QUANTUM FIELD THEORY
Much of my research is focused on understanding quantum field theory, from its foundations to its applications in particle physics. This is a very broad subject.
One specific aspect that has taken much of my attention over the past several years is the behavior of quantum field theories at long distances. In particular, I have been fasciated by the wauy field theories simplify at the longest distances. For example I have worked on

The S matrix
 How do we define an Smatrix in a theory with massless particles? This is a challenging question, but we are making progress. In A Finite SMatrix, we try to present a concise definition of an Smatrix valid in theories with massless particles. By exploiting factorization and simpliciations induced by dimensional regularization, this reformulation of the old idea of using dressed or coherent states becomes relatively simple.

Factorization:
 In HardSoftCollinear Factorization to All Orders we prove a complete factorization formula at the amplitude level in gauge theories.

Forward scattering
 In the forward scattering region, funny things happen. Some papers on forward scattering are
 In Infrared Finiteness and Forward Scattering, we clarify the sufficient and necessary conditions for infrared finitness of the Smatrix. This paper presents a stronger version of the famous KinoshitaLeeNauenberg theorem.

Other aspects of QFT that I have worked on are
 Nonpertubative effects. See
 Factorizationviolating effects. See
 Massive Gravity. See Precision calculations in the Standard Model. See
MACHINE LEARNING
Machine learning has been a part of particle physics for at least 40 years. Recently however, modern machine learning methods have fueled a revolution in the way collider physics is done.
Some machine learning projects I have worked on
 Interpretable, unsupervised learning. See Binary JUNIPR: an interpretable probabilistic model for discrimination and JUNIPR: a Framework for Unsupervised Machine Learning in Particle Physics.
 Using convolutional neural networks for jet physics. See Deep learning in color: towards automated quark/gluon jet discrimination
 Applying recurrent and recursive neural nets to classification problems in particle physics. See Jet Charge and Machine Learning
 Pilleup removal as a regression problem. See Pileup Mitigation with Machine Learning (PUMML) .
 Weaksupersion methods for datadriven analysis. See Learning to classify from impure samples with highdimensional data.
VACUUM STABILITY
One topic I have been interested in nonperturbative effects in quantum field theory and the stability of our universe.
 The universe, as described by the Standard Model is unstabile to the formation of bubbles of negative energy density through quantum tunneling.
 Wth my students Anders Andrassen, David Farhi and Will Frost, we figured out a way to caluclate this tunneling rate in quantum field theory, resolving a number of inconsistancies in previous treatments.
 Here is the resulting phase diagram, with experimental errors include in the ellipses and theoretical errors in the phase boundaries:
 The current lifetime is estimated to be T_{universe }= 10^{167} years.

Relevant papers

Scale Invariant Instantons and the Complete Lifetime of the Standard Model by Anders Andreassen, William Frost and Matthew D. Schwartz, Phys.Rev. D97 (2018) no.5, 056006.
 Resolves inconstancies in previous treatments and produces analytic formulas for the decay rate.
 Computes the decay rate to high precision
 Precision decay rate calculations in quantum field theory by Anders Andreassen, David Farhi, William Frost and Matthew D. Schwartz, Phys.Rev. D95 (2017) no.8, 085011

Direct Approach to Quantum Tunneling by Anders Andreassen, David Farhi, William Frost and Matthew D. Schwartz Phys.Rev.Lett. 117 (2016) no.23, 231601
 These two papers give a physics derivation of the formula for tunneling. A careful discussion is given of how to do saddle point integrals along Lefshiz thimbles and avoid stokes lines.
 Consistent Use of Effective Potentials by Anders Andreassen, William Frost and Matthew D. Schwartz, Phys.Rev. D91 (2015) no.1, 016009

Consistent Use of the Standard Model Effective Potential by Anders Andreassen, William Frost and Matthew D. Schwartz Phys.Rev.Lett. 113 (2014) no.24, 241801

These two papers explain how to use the standard model effective potential in a way that the results are gaugeinvariant orderbyorder in pertubation theory.

These two papers explain how to use the standard model effective potential in a way that the results are gaugeinvariant orderbyorder in pertubation theory.

