arXiv subjects

Arshad Momen

Publications and source records attributed to Arshad Momen.

At least 19 recordsLinked to original sources

arXiv2026

Semi-classical Imprint of Horizon Induced Instability

We consider an inverted harmonic oscillator in the space $L^{2} (\mathbb{S})$ of square-integrable functions on the circle $\mathbb{S}$ and compute its density of states employing the stationary phase approximation. Our computation is based on an oscillatory integral representation of the Schwartz kernel of the time-evolution operator. This demonstrates thermalisation as a semi-classical manifestation of the classical Lyapunov instability -- reported earlier in [Phys. Rev. D 102, 044006; Phys. Rev. D 102, 124047] using heuristic analytic continuation. Our spectral analysis of the Hamiltonian points out and closes the conceptual and mathematical gaps in the preceding literature.

hep-th↗

arXiv2025

BD Open LULC Map: High-resolution land use land cover mapping & benchmarking for urban development in Dhaka, Bangladesh

Land Use Land Cover (LULC) mapping using deep learning significantly enhances the reliability of LULC classification, aiding in understanding geography, socioeconomic conditions, poverty levels, and urban sprawl. However, the scarcity of annotated satellite data, especially in South/East Asian developing countries, poses a major challenge due to limited funding, diverse infrastructures, and dense populations. In this work, we introduce the BD Open LULC Map (BOLM), providing pixel-wise LULC annotations across eleven classes (e.g., Farmland, Water, Forest, Urban Structure, Rural Built-Up) for Dhaka metropolitan city and its surroundings using high-resolution Bing satellite imagery (2.22 m/pixel). BOLM spans 4,392 sq km (891 million pixels), with ground truth validated through a three-stage process involving GIS experts. We benchmark LULC segmentation using DeepLab V3+ across five major classes and compare performance on Bing and Sentinel-2A imagery. BOLM aims to support reliable deep models and domain adaptation tasks, addressing critical LULC dataset gaps in South/East Asia.

cs.CV↗

arXiv2025

RGC-Bent: A Novel Dataset for Bent Radio Galaxy Classification

We introduce a novel machine learning dataset tailored for the classification of bent radio active galactic nuclei (AGN) in astronomical observations. Bent radio AGN, distinguished by their curved jet structures, provide critical insights into galaxy cluster dynamics, interactions within the intracluster medium, and the broader physics of AGN. Despite their astrophysical significance, the classification of bent radio AGN remains a challenge due to the scarcity of specialized datasets and benchmarks. To address this, we present a dataset, derived from a well-recognized radio astronomy survey, that is designed to support the classification of NAT (Narrow-Angle Tail) and WAT (Wide-Angle Tail) categories, along with detailed data processing steps. We further evaluate the performance of state-of-the-art deep learning models on the dataset, including Convolutional Neural Networks (CNNs), and transformer-based architectures. Our results demonstrate the effectiveness of advanced machine learning models in classifying bent radio AGN, with ConvNeXT achieving the highest F1-scores for both NAT and WAT sources. By sharing this dataset and benchmarks, we aim to facilitate the advancement of research in AGN classification, galaxy cluster environments and galaxy evolution.

astro-ph.GA↗

arXiv2023

Violation of the Landau-Yang theorem from Infrared Lorentz Symmetry Breaking

Lorentz symmetry forbids decays of massive spin-1 particle like the $Z^0$ into two massless photons, a result known as the Landau-Yang theorem. But it is known that infrared effects can break Lorentz invariance. Employing the construction of Mund et. al. \cite{MRS} which incorporated this Lorentz violation, we propose an interaction leading to the decay $Z^0 \rightarrow 2 γ$ and study the dependence of the decay on the parameter of this Lorentz violation.

hep-ph↗

arXiv2023

Morphological Classification of Radio Galaxies using Semi-Supervised Group Equivariant CNNs

