Stuart Samuel is a theoretical physicist known
for his work on the speed of gravity and for
his work with Alan Kostelecký on spontaneous
Lorentz violation in string theory, now called
the Bumblebee model. He also made significant
contributions in field theory and particle
physics.
Samuel graduated from Princeton University
with a Bachelor of Arts in mathematics in
1975, and in 1979, he graduated from the UC
Berkeley, with a Doctor of Philosophy in physics.
He was formerly a member of the Institute
for Advanced Study at Princeton, a professor
of physics at Columbia University, and a professor
of physics at City College of New York.
== Earlier work ==
In early work, Samuel used particle field
theory methods to obtain results in statistical
mechanics.
In particular, Samuel uncovered a particularly
simple way to solve the two-dimensional Ising
model. It was shown to be equivalent to a
non-interacting field theory of fermionic-like
particles. This allowed a rapid computation
of the partition function and correlation
functions. Samuel went on to treat certain
interacting statistical mechanics systems
using perturbative field theory.
== Scalar lattice QCD ==
In 1985, Samuel and co-worker K.J.M. Moriarty
were among the first to obtain a reasonably
accurate computation of the hadron mass spectrum
using computer simulations of lattice quantum
chromodynamics (QCD). They overcame the difficulties
that other theorists were encountering at
the time by making an approximation: They
replaced the spin 1/2, fermionic quarks with
spin zero scalar particles and corrected for
this approximation by treating the spin degrees
of freedom using perturbation theory. There
were three advantages to doing this: (i) scalar
quarks required less computer memory, (ii)
simulations using scalar quarks required less
computer time, and (iii) it avoided the fermion
doubling problem. Their lattice QCD computation
of the meson mass spectrum agreed well with
the one in nature with the exception of the
pion mass, where it is known that treating
spin perturbatively is not a good approximation
due to approximate spontaneous breaking of
chiral symmetry. The lattice computation of
the baryon spectrum was equally impressive.
Samuel and Moriarty went on to make mass predictions
for hadrons involving the bottom quark that
had not yet been produced in accelerators.
These predictions were later confirmed except
for the one for the Λb baryon.
== Supersymmetry work ==
Samuel's most important work in supersymmetry
arose in a collaboration with the theorist
Julius Wess in a publication called "Secret
Supersymmetery." In this work, the two physicists
constructed an effective low-energy theory
of the supersymmetric generalization of the
Standard Model of particle physics for the
situation in which supersymmetry is spontaneously
broken. The main conclusion was: Although
there may be few low-energy manifestations
of spontaneously broken supersymmetry, there
should be at least one charged Higgs field
and two neutral Higgs fields beyond the usual
neutral one of the Standard Model. All supersymmetric
extensions of the Standard Model have these
extra spin-0 boson particles. The important
conclusion is that if additional Higgs particles
are discovered in nature then it is suggestive
of an underlying supersymmetric structure
even if the supersymmetric partners of the
particles in the Standard Model are not observed
experimentally.
== String theory work ==
Samuel's most important contribution in string
theory was the development of off-shell conformal
field theory. This allowed the computation
of the scattering of string states when the
on-shell condition E2 = m2c4 + p2c2 is analytically
continued so that it no longer holds. The
off-shell extension of string scattering amplitudes
was thought to be impossible because of a
no-go theorem. However, Samuel was able to
use Witten's version of string field theory
to achieve this result. One of the assumptions
of the "no-go" theorem was avoided (the use
of an infinite number of ghost states).
== Bosonic technicolor ==
Samuel is the creator of bosonic technicolor.
Two approaches to solving to the hierarchy
problem are technicolor and supersymmetry.
The former has difficulties with flavor-changing
neutral currents and light pseudo-Goldstone
bosons, while the latter predicts superpartner
particles that have not been currently observed.
Bosonic technicolor is a supersymmetric version
of technicolor that eliminates the difficulties
that technicolor and supersymmetry have separately.
In this model, the masses of superpartners
can be about two orders of magnitude higher
than in usual supersymmetry extensions of
the standard model.
== Neutrino oscillations in dense neutrino
gases ==
Because neutrinos have masses, the three flavors
of neutrinos (electron neutrino νe, muon
neutrino νμ and tau neutrino ντ) change
into each other and back, a phenomenon called
neutrino oscillations. When one has a dense
gas of neutrinos, it is not straightforward
to determine how neutrino oscillations behave.
This is because the oscillation of a single
neutrino in the gas depends on the flavors
of the neutrinos nearby, and the oscillation
of the nearby neutrinos depend on the flavor
of that single neutrino (and of other individual
nearby neutrinos). Samuel was the first to
develop a self-consistent formalism to address
this. He observed a number of interesting
phenomena that can occur in such systems including
a self-induced Mikheyev–Smirnov–Wolfenstein
effect and a parametric resonant conversion.
Samuel and colleague Alan Kostelecký have
used Samuel's formalism to analyze neutrino
oscillations in the early universe.
== Awards and prizes ==
Samuel has received a number of awards for
his research including a Control Data Corporation
PACER Award (with Dr. K. M. Moriarty) for
outstanding computer programming, an Alexander
von Humboldt Fellowship, and the Chester–Davis
Prize (from Indiana University). He was one
of 90 scientists in 1984 to be honored as
an Alfred P. Sloan Research Recipient
