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- Natalia Toro

**University of Waterloo**

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Particle physics today faces a conundrum: We have spectacularly precise "standard model" for the building blocks of matter and their interactions and symmetries, from the first minutes after the Big Bang to today. Yet this detailed understanding has sharpened some basic puzzles. Most of the matter in the Universe and even in our own Galaxy appears to be "dark" -- interacting much more weakly with ordinary matter than any known particles. In addition, the weakness of gravity compared to other forces and the large size of the Universe defy explanation in the Standard Model, arising instead as absurdly precise fine-tunings of parameters.

These puzzles teach us that for all its successes, the Standard Model is incomplete; my research aims to find new approaches to finding the missing pieces and putting them together.

Below are summarized three of my specific interests: understanding the implications of Large Hadron Collider data for physics beyond the Standard Model; probing new physics very weakly coupled to ordinary matter, and exploring the symmetry properties of Nature's long-range forces, electromagnetism and gravity.

The ATLAS and CMS experiments at the Large Hadron Collider are exploring particle interactions at higher energies and shorter distances than ever before. Not only have these experiments discovered the Higgs boson, the capstone of the Standard Model, but they are also searching for new physical phenomena at high energy which may help us to resolve the hierarchy problem. With collaborators, I have developed the "simplified model" approach to characterizing the results of these searches and explored new searches to find new-physics scenarios that escape more conventional missing-energy-based searches.

The strong cosmological evidence for dark matter teaches us that Nature's building blocks include some unfamiliar pieces, beyond those of the Standard Model. A natural question is whether Nature also makes use of other forces beyond those we have discovered? Such new forces can generically be very weakly coupled to ordinary matter, which explains why we might not have found them yet! With Bjorken, Essig, Schuster, and Wojtsekhowski, I have found several new approaches to search systematically for such forces -- or, more precisely, for the light particles that mediate them -- using existing collider data and new fixed-target experiments. The APEX and HPS (https://confluence.slac.stanford.edu/display/hpsg/Heavy+Photon+Search+Experiment) experiments at Jefferson Lab, expected to run in the next few years, represent the state of the art of this effort.

Similar techniques can be used to search for the dark matter itself, a possibility that I have explored with Izaguirre, Krnjaic, and Schuster; with the BDX collaboration, I am working to develop the first experiment to detect dark matter produced by an electron beam (arXiv:1406.3028).

Symmetry properties are an one of the main theoretical tools that we use to understand Nature, and the symmetries of special relativity (Poincare symmetry) are among the most important and well-tested, underlying the classification of particles by their "spin". Yet strikingly, the spin of massless particles is not yet fully understood. In several recent papers with P. Schuster, I have explored the possibility, first observed by Wigner in 1939, that massless particles can have multiple polarization states that transform under Poincare symmetry (just as massive particles' spins do), rather than the Poincare-invariant polarization states that arise in Maxwell electromagnetism or perturbative general relativity. We have found the first field theory action for such a "continuous spin" particle (CSP) (arXiv:1404.0675), as well as its generation to two-dimensional space. We have also found a consistent scattering matrix element for emission or absorption of CSPs, which in fact reproduces familiar massless-particle emission/absorption amplitudes in an appropriate limit. This suggests the possibility that massless "continuous-spin" particles could consistently mediate long-range forces. The ultimate goal of this work is to learn whether "continuous spin" generalizations of electromagnetism and gravity are theoretically consistent, and if they are, how they can be tested experimentally and what implications they may have for physics at long distances.

- Jan-July 2011 School of Natural Sciences, Institute for Advanced Study Member
- 2007-2010 Department of Physics/SITP, Stanford University Postdoctoral Scholar

