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Farrukh Chishtie

Publications and source records attributed to Farrukh Chishtie.

17 recordsLinked to original sources
arXiv2026

Vacuum Birefringence, Ellipticity, and the Anomalous Magnetic Moment of a Photon

We study photon propagation in a strong magnetic field $B\sim B_{\rm{cr}}$, where $B_{\rm cr}= \frac{m^2}{e} \simeq 4.4 \times 10^{13}$ Gauss is the Schwinger critical field. We show that the expected value of the Hamiltonian of a quantized photon for a perpendicular mode is a convex function of the magnetic field $B$. We find that the anomalous magnetic moment of a photon in the one-loop approximation is a non-decreasing function of the magnetic field $B$ in the range $0\leq B \leq 30 \, B_{\rm cr}$. We find that the anomalous magnetic moment $μ_γ$ of a photon for $B=30\, B_{\rm cr}$ is $\sim 8/3$ of the anomalous magnetic moment of a photon for $B = 1/2 ~ B_{\rm cr}$. We establish new connections between $μ_γ$, vacuum birefringence, and directly measurable polarization observables. Based on recent experimental observations -- including the ATLAS detection of light-by-light scattering at $8.2σ$ significance, IXPE X-ray polarimetry of magnetars revealing polarization degrees up to 80\%, and continuing PVLAS measurements approaching QED sensitivity -- we provide predictions for ellipticity and polarization degree as important observables for future experiments. Numerical verification of our analytical results confirms the theoretical predictions with high precision.

hep-ph↗
arXiv2024

Generating Physically-Consistent Satellite Imagery for Climate Visualizations

Deep generative vision models are now able to synthesize realistic-looking satellite imagery. But, the possibility of hallucinations prevents their adoption for risk-sensitive applications, such as generating materials for communicating climate change. To demonstrate this issue, we train a generative adversarial network (pix2pixHD) to create synthetic satellite imagery of future flooding and reforestation events. We find that a pure deep learning-based model can generate photorealistic flood visualizations but hallucinates floods at locations that were not susceptible to flooding. To address this issue, we propose to condition and evaluate generative vision models on segmentation maps of physics-based flood models. We show that our physics-conditioned model outperforms the pure deep learning-based model and a handcrafted baseline. We evaluate the generalization capability of our method to different remote sensing data and different climate-related events (reforestation). We publish our code and dataset which includes the data for a third case study of melting Arctic sea ice and $>$30,000 labeled HD image triplets -- or the equivalent of 5.5 million images at 128x128 pixels -- for segmentation guided image-to-image translation in Earth observation. Code and data is available at \url{https://github.com/blutjens/eie-earth-public}.

cs.CV↗
arXiv2022

Platial mobility: expanding place and mobility in GIS via platio-temporal representations and the mobilities paradigm

While platial representations are being developed for sedentary entities, a parallel and useful endeavour would be to consider time in so-called "platio-temporal" representations that would also expand notions of mobility in GIScience, that are solely dependent on Euclidean space and time. Besides enhancing such aspects of place and mobility via spatio-temporal, we also include human aspects of these representations via considerations of the sociological notions of mobility via the mobilities paradigm that can systematically introduce representation of both platial information along with mobilities associated with 'moving places.' We condense these aspects into 'platial mobility,' a novel conceptual framework, as an integration in GIScience and the mobilities paradigm in sociology, that denotes movement of places in our platio-temporal and sociology-based representations. As illustrative cases for further study using platial mobility as a framework, we explore its benefits and methodological aspects toward developing better understanding for disaster management, disaster risk reduction and pandemics. We then discuss some of the illustrative use cases to clarify the concept of platial mobility and its application prospects in the areas of disaster management, disaster risk reduction and pandemics. These use cases, which include flood events and the ongoing COVID-19 pandemic, have led to displaced and restricted communities having to change practices and places, which would be particularly amenable to the conceptual framework developed in our work.

cs.SI↗
arXiv2021

Physics-informed GANs for Coastal Flood Visualization

As climate change increases the intensity of natural disasters, society needs better tools for adaptation. Floods, for example, are the most frequent natural disaster, but during hurricanes the area is largely covered by clouds and emergency managers must rely on nonintuitive flood visualizations for mission planning. To assist these emergency managers, we have created a deep learning pipeline that generates visual satellite images of current and future coastal flooding. We advanced a state-of-the-art GAN called pix2pixHD, such that it produces imagery that is physically-consistent with the output of an expert-validated storm surge model (NOAA SLOSH). By evaluating the imagery relative to physics-based flood maps, we find that our proposed framework outperforms baseline models in both physical-consistency and photorealism. While this work focused on the visualization of coastal floods, we envision the creation of a global visualization of how climate change will shape our earth.

cs.CV↗
arXiv2018

DLA and sub-DLA metallicity evolution: A case study of absorbers towards Q0338-0005