Out of the estimated few trillion galaxies, only around a million have been detected through radio frequencies, and only a tiny fraction, approximately a thousand, have been manually classified. We have addressed this disparity between labeled and unlabeled images of radio galaxies by employing a semi-supervised learning approach to classify them into the known Fanaroff-Riley Type I (FRI) and Type II (FRII) categories. A Group Equivariant Convolutional Neural Network (G-CNN) was used as an encoder of the state-of-the-art self-supervised methods SimCLR (A Simple Framework for Contrastive Learning of Visual Representations) and BYOL (Bootstrap Your Own Latent). The G-CNN preserves the equivariance for the Euclidean Group E(2), enabling it to effectively learn the representation of globally oriented feature maps. After representation learning, we trained a fully-connected classifier and fine-tuned the trained encoder with labeled data. Our findings demonstrate that our semi-supervised approach outperforms existing state-of-the-art methods across several metrics, including cluster quality, convergence rate, accuracy, precision, recall, and the F1-score. Moreover, statistical significance testing via a t-test revealed that our method surpasses the performance of a fully supervised G-CNN. This study emphasizes the importance of semi-supervised learning in radio galaxy classification, where labeled data are still scarce, but the prospects for discovery are immense.

astro-ph.IM↗

arXiv2019

Classicalization in Derivatively Coupled Scalar Field Theories: A Feasibility Study

It has been suggested that a certain class of UV-incomplete quantum field theories can avoid unitarity violation above the cut-off energy scale by forming classical configurations at a length scale much larger than the cut-off length. This phenomenon has been named classicalization and is characterized by a length scale called classicalization radius $r_*$ which increases with energy. It has been argued that scalar field theories with derivative self-interactions are likely candidate for UV-completetion by classicalization and are much likely to form classicalons compared to non-classicalizing theories like $ϕ^4$ scalar field theory. To look further into this claim, in this paper 2 to N particle scattering amplitude, scattering cross-section and the amplitude of classical structure formation has been calculated and compared for a classicalizing and non-classicalizing theory. As the phenomenon of classicalization relies on creating a large number of low energy particles from high energy two particle scattering, the ratios between the scattering amplitudes and the amplitude of classical structure formation in these two cases are an indicator of the feasibility of the classicalization process. From our calculation, it has been observed that with the increase of energy, the ratios of the relevant quantities between classicalizing and non-classicalizing theory actually decrease which is quite contrary to the expected behaviour if classicalization is supposed to self-unitarize certain class of theories beyond cut-off energy.

hep-th↗

arXiv2018

Spacetime Dimensionality from de Sitter Entropy

We argue that de Sitter universes with a small cosmological constant are entropically favored to have three spatial dimensions. The conclusion relies on the causal-patch description of de Sitter space, where fiducial observers experience local thermal equilibrium up to a stretched horizon, on the holographic principle, and on some assumptions about the nature of gravity and the constituents of Hawking/Unruh radiation.

hep-th↗

arXiv2017

Equations of Motion as Covariant Gauss Law: The Maxwell-Chern-Simons Case

Time-independent gauge transformations are implemented in the canonical formalism by the Gauss law which is not covariant. The covariant form of Gauss law is conceptually important for studying asymptotic properties of the gauge fields. For QED in $3+1$ dimensions, we have developed a formalism for treating the equations of motion (EOM) themselves as constraints, that is, constraints on states using Peierls' quantization. They generate spacetime dependent gauge transformations. We extend these results to the Maxwell-Chern-Simons (MCS) Lagrangian. The surprising result is that the covariant Gauss law commutes with all observables: the gauge invariance of the Lagrangian gets trivialized upon quantization. The calculations do not fix a gauge. We also consider a novel gauge condition on test functions (not on quantum fields) which we name the "quasi-self-dual gauge" condition. It explicitly shows the mass spectrum of the theory. In this version, no freedom remains for the gauge transformations: EOM commute with all observables and are in the center of the algebra of observables.

hep-th↗

arXiv2011

Classicalization via Path Integral

Recently, it was suggested that a large class of non-renormalizable theories may need no UV completion. By analogy with gravity where classical black holes are expected to be created in high-energy scatterings, it is conjectured that similar classical solutions, so-called classicalons, should occur. In this way the theory protects itself against non-unitarity, for instead of probing small distances at high energies one enters a classical regime. An effective theory of Goldstone bosons provides and example in which the size of classicalons grows with energy, and the high energy scattering is cut-off by small momenta, inversely proportional to the classicalon size. In this note we offer an alternative, path integral discussion of this important result.

hep-ph↗

arXiv2006

Accelerating Universe Around A Blackhole

We have assumed that in a physical universe a blackhole is created some where. We conjecture that this blackhole will then separate itself from the physical universe and will build up an extra dimensional entity associated with the physical universe. The extra dimensional entity we suppose to be orthogonal to the physical universe. We further conjecture that this blackhole is a Schwartzschild blackhole. We assume that this physical universe and the blackhole span a seven dimensional space with a common time coordinate. We then generate the Einstein equation. Using the time-blackhole and the time-time component of the equation we show that the Hubble parameter is positive and time dependent if we conjecture that both scale factor and the radius of the blackhole reduces exponetially. Under the same assumption we have also calculated the deacceleration parameter and shown that under certain constrain the universe accelerates.

