Gaurav Khanna (physicist)

Gaurav Khanna is an Indian-American black hole physicist, supercomputing innovator, academic and researcher. He is a Professor of Physics, and the founding Director of Research Computing and the Center for Computational Research at University of Rhode Island.[1][2]

Gaurav Khanna
Born
Chandigarh, India
NationalityAmerican
Occupation(s)Black hole physicist, supercomputing innovator, academic and researcher
TitleProfessor/Director
AwardsFellow of the American Physical Society
Academic background
EducationB. Tech., Electrical Engineering
Ph. D., Physics
Alma materIndian Institute of Technology, Kanpur
Pennsylvania State University
ThesisBinary Black Hole Coalescence: The Close Limit (2000)
Doctoral advisorJorge Pullin
Academic work
InstitutionsUniversity of Rhode Island
University of Massachusetts Dartmouth
Websitehttps://ccr.uri.edu https://web.uri.edu/gravity

Khanna has authored 100 publications. His work is focused in the areas of gravitational physics, computational physics, black holes, and quantum gravity. He has also made contributions in the area of black hole perturbation theory, loop quantum cosmology, singularities and gravitational wave science. He is the creator of the OpenMacGrid,[3] PlayStation 3 Gravity Grid,[4] and developer of open-source software for scientific computing for the Mac.[5] His work has been featured multiple times in newspapers and blogs, including The New York Times,[6] HPCWire,[7] Physics Buzz,[8] The Verge,[9] Forbes,[10][11][12] Wired,[13][14] Scientific American,[15] among others. He was named a Fellow of the American Physical Society in 2021.[16]

Khanna served as a guest editor for a 2018 special issue of IEEE CiSE with a focus on supercomputing.[17]

Education

Khanna studied at Indian Institute of Technology, Kanpur and completed his B. Tech degree in Electrical Engineering in 1995. He then moved to United States and earned his Ph. D. degree in Physics from Pennsylvania State University in 2000.[1]

Career

Beginning in September 2000, he held appointment as an Assistant Professor of Mathematics at Long Island University Southampton. He was then appointed by University of Massachusetts Dartmouth in 2003 as an Assistant Professor of Physics. He was promoted to Associate Professor in 2009, and to Full Professor of Physics in 2015. He is currently a Professor of Physics, and Director of Research Computing at the University of Rhode Island. He is the founding Director of Research Computing and the Center for Computational Research at the university.[1]

His career choices were heavily influenced by his father,[18] Dr. Mohinder P. Khanna, a well-known theoretical particle physicist in Panjab University, India.

Research

Khanna's work is focused in the areas of gravitational physics, computational physics, black holes, and quantum gravity. He has also worked on black hole perturbation theory, loop quantum cosmology, singularities and gravitational wave science.

Khanna is well-known for his research on late-time radiative "tails" in black hole spacetimes, also called "Price tails" named after Richard H. Price. With research collaborators, he was the first to discover the equivalent Price tails formula in the context of (astrophysical, i.e. rotating) Kerr black holes.[19][20] This formula was later placed on a rigorous mathematical foundation by Aretakis and others.[21]

In another work, Khanna has introduced a reduced-order surrogate model called "EMRISur1dq1e4" for gravitational waveforms. He trained this model on the basis of waveform data generated by point-particle black hole perturbation theory (ppBHPT), and evaluated its applicability for large-mass-ratio and comparable mass-ratio binaries finding that it was unreasonably effective.[22][23] In his paper published in 2016, he solved the inhomogeneous Teukolsky equation, and focused linearized gravitational waves emitted from a plunge into a nearly extremal Kerr black hole.[24]

Khanna has also studied black hole binaries, and demonstrated that coalescence of two black holes generates gravitational waves that provide information regarding the properties of those black holes and their binary configuration. He further described the ringdown form of final coalescence cycles as a superposition of quasinormal modes in context of the merged remnant black hole.[25]

Scientific Computing

In his study regarding scientific computation, Khanna introduced a strategy to scale complex hybrid systems, and also discussed a prototype tool which was built over the theorem prover PVS.[26] He also presented techniques that generate information in context of nonlinear dynamical systems, and discussed their applications in terms of automation for polynomial systems using algorithms from computational algebraic geometry. Furthermore, he suggested the application of formal qualitative abstraction approach in terms of nonlinear systems.[27]

Khanna also studied time-domain methods, and proposed their applications in computing gravitational waveforms and fluxes from extreme mass-ratio inspirals. He further explained the computation of low-m modes using the frequency-domain approach, and computation of high-m modes using the time-domain approach.[28]

In the area of scientific computing he is perhaps best known for his innovative work on low-cost supercomputing, making it more accessible to lesser-resourced universities and countries.[29][30][31]

