RESUMÉ: Warren Siegel
HISTORY
DEGREES:
| Univ. of California, Berkeley | 6/70-12/72 | A.B. | Physics, Math. |
| Univ. of California, Berkeley | 1/73- 6/77 | Ph.D. | Physics |
GRADUATE ADVISOR: Martin B. Halpern
POSITIONS HELD:
| Harvard University | 7/77-7/79 | Honorary Postdoctoral Fellow |
| Brandeis University | 3/79-6/79 | Postdoctoral Fellow |
| Inst. for Advanced Study | 8/79-8/80 | Postdoctoral Fellow |
| Calif. Inst. of Technology | 8/80-8/82 | Postdoctoral Fellow |
| Univ. of Calif., Berkeley | 8/82-8/85 | Postdoctoral Fellow |
| Univ. of Md., College Park | 8/85-6/87 | Assistant Professor |
| " | 7/87-9/88 | Professor |
| State Univ. of N.Y., Stony Brook | 9/88- | Professor |
MISCELLANY
PRESENT ADDRESS:
C.N. Yang Institute for Theoretical Physics
State University of New York
Stony Brook, NY 11794-3840
GRANT: NSF # PHY-0354776 (P.I.'s: G. Sterman & J. Smith)
AWARDS, CONSULTING, PROFESSIONAL AFFILIATIONS: none
Local expert on some computer stuff: Mac, TeX, WWW, etc.
RESEARCH:
High-energy theoretical physics
BEFORE STONY BROOK
Superspace
My early work ('77-'83) involved mostly the use of superspace to treat
supersymmetric theories, including supergravity. Gates, Grisaru, Roček, and I
discovered methods for both deriving classical actions, and performing
Feynman graph calculations more simply than those in nonsupersymmetric
theories. I also found a new method of dimensional regularization
("dimensional reduction") which preserves supersymmetry, and is also
commonly used in QCD.
Strings
In later work ('83-'88) I focused primarily on string theory. I invented
(covariant) string field theory. With Zwiebach I generalized these
methods outside of string theory to give a universal free field theory
action for arbitrary representations of the Poincaré group in arbitrary
dimensions. I also discovered new gauge symmetries of classical mechanics,
useful for strings.
PAST RESEARCH AT STONY BROOK
Selfduality
I showed that a string thought to be inconsistent in
positive dimensions ("N=4") was actually a more symmetric formulation of a
consistent string theory ("N=2") known to describe selfdual theories.
Chalmers and I showed that selfdual theories can be used as the lowest
order in a perturbative helicity expansion in theories such as QCD,
and developed spacecone gauge quantization to explain, systematize, and further
simplify spinor helicity methods in QCD.
More strings
I showed how so-called T-duality,
rather than being a symmetry of certain string solutions, can actually be
considered a spontaneously broken symmetry of the full (super)string
theory. I showed that the apparent phenomenon of closed strings appearing as bound
states of open strings actually occurs as a kinematic effect in the free theory,
analogously to a
similar phenomenon in field theory in two dimensions ("bosonization"). I
extended to superstrings the random matrix approach to string theory,
in which the string appears as a bound state of particles, and early results
suggest that the superstring arises as a bound state of a type of
supersymmetric quantum chromodynamics.
AdS/CFT
With Nastase, Roiban, and Hatsuda I studied a new version of the correspondence between 4D conformal
field theory and string theory on anti-de Sitter backgrounds, initiated by
Maldacena. Based on the
random lattice worldsheet, Dirac's projective lightcone, supertwistors,
and a double holography for both anti deSitter space and the 5-sphere,
we found a relation in projective superspace to the conformal
field theory describing the constituents of strings (partons/preons), as
distinguished from the usual one describing open string states themselves (e.g.,
"gluons" instead of massless "rho mesons" in hadronic string language).
Extra dimensions
Biswas and I studied the various ways extra internal dimensions could be used to describe N=2 supersymmetric theories, and evaluate their actions. We also found a new type of dimensional reduction, radial instead of linear, which gives theories in (anti) de Sitter space from flat space.
