Gaurav Khanna (physicist)

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.

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.

His career choices were heavily influenced by his father,{{cite web|url=https://widdershinspodcast.podbean.com/e/s01e01-hyperspace-with-dr-gaurav-khanna/|title= Hyperspace with Dr Gaurav Khanna}} Dr. Mohinder P. Khanna, a well-known theoretical particle physicist in Panjab University, India.

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.{{cite journal|url=https://link.springer.com/article/10.1007/s10714-014-1672-8|title= Intermediate behavior of Kerr tails|year= 2014|doi= 10.1007/s10714-014-1672-8|last1= Zenginoğlu|first1= Anıl|last2= Khanna|first2= Gaurav|last3= Burko|first3= Lior M.|journal= General Relativity and Gravitation|volume= 46|issue= 3|page= 1672|s2cid= 254510095|arxiv= 1208.5839|bibcode= 2014GReGr..46.1672Z}}{{cite journal|url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.89.044037|title= Mode coupling mechanism for late-time Kerr tails|year= 2014|doi= 10.1103/PhysRevD.89.044037|last1= Burko|first1= Lior M.|last2= Khanna|first2= Gaurav|journal= Physical Review D|volume= 89|issue= 4|page= 044037|arxiv= 1312.5247|bibcode= 2014PhRvD..89d4037B|s2cid= 119253044}} This formula was later placed on a rigorous mathematical foundation by Aretakis and others.{{cite arXiv|title= Late-time tails and mode coupling of linear waves on Kerr spacetimes|eprint= 2102.11884|last1= Angelopoulos|first1= Yannis|last2= Aretakis|first2= Stefanos|last3= Gajic|first3= Dejan|year= 2021|class= gr-qc}}

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.{{cite journal|title= Surrogate model for gravitational wave signals from comparable and large-mass-ratio black hole binaries|year= 2020|doi= 10.1103/PhysRevD.101.081502|last1= Rifat|first1= Nur E. M.|last2= Field|first2= Scott E.|last3= Khanna|first3= Gaurav|last4= Varma|first4= Vijay|journal= Physical Review D|volume= 101|issue= 8|page= 081502|s2cid= 204837954|doi-access= free|arxiv= 1910.10473|bibcode= 2020PhRvD.101h1502R}}{{cite web|url=https://www.quantamagazine.org/new-black-hole-math-closes-cosmic-blind-spot-20210513|title= New Black Hole Math Closes Cosmic Blind Spot|date= 13 May 2021}} 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.{{cite journal|title= Gravitational waves from a plunge into a nearly extremal Kerr black hole|year= 2016|doi= 10.1103/PhysRevD.94.084049|last1= Burko|first1= Lior M.|last2= Khanna|first2= Gaurav|journal= Physical Review D|volume= 94|issue= 8|page= 084049|s2cid= 118532069|doi-access= free|arxiv= 1608.02244|bibcode= 2016PhRvD..94h4049B}}

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.{{cite journal|url=https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.161101|title= Learning about Black Hole Binaries from their Ringdown Spectra |year= 2019 |doi= 10.1103/PhysRevLett.123.161101 |last1= Hughes |first1= Scott A. |last2= Apte |first2= Anuj |last3= Khanna |first3= Gaurav |last4= Lim |first4= Halston |journal= Physical Review Letters |volume= 123 |issue= 16 |page= 161101 |pmid= 31702329 |arxiv= 1901.05900 |bibcode= 2019PhRvL.123p1101H |hdl= 1721.1/136506.2 |s2cid= 119437027 |hdl-access= free }}

