Paul Langacker
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Paul Langacker
Theoretical Elementary Particle Physics
Born 1946
B.S. M.I.T. (1968)
Ph.D. University of California at Berkeley (1972)
Emeritus Professor of Physics (University of Pennsylvania)
Email: pgl@upenn.edu
In the last 50 years, there has been a tremendous advance in our understanding
of the elementary
particles and their interactions. We now have a mathematically consistent theory
of the strong,
electromagnetic, and weak interactionsthe standard modelmost aspects of which have been
successfully tested in detail at colliders, accelerators, and nonaccelerator experiments.
It also provides a successful framework and has been strongly constrained by many observations
in cosmology and astrophysics. The standard model
is almost certainly an approximately correct description of Nature down to a distance scale 1/1000^{th} the size of the atomic nucleus.
However,
nobody believes that the standard model is the ultimate theoryit is too
complicated and arbitrary and leaves too many questions unanswered.
Therefore, most current activity is directed towards discovering the new physics
which must
underly the standard model. One approach, exemplified by superstring theories,
is to try to
develop a "theory of everything". However, promising ideas
involve incredibly
short distance scales, and it is challenging to make contact with accessible energies at
present. Another
direction is to build larger
accelerators to
directly search for new particles and interactions, and much attention is focussed on the Large Hadron Collider (LHC), which is currently starting up. An important
complementary
approach is to subject the standard model to diverse highprecision tests to
determine how good it
is and where it might break down. Finally, there are probes from the important overlaps of particle physics with cosmology and astrophysics. All of these approaches are likely to be essential in understanding what underlies the standard model. It is my hope that within the coming decades we will be able to combine progress in these directions to develop and test the essential aspects of a new standard model of everything, which incorporates the microscopic interactions, quantum gravity, and the origin of the Universe, and describes Nature down to the Planck scale, ∼ 10^{−33} cm.
My research has been directed towards
the theoretical interpretation of the various experimental and observational probes, and
the phenomenological implications of fundamental theoriesi.e., in connecting theory and experiment.
For over three decades much of my effort has involved the interpretation of
highprecision tests of the standard model,
and has exploited the fact that the global analysis of many experiments often
yields more
information than the individual experiments alone. Such global analyses
involve collecting
the data, deriving uniform and accurate theoretical formulas to interpret it,
developing
expressions for the possible effects of new physics, and fitting the data to
search for or set limits
on new physics.
A related effort has been a study of the existing constraints, physics and cosmological implications, and
the discovery/diagnostic potential at present and future colliders for classes of extensions of the standard model and its minimal supersymmetric extension,
especially those types that frequently occur as theorymotivated remnants of specific superstring constructions. These include additional possible gauge bosons
(especially heavy Z' s), extended Higgs/neutralino
sectors, and exotic fermions (with nonstandard weak interactions).
Other recent work has involved possibilities for studying CP violation at the LHC and new methods for mediating supersymmetry breaking between the ordinary and a
quasihidden sector.