Noncommutativity
Lee and I showed how to reproduce supergravity at one loop as a bound state
of super Yang-Mills using higher-derivative couplings, a result previously
thought unique to string theory. The mechanism is similar to the UV/IR
correspondence found in noncommutative field theory, but is Lorentz covariant.
Like string theory, this phenomenon uniquely requires D=10 and supersymmetry.
Hatsuda and I generalized to superspace results of Snyder on compact momentum space, which has the same form of Lorentz covariant noncommutativity, describing supersymmetric theories on a Lorentz covariant "lattice".
RECENT RESEARCH
I showed that the gravity implied by string theory weakens at short distances, as was suggested by its preonic substructure found in random lattice quantization, and implies the absence of black holes. Biswas, Mazumdar, & I generalized this to cosmology, showing the absence of a singularity at the Big Bang.
I found new formulations of the twistor superstring (of Nair; Witten; Roiban, Spradlin, and Volovich; and Berkovits) that allowed its generalization off-shell, and to a new string for which it is the tensionless limit.
Feng and I showed how to use gauge covariant vertex operators in string theory that automatically give S-matrices with gauge independent external line factors.
Biswas, Grisaru, and I calculated explicit ladder diagrams in random lattice theory to derive linear Regge trajectrories.
Andreev and I proposed strings that perturbatively exhibit both asymptotic freedom and the usual Regge behavior and spectrum.
Lee and I solved the long-standing problem of finding the BRST operator for the manifestly supersymmetric superstring, and used this formalism to give simpler calculations of tree & 1-loop superstring amplitudes.
CURRENT RESEARCH
QCD exhibits asymptotic freedom and confinement only in D ≤ 4, thus "predicting" D=4 as its critical dimension. But known string theories predict D ≫ 4, requiring compactification and its resultant loss of predictability. This suggests the search for new string theories corresponding to the hadronic string and related 4D theories.
Selfduality
Any theory can be treated as a gauge-invariant perturbation about an almost-trivial selfdual theory, a perturbation in helicity.
Almost all selfdual amplitudes vanish; the first order in perturbation about them ("maximal helicity violating") are much simpler than expected.
Twistor superstrings are an explicit realization of the helicity expansion in tree graphs: Using a worldsheet theory of only one handedness, and twistors as variables, the expansion in helicity is an expansion in the number of worldsheet U(1) instantons. This formulation is manifestly maximally (N=4) superconformal, but describes only massless states (N=4 super Yang-Mills). It has an extension that allows loop calculations and can be expressed as the tensionless limit of a manifestly supersymmetric, QCD-like string, with N=4 super Yang-Mills also as its partons.
Strings with N=2 or 4 worldsheet supersymmetry have critical dimension 4 and describe selfdual theories, suggesting they might also be generalized to non-selfdual theories.
New 4D strings
So-called "perturbative QCD" is actually perturbative only for "hard" (large transverse energy) factors of any amplitude. On the other hand Regge theory, and in particular string theory, attempts to calculate soft processes (and the hadron spectrum) perturbatively.
Experiment shows that the range of validity of both Regge theory and perturbative QCD are greater than expected, and have some overlap. This suggests the possibility of models that at lowest perturbative order would accurately describe both hard and soft processes, without requiring poorly defined and difficult-to-calculate "nonperturbative" contributions, putting them on a par with QED for electromagnetism (and to a great extent unified models of electroweak interactions).
Motivated by, and combining the good points of, earlier attempts to incorporate calculability of both asymptotic freedom and confinement within the same formalism, such an approach can be obtained by assuming the usual strings (but applied to 4 dimensions) have multiple values of the tension, all integers (in terms of some unit). Although this model does give realistic predictions, its self-consistency (and the corresponding fixing of its many arbitrary parameters) has yet to be determined.
Random lattices
The random lattice approach to strings replaces the continuous worldsheet with a lattice, whose random nature reflects the arbitrariness in the worldsheet metric. Each lattice is directly identified with a Feynman diagram of an underlying particle theory that forms strings as bound states.
The geometry of strings follows from the 1/N expansion of QCD.
The random matrix model following from standard strings describes particles with Gaussian propagators. Consequently, each Feynman graph is finite. The condition for the critical dimension is found only after summing graphs, corresponding to integration over the worldsheet metric.