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.{{cite book|chapter-url=https://link.springer.com/chapter/10.1007/3-540-45873-5_36|chapter= Series of Abstractions for Hybrid Automata |doi= 10.1007/3-540-45873-5_36 |title= Hybrid Systems: Computation and Control |series= Lecture Notes in Computer Science |year= 2002 |last1= Tiwari |first1= Ashish |last2= Khanna |first2= Gaurav |volume= 2289 |pages= 465–478 |isbn= 978-3-540-43321-7 }} 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.{{cite book|chapter-url=https://link.springer.com/chapter/10.1007/978-3-540-24743-2_40|chapter= Nonlinear Systems: Approximating Reach Sets|doi= 10.1007/978-3-540-24743-2_40|title= Hybrid Systems: Computation and Control|series= Lecture Notes in Computer Science|year= 2004|last1= Tiwari|first1= Ashish|last2= Khanna|first2= Gaurav|volume= 2993|pages= 600–614|isbn= 978-3-540-21259-1|s2cid= 4374220}}

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.{{cite journal|url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.78.064042|title= Computational efficiency of frequency- and time-domain calculations of extreme mass-ratio binaries: Equatorial orbits|year= 2008|doi= 10.1103/PhysRevD.78.064042|last1= Barton|first1= Jonathan L.|last2= Lazar|first2= David J.|last3= Kennefick|first3= Daniel J.|last4= Khanna|first4= Gaurav|last5= Burko|first5= Lior M.|journal= Physical Review D|volume= 78|issue= 6|page= 064042|arxiv= 0804.1075|bibcode= 2008PhRvD..78f4042B|s2cid= 119198510}}

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.{{cite news|url=https://www.bbc.com/news/technology-11168150|title=The PlayStation powered super-computer|work=BBC News |date=4 September 2010 }}{{cite web|url=https://www.southcoasttoday.com/article/20160326/news/160329508|title=SUPER POWER}}{{cite web|url=https://www.umassd.edu/news/2015/a-supercomputer-in-the-palm-of-your-hand.html|title=A supercomputer in the palm of your hand}}

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.{{cite journal|url=https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.261102|title= Test Bodies and Naked Singularities: Is the Self-Force the Cosmic Censor? |year= 2010 |doi= 10.1103/PhysRevLett.105.261102 |last1= Barausse |first1= Enrico |last2= Cardoso |first2= Vitor |last3= Khanna |first3= Gaurav |journal= Physical Review Letters |volume= 105 |issue= 26 |page= 261102 |pmid= 21231640 |arxiv= 1008.5159 |bibcode= 2010PhRvL.105z1102B |s2cid= 38015433 }} 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.{{cite journal|url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.76.064018|title= Lattice refining loop quantum cosmology, anisotropic models, and stability|year= 2007|doi= 10.1103/PhysRevD.76.064018|last1= Bojowald|first1= Martin|last2= Cartin|first2= Daniel|last3= Khanna|first3= Gaurav|journal= Physical Review D|volume= 76|issue= 6|page= 064018|arxiv= 0704.1137|bibcode= 2007PhRvD..76f4018B|s2cid= 15404779}}

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.{{cite journal|title= Marolf-Ori singularity inside fast spinning black holes |year= 2019 |doi= 10.1103/PhysRevD.99.081501 |last1= Burko |first1= Lior M. |last2= Khanna |first2= Gaurav |journal= Physical Review D |volume= 99 |issue= 8 |page= 081501 |s2cid= 119207858 |doi-access= free |arxiv= 1901.03413 |bibcode= 2019PhRvD..99h1501B }} He also studied how Cauchy horizon singularity inside perturbed Kerr black holes develops an instability that leads to its transformation into a curvature singularity.{{cite journal|title=Cauchy-horizon singularity inside perturbed Kerr black holes|year=2016 |doi=10.1103/PhysRevD.93.041501 |last1=Burko |first1=Lior M. |last2=Khanna |first2=Gaurav |last3=Zenginoǧlu |first3=Anıl |journal=Physical Review D |volume=93 |issue=4 |page=041501 |s2cid=14112487 |doi-access=free |arxiv=1601.05120 |bibcode=2016PhRvD..93d1501B }}{{cite web|url=https://www.discovermagazine.com/the-sciences/maybe-you-really-can-use-black-holes-to-travel-the-universe|title=Maybe You Really Can Use Black Holes to Travel the Universe}}{{cite web|url=https://www.forbes.com/sites/johnfarrell/2016/02/10/black-holes-could-be-gateways-after-all/?sh=29f304b49386|title=Black Holes Could Be Gateways After All|website=Forbes }}

