Faculty & Staff

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Dr. Neil Christensen

Assistant Professor
  • CURRENT COURSES
  • PHY 112.Sec 001 Physics For Science And Engineering III
  • PHY 112.Sec 002 Physics For Science And Engineering III
  • PHY 290.Sec 016 Research In Physics
  • PHY 380.04Sec 001 Topics in Contemporary Physics: General Relativity
  • RESEARCH INTERESTS
  • Relativistic Quantum Mechanics

    Two of the great revolutions of physics in the 20th century were relativity and quantum mechanics. Combining special relativity and quantum mechanics produced relativistic quantum mechanics or, as it is better known, quantum field theory. As soon as it was created, quantum field theory predicted the existence of antiparticles which were discovered shortly afterwards. Almost a century later, quantum field theory has become a mature field and is the framework within which the Standard Model of particle physics is built. The Standard Model has been extremely successful at predicting and explaining almost all experiments to date, with the most recent success being the spectacular confirmation of the Higgs boson predicted by the Standard Model. Nevertheless, there are many outstanding problems that are not yet accounted for by the Standard Model. Among those are the fine-tuning problem of the Higgs boson, the properties of dark matter, the explanation for dark energy, a detailed understanding of the hierarchy of fermion masses and the abundance of matter but not antimatter in the universe. On the other hand, there are also fundamental problems with quantum field theory itself. It is not able to successfully accommodate gravity at very small scales and therefore appears to be incomplete. Furthermore, new methods of calculating the probability of particle scattering appear to be leading us towards a more fundamental theory of relativistic quantum mechanics opening up new areas of research into fundamental physics.

    My research deals with the exploration of these problems, both in the Standard Model and in the fundamental aspects of relativistic quantum mechanics itself. I use a combination of analytical and computational methods to explore these problems, sometimes emphasizing one and sometimes the other. Computational power continues to grow exponentially, following Moore's law, enabling ever more complex calculations. It is my belief that this will create one of the next revolutions in fundamental physics and therefore apply a good amount of my time in this direction. On the other hand, a new theoretical understanding of a problem can often far surpass even the most powerful computational model. So, I think it is important to approach fundamental physics from both directions and find the most advantageous route at a particular time. Here are a few of my recent publications:

    On Tree-Level Unitarity in Theories of Massive Spin-2 Bosons NDC and Stefanus (a graduate student at the University of PIttsburgh) We analyzed the scattering of massive spin-2 bosons in a theory with generic couplings in order to determine whether conservation of probability could be achieved at "tree-level". We wrote a computational code to calculate these complicated scattering amplitudes and analyze whether the probability conservation could be achieved in each case.

    A New Method for the Spin Determination of Dark Matter NDC and Daniel Salmon (an undergraduate at the University of Pittsburgh) We developed and simulated the use of a new analytical formula to determine the spin of dark matter at an electron-positron collider that is planned to be built in the near future. We wrote computational code and ran extensive simulations of particle collisions to show the efficacy of our new formula for determining the dark matter spin.

    FeynRules 2.0 - A Complete Toolbox for Tree-Level Phenomenology Adam Alloul, NDC, Celine Degrande, Claude Duhr and Benjamin Fuks We released version 2.0 of a computational physics code that we wrote that enables physicists to implement and study new theoretical models that attempt to explain the challenges with the Standard Model described above. This is an update of version 1.0 which was authored by myself and Claude Duhr (who was a graduate student at the time) and has been extremely popular in our field.