- E. Izaguirre, G. Krnjaic, P. Schuster, N. Toro "Physics Motivation for a Pilot Dark Matter Search at Jefferson Laboratory", Physical Review D 90:014052, 2014, arXiv: 1403.6826 [hep-ph]
- New Electron Beam-Dump Experiments to Search for MeV to few-GeV Dark Matter. Eder Izaguirre, Gordan Krnjaic, Philip Schuster, Natalia Toro,Phys.Rev. D88 (2013) 114015, arXiv: 1307.6554
- A Gauge Field Theory of Continuous-Spin Particles, Philip Schuster, Natalia Toro, JHEP 1310 (2013) 061, arXiv: 1302.3225
- On the Theory of Continuous-Spin Particles: Wavefunctions and Soft-Factor Scattering Amplitudes. Philip Schuster, Natalia Toro, JHEP 1309 (2013) 104, arXiv: 1302.1198
- On the Theory of Continuous-Spin Particles: Helicity Correspondence in Radiation and Forces, Philip Schuster, Natalia Toro, JHEP 1309 (2013) 105, arXiv: 1302.1577
- N. Toro, I. Yavin "Multiphotons and Photon-Jets", PhysRevD.86.055005, arXiv: 1202.6377 [hep-ph].
- APEX Collaboration (S. Abrahamyan et al.), "Search for a New Gauge Boson in Electron-Nucleus Fixed-Target Scattering by the APEX Experiment", Phys.Rev.Lett. 107 (2011) 191804, arXiv: 1108.2750 [hep-ex]
- M. Lisanti, P. Schuster, M. Strassler, N. Toro "Study of LHC Searches for a Lepton and Many Jets", JHEP 1211 (2012) 081, arxiv:hep-ph/1107.5055
- T. Slatyer, N. Toro, N. Weiner "Sommerfeld-Enhanced Annihilation in Dark Matter Substructure: Consequences for Constraints on Cosmic-Ray Excesses", Accepted by Physical Review D, arXiv: 1107.3546 [hep-ph]
- LHC New Physics Working Group (D. Alves et al.), "Simplified Models for LHC New Physics Searches", J. Phys. G: Nucl. Part. Phys. 39 105005, arXiv: 1105.2838 [hep-ph].
- R. Essig, R. Harnik, J. Kaplan, and N. Toro, "Discovering New Light States at Neutrino Experiments", Physical Review D82:113008,2010, arXiv: 1008.0636 [hep-ph]
- R. Essig, P. Schuster, N. Toro, B. Wojtsekhowski "An Electron Fixed Target Experiment to Search for a New Vector Boson A' Decaying to e+e-", JHEP 1102:009,2011, arXiv: 1001.2557 [hep-ph]
- P. Schuster, N. Toro, I. Yavin, N. Weiner "High Energy Electron Signals from Dark Matter Annihilation in the Sun", Physical Review D82:115012,2010, arXiv: 0910.1839 [hep-ph]
- P. Schuster, N. Toro, I. Yavin "Terrestrial and Solar Limits on Long-Lived Particles in a Dark Sector", Physical Review D 81:016002,2010, arXiv: 0910.1602 [hep-ph]
- J. Bjorken, R. Essig, P. Schuster, N. Toro "New Fixed-Target Experiments to Search for Dark Gauge Forces", Physical Review D 80:075018,2009, arXiv: 0906.0580 [hep-ph]
- R. Essig, P. Schuster, N. Toro "Probing Dark Forces and Light Hidden Sectors at Low-Energy e+e- Colliders", Physical Review D 80:015003,2009, arXiv: 0903.3941 [hep-ph]
- The Heavy Photon Search Test Detector, Marco Battaglieri et al., arXiv: 1406.6115 [physics.ins-det].
- Dark matter search in a Beam-Dump eXperiment (BDX) at Jefferson Lab, BDX Collaboration (M. Battaglieri et al.). arXiv: 1406.3028 [physics.ins-det].
- A New Class of Particle in 2+1 Dimensions, Philip Schuster, Natalia Toro, arXiv: 1404.1076 [hep-th].
- A CSP Field Theory with Helicity Correspondence, Philip Schuster, Natalia Toro. arXiv: 1404.0675 [hep-th].
- Working Group Report: New Light Weakly Coupled Particles, Rouven Essig, John A. Jaros, William Wester, P. Hansson Adrian, et al., arXiv: 1311.0029 [hep-ph].
- On the Origin of Light Dark Matter Species, Rouven Essig, Jared Kaplan, Philip Schuster, Natalia Toro arXiv: 1004.0691 [hep-ph]
- MARMOSET: The Path from LHC Data to the New Standard Model via On-Shell Effective Theories Nima Arkani-Hamed, Bruce Knuteson, Stephen Mrenna, Philip Schuster, Jesse Thaler, Natalia Toro, Lian-Tao Wang, arXiv: hep-ph/0703088
- Snowmass 2014 Working Group Report: High Intensity Electron and Photon Beams By J.M. Byrd, J.W. Flanagan, G.S. Varner, et al. http://inspirehep.net/record/1297179