Scale Invariant Instantons and the Complete Lifetime of the Standard Model by Anders Andreassen, William Frost and Matthew D. Schwartz, Phys.Rev. D97 (2018) no.5, 056006.
JET PHYSICS PROJECTS
Click on any of the following to see more information about some of my jet physics projects.
PAPERS
The full list of papers I have written can be found here.
My citations on inspires and on google scholar.
Here is a summary of some of my papers:

A Finite SMatrix by Hofie Hannesdottir and Matthew D Schwartz, June 2019
 We try to present a concise definition of an Smatrix valid in theories with massless particles. By exploiting factorization and simpliciations induced by dimensional regularization, this reformulation of the old idea of using dressed or coherent states becomes relatively simple.

JUNIPR: a Framework for Unsupervised Machine Learning in Particle Physics by Anders Andreassen, Ilya Feige, Chris Fryee and Matthew D. Schwartz. Eur.Phys.J. C79 (2019) no.2, 102
 An approach to unsupervised machine learning in particule physics is introduced which is both interpretable and powerful.

Consistent Use of the Standard Model Effective Potential by Anders Andreassen, William Frost and Matthew D. Schwartz. Phys. Rev. Lett., 113 (2014) no.24, 241801
 In this paper and this one, we show that the usual way by which vacuum stability is calculated in gaugedependent. We then present the first scheme which is gaugeinvariant orderbyorder in pertubation theory, and discuss its implications for the Standard Model.

HardSoftCollinear Factorization to All Orders by Ilya Feige and Matthew D. Schwartz
 This paper gives the first complete formulation and proof of a closed form, gaugeinvariant and regulatorindependent statement of softcollinear factorization to all orders in pertubation theory. Special cases include the universality of splitting functions and of soft currents.Phys.Rev. D90 (2014) no.10, 105020

Jet Charge at the LHC. by David Krohn, Tongyin Lin, Matthew D. Schwartz and Wouter Waalewijn. Phys. Rev. Lett. 110 (2013) 212001
 We show that the charge of an underlying parton can be extracted from the distributon of charged hadrons in a jet at the LHC. This lets us distinguish upquark jets from downquark jets, for example, on a statistical basis.

Precision Jet Substructure from Boosted Event Shapes. by Ilya Feige, Matthew D. Schwartz, Iain W. Stewart and Jesse Thaler, Phys.Rev.Lett. 109 (2012) 092001 .
 We perform the first analytic jet substructure calcualtion, of an observable called 2subjettiness. We also introduce a novel way of controlling for power corrections from hadronization, pileup and the underlying event.
 Qjets: A NonDeterministic Approach to TreeBased Jet Substructure by Stephen D. Ellis, Andrew Hornig, David Krohn,, Tuhin S. Roy and and Matthew D. Schwartz, Phys.Rev.Lett. 108 (2012) 1820031.

Resummation for W and Z production at large pT., by Thomas Becher, Christian Lorentzen and Matthew D. Schwartz, Phys.Rev.Lett. 108 (2012) 012001.
 Describes our caculation of the spectrum of W or Z bosons at the LHC when produced in associatino with a single jet. We compute this cross section with the help of SoftCollinear Effective Theory. This is currently the world's best calculation of this observable.

Quark and Gluon Tagging at the LHC. by Jason Gallicchio and Matthew D. Schwartz, Phys.Rev.Lett. 107 (2011) 172001.
 A comprehensive study on how to distinguish quark jets from gluon jets on an eventbyevent basis. These ideas are currently being explored by the ATLAS collaboration at the LHC.

Seeing in Color: Jet Superstructure. by Jason Gallicchio and Matthew D. Schwartz, Phys.Rev.Lett. 105 (2010) 022001.
 Introduces a variable called pull which can be used to measure color flow. This variable has since been measured by the D0 collaboration at the Tevatron in top events, and is currently being studied by the ATLAS collaboration at the LHC.

Top Tagging: A Method for Identifying Boosted Hadronically Decaying Top Quarks. by David E. Kaplan, Keith Rehermann, Matthew D. Schwartz, Brock Tweedi, Phys.Rev.Lett. 101 (2008) 142001.
 This was the first practical method to find topjets at hadron colliders, and one of the pioneering papers on jet substructure. This method is now known as the Hopkins Toptagger and is used by the CMS collaboratino at the LHC to search for topantitop resonances.