    A complete listing of my publications can be found on the inSpire website.
  • Ph D Theoretical Physics - 2006
  • Stony Brook University
  • Stony Brook, NY
  • Dissertation/Thesis topic: Studies of Dynamical Electroweak Symmetry Breaking
  • BA Mathematics - 2000
  • University of Utah
  • Salt Lake City, UT
  • AA - 1996
  • Snow College
  • Ephraim, UT
  • SELECTED PUBLICATIONS
  • “Diagonalizing the Hamiltonian of λφ4 Theory in 2 Space-Time Dimensions”, Neil Christensen, Computer Physics Communication 222, 167-188 (2018).
  • “A First Step Towards Effectively Nonperturbative Scattering Amplitudes in the Perturbative Regime,” N. Christensen, J. Henderson, S. Pinto and C. Russ, Journal of Physics Communication, Volume 2, Number 7 (2018).
  • “The Constructive Standard Model,” N. Christensen and B. Field, Physics Review D98 (2018) 016014.
  • "Spatial Evolution of Quantum Mechanical States," N. Christensen, J. Unger, S. Pinto, Q. Su and R. Grobe, Annals of Physics 389 (2018) 239-249.
  • “Handbook of LHC Higgs Cross Sections: 4. Deciphering the Nature of the Higgs Sector”, D. de Florian et. al. (N. Christensen), arXiv:1610.07922 [hep-ph] (461 citations as of Aug 2018.)
  • “Validity of One-Dimensional QED for a System with Spatial Symmetry ”, Q.Z. Lv, N.D. Christensen, Q. Su and R. Grobe, Physical Review A92, 052115 (2015).
  • “Spin and Chirality Effects in Antler-Topology Processes at High Energy e+e− Colliders”, Seong Youl Choi, Neil D. Christensen, Daniel Salmon, Xing Wang, European Physical Journal C75, 481 (2015).
  • “A New Method for the Spin Determination of Dark Matter”, Neil D. Christensen and Daniel Salmon, Physical Review D90, 014025 (2014).
  • “Determining the Dark Matter Particle Mass through Antler Topology Processes at Lepton Colliders”, Neil D. Christensen, Tao Han, Jeonghyeon Song and Stefanus, Physical Review D90, 114029 (2014).
  • “FeynRules 2.0 - A complete toolbox for tree-level phenomenology”, Adam Alloul, Neil Christensen, Celine Degrande, Claude Duhr, and Benjamin Fuks, Computer Physics Communication 185, 2250 (2014) (938 citations as of Aug 2018.)
  • “On Tree-Level Unitarity in Theories of Massive Spin-2 Bosons”, Neil D. Christensen and Stefanus, arXiv:1407.0438.
  • “CalcHEP 3.4 for collider physics within and beyond the Standard Model”, Alexander Belyaev, Neil D. Christensen and Alexander Pukhov, Computer Physics Communica- tion 184, 1729-1769 (2013) (557 citations as of Aug 2018.)
  • “Low-Mass Higgs Bosons in the NMSSM and Their LHC Implications”, Neil D. Christensen, Tao Han, Zhen Liu and Shufang Su, Journal of High Energy Physics 1308, 019 (2013) (64 citations as of Aug 2018.)
  • “Simulating spin-3/2 particles at colliders”, Neil D. Christensen, P. de Aquino, N. Deutschmann, C. Duhr, B. Fuks, C. Garcia-Cely, O. Mattelaer, K. Mawatari, B. Oexl, Y. Takaesu, European Physics Journal C73 (2013) 2580 (31 citations as of Aug 2018.)
  • “Computing for Perturbative QCD – A Snowmass White Paper”, Christian Bauer, Zvi Bern, Radja Boughezal, John Campbell, Neil Christensen, Lance Dixon, Thomas Gehrmann, Stefan Hoeche, Junichi Kanzaki, Alexander Mitov, Pavel Nadolsky, Fred- erick Olness, Michael Peskin, Frank Petriello, Stefano Pozzorini, laura Reina, Frank Siegert, Doreen Wackeroth, Jonathan Walsh, Ciaran Williams, and Markus Wobisch, arXiv:1309.3598.
  • “Discovering New Gauge Bosons of Electroweak Symmetry Breaking at LHC-8”, Chun Du, Hong-Jian He, Yu-Ping Kuang, Bin Zhang, Neil D. Christensen, R. Sekhar Chivukula and Elizabeth Simmons, Physics Review D 86, 095011 (2012).
  • “Discovery in Drell-Yan Processes at the LHC”, Cheng-Wei Chiang, Neil D. Chris- tensen, Gui-Jun Ding and Tao Han, Physics Review D 85, 015023 (2012) (33 citations as of Aug 2018.)