gr-qc↗

arXiv2002

A Comment on Curvature Effects In CFTs And The Cardy-Verlinde Formula

We examine the Cardy-Verlinde formula for finite temperature N=4 Super Yang-Mills theory on $R\times S^3$, and its AdS dual. We find that curvature effects introduce non-trivial corrections to thermodynamic quantities computed on both sides. We find a modified version of the Cardy-Verlinde formula for the SYM theory, incorporating these. On the gravity side, these corrections imply that the Cardy-Verlinde formula is exact.

hep-th↗

arXiv2000

Quark-Antiquark Potential for Siegel Strings

We compute the quark-antiquark potential employing the continuum action for QCD-like random lattice strings proposed by Siegel. The model leads to a potential similar to those obtained from Nambu-Goto string theory but has some modifications which we interpret as velocity dependent contributions. We also propose to add extra terms in the action which lead to physically interesting propagators for partons for the infrared region.

hep-th↗

arXiv1999

On magnetic catalysis in even-flavor QED3

In this paper, we discuss the role of an external magnetic field on the dynamically generated fermion mass in even-flavor QED in three space-time dimensions. Based on some reasonable approximations, we present analytic arguments on the fact that, for weak fields, the magnetically-induced mass increases quadratically with increasing field, while at strong fields one crosses over to a mass scaling logarithmically with the external field. We also confirm this type of scaling behavior through quenched lattice calculations using the non-compact version for the gauge field. Both the zero and finite temperature cases are examined. A preliminary study of the fermion condensate in the presence of magnetic flux tubes on the lattice is also included.

hep-ph↗

arXiv1998

Domain Formation in Finite-Time Quenches

We study the formation of domains in a continuous phase transition with a finite-temperature quench. The model treated is the $Φ^4$ theory in two spatial dimensions with global O(2) symmetry. We investigate this using real-time thermal field theory, following Boyanovsky and collaborators, and find that domain sizes appear to be smaller than those produced in an instantaneous quench in the tree-level approximation. We also propose that a more physical picture emerges by examining the two-point functions which do not involve any cutoff on the short wavelength Goldstone modes.

hep-ph↗

arXiv1997

Anomalous Defects and Their Quantized Transverse Conductivities

Using a description of defects in solids in terms of three-dimensional gravity, we study the propagation of electrons in the background of disclinations and screw dislocations. We study the situations where there are bound states that are effectively localized on the defect and hence can be described in terms of an effective 1+1 dimensional field theory for the low energy excitations. In the case of screw dislocations, we find that these excitations are chiral and can be described by an effective field theory of chiral fermions. Fermions of both chirality occur even for a given direction of the magnetic field. The ``net'' chirality of the system however is not always the same for a given direction of the magnetic field, but changes from one sign of the chirality through zero to the other sign as the Fermi momentum or the magnitude of the magnetic flux is varied. On coupling to an external electromagnetic field, the latter becomes anomalous, and predicts novel conduction properties for these materials.

hep-th↗

arXiv1997

Deconfinement Transition and Flux-String Models

Flux-string models can be used to study the deconfining phase transition. In this note, we study the models proposed by Patel. We also study the large N_c limits of Patel's model. To discuss the validity of the mean field theory results, the one-loop Coleman-Weinberg effective potential is calculated for N_c=3. We argue that the quantum corrections vanish at large N_c when the energy of the so-called baryonic vertices scale with N_c.

hep-th↗

arXiv1996

Edge Dynamics for BF Theories and Gravity

We discuss BF theories defined on manifolds with spatial boundaries. Variational arguments show that one needs to augment the usual action with a boundary term for specific types of boundary conditions. We also show how to use this procedure to find the boundary actions for theories of gravity with first order formulations. Possible connection with the membrane approach is also discussed.

hep-th↗

arXiv1996

Edge States and Entanglement Entropy

It is known that gauge fields defined on manifolds with spatial boundaries support states localized at the boundaries. In this paper, we demonstrate how coarse-graining over these states can lead to an entanglement entropy. In particular, we show that the entanglement entropy of the ground state for the quantum Hall effect on a disk exhibits an approximate ``area " law.

hep-th↗