- ``Searching for Dark Forces'', DESY Theory Workshop Cosmology After Planck, invited plenary talk , September 25, 2014
- ``The Physics of Light Dark Matter'', DHF 2014 (Dark Matter, Hadron Physics and Nuclear Physics) invited plenary talk , September 24, 2014
- Lecture on Theory of Dark Sectors at SLAC Summer Institute August 14, 2014
- ``Searching for Dark Forces'' lecture at CERN/Fermilab Hadron Collider Physics Summer School August 20, 2014
- ``Spin and Long-Range Forces: The Unfinished Tale of the Last Massless Particle'', Theory Canada 9 invited plenary talk, , Waterloo ON June 12, 2014
- ``Searching for Dark Forces'', Harvard-Smithsonian Annual Conference on Theoretical Astrophysics, Debates on the Nature of Dark Matter, invited plenary talk , Cambridge MA May 21, 2014
- ``Spin And Long-Range Forces: Continuous-Spin Particles De-Mystified'', International Center for Theoretical Physics (ICTP) Trieste Seminar, May 27 2014.
- ``APEX Goals and Strategy'' and ``Future APEX'', APEX Collaboration Meeting April 2014
- Lecture on Dark Forces at Beijing Center for Future High Energy Physics, April 2014
- ``On Spin, Long-Range Forces, and Lorentz-Transformation of Helicity'', Caltech Theory Seminar Oct 21, 2013
- ``On Spin, Long-Range Forces, and Lorentz-Transformation of Helicity'', Stony Brook University Sep 19, 2013
- ``Probing Dark Forces at Accelerators'', International Meson-Nucleon (MeNu) Conference, invited plenary talk , Rome September 2013
- "Natural Supersymmetry", two lectures at Princeton Institute for Theoretical Physics summer school July 2013
- "Closing the Door on Weak-Scale SUSY", Fermilab LHC Physics Center May 2013
- "Dark Force Searches at Accelerators: the new GeV Frontier" Canadian Association of Physicists (CAP) Congress, Montreal QC May 2013
- "Status of the APEX Experiment", HPS Collaboration Meeting at Jefferson Lab, May 2013
- "GeV-Scale Dark Forces: Motivation and Status'', Snowmass Intensity Frontier Meeting, Argonne National Lab, IL April 2013
- "(Why) Is Helicity Lorentz-Invariant?" Columbia University, New York University, Stanford University, and Fermi National Laboratory (April-May 2013)
- "Dark Matter and Accelerators", Queens University Colloquium, March 2013
- "On the hunt for new fundamental forces", Western, Nov 2012
- Summary Talk, Dark Forces at Colliders, INFN Frascati, Oct 2012
- "Continuous-Spin Particles and Their Interactions", Harvard, Oct 2012
- "Dark Forces and the GeV Frontier", Conference on Intersections of Particle And Nuclear Physics (CIPANP) 2012, Plenary Talk
- "WIMP Dark Matter and Accelerator-Based Particle Physics", SNOLAB Grand Opening Workshop, May 2012
- "Theory and Status of New Sub-GeV Forces" (invited talk during mini-symposium on "Dark forces beneath the proton mass), American Physical Society April Meeting, 2012
- "New Forces at a GeV? Motivation, Search Prospects, and Status", MIT Nuclear and Particle Physics Colloquium May 2012
- "New Forces at a GeV: Search Prospects and a Window for Dark Matter", Wayne State University and University of Michigan, Feb 2012
- "LHC searches with a lepton and many jets", TRIUMF, Jan 2012
- "The A Prime Experiment (APEX): Search for a New Vector Boson A' Decaying to e+e-", Intensity Frontier Workshop, Nov 2011
- "Update on Dark Matter and Dark Forces", HPS Collaboration Meeting, Oct 2011
- "Simplified Models with MET at 1 fb-1", Workshop on Implications of LHC Results for TeV-Scale Physics, CERN, Aug 2011