In contrast, QCD is renormalizable and confining only in D ≤ 4. This suggests that the four-dimensional nature of physics might be enforced in string theory only for theories whose random-matrix models have the usual 1/p2 propagators, rather than Gaussians.
Such propagators can be incorporated into string theory by the introduction of a second worldsheet metric, which acts as Schwinger parameters for the Feynman diagrams of the random lattice. For the bosonic string, the underlying theory is (wrong-sign, asymptotically free) φ4. The four-point vertices of the Feynman diagrams are the light-cones of the random-lattice worldsheet. Critical dimension 4 follows not only from renormalizability, but also from T-duality.
Short distance modifications to spacetime
One convenient ultraviolet cutoff is the lattice. Unfortunately, it breaks Lorentz invariance by specifying preferred axes, and so cannot be considered realistic, but only a regularization, to be removed at the end of the calculation. (An exception is random lattices, describing discretized curved space.) A related alternative is to choose a compact momentum space: Snyder proposed choosing a sphere; then Lorentz invariance is preserved. This may provide a solution to the long-standing problem of putting fermions on a lattice.
Bound-state gravity is the only known viable alternative to string theory as a quantum theory of gravity. But also in string theory, the graviton (closed-string sector) appears as a bound state (of states of the open-string) at one loop. A simple (Lorentz covariant) higher-derivative generalization of ordinary field theory for spins ≤ 1 is sufficient to reproduce this string effect.
Besides its nonrenormalizability, the main deficiency of general relativity is the appearance of singularities in any solution where matter is contained in a sufficiently compact region. These "black holes" would be unavoidable in situations known to occur in the gravitational collapse of stars; similarly, the Big Bang would necessarily begin with a singularity. However, a fundamental property of relativistic bound states, "Regge behavior", implies that forces carried by bound states weaken at short distance, where their bound-state nature emerges. Thus, in any theory where the graviton appears as a bound-state, including string theory, black holes do not form, and the consequent problems of singularities and information loss are avoided; in cosmology, the Big Bang starts from a nonsingular minimum, which is preceded by a contraction that may account for the features of inflation.
THE FREE LIBRARY
Fields
I spent a considerable portion of 1996-99 writing the book "Fields" --- the first
free comprehensive (731 pages) textbook on quantum (and classical) field
theory.
I recently released the third edition (885 pages).
It is published only electronically.
This book is available at the usual Web
archives (at arXiv.org
or my Web page,
which has more details).
Its approach to field theory is pragmatic, rather than traditional or
artistic: It includes practical techniques, such as the 1/N expansion
(color ordering) and spacecone (spinor helicity), and diverse topics, such
as supersymmetry and general relativity, as well as introductions to
supergravity and strings.
Other books
In 2001 I also released my 1988 book,
"Introduction to String Field Theory," freely to the Web
(e.g., at
arXiv.org) and, with the help of my coauthors
S.J. Gates, M.T. Grisaru, and M. Roček, our 1983 standard,
"Superspace, or One Thousand and One Lessons in Supersymmetry"
(at arXiv.org).
The program
Today most physics books (as well as almost all papers) are typeset in TeX.
This makes it possible for any author to release his book for free, with
no publishing costs to himself or the reader, should he so choose, either after
a period of commercial sales (and return of copyright by the publisher)
or immediately.
Such electronic distribution of books is more
convenient, cheaper, faster, and more ecologically friendly than paper
books. In particular, the PDF versions of my books have Web links and
clickable outline (contents) windows.
My hope is that these books will help set new standards in both format and
content that will make physics more accessible and relevant to students.