Other phenomenological areas in which I worked extensively in the past include
chiral symmetry breaking and its consequences, and theoretical
models for neutrino mass and their laboratory, astrophysical,
and cosmological implications.
In terms of more fundamental theory,
I have had a long standing interest in
grand unified theories and their consequences. More recently, I have become
interested in the phenomenological consequences of semirealistic
superstring compactifications.
My collaborators and I have examined classes of string constructions and specific models, with emphasis on their consequences for the masses of the quarks and charged leptons, standard and nonstandard mechanisms for generating small neutrino masses, and the most likely
types of observable new physics at the
TeV scale.
I have written an advanced textbook,
The Standard Model and Beyond
(CRC press, December 2009),
a second edition (June, 2017), and a
colloquiumlevel monograph Can the Laws of Physics be Unified?
(Princeton University Press, March 2017).
Professional Activities
 Member/Visitor, Institute for Advanced Study, Princeton, 20062019.
 Senior Scientist/Lecturer, Princeton University, 20112018.
 Coconvenor, Workshop on Probing the TeV Scale and Beyond,
Mainz Institute for Theoretical Physics, July 2014.
 Editorial Committee, Annual Reviews of Nuclear and Particle Science, 20122015.
 Coconvener, Workshop on
First Two Years of the LHC, Kavli Institute for Theoretical Physics in China,
Beijing, Summer, 2012.
 Coconvener, Workshop on
Strings at the LHC and in the Early Universe, Kavli Institute for Theoretical Physics,
Santa Barbara, Spring, 2010.
 Associate Editor, Reviews of Modern Physics, 20072013.
 Member, organizing committee for International Conference on
High Energy Physics, Philadelphia, 2008 (ICHEP2008).
 Member, Organizing Committee, String Phenomenology, 2008,
Philadelphia, May, 2008.
 Chair, Steering Committee for the LHC Theory Initiative, 20062015.
 Member, HEPAP subpanel on the University Grants Program, 20062007.
 LangackerFest, 60th birthday celebration, University of Pennsylvania, 2006
 Henry Primakoff Lecturer, University of Pennsylvania, 2006
 Fermilab Frontier Fellow, 2005
 Member, High Energy Physics Advisory Panel (HEPAP) of the Department of
Energy and National Science Foundation (20022005).
 Coorganizer, Aspen Winter Conference
At the Frontiers of Particle Physics, 2003.
 Keck Distinguished Visiting Professor, Institute for Advanced Study, 2001
 Chair, Department of Physics and Astronomy, University of Pennsylvania (1/966/01)
 William Smith Term Professor of Physics, University of Pennsylvania (7/936/98)
 Fellow, American Physical Society and AAAS
 Divisional Associate Editor, Physical Review Letters (19982004)
 Member, Particle Data Group (19982016)
 Member, Steering Committee for SUSY conferences, 1998 .
 Cochair, SUSY 97, Philadelphia (1997)
 Coconvener, Workshop on
Unification: From the Weak Scale to the Planck Scale,
Institute for Theoretical Physics,
Santa Barbara (1995)
 Editorial Board, Physical Review (198688, 199193)
 Executive Committee, Division of Particles and Fields of the American
Physical Society (19891991)
 Scientific Director, Theoretical Advanced Study Institute (TASI)
(1990 and 1998)
 Alexander von Humboldt Prize (1988)
Selected Publications
 Light Quark Mass Spectrum in Quantum Chromodynamics (with H.
Pagels), Phys. Rev. D19, 20702079 (1979).
 Magnetic Monopoles in Grand Unified Theories (with S.Y. Pi),
Phys. Rev. Lett. 45, 14 (1980).
 Grand Unified Theories and Proton Decay, Physics Reports
72, 185385 (1981).
 A Comprehensive Analysis of Data Pertaining to the Weak
Neutral Current and the Intermediate Vector Boson Masses (with
U. Amaldi, A. Böhm, L. S. Durkin, A. K. Mann, W. J. Marciano,
A. Sirlin, and H. H. Williams), Phys. Rev. D36, 1385 (1987).