- "The A-Prime Experiment (APEX) and Searches for New Vector Bosons at JLab", Workshop on Machine Aspects and Physics of the MESA Accelerator (Mainz Microtron Center), May 2011
- "SUSY with light stops at 35pb-1 and beyond ", Status of Higgs and BSM searches at the LHC (CERN), April 2011
- "Searching for Very Weakly-Coupled New Physics", CIFAR Cosmology and Gravity AGM 2011, April 2011
- "The A-Prime Experiment (APEX): Search for a New Vector Boson A' Decaying to e+e-", New Data from the Energy Frontier (Aspen), Feb 2011
- "Characterizing Early LHC Data in Simple Terms: Recent Developments", Dawn on the LHC Era (TRIUMF), Jan 2011
- "Simplified Models in Searches: An Illustration", Characterization of new physics at the LHC, II (CERN), Nov 2010
- "Topologies for Early LHC Searches", University of Toronto Seminar, Oct 2010
- PIRSA:14070027, Life as a Physicist, 2014-07-22, ISSYP 2014
- PIRSA:13110047, Spin and Long-Range Forces: The Unfinished Tale of the Last Massless Particle, 2013-11-13, Colloquium
- PIRSA:13030037, 12/13 PSI - Beyond the Standard Model Lecture 14, 2013-03-08, 12/13 PSI - Beyond the Standard Model
- PIRSA:13030036, 12/13 PSI - Beyond the Standard Model Lecture 13, 2013-03-07, 12/13 PSI - Beyond the Standard Model
- PIRSA:13030035, 12/13 PSI - Beyond the Standard Model Lecture 12, 2013-03-06, 12/13 PSI - Beyond the Standard Model
- PIRSA:13030034, 12/13 PSI - Beyond the Standard Model Lecture 11, 2013-03-05, 12/13 PSI - Beyond the Standard Model
- PIRSA:13030033, 12/13 PSI - Beyond the Standard Model Lecture 10, 2013-03-04, 12/13 PSI - Beyond the Standard Model
- PIRSA:13030030, 12/13 PSI - Beyond the Standard Model Lecture 9, 2013-03-01, 12/13 PSI - Beyond the Standard Model
- String/Particle Group Meeting "(Why) Is the Photon's Helicity Lorentz-Invariant?"
- PIRSA:13020098, 12/13 PSI - Beyond the Standard Model Lecture 8, 2013-02-28, 12/13 PSI - Beyond the Standard Model
- PIRSA:13020097, 12/13 PSI - Beyond the Standard Model Lecture 7, 2013-02-27, 12/13 PSI - Beyond the Standard Model
- PIRSA:13020096, 12/13 PSI - Beyond the Standard Model Lecture 6, 2013-02-26, 12/13 PSI - Beyond the Standard Model
- PIRSA:13020095, 12/13 PSI - Beyond the Standard Model Lecture 5, 2013-02-25, 12/13 PSI - Beyond the Standard Model
- PIRSA:13020092, 12/13 PSI - Beyond the Standard Model Lecture 4, 2013-02-22, 12/13 PSI - Beyond the Standard Model
- PIRSA:13020091, 12/13 PSI - Beyond the Standard Model Lecture 3, 2013-02-21, 12/13 PSI - Beyond the Standard Model
- PIRSA:13020090, 12/13 PSI - Beyond the Standard Model Lecture 2, 2013-02-20, 12/13 PSI - Beyond the Standard Model
- PIRSA:13020089, 12/13 PSI - Beyond the Standard Model Lecture 1, 2013-02-19, 12/13 PSI - Beyond the Standard Model
- PIRSA:12070007, From the Higgs to the Heavens: Physics of the Large Hadron Collider, 2012-07-26, ISSYP 2012
- PIRSA:12070002, Smash, Bang, Boom: Fundamental Physics at the LHC, 2012-07-11, Particle Physics
- PIRSA:12010018, Standard Model (Review) - Lecture 15, 2012-01-20, 11/12 PSI - Standard Model (Review)
- PIRSA:12010017, Standard Model (Review) - Lecture 14, 2012-01-19, 11/12 PSI - Standard Model (Review)
- PIRSA:12010016, Standard Model (Review) - Lecture 13, 2012-01-18, 11/12 PSI - Standard Model (Review)
- PIRSA:12010015, Standard Model (Review) - Lecture 12, 2012-01-17, 11/12 PSI - Standard Model (Review)