The damped and sub-damped Lyman alpha systems (DLAs and sub-DLAs) traced in absorption against bright background quasars represent the main reserve of neutral hydrogen at high redshifts. We used the archival Very Large Telescope (VLT) instrument Ultraviolet and Visual Echelle Spectrograph (UVES) high-resolution data of Q0338-0005 (zem = 3.049) to study abundances of the DLA (zabs = 2.2298) and sub-DLA (zabs =2.7457) along the line of sight. We estimated column densities of HI and various elements present in the DLA and sub-DLA through Voigt profile fitting. The DLA trough shows the Lyman alpha emission from its host galaxy. We derive the metallicities of the DLA and sub-DLA with [Zn/H] = -0.67 +/- 0.18 and [S/H] = -1.45 +/-0.17, respectively. We compared our abundances of the DLA and sub-DLA with other high resolution DLA and sub-DLA metallicities and find that both populations show an overall increase of metallicity with decreasing redshift. However, sub-DLAs usually have higher metallicities than the DLAs.

astro-ph.GA↗
arXiv2017

The pion holographic wavefunction with dynamical spin effects

We report that the inclusion of dynamical spin effects in the pion holographic light-front wavefunction leads to a remarkable improvement in describing pion observables (pion mean charge radius, decay constant, spacelike electromagnetic form factor) without the need to invoke higher Fock state contributions and/or a special AdS/QCD mass scale for the pion.

hep-ph↗
arXiv2017

Galaxy Rotation and Supermassive Black Hole Binary Evolution

Supermassive black hole (SMBH) binaries residing at the core of merging galaxies are recently found to be strongly affected by the rotation of their host galaxies. The highly eccentric orbits that form when the host is counterrotating emit strong bursts of gravitational waves that propel rapid SMBH binary coalescence. Most prior work, however, focused on planar orbits and a uniform rotation profile, an unlikely interaction configuration. However, the coupling between rotation and SMBH binary evolution appears to be such a strong dynamical process that it warrants further investigation. This study uses direct N-body simulations to isolate the effect of galaxy rotation in more realistic interactions. In particular, we systematically vary the SMBH orbital plane with respect to the galaxy rotation axis, the radial extent of the rotating component, and the initial eccentricity of the SMBH binary orbit. We find that the initial orbital plane orientation and eccentricity alone can change the inspiral time by an order of magnitude. Because SMBH binary inspiral and merger is such a loud gravitational wave source, these studies are critical for the future gravitational wave detector, LISA, an ESA/NASA mission currently set to launch by 2034.

astro-ph.GA↗
arXiv2017

Spin effects in the pion holographic light-front wavefunction

We account for dynamical spin effects in the holographic light-front wavefunction of the pion in order to predict its mean charge radius, decay constant, spacelike electromagnetic form factor, twist-2 Distribution Amplitude and the photon-to-pion transition form factor. Using a universal fundamental AdS/QCD scale of 523 MeV and a constituent quark mass of 330 MeV, we find a remarkable improvement in describing all observables.

hep-ph↗
arXiv2016

Renormalization Scheme Dependence in a QCD Cross Section

The zero to four loop contribution to the cross section $R_{e^{+}e^{-}}$ for $e^{+}e^{-} \longrightarrow$ hadrons, when combined with the renormalization group equation, allows for summation of all leading-log ($LL$), next-to-leading-log $(NLL) \ldots N^3LL$ perturbative contributions. It is also shown how all logarithmic contributions to $R_{e^{+}e^{-}}$ can be summed and that $R_{e^{+}e^{-}}$ can be expressed in terms of the log independent contributions, and once this is done the running coupling $a$ is evaluated at a point independent of the renormalization scale $μ$. All explicit dependence of $R_{e^{+}e^{-}}$ on $μ$ cancels against its implicit dependence on $μ$ through the running coupling $a$ so that the ambiguity associated with the value of $μ$ is shown to disappear. The renormalization scheme dependency of the "summed" cross section $R_{e^{+}e^{-}}$ is examined in three distinct renormalization schemes. In each case, $R_{e^{+}e^{-}}$ is expressible in terms of renormalization scheme independent parameters $τ_i$ and is explicitly and implicitly independent of the renormalization scale $μ$. Two of the forms are then compared graphically both with each other and with the purely perturbative results and the $RG$-summed $N^3LL$ results.

hep-ph↗
arXiv2016

Renormalization Group Summation of Laplace QCD Sum Rules for Scalar Gluon Currents

We employ renormalization group (RG) summation techniques to obtain portions of Laplace QCD sum rules for scalar gluon currents beyond the order to which they have been explicitly calculated. The first two of these sum rules are considered in some detail, and it is shown that they have significantly less dependence on the renormalization scale parameter $μ^2$ once the RG summation is used to extend the perturbative results. Using the sum rules, we then compute the bound on the scalar glueball mass and demonstrate that the 3 and 4-Loop perturbative results form lower and upper bounds to their RG summed counterparts. We further demonstrate improved convergence of the RG summed expressions with respect to perturbative results.

hep-ph↗
arXiv2013

The Canonical Structure of the First Order Einstein-Hilbert Action with a Flat Background