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.{{cite journal|title= Transient scalar hair for nearly extreme black holes|year= 2019|doi= 10.1103/PhysRevResearch.1.033106|last1= Burko|first1= Lior M.|last2= Khanna|first2= Gaurav|last3= Sabharwal|first3= Subir|journal= Physical Review Research|volume= 1|issue= 3|page= 033106|s2cid= 174801218|doi-access= free|arxiv= 1906.03116|bibcode= 2019PhRvR...1c3106B}}{{cite web|url=https://phys.org/news/2019-11-extreme-black-holes-regrow-hair.html|title=Nearly extreme black holes which attempt to regrow hair become bald again}} 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.{{cite journal|title= Linearized stability of extreme black holes|year= 2018|doi= 10.1103/PhysRevD.97.061502|last1= Burko|first1= Lior M.|last2= Khanna|first2= Gaurav|journal= Physical Review D|volume= 97|issue= 6|page= 061502|s2cid= 119464311|doi-access= free|arxiv= 1709.10155|bibcode= 2018PhRvD..97f1502B}}{{cite web|url=https://www.forbes.com/sites/johnfarrell/2018/05/27/physicists-reconsider-the-existence-of-extreme-black-holes-once-thought-to-be-impossible/?sh=4528f6065b36|title=Physicists Reconsider The Existence Of Extreme Black Holes Once Thought To Be Impossible|website=Forbes }}

His most recent work on gravitational hair in the context of extremal black holes received significant attention in the community and popular media.{{cite journal|url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.103.L021502|title=Scalar and gravitational hair for extreme Kerr black holes|year=2021 |doi=10.1103/PhysRevD.103.L021502 |last1=Burko |first1=Lior M. |last2=Khanna |first2=Gaurav |last3=Sabharwal |first3=Subir |journal=Physical Review D |volume=103 |issue=2 |arxiv=2005.07294 |bibcode=2021PhRvD.103b1502B |s2cid=218665440 }}{{cite web|url=https://www.quantamagazine.org/in-violation-of-einstein-black-holes-might-have-hair-20210211/|title=In Violation of Einstein, Black Holes Might Have 'Hair'|date=11 February 2021 }}

• 2024 - Rhode Island Monthly Tech10 awardee{{cite web|url=https://www.rimonthly.com/our-2024-tech10-and-next-tech-generation-award-recipients|title= Tech10 Awardees}}
• 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.{{cite web|url=https://www.aps.org/programs/honors/fellowships/archive-all.cfm|title= APS Fellows}}
• 2021-2022 - Board member at OSHEAN.org{{cite web|url=https://www.oshean.org/page/team|title= OSHEAN Team|date= 17 August 2024}}
• 2011-2013 - Distinguished Scientist at HPC Research Inc.{{citation needed|date=March 2021}}
• 2008–present - Member of the Foundational Questions Institute{{cite web|url=https://fqxi.org/members|title= FQXi member listing}}
• 1997-1998 - Teaching Award, The Pennsylvania State University{{citation needed|date=March 2021}}
• 1995-2000 - Braddock, Duncan, Roberts, T. Das Fellowships, The Pennsylvania State University{{citation needed|date=March 2021}}

• 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.{{cite web|url=https://scholar.google.com/citations?user=382Ttr0AAAAJ&hl=en|title= Gaurav Khanna Google Scholar page}}

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

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Category:Living people

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Category:Indian emigrants to the United States

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Category:IIT Kanpur alumni

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Category:Fellows of the American Physical Society