Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
5 results
Search Results
Item Superconducting and Antiferromagnetic Phases of Space-Time(Hindawi Limited, 2017) Vaid, D.A correspondence between the SO5 theory of high-TC superconductivity and antiferromagnetism, put forward by Zhang and collaborators, and a theory of gravity arising from symmetry breaking of a SO5 gauge field is presented. A physical correspondence between the order parameters of the unified SC/AF theory and the generators of the gravitational gauge connection is conjectured. A preliminary identification of regions of geometry, in solutions of Einstein's equations describing charged-rotating black holes embedded in de Sitter space-time, with SC and AF phases is carried out. © 2017 Deepak Vaid.Item Greybody factor for an electrically charged regular-de Sitter black holes in d-dimensions(Springer Nature, 2025) Ali, M.S.; Naveena Kumara, A.N.; Hegde, K.; Ahmed Rizwan, C.L.A.; Punacha, S.; Ajith, K.M.We investigate the propagation of scalar fields in the gravitational background of higher-dimensional, electrically charged, regular de Sitter black holes. Using an approximate analytical approach, we derive expressions for the greybody factor for both minimally and non-minimally coupled scalar fields. In the low-energy regime, we find that the greybody factor remains non-zero for minimal coupling but vanishes for non-minimal coupling, indicating a significant influence of curvature coupling on the emission profile. Examining the greybody factor alongside the effective potential, we explore how particle parameters (the angular momentum number and the non-minimal coupling constant) and spacetime parameters (the dimension, the cosmological constant, and the non-linear charge parameter) affect particle emission. While non-minimal coupling and higher angular momentum modes generally suppress the greybody factor, the non-linear charge parameter enhances it. We then compute the Hawking radiation spectra for these black holes and observe that, despite the non-linear charge enhancing the greybody factor, both non-minimal coupling and the non-linear charge ultimately reduce the total energy emission rate. These results provide insights into how modifications to classical black hole solutions in higher dimensions, through the inclusion of non-linear electrodynamics, impact their quantum emission properties. © The Author(s) 2025.Item Orbit design for mitigating interstellar scattering effects in Earth-space very long baseline interferometry observations of Sagittarius A(EDP Sciences, 2025) Tamar, A.; Hudson, B.; Palumbo, D.The black hole Sagittarius A? (Sgr A?) is a prime target for next-generation Earth-space very long baseline interferometry missions such as the Black Hole Explorer (BHEX), which aims to probe baselines on the order of 20 G?. At these baselines, Sgr A? observations will be affected by the diffractive scattering effects from the interstellar medium (ISM). Therefore, we study how different parameter choices for turbulence in the ISM affect BHEX's observational capabilities to probe strong lensing features of Sgr A?. By using a simple geometric model of concentric Gaussian rings for Sgr A?'s photon ring signal and observing at 320 GHz, we find that the BHEX-ALMA baseline has the required sensitivity to observe Sgr A? for a broad range of values of the power-law index of density fluctuations in the ISM and the inner scale of turbulence. For other baselines with moderate sensitivities, a strong need for observations at shorter scales of 13.5 G? is identified. For this purpose, an orbit migration scheme is proposed. It is modeled using both chemical propulsion (CP)-based Hohmann transfers and electric propulsion (EP)-based orbit raising with the result that a CP-based transfer can be performed in a matter of hours, but with a significantly higher fuel requirement as compared to EP which, however, requires a transfer time of around 6 weeks. The consequences of these orbits for probing Sgr A?'s space-time are studied by quantifying the spatial resolution, temporal resolution, and angular sampling of the photon ring signal in the Fourier coverage of each of these orbits. We show that higher orbits isolate space-time features while sacrificing both signal lost to scattering and temporal resolution, but gaining greater access to the morphology of the photon ring. Thus, we find that orbits between the low Earth regime and the reference BHEX orbit can provide rich access to Sgr A?'s parameter space. © The Authors 2025.Item Euclidean thermodynamics and Lyapunov exponents of Einstein–Power–Yang–Mills AdS black holes(Springer Nature, 2025) Karthik, R.; Dillirajan, D.; Ajith, K.M.; Hegde, K.; Punacha, S.; Naveena Kumara, A.N.We study the thermodynamics of Einstein–Power–Yang–Mills AdS black holes via the Euclidean path integral method, incorporating appropriate boundary and counterterms. By analyzing unstable timelike and null circular geodesics, we demonstrate that their Lyapunov exponents reflect the thermodynamic phase structure obtained from the Euclidean action. Specifically, the small-large black hole phase transition, analogous to a van der Waals fluid, is signaled by a discontinuity in the Lyapunov exponent. Treating this discontinuity as an order parameter, we observe a universal critical exponent of 1/2, consistent with mean-field theory. These results extend previous insights from black hole spacetimes with Abelian charges to scenarios involving nonlinear, non-Abelian gauge fields, highlighting the interplay between black hole thermodynamics and chaotic dynamics. © The Author(s) 2025.Item Fundamental physics opportunities with future ground-based mm/sub-mm VLBI arrays(Springer Science and Business Media Deutschland GmbH, 2025) Ayzenberg, D.; Blackburn, L.; Brito, R.; Britzen, S.; Broderick, A.E.; Carballo-Rubio, R.; Cardoso, V.; Chael, A.; Chatterjee, K.; Chen, Y.; Cunha, P.V.P.; Davoudiasl, H.; Denton, P.B.; Doeleman, S.S.; Eichhorn, A.; Eubanks, M.; Fang, Y.; Foschi, A.; Fromm, C.M.; Galison, P.; Ghosh, S.G.; Gold, R.; Gurvits, L.I.; Hadar, S.; Held, A.; Houston, J.; Hu, Y.; Johnson, M.D.; Kocherlakota, P.; Natarajan, P.; Olivares Sánchez, H.; Palumbo, D.; Pesce, D.W.; Rajendran, S.; Roy, R.; Saurabh; Shao, L.; Tahura, S.; Tamar, A.; Tiede, P.; Vincent, F.H.; Visinelli, L.; Wang, Z.; Wielgus, M.; Xue, X.; Yakut, K.; Yang, H.; Younsi, Z.The Event Horizon Telescope (EHT) Collaboration recently published the first images of the supermassive black holes in the cores of the Messier 87 and Milky Way galaxies. These observations have provided a new means to study supermassive black holes and probe physical processes occurring in the strong-field regime. We review the prospects of future observations and theoretical studies of supermassive black hole systems. Current ground-based very-long-baseline interferometry (VLBI) arrays like the EHT and proposed future extensions like the next-generation Event Horizon Telescope will greatly enhance the capabilities of black-hole imaging interferometry. These enhancements will open up several previously inaccessible avenues of investigation, thereby providing important new insights into the properties of supermassive black holes and their environments. This review describes the current state of knowledge for five key science cases, summarising the unique challenges and opportunities for fundamental physics investigations that future mm/sub-mm VLBI developments will enable. © The Author(s) 2025.