Unification of Two Fundamental Forces (with A. K. Mann),
Physics Today 42, #12, p. 22 (1989).

Implications of Recent M_{W,Z} and NeutralCurrent Measurements for the
TopQuark Mass, Phys. Rev. Lett. 63, 1920 (1989).

On the Cosmological Production of Light Sterile Neutrinos,
UPR0401T.
paper, or
figure.

High Precision Electroweak Experiments: A Global Search for
New Physics Beyond the Standard Model (with M. Luo and A. K. Mann),
Rev. Mod. Phys. 64, 87 (1992).

Implications of Precision Electroweak Experiments for
m_{t}, rho _{0}, sin^{2}theta _{W} , and Grand Unification (with M. Luo),
Phys. Rev. D44, 817 (1991).

W and Z Physics, in TeV Physics, ed. T. Huang et al.,
(Gordon and Breach, Philadelphia, 1991), p. 53.

Editor (with M. Cvetic) of Testing the Standard Model
(Proceedings of TASI90), (World, Singapore, 1991).

Constraints on Additional Z Bosons (with M. Luo), Phys. Rev. D45, 278 (1992).

Uncertainties in Coupling Constant Unification (with N. Polonsky),
Phys. Rev. D47, 4028 (1993),
hepph/9210235.

Five Phases of Weak Neutral Current Experiments From the
Perspective of a Theorist, Discovery of Weak Neutral
Currents: The Weak Interaction Before and After, ed.
A. K. Mann and D. B. Cline, AIP Conference Proceedings 300
(AIP, New York, 1994), p. 289,
hepph/9305255.

Astrophysical Solutions are Incompatible with the
Solar Neutrino Data (with S. Bludman and N. Hata), Phys. Rev. D49, 3622 (1994),
hepph/9306212.

Editor of Precision Tests of the Standard Electroweak Model,
(World, Singapore, 1995), and articles on pp 1, 15, 883.

The Strong Coupling, Unification, and Recent Data (with N. Polonsky),
Phys. Rev. D52, 3081 (1995),
hepph/9503214.

Big Bang Nucleosynthesis in Crisis (with
N. Hata, R. Scherrer, G. Steigman, D. Thomas, T. Walker, and
S. Bludman), Phys. Rev. Lett. 75, 3977 (1995),
hepph/9505319.

Implications of Abelian Extended Gauge Structures From String Models
(with M. Cvetic), Phys. Rev. D54, 3570 (1996),
hepph/9511378.

Phase Transitions and Vacuum Tunneling Into Charge
and Color Breaking Minima in the MSSM (with A. Kusenko and
G. Segre), Phys. Rev. D54, 5824 (1996),
hepph/9602414.

Electroweak Breaking and the Mu Problem in Supergravity Models with an
Additional U(1) (with M. Cvetic, D. A. Demir, J. R. Espinosa,
and L. Everett),
Phys. Rev. D56, 2861 (1997),
hepph/9703317.

Solutions to Solar Neutrino Anomaly (with N. Hata), Phys. Rev. D56, 6107 (1997),
hepph/9705339.

Z' Physics and Supersymmetry
(with M. Cvetic), in
Perspectives on Supersymmetry, ed. G. Kane (World, Singapore, 1998),
p312,
hepph/9707451.
Revised version in the reprinted edition, 2010.

Classification of Flat Directions in Perturbative Heterotic
Superstring Vacua with Anomalous U(1)
(with G. Cleaver, M. Cvetic, J. R. Espinosa, and L. Everett),
Nucl. Phys. B525, 3 (1998),
hepth/9711178.
 Editor (with M. Cvetic),
SUSY '97,
Proceedings of the Fifth International
Conference on Supersymmetries in Physics,
Nucl. Phys. B (Proc. Suppl.) 62 (1998)
(North Holland, 1998).

Physics Implications of Flat Directions in Free Fermionic
Superstring Models I:
Mass Spectrum and Couplings (with
G. Cleaver, M. Cvetic, J. R. Espinosa, L. Everett, and J. Wang),
Phys. Rev. D59, 055005 (1999),
hepph/9807479.

Physics Implications of Flat Directions in
Free Fermionic Superstring Models II:
Renormalization Group Analysis (with
G. Cleaver, M. Cvetic, J. R. Espinosa, L. Everett, and J. Wang),
Phys. Rev. D59, 115002 (1999),
hepph/9811355.

Flavor Changing Effects in
Theories with a Heavy Z' Boson with Family NonUniversal
Couplings (with M. Pluemacher),
Phys. Rev. D62, 013006 (2000),
hepph/0001204.
 Editor,
Neutrinos in Physics and Astrophysics:
From 10^{−33} to 10^{+28} cm,
(Proceedings of TASI98), (World, Singapore, 2000).

Implications of gauge unification for
time variation of the fine structure constant
(with G. Segre and M. J. Strassler),
Phys. Lett. B 528, 121 (2002),
hepph/0112233.

The Z−Z' Mass Hierarchy in a Supersymmetric
Model with a Secluded U(1)' Breaking Sector
(with J. Erler and T. Li), Phys. Rev. D 66, 015002 (2002),
hepph/0205001.

Phenomenology of A ThreeFamily Standardlike String Model
(with M. Cvetic and G. Shiu), Phys. Rev. D 66, 066004 (2002),
hepph/0205252.