  • “Exploring compactified HEIDI models at the LHC”, Neil D. Christensen, Claude Duhr, Benjamin Fuks, Jurgen Reuter, Christian Speckner, arXiv:1204.6264.
  • “From Lagrangians to Events: Computer Tutorial at the MC4BSM-2012 Workshop”, Stefan Ask, Neil D. Christensen, Claude Duhr, Christophe Grojean, Stefan Hoeche, Konstantin Matchev, Olivier Mattelaer, Stephen Mrenna, Andreas Papaefstathiou, Myeonghun Park, Maxim Perelstein and Peter Skands, arXiv:1209.0297.
  • “Introducing an interface between FeynRules and WHIZARD”, Neil D. Christensen, Claude Duhr, Benjamin Fuks, Juergen Rueter and Christian Speckner, European Phys- ical Journal C 72, 1990 (2012) (63 citations as of Aug 2018.)
  • “Les Houches 2011: Physics at TeV Colliders New Physics Working Group Report”, G. Brooijmans, et al., arXiv:1203.1488 (84 citations as of Aug 2018.)
  • “MSSM Higgs Bosons at the LHC”, Neil Christensen, Tao Han and Shufang Su, Physics Review D 85, 115018 (2012) (133 citations as of Aug 2018.)
  • “Pair Production of MSSM Higgs Bosons in the Non-decoupling Region at the LHC”, Neil D. Christensen, Tao Han and Tong Li, Physics Review D 86, 074003 (2012) (26 citations as of Aug 2018.)
  • “SLHAplus: a library for implementing extensions of the standard model”, G. Be- langer, Neil D. Christensen, A. Pukhov, A. Semenov, Computer Physics Communica- tion 182, 763-774 (2011) (35 citations as of Aug 2018.)
  • “Testing CP Violation in ZZH Interactions at the LHC”, Neil D. Christensen, Tao Han, Yingchuan Li, Physics Letters B 693, 28-35 (2010) (36 citations as of Aug 2018.)
  • “W(L) W(L) Scattering in Higgsless Models: Identifying Better Effective Theo- ries”, Alexander S. Belyaev, R. Sekhar Chivukula, Neil D. Christensen, Hong-Jian He, Masafumi Kurachi, Elizabeth H. Simmons, Masaharu Tanabashi, Physics Review D 80, 055022 (2009) (16 citations as of Aug 2018.)
  • “A Comprehensive approach to new physics simulations”,NeilD.Christensen,Priscila de Aquino, Celine Degrande, Claude Duhr, Benjamin Fuks, Michel Herquet, Fabio Mal- toni, Steffen Schumann, European Physical Journal C 71, 1541 (2011) (102 citations as of Aug 2018.)
  • “The Top Triangle Moose: Combining Higgsless and Topcolor Mechanisms for Mass Generation”, R. Sekhar Chivukula, Neil D. Christensen, Baradhwaj Coleppa, Elizabeth H. Simmons, Physics Review D 80, 035011 (2009) (26 citations as of Dec 2016.)
  • “Z → b anti-b and Chiral Currents in Higgsless Models”, Tomohiro Abe, R.Sekhar Chivukula, Neil D. Christensen, Ken Hsieh, Shinya Matsuzaki, Elizabeth H. Simmons, Masaharu Tanabashi, Physics Review D 79, 075016 (2009) (15 citations as of Dec 2016.)
  • “FeynRules -Feynman rules made easy”, Neil D. Christensen and Claude Duhr, Computer Physics Communication 180, 1614-1641 (2009) (647 citations as of Aug 2018.)
  • “Low-energy effective theory, unitarity, and non-decoupling behavior in a model with heavy Higgs-triplet fields”, R. Sekhar Chivukula, Neil D. Christensen, Elizabeth H. Simmons, Physics Review D 77, 035001 (2008) (17 citations as of Aug 2018.)
  • “CERN LHC Signatures of New Gauge Bosons in the Minimal Higgsless Model”, Hong-Jian He, Yu-Ping Kuang, Yong-Hui Qi, Bin Zhang, Alexander Belyaev, R. Sekhar Chivukula, Neil D. Christensen, Alexander Pukhov and Elizabeth H. Simmons, Physics Review D 78, 031701 (2008) (101 citations as of Aug 2018.)
  • “Unitarity and Bounds on the Scale of Fermion Mass Generation”,R.SekharChivukula, Neil D. Christensen, Baradhwaj Coleppa and Elizabeth H. Simmons, Physics Review D 75, 053018 (2007) (8 citations as of Aug 2018).
  • “Extended technicolor models with two ETC groups”, Neil D. Christensen and Robert Shrock, Physics Review D 74, 015004 (2006) (10 citations as of Dec 2016.)
