim 49.69\%$, $\sim 61.25\%$ and $\sim 69.67\%$ of injections in 2, 3, 4 and 5 detector networks respectively in the case of neutron star-black hole injections for a fixed false alarm probability of $10^{-7}$ in Gaussian noise. Further, we note that, compared to the maximum likelihood ratio statistic, the {\it hybrid} statistic recovers $\sim 7.45\%$, $\sim 4.57\%$, $\sim 2.56\%$ and $\sim 1.22\%$ more injections in 2, 3, 4 and 5 detector networks respectively for the same false alarm probability in Gaussian noise. On the other hand, among binary neutron star injections, the maximum likelihood ratio statistic recovers $\sim 5.587\%$, $\sim 9.917\%$, $\sim 14.73\%$ and $\sim 19.86\%$ of injections in 2, 3, 4 and 5 detector networks respectively and the {\it hybrid} statistic recovers $\sim 14.63\%$, $\sim 12.91\%$, $\sim 11.49\%$ and $\sim 10.29\%$ more injections compared to maximum likelihood ratio statistic in 2, 3, 4 and 5 detector networks respectively.

astro-ph.IM↗