Nogo for detecting CP violation via neutrinoless double beta decay
(with V. Barger, S. L. Glashow, and D. Marfatia),
Phys. Lett. B 540, 247 (2002),
hepph/0205290.

Primordial nucleosynthesis constraints on Z' properties
(with V. Barger and H. S. Lee),
Phys. Rev. D 67, 075009 (2003),
hepph/0302066.

Dynamical supersymmetry breaking in
standardlike models with intersecting D6branes
(with M. Cvetic and J. Wang),
Phys. Rev. D 68, 046002 (2003),
hepth/0303208.

Electroweak baryogenesis in a supersymmetric U(1)' model,
(with J. Kang, T. j. Li, and T. Liu),
Phys. Rev. Lett. 94, 061801 (2005),
hepph/0402086.

The Higgs sector in a U(1)' extension of the MSSM,
(with T. Han and B. McElrath),
Phys. Rev. D 70, 115006 (2004),
hepph/0405244.

D6brane splitting on type IIA orientifolds,
(with M. Cvetic, T. J. Li, and T. Liu),
Nucl. Phys. B 709, 241 (2005),
hepth/0407178.

Neutrino physics (theory),
ICHEP 2004, ed. H. Chen et al., (World Singapore, 2005), p198,
hepph/0411116.

Neutrino masses in supersymmetric SU(3)_{C} ×SU(2)_{L} ×U(1)_{Y} ×U(1)' models,
(with J. H. Kang and T. J. Li,),
Phys. Rev. D 71, 015012 (2005),
hepph/0411404.

Z' discovery limits for supersymmetric E(6) models,
(with J. Kang),
Phys. Rev. D 71, 035014 (2005),
hepph/0412190.

Toward realistic intersecting Dbrane models,
(with R. Blumenhagen, M. Cvetic, and G. Shiu),
ARNPS 55, 71 (2005),
hepth/0502005.

Massive neutrinos and (heterotic) string theory,
(with J. Giedt, G. L. Kane, and B. D. Nelson),
Phys. Rev. D 71, 115013 (2005),
hepth/0502032.

Elementary Particles in Physics (with S. Gasiorowicz),
in Encyclopedia of Physics, Third Edition,
ed. R. C. Lerner and G. L. Trigg, (WileyVCH, 2005), p671.

Higgs sector in extensions of the MSSM,
(with V. Barger, H. S. Lee and G. Shaughnessy),
Phys. Rev. D 73, 115010 (2006),
hepph/0603247.

Neutralino signatures of the singlet extended MSSM
(with V. Barger and G. Shaughnessy),
Phys. Lett. B 644, 361 (2007),
hepph/0609068.

Collider signatures of singlet extended Higgs sectors
(with V. Barger and G. Shaughnessy),
Phys. Rev. D 75, 055013 (2007),
hepph/0611239.

TeV physics and the Planck scale
(with V. Barger and G. Shaughnessy),
New J. Phys. 9, 333 (2007),
hepph/0702001.

A Todd observable sensitive to CP violating phases in squark decay
(with G. Paz, L. T. Wang and I. Yavin),
JHEP 0707, 055 (2007),
hepph/0702068.

LHC Phenomenology of an Extended Standard Model with a Real Scalar
Singlet,
(with V. Barger, M. McCaskey, M. J. RamseyMusolf and G. Shaughnessy),
Phys. Rev. D 77, 035005 (2008),
0706.4311 [hepph].

Theory and Phenomenology of Exotic Isosinglet Quarks and Squarks,
(with J. Kang and B. D. Nelson),
Phys. Rev. D 77, 035003 (2008),
0708.2701 [hepph].

Z' mediated Supersymmetry Breaking,
(with G. Paz, L. T. Wang and I. Yavin),
Phys. Rev. Lett. 100, 041802 (2008),
0710.1632 [hepph].

Dirac Neutrino Masses from Generalized Supersymmetry Breaking,
(with D. A. Demir and L. L. Everett),
Phys. Rev. Lett. 100, 091804 (2008),
0712.1341 [hepph].

The Physics of Heavy Z' Gauge Bosons,
Rev. Mod. Phys. 81, 1199 (2008),
0801.1345 [hepph].