  • “Technifermion Representations and Precision Electroweak Constraints”, Neil D. Christensen and Robert Shrock, Physics Letters B 632, 92 (2006) (60 citations as of Aug 2018.)
  • “On the Unification of Gauge Symmetries in Theories with Dynamical Symmetry Breaking”, Neil D. Christensen and Robert Shrock, Physical Review D 72, 035013 (2005) (27 citations as of Aug 2018.)
  • “Implications of Dynamical Generation of Standard-Model Fermion Masses”, Neil D. Christensen and Robert Shrock, Physical Review Letters 94, 241801 (2005) (31 citations as of Aug 2018.)
  • “Flavor-Changing Processes in Extended Technicolor”, Thomas Appelquist, Neil D. Christensen, Maurizio Piai and Robert Shrock, Physical Review D70, 903010 (2004) (77 citations as of Aug 2018.)
  • PRESENTATIONS
  • “The Constructive SM,” N. Christensen, Phenomenology 2018 Symposium, University of Pittsburgh, Pittsburgh, PA, May 7, 2018.
  • “S-Matrix without Fields, Part I”, N. Christensen, Algebra Seminar, Department of Mathematics, Illinois State University, Normal, IL, October 12, 2017.
  • “Algebras in Particle Physics, Part II”, N. Christensen, Algebra Seminar, Department of Mathematics, Illinois State University, Normal, IL, October 5, 2017.
  • “A New Approach to Scattering Amplitudes”, N. Christensen, Phenomenology 2017 Symposium, University of Pittsburgh, Pittsburgh, PA, May 9, 2017.
  • “Algebras in Particle Physics, Part I”, N. Christensen, Algebra Seminar, Department of Mathematics, Illinois State University, Normal, IL, April 6, 2017.
  • “The S-Matrix without Fields,” N. Christensen, High Energy Physics Seminar, Department of Physics and Astronomy, Michigan State University, East Lansing, MI, February 15, 2017.
  • “Relativistic Quantum Mechanics and the Higgs Boson”, N. Christensen, Physics Seminar, Wichita State University, Wichita, KS, December 2, 2015.
  • “Relativistic Quantum Mechanics and the Higgs Boson”, N. Christensen, Physics Department Colloquium, Illinois State University, Normal, IL, September 16, 2014.
  • FUNDED GRANTS
  • Pre-tenure Faculty Initiative Grant
  • Illinois State University
  • 2016
  • New Faculty Initiative Grant
  • Illinois State University
  • 2015
  • Honorable Teaching Award
  • Society of Physics Students, Illinois State University
  • 2015
  • Summer Undergraduate Research Award for Independent Research
  • The Dietrich School of Arts and Sciences
  • 2013
  • Research Grant
  • Department of Energy
  • 2012
  • The Pennsylvania Space Grant Consortium Research Scholarship
  • 2012
  • Samuel P. Langley PITT-PACC Fellowship
  • Pittsburgh Particle physics, Astrophysics and Cosmology Center
  • 2011
  • LHC-TI Fellowship
  • National Science Foundation
  • 2009
  • Max Dresden Theoretical Physics Thesis Prize
  • Dept. of Physics, Stony Brook University
  • 2006
  • NSF TASI Grant
  • National Science Foundation
  • 2004
  • Peter B. Kahn Travel Fellowship
  • Dept. of Physics and Astronomy, Stony Brook University
  • 2004
  • H.B. Silsbee Award of Excellence
  • Dept. of Physics and Astronomy, Stony Brook University
  • 2002
  • Highest Score on the Ph.D. Qualifying Exam
  • Dept. of Physics and Astronomy, Stony Brook University
  • 2001
  • Dept. of Education GAANN Fellowship
  • Department of Education
  • 2000
  • Biesele Award
  • Dept. of Mathematics, University of Utah
  • 2000
  • Outstanding Undergraduate Student Award
  • Dept. of Physics and Astronomy, University of Utah
  • 2000
  • Kennecott Scholar
  • Kennecott Scholar Association, University of Utah
  • 1999
  • Kennecott Scholar
  • Kennecott Scholar Association, University of Utah
  • 1998