Constraining Light Colored Particles with Event Shapes. by David E. Kaplan and Matthew D. Schwartz.Phys.Rev.Lett. 101 (2008) 022002.
 Using precision event shape calculations (see also arXiv:0803) and data from LEP, this paper put a modelindependent lower bound of 54 GeV on the mass of the gluino. This was nearly an order of magnitude better than the previous bound of 6.2 GeV.

Improving Jet Distributions with Effective Field Theory. by Christian W. Bauer and Matthew D. Schwartz Phys.Rev.Lett. 97 (2006) 142001.
 This paper demonstrated that the parton shower picture used in Monte Carlo event generators, such as pythia, has a precise correspondance with the evolution of operators in SoftCollinear effective Theory

Infrared Lorentz violation and Slowly Instantaneous Electricity by Gia Dvali, Michele Papucci and Matthew D. Schwartz Phys.Rev.Lett. 94 (2005) 191602.
 This paper considered for the first time the physical consequences of a scenario in which the photon has a small Lorentzviolating mass. The bounds in this case were shown to be weaker than the Lorentzinvarariant case, because electromagnetic waves maintain their massless dispersion relation, so the strongest astrophysical constraints are avoided.

Unification and the Hierarchy from AdS5. by Lisa Randall and Matthew D. Schwartz, Phys.Rev.Lett. 88 (2002) 081801.
 This paper showed that unification is consistent with warped extra dimensions. To show this, a method for calculated loops in mixed positionmomentum space was developed.
TALKS
Here are some selected talks I have given
 Modern Machine Learning and the Large Hadron Collider, KIAS QQUC School on "AI in High Energy Pjhysics, July 24, 2020
 Jet Physics with Machine Learning, Chicagoland MiniWorkshop on LHC Run II Analsysis, Jan 15, 2019.
 Quark and Gluon Jet Discrimination, CERN, May 2017.
 Top Quark Mass Theory Developments, August 11, 2017
 Scale Setting: Lessons from SCET, Cambridge England, March 31, 2017.
 The Fate of the Universe, McGill, Montreal, Canada, October 11, 2017
 Tunneling in Quantum Field Theory, November 18, 2016
 Factorization Simplified, Loopfext XIII, City Tech, NY, June 19, 2014.
 Jet Cleansing, Mitigation of Pileup workshop, CERN, May 17, 2014.
 Why 100 TeV needs effective field theory, and vice versa, 100 TeV workshop, SLAC April 24, 2014.
 Nonglobal logarithms at 3,4 and 5 loops, symbols, and the Poincare disk, SCET XI workshop Munich, Germany, March 27, 2014.
 Jet Quantum Numbers, Using Jet Substructure Workshop, University of Oregon, April 23, 2013.
 Jet substructure and the Standard Model, ATLAS SM workshop, Harvard University, September 19, 2013.
 Amplitudes, Jets and AntideSitter space, University of Washington, Jan 8, 2013.
 Jets Lecture 1, Summer School Lecture, Cargese, France, August 2012.
 Jets Lecture 2, Summer School Lecture, Cargese, France, August 2012.
 The inside of a jet, UCSD, February 27, 2012.
 The Emergence of Jets at the Large Hadron Collider, Colloqium, Harvard University, Oct. 17, 2011.
 Multivariate Overview. Boost Conference, Princeton, NJ, Mar. 24, 2011.
 Jet Substructure and Multivariate Studies, CERN LHC Physics Day, Feb. 4, 2011.
 Demystifying Multivariate Searches and the Hunt for the Higgs, Seminar Johns Hopkins University, Sep 20, 2010.
 Seeing in Color: Jet Superstructure, Boost Conference, Seattle, Washington.
 Theoretical Particle Physics and the Hunt for the Next Standard Model, Wednesday Night Research Seminar, 2009.
 Precision Jet Physics at the LHC, IMPU Focus week, Nov. 10, 2009.
 TopTagging, SLAC seminar, 2009.
 Expectations for the LHC: Perspectives on the State of Particle Physics, Colloqium at Brandeis, Massachusetts, Mar. 31, 2009.