Aspects of Z' mediated Supersymmetry Breaking,
(with G. Paz, L. T. Wang and I. Yavin),
Phys. Rev. D 77, 085033 (2008),
0801.3693 [hepph].

DInstanton Generated Dirac Neutrino Masses,
(with M. Cvetic),
Phys. Rev. D 78, 066012 (2008),
0803.2876 [hepth].

Electroweak Physics, (with J. Erler),
Acta Phys. Polon. B 39, 2595 (2008),
0807.3023 [hepph].

Complex Singlet Extension of the Standard Model,
(with V. Barger, M. McCaskey, M. RamseyMusolf and G. Shaughnessy),
Phys. Rev. D 79, 015018 (2009),
0811.0393 [hepph].
 Scalar Potentials and Accidental Symmetries in Supersymmetric U(1)'
Models,
(with G. Paz and I. Yavin),
Phys. Lett. B 671, 245 (2009),
0811.1196 [hepph].

Introduction to the Standard Model and Electroweak Physics,
Proceedings of TASI08, The Dawn of the LHC Era, ed. Tao Han (World, Singapore, 2010), p 3,
0901.0241 [hepph].

Family Nonuniversal U(1)' Gauge Symmetries and b − > s Transitions,
(with V. Barger, L. Everett, J. Jiang, T. Liu and C. Wagner),
Phys. Rev. D 80, 055008 (2009),
0902.4507 [hepph].

Improved Constraints on Z' Bosons from Electroweak Precision Data,
(with J. Erler, S. Munir and E. R. Pena),
JHEP 0908, 017 (2009),
0906.2435 [hepph].

b − > s Transitions in Familydependent U(1)' Models,
(with V. Barger, L. Everett, J. Jiang, T. Liu and C. Wagner),
JHEP 0912, 048 (2009),
0906.3745 [hepph].

Sixlepton Z' resonance at the LHC,
(with V. Barger and H. S. Lee),
Phys. Rev. Lett. 103, 251802 (2009),
0909.2641 [hepph].

The Physics of New U(1)' Gauge Bosons,
Proceedings of SUSY09,
AIP Conf. Proc. 1200, 55 (2010),
0909.3260 [hepph].

Combining Anomaly and Z' Mediation of Supersymmetry Breaking,
(with J. de Blas, G. Paz and L. T. Wang),
JHEP 1001, 037 (2010),
0911.1996 [hepph].

Electroweak Baryogenesis, CDM and Anomalyfree Supersymmetric U(1)' Models,
(with J. Kang,T. Li and T. Liu),
JHEP 1104, 097 (2011),
0911.2939 [hepph].

Z' Physics at the LHC, 0911.4294 [hepph],
in Hunt for New Physics at the Large Hadron Collider,
ed. P. Nath and B. Nelson,
Nucl. Phys. Proc. Suppl. 200202, 185 (2010),
1001.2693 [hepph].

Phenomenological Implications of Supersymmetric Family Nonuniversal
U(1)' Models,
(with L. L. Everett, J. Jiang, and T. Liu),
Phys. Rev. D 82, 094024 (2010),
0911.5349 [hepph].

The Standard Model and Beyond
(CRC Press, New York, 2009).

The Weinberg Operator and a Lower String Scale in Orientifold Compactifications,
(with M. Cvetic, J. Halverson, and R. Richter),
JHEP 1010, 094 (2010),
1001.3148 [hepth].

Precision Constraints on Extra Fermion Generations,
(with J. Erler), Phys. Rev. Lett. 105, 031801 (2010),
1003.3211 [hepph].

Singlet Extensions of the MSSM in the Quiver Landscape,
(with M. Cvetic and J. Halverson), JHEP 1009, 076 (2010),
1006.3341 [hepth].

Sterile Neutrinos  A General Introduction, to be published in
A White Paper on keV Sterile Neutrino Dark Matter,
(A. de Gouvêa et al.).

Z' Bosons at Colliders: a Bayesian Viewpoint,
(with J. Erler, S. Munir, and E. Rojas),
JHEP 1111, 076 (2011),
1103.2659 [hepph].