Singularities in Classical and Quantum Black Holes

While studying singularities, Khanna highlighted the work of Jacobson and Sotiriou in the context of rotating black holes, and then described that if radiative effects can be neglected for the trajectories, that gives rise to naked singularities. He also discussed the significance of the conservative self-force in context of these orbits.[32] He also introduced a class of loop quantizations in terms of anisotropic models including the black hole interior, and studied the refinement process of lattice in context of dynamical changes of the volume.[33]

Khanna published a paper focused on the numerical study of Marolf-Ori singularity inside fast spinning black holes in terms of scalar field or vacuum gravitational perturbations.[34] He also studied how Cauchy horizon singularity inside perturbed Kerr black holes develops an instability that leads to its transformation into a curvature singularity.[35][36][37]

Extremal Black Holes and Mathematical Relativity

Khanna conducted a study in 2019 focused the transient scalar hair, and described the behavior of this nearly extreme black hole hair along with its measurement at future null infinity as a transient phenomenon.[38][39] Furthermore, he studied about the stability of extreme black holes against linearized gravitational perturbations, and argued that the divergence of ψ4 is a consequence of the choice of a fixed tetrad.[40][41]

His most recent work on gravitational hair in the context of extremal black holes received significant attention in the community and popular media.[42][43]

Awards and honors
  • 2021–present - Fellow of the American Physical Society (APS): For pioneering work in computational relativity, including innovative supercomputing techniques, computations of gravitational perturbations of black holes, gravitational waveforms from extreme mass-ratio binaries, classical black hole physics, and quantum gravity.[44]
  • 2021-2022 - Board member at OSHEAN.org[45]
  • 2011-2013 - Distinguished Scientist at HPC Research Inc.
  • 2008–present - Member of the Foundational Questions Institute[46]
  • 1997-1998 - Teaching Award, The Pennsylvania State University
  • 1995-2000 - Braddock, Duncan, Roberts, T. Das Fellowships, The Pennsylvania State University

Bibliography
  • Tiwari, A., & Khanna, G. (2002, March). Series of abstractions for hybrid automata. In International Workshop on Hybrid Systems: Computation and Control (pp. 465–478). Springer, Berlin, Heidelberg.
  • Tiwari, A., & Khanna, G. (2004, March). Nonlinear systems: Approximating reach sets. In International Workshop on Hybrid Systems: Computation and Control (pp. 600–614). Springer, Berlin, Heidelberg.
  • Bojowald, M., Cartin, D., & Khanna, G. (2007). Lattice refining loop quantum cosmology, anisotropic models, and stability. Physical Review D, 76(6), 064018.
  • Barausse, E., Cardoso, V., & Khanna, G. (2010). Test bodies and naked singularities: is the self-force the cosmic censor?. Physical review letters, 105(26), 261102.
  • Barausse, E., Cardoso, V., & Khanna, G. (2011). Testing the Cosmic Censorship Conjecture with point particles: the effect of radiation reaction and the self-force. Physical Review D, 84(10), 104006.

A more complete list is available on Khanna's Google Scholar page.[47]

Personal

Khanna has lived in Dartmouth, MA and also in Rhode Island with his wife, April and two daughters Sarah and Rachel.