It has been shown that the canonical structure of the first order Einstein-Hilbert (1EH) action involves three generations of constraints and that these can be used to find the generator of a gauge transformation which leaves the action invariant; this transformation is a diffeomorphism with field-dependent gauge function while on shell. In this paper we examine the relationship between the canonical structure of this action and that of the first order spin-2 (1S2) action, which is the weak field limit of the Einstein-Hilbert action. We find that the weak field limit of the Possion Brackets (PB) algebra of first class constraints associated with the 1EH action is not that of the 1S2 action.

gr-qc↗
arXiv2012

Path Integral Quantization of the First Order Einstein-Hilbert Action from its Canonical Structure

We consider the form of the path integral that follows from canonical quantization and apply it to the first order form of the Einstein-Hilbert action in $d > 2$ dimensions. We show that this is inequivalent to what is obtained from applying the Faddeev-Popov (FP) procedure directly. Due to the presence of tertiary first class constraints, the measure of the path integral is found to have a substantially different structure from what arises in the FP approach. In addition, the presence of second class constraints leads to non-trivial ghosts, which cannot be absorbed into the normalization of the path integral. The measure of the path integral lacks manifest covariance.

hep-th↗
arXiv2012

Non-Trivial Ghosts and Second Class Constraints

In a model in which a vector gauge field $W_μ^a$ is coupled to an antisymmetric tensor field $ϕ_{μν}^a$ possessing a pseudoscalar mass, it has been shown that all physical degrees of freedom reside in the vector field. Upon quantizing this model using the Faddeev-Popov procedure, explicit calculation of the two-point functions $<ϕϕ>$ and $ $ at one-loop order seems to have yielded the puzzling result that the effective action generated by radiative effects has more physical degrees of freedom than the original classical action. In this paper we point out that this is not in fact a real effect, but rather appears to be a consequence of having ignored a "ghost" field arising from the contribution to the measure in the path integral arising from the presence of non-trivial second-class constraints. These ghost fields couple to the fields $W_μ^a$ and $ϕ_{μν}^a$, which makes them distinct from other models involving ghosts arising from second-class constraints (such as massive Yang-Mills (YM) models) that have been considered, as in these other models such ghosts decouple. As an alternative to dealing with second class constraints, we consider introducing a "Stueckelberg field" to eliminate second-class constraints in favour of first-class constraints and examine if it is possible to then use the Faddeev-Popov quantization procedure. In the Proca model, introduction of the Stueckelberg vector is equivalent to the Batalin-Fradkin-Tyutin (BFT) approach to converting second-class constraints to being first class through the introduction of new variables. However, introduction of a Stueckelberg vector is not equivalent to the BFT approach for the vector-tensor model. In an appendix, the BFT procedure is applied to the pure tensor model and a novel gauge invariance is found.

hep-th↗
arXiv2011

The Apparent Velocity and Acceleration of Relativistically Moving Objects

Although special relativity limits the actual velocity of a particle to $c$, the velocity of light, the observed velocity need not be the same as the actual velocity as the observer is only aware of the position of a particle at the time in the past when it emits the detected signal. We consider the apparent speed and acceleration of a particle in two cases, one when the particle is moving with a constant speed and the other when it is moving with a constant acceleration. One curious feature of our results is that in both cases, if the actual velocity of the particle approaches $c$, then the apparent velocity approaches infinity when it is moving toward the observer and $c/2$ when it is moving away from the observer.

physics.gen-ph↗
arXiv2006

Nonspectator effects in B-> K^*+photon within the vector quark model

The tree level FCNC due to the presence of an additional generation of vector quarks result in the leading order nonspectator contributions to rare B-> K^*+photon decay mode. These tree level contributions are sensitive only to b-> s nonunitary parameter U^{sb} and therefore, provide a direct constraint on this model parameter. We obtain the isospin asymmetry between \bar B^0->\bar K^{*0}+photon and B^--> K^{*-}+photon to be Δ_{0-}=-0.03*Re (U^{sb}/(a^c_7V_{tb}V^*_{ts})) and the direct CP asymmetry between B^+->K^{*+}+photon and B^--> K^{*-}+photon to be A_{CP}^{VQM}=0.27|U^{sb}/(V_{tb}V_{ts}^*)|*sinθ*sin{ϕ_s}, where θis the weak phase of U^{sb} and ϕ_s is the strong phase of decay amplitude. We predict a direct CP asymmetry of around a few percent if the current experimental difference between Δ_{0-} and Δ_{0+} is to be explained by the presence of the additional vector quarks.

hep-ph↗
arXiv2005

Isospin Symmetry Breaking in B->K^* γDecay due to an Extra Generation of Vector Quarks

The extra contributions due to an extra generation of vector-like quarks to the isospin symmetry breaking observable associated with the radiative B->K^* γdecay is obtained. It is shown that this additional contribution is sensitive to the nonunitarity parameter U^{sb}, which is a measure of the the strength of the non-zero tree-level flavor changing neutral current in this model. The significance of this result is that, once accurate experimental resultson the isospin asymmetry becomes available, one can constrain the U^{sb} independent of the mass of the extra quarks and so a much more stringent acceptablemodel parameter space could be obtained.

hep-ph↗