Impact of extra particles on indirect Z' limits,
(with F. del Aguila, J. de Blas, and M. PerezVictoria),
Phys. Rev. D 84, 015015 (2011),
1104.5512 [hepph].

A Higgsophilic schannel Z' and the CDF W+2J Anomaly,
(with J. Fan, D. Krohn, and I. Yavin),
Phys. Rev. D 84, 105012 (2011),
1106.1682 [hepph].

Requiem for an FCHAMP? Fractionally CHArged, Massive Particle,
(with G. Steigman),
Phys. Rev. D 84, 065040 (2011),
1107.3131 [hepph].

Implications of String Constraints for Exotic Matter and Z' s Beyond the Standard Model,
(with M. Cvetic and J. Halverson),
JHEP 1111, 058 (2011),
1108.5187 [hepph].

Neutrino Masses from the Top Down,
Ann. Rev. Nucl. Part. Sci. 62, 215 (2012),
1112.5992 [hepph].

Electroweak Model and Constraints on New Physics (with J. Erler),
in 2012 WWW update for 2012 edition of Review of Particle Properties,
(URL: http://pdg.lbl.gov/). Print edition: J. Beringer et al. [Particle Data Group],
Phys. Rev. D 86, 010001 (2012).

Light Sterile Neutrinos and Short Baseline Neutrino Oscillation Anomalies,
(with J. Fan), JHEP 1204, 083 (2012),
1201.6662 [hepph].

Light Sterile Neutrinos: A White Paper,
(K. Abazajian et al.),
1204.5379 [hepph].

Ultraviolet Completions of Axigluon Models and Their Phenomenological Consequences,
(with M. Cvetic and J. Halverson),
JHEP 1211, 064 (2012),
1209.2741 [hepph].

Grand unification, review article on Scholarpedia 7, 11419 (2012).
 Exploring Quantum Physics at the ILC,
(with A. Freitas, K. Hagiwara, S. Heinemeyer, K. Moenig, M. Tanabashi and G. W. Wilson),
1307.3962 [hepph].

Diagnosis of a New Neutral Gauge Boson at the LHC and ILC for Snowmass 2013,
(with T. Han, Z. Liu and L. T. Wang),
1308.2738 [hepph].

Study of Electroweak Interactions at the Energy Frontier,
(M. Baak et al.),
1310.6708 [hepph].

New Particles Working Group Report of the Snowmass 2013 Community Summer Study,
(Y. Gershtein et al.),
1311.0299 [hepex].

Baryon Number Violation,
(K. S. Babu et al.),
1311.5285 [hepph].
 Neutrino Mass and Mixing, December, 2014. Update of Section 7.7 of
The Standard Model and Beyond
(CRC Press, New York, 2009).
 The Higgs, December, 2014. Update of Section 7.5 of The Standard Model and Beyond.

Review Of Particle Physics
(C. Patrignani et al. [Particle Data Group]),
Chin. Phys. C 40, 100001 (2016),
(URL: http://pdg.lbl.gov/).

String Consistency, Heavy Exotics, and the 750 GeV Diphoton Excess at the LHC,
(with M. Cvetic and J. Halverson),
Fortschr. Phys. 64, 748 (2016),
1512.07622 [hepph].

Sterile Neutrinos  A General Introduction, in
A White Paper on keV Sterile Neutrino Dark Matter,
(M. Drewes et al.),
J. Cosm. Astroparticle Phys. 01, 025 (2017),
1602.04816 [hepph].
 Physics Behind Precision,
(P. Azzi et al.),
1703.01626 [hepph].
 Can the Laws of Physics be Unified?
(Princeton University Press, March 2017).

The Standard Model and Beyond, Second
Edition (CRC Press, New York, 2017).
 TASI Lectures on Remnants from the String Landscape (with J. Halverson),
in TASI 2017,
PoS TASI 2017, 019 (2018),
1801.03503 [hepth].

Conference Summary and Outlook: Particle Physics Past, Present, and Future,
in ICHEP 2018,
PoS ICHEP2018, 733 (2019),
1811.07396 [hepph].

Constructing the Theory of the Standard Model (with M. K. Gaillard),
Physics Today 72, #2, p. 52 (2019).
Recent talks,
SLAC Spires publication list
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