- PIRSA:12010014, Standard Model (Review) - Lecture 11, 2012-01-16, 11/12 PSI - Standard Model (Review)
- PIRSA:12010011, Standard Model (Review) - Lecture 10, 2012-01-13, 11/12 PSI - Standard Model (Review)
- PIRSA:12010010, Standard Model (Review) - Lecture 9, 2012-01-12, 11/12 PSI - Standard Model (Review)
- PIRSA:12010009, Standard Model (Review) - Lecture 8, 2012-01-11, 11/12 PSI - Standard Model (Review)
- PIRSA:12010008, Standard Model (Review) - Lecture 7, 2012-01-10, 11/12 PSI - Standard Model (Review)
- PIRSA:12010007, Standard Model (Review) - Lecture 6, 2012-01-09, 11/12 PSI - Standard Model (Review)
- PIRSA:12010004, Standard Model (Review) - Lecture 5, 2012-01-06, 11/12 PSI - Standard Model (Review)
- PIRSA:12010003, Standard Model (Review) - Lecture 4, 2012-01-05, 11/12 PSI - Standard Model (Review)
- PIRSA:12010002, Standard Model (Review) - Lecture 3, 2012-01-04, 11/12 PSI - Standard Model (Review)
- PIRSA:12010001, Standard Model (Review) - Lecture 2, 2012-01-03, 11/12 PSI - Standard Model (Review)
- PIRSA:12010000, Standard Model (Review) - Lecture 1, 2012-01-02, 11/12 PSI - Standard Model (Review)
- PIRSA:11120083, What the Higgs is going on at the LHC?, 2011-12-13, 11/12 PSI - Standard Model (Review)
- PIRSA:11120084, What the Higgs is going on at the LHC?, 2011-12-13, 11/12 PSI - Standard Model (Review)
- PIRSA:11090135, P.I. Chats: Faster-than-light neutrinos?, 2011-09-28, Black Hole Science Cafes
- PIRSA:11090139, Smash, Bang, Boom: Fundamental Physics at the LHC, 2011-09-18, Perimeter Institute Public Lecture Series
- PIRSA:11040037, Explorations in Particle Theory - Lecture 13, 2011-04-22, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040035, Explorations in Particle Theory - Lecture 11, 2011-04-22, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040036, Explorations in Particle Theory - Lecture 12, 2011-04-22, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040038, Explorations in Particle Theory - Lecture 14, 2011-04-22, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040032, Explorations in Particle Theory - Lecture 10, 2011-04-21, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040031, Explorations in Particle Theory - Lecture 9, 2011-04-20, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040030, Explorations in Particle Theory - Lecture 8, 2011-04-19, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040029, Explorations in Particle Theory - Lecture 7, 2011-04-18, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040028, Explorations in Particle Theory - Lecture 6, 2011-04-15, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040025, Explorations in Particle Theory - Lecture 5, 2011-04-08, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040024, Explorations in Particle Theory - Lecture 4, 2011-04-07, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040023, Explorations in Particle Theory - Lecture 3, 2011-04-06, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040022, Explorations in Particle Theory - Lecture 2, 2011-04-05, 10/11 PSI - Explorations In Particle Theory
- PIRSA:11040021, Explorations in Particle Theory - Lecture 1, 2011-04-04, 10/11 PSI - Explorations In Particle Theory
- PIRSA:10020033, Dark Matter: New Data and New Dynamics?, 2010-02-02, Cosmology & Gravitation
- PIRSA:09120098, Building Massless Tree Amplitudes without a Lagrangian, 2009-12-02, Particle Physics

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