References
  1. "URI Today From the Department of External Relations and Communications".
  2. "URI Today From the Department of External Relations and Communications".
  3. "OpenMacGrid for Mac OS X".
  4. "PlayStation 3 Gravity Grid".
  5. "Computation Tools :: C/Fortran".
  6. "That Old PlayStation Can Aid Science". The New York Times.
  7. "Alternative Supercomputing or How to Misuse a Computer".
  8. "Gargantua: The Science behind Interstellar's black hole".
  9. "The rise and fall of the PlayStation supercomputers".
  10. "Black Holes and Quantum Loops: More Than Just a Game". Forbes.
  11. "Modeling Black Holes With Sony Playstations: The Next Challenge". Forbes.
  12. "Black Holes Could Be Gateways After All". Forbes.
  13. "Astrophysicist Replaces Supercomputer with Eight PlayStation 3s".
  14. "Don't Tell Einstein, but Black Holes Might Have 'Hair'".
  15. "Is Time-Travel Possible?".
  16. "APS Fellow Archive". www.aps.org. Retrieved 2021-10-15.
  17. "Computing in Science and Engeering".
  18. "Hyperspace with Dr Gaurav Khanna".
  19. Zenginoğlu, Anıl; Khanna, Gaurav; Burko, Lior M. (2014). "Intermediate behavior of Kerr tails". General Relativity and Gravitation. 46 (3). doi:10.1007/s10714-014-1672-8. S2CID 254510095.
  20. Burko, Lior M.; Khanna, Gaurav (2014). "Mode coupling mechanism for late-time Kerr tails". Physical Review D. 89 (4). arXiv:1312.5247. doi:10.1103/PhysRevD.89.044037. S2CID 119253044.
  21. Angelopoulos, Yannis; Aretakis, Stefanos; Gajic, Dejan (2021). "Late-time tails and mode coupling of linear waves on Kerr spacetimes". arXiv:2102.11884 [gr-qc].
  22. Rifat, Nur E. M.; Field, Scott E.; Khanna, Gaurav; Varma, Vijay (2020). "Surrogate model for gravitational wave signals from comparable and large-mass-ratio black hole binaries". Physical Review D. 101 (8). doi:10.1103/PhysRevD.101.081502. S2CID 204837954.
  23. "New Black Hole Math Closes Cosmic Blind Spot".
  24. Burko, Lior M.; Khanna, Gaurav (2016). "Gravitational waves from a plunge into a nearly extremal Kerr black hole". Physical Review D. 94 (8). doi:10.1103/PhysRevD.94.084049. S2CID 118532069.
  25. Hughes, Scott A.; Apte, Anuj; Khanna, Gaurav; Lim, Halston (2019). "Learning about Black Hole Binaries from their Ringdown Spectra". Physical Review Letters. 123 (16): 161101. doi:10.1103/PhysRevLett.123.161101. hdl:1721.1/136506.2. PMID 31702329. S2CID 119437027.
  26. Tiwari, Ashish; Khanna, Gaurav (2002). "Series of Abstractions for Hybrid Automata". Hybrid Systems: Computation and Control. Lecture Notes in Computer Science. Vol. 2289. pp. 465–478. doi:10.1007/3-540-45873-5_36. ISBN 978-3-540-43321-7.
  27. Tiwari, Ashish; Khanna, Gaurav (2004). "Nonlinear Systems: Approximating Reach Sets". Hybrid Systems: Computation and Control. Lecture Notes in Computer Science. Vol. 2993. pp. 600–614. doi:10.1007/978-3-540-24743-2_40. ISBN 978-3-540-21259-1.
  28. Barton, Jonathan L.; Lazar, David J.; Kennefick, Daniel J.; Khanna, Gaurav; Burko, Lior M. (2008). "Computational efficiency of frequency- and time-domain calculations of extreme mass-ratio binaries: Equatorial orbits". Physical Review D. 78 (6). arXiv:0804.1075. doi:10.1103/PhysRevD.78.064042. S2CID 119198510.
  29. "The PlayStation powered super-computer".
  30. "SUPER POWER".
  31. "A supercomputer in the palm of your hand".
  32. Barausse, Enrico; Cardoso, Vitor; Khanna, Gaurav (2010). "Test Bodies and Naked Singularities: Is the Self-Force the Cosmic Censor?". Physical Review Letters. 105 (26): 261102. arXiv:1008.5159. doi:10.1103/PhysRevLett.105.261102. PMID 21231640. S2CID 38015433.
  33. Bojowald, Martin; Cartin, Daniel; Khanna, Gaurav (2007). "Lattice refining loop quantum cosmology, anisotropic models, and stability". Physical Review D. 76 (6). arXiv:0704.1137. doi:10.1103/PhysRevD.76.064018. S2CID 15404779.
  34. Burko, Lior M.; Khanna, Gaurav (2019). "Marolf-Ori singularity inside fast spinning black holes". Physical Review D. 99 (8). doi:10.1103/PhysRevD.99.081501. S2CID 119207858.
  35. Burko, Lior M.; Khanna, Gaurav; Zenginoǧlu, Anıl (2016). "Cauchy-horizon singularity inside perturbed Kerr black holes". Physical Review D. 93 (4). doi:10.1103/PhysRevD.93.041501. S2CID 14112487.
  36. "Maybe You Really Can Use Black Holes to Travel the Universe".
  37. "Black Holes Could Be Gateways After All". Forbes.
  38. Burko, Lior M.; Khanna, Gaurav; Sabharwal, Subir (2019). "Transient scalar hair for nearly extreme black holes". Physical Review Research. 1 (3). doi:10.1103/PhysRevResearch.1.033106. S2CID 174801218.
  39. "Nearly extreme black holes which attempt to regrow hair become bald again".
  40. Burko, Lior M.; Khanna, Gaurav (2018). "Linearized stability of extreme black holes". Physical Review D. 97 (6). doi:10.1103/PhysRevD.97.061502. S2CID 119464311.
  41. "Physicists Reconsider The Existence Of Extreme Black Holes Once Thought To Be Impossible". Forbes.
  42. Burko, Lior M.; Khanna, Gaurav; Sabharwal, Subir (2021). "Scalar and gravitational hair for extreme Kerr black holes". Physical Review D. 103 (2). arXiv:2005.07294. doi:10.1103/PhysRevD.103.L021502. S2CID 218665440.
  43. "In Violation of Einstein, Black Holes Might Have 'Hair'".
  44. "APS Fellows".
  45. "OSHEAN Team".
  46. "FQXi member listing".
  47. "Gaurav Khanna Google Scholar page".
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