PUBLICATIONS, incl. CONFERENCE TALKS:
Complete
publication list (159 last time I looked)
Preprints at arXiv.org
Past year
"MAJOR" PUBLICATIONS (see also "The Free Library" above):
- Simplifying algebra in Feynman graphs, part II: Spinor helicity
from the spacecone,
hep-ph/9801220,
Phys.Rev.D59(1999)045013 (with G. Chalmers)
--- new, easiest way to do QCD graphs
- Actions for QCD-like strings,
hep-th/9601002,
Int.J.Mod.Phys.A13(1998)381
--- asymptotically free strings
- Gauge string fields from the light cone,
Nucl.Phys.B282(1987)125 (with B. Zwiebach)
--- free gauge-invariant actions for any theory in any dimension
- Covariantly second-quantized string II, Phys.Lett.149B(1984)157,
151B(1985)391
- Manifest Lorentz invariance sometimes requires nonlinearity,
Nucl.Phys.B238(1984)307
--- chiral bosons
- Hidden local supersymmetry in the supersymmetric particle
action, Phys.Lett.128B(1983)397
--- "kappa" symmetry
- Supergraphity (II).
Manifestly covariant rules and higher loop finiteness,
Nucl.Phys.B201(1982)292 (with M.T. Grisaru)
--- power counting for extended supersymmetry
(later used for finiteness proof for N=4)
- Improved methods for supergraphs, Nucl.Phys.B159(1979)429,
(with M.T. Grisaru and M. Roček)
- Unextended superfields in extended supersymmetry,
Nucl.Phys.B156(1979)135
--- Chern-Simons terms in actions
- Supersymmetric dimensional
regularization via dimensional reduction, Phys.Lett.84B(1979)193
STUDENTS
RESEARCH STUDENTS at Stony Brook
(linked to PUBLICATIONS):
|
Hatsuda, Machiko | S'90-S'91 |
Theory Division, KEK
Tsukuba, Ibaraki
305-0801, JAPAN |
mhatsuda@post.kek.jp |
|
Eßler, Fabian | S'91-S'93 |
Rudolf Peierls Centre for Theoretical Physics
University of Oxford
1 Keble Road
Oxford, OX1 3NP
UK
|
fab@thphys.ox.ac.uk |
|
Gasparakis, Charidimos | F'91-F'95 |
Vital Images, Inc.
3100 West Lake St.
Suite 100
Minneapolis, MN
55416-4510 |
harry@vitalimages.com |
| Martinez, Mario | F'92-S'94 | (didn't finish Ph.D.) | |
| Weiser, Harold | F'92-F'99 | | |
|
Peeters, Bastiaan | S'93-S'95 |
Instituut voor
Theoretische Fysica
KU Leuven
Celestijnenlaan 200D
3001 Heverlee
Belgium |
bas.peeters@fys.kuleuven.ac.be |
|
Schalm, Koenraad | F'95-S'99 |
Institute for
Theoretical Physics
University of Amsterdam
Valckenierstraat 65
1018 XE Amsterdam
Netherlands
|
schalm@science.uva.nl |
|
Biswas, Tirthabir | F'00-S'03 |
104 Davey Lab, #035
University Park, PA
16802-6300
|
tub10@psu.edu |
|
Feng, Haidong | F'03-S'07 |
Chemistry
Stony Brook |
hfeng@ic.sunysb.edu |
|
Lee, Kiyoung | F'03-S'07 |
Manhattan College
Riverdale, Bronx, NY
10471 |
klee@insti.physics.sunysb.edu |
|
Martinez-Torteya, Carlos | F'04- |
Stony Brook |
martinez@grad.physics.sunysb.edu |
|
Huang, Yu-tin | F'05- |
Stony Brook |
yhuang@grad.physics.sunysb.edu |
|
Dai, Peng | F'06- |
Stony Brook |
pdai@grad.physics.sunysb.edu |
I also advised
Aleksandar
Miković and others at Maryland, and was the unofficial adviser of
Jon
Yamron and
Nathan
Berkovits at Berkeley.
COURSES TAUGHT @ Stony Brook (incl. lecture notes):
| Relativity | PHY 408 | S 95, 04 |
| Relativity | PHY 620 | S 92, 93, 96, 99, F 03, 05, 07 |
| Quantum Field Theory | PHY 610-1 | F 97-S 98, F 01-S 02, F 04-S 05, F 06-S 07 |
| Advanced Quantum Field Theory | PHY 621 | S 08 |
| String Theory (with others) | PHY 622-3 | S-F 03, F 04-∞ (& beyond) |
TIME SPENT TEACHING & ADVISING GRADUATE STUDENTS: 25%
