Groundbreaking research in theoretical particle physics
has earned international acclaim for two University physicists
and their collaborator
by Joe Carlson
The 1970s were an exciting decade for
young physicist Arkady Vainshtein. His ideas were coming
to fruition, his papers were getting published, and his
theories were gaining acceptance in the international arena.
He was developing a closely-knit group of colleagues who
together aspired to make major contributions to theoretical
particle physics. The fact that his collaborators Mikhail
Shifman and Valentine Zakharov were in Moscow while he was
hours away in Novosibirsk, Siberia, didn't matter; their
passion for physics would overcome the difficulty of long-distance
collaboration.
Twenty-odd years later, Vainshtein and Shifman still work
side-by-side, now as full-time faculty in the Theoretical
Physics Institute (TPI), tucked away on the fourth floor
of the University's Tate Laboratory of Physics. Zakharov
is currently at the Max Planck Institute for Physics in
Munich, Germany.
From the beginning, the three always aimed to be at the
forefront of cutting-edge physics. But it wasn't until this
year that the international physics community confirmed
their status as world-class theorists.
Last March, more than 12,000 physicists, including Nobel
laureates and leading theorists, descended on the World
Conference Center in Atlanta, Georgia—site of the
1996 Summer Olympic Games—for the American Physical
Society's centennial celebration. During that unprecedented
meeting, the society honored Shifman, Vainshtein, and Zakharov
with the 1999 J.J. Sakurai Prize for Theoretical Particle
Physics.
The prestigious award bears the name of the late Jun John
Sakurai, a noted physicist born in Tokyo in 1933. His theories
encouraged particle physicists to examine major ideas in
diverse ways and to seek out new theories that crossed distinct
genres of physics research. Established in 1985, the prize
is given annually to physicists judged by their peers to
have made major contributions to theoretical particle physics.
The list of the award's recipients reads like a “who's
who” of the high-energy physics community.
Shifman, Vainshtein, and Zakharov were honored for their
contributions to three major research areas. The Sakurai
prize citation credits them with “fundamental contributions
to the understanding of nonperturbative QCD, nonleptonic
weak decays, and the analytic properties of supersymmetric
gauge theories.”
That's a pretty concise description, considering that it
represents about 25 years of work by the three physicists.
The first penguin flies
In the early days, Vainshtein often traveled to the Institute
of Theoretical and Experimental Physics in Moscow, where
Shifman and Zakharov worked. Time was never wasted during
those visits, and the group would spend days trying to resolve
a single problem.
When travel wasn't possible, Vainshtein and his friends
consulted each other frequently by telephone and began to
formulate new theories in the burgeoning field of quantum
chromodynamics (QCD).
Because new theories are meaningless until they are published
and debated, the three colleagues submitted an article for
publication in Nuclear Physics, a leading international
journal. For a year and a half, the journal's referees tried
to refute the trio's QCD theories on nonleptonic decay.
In 1977, following an appeal to the editorial board, the
journal finally agreed to publish the paper without any
revisions.
Finally, Vainshtein quips, the penguins were starting to
fly.
Two decades later, that odd phrase became the title of
Vainshtein's acceptance speech for the Sakurai prize, awarded
to the three researchers in part for their 1975 discovery
of so-called penguin diagrams.
"It was an exciting period, with quantum chromodynamics
emerging as the theory of strong interactions,” Vainshtein
wrote in the transcript of his Sakurai address, “when
three of us . . . started in 1973 to work on QCD effects
in weak processes.”
Physicists have concluded that the universe has four fundamental
forces: gravity, the electromagnetic force, the nuclear
or strong force, and the weak force. Scientists believe
that these forces, which determine the interactions between
the tiniest bits of matter, are also related.
Shifman, Vainshtein, and Zakharov were studying the weak
force, a factor in some radioactive decays. They wanted
to learn why two similar mesons, charged kaon K+ and neutral
kaon KS, decayed at different rates. Theoretical estimates
predicted that the two particles would have similar life
spans, but experiments proved that the K+ meson lived about
500 times longer than the KS meson.
"The puzzle was to explain this number,” Vainshtein
says. “The answer [to the puzzle] was strong interaction.”
Each force employs its own set of particles to do its work,
he explains. Normally, the weak force causes quarks to decay
when they interact with W bosons, which serve as a mediator
of weak forces. The three researchers discovered that a
mediator of strong interaction—a gluon enhanced the
decay of KS at a rate 500 times faster than normal.
News of the discovery gradually seeped from Russia to the
outside world. By about 1977, their gluon interference theory
gained acceptance after prominent American physicist Mary
K. Gaillard, now at the Lawrence Berkeley National Laboratory,
discussed it in one of her summary talks. She also incorporated
the theory into one of her works on b quark decays, written
with John Ellis of the world-renowned European Laboratory
for Nuclear Physics (CERN) in Geneva, Switzerland.
In a preface written for Shifman's 1999 book, ITEP Lectures
on Particle Physics and Field Theory, Ellis recalls how
the gluon interference diagram came to be called a penguin
diagram.
One night in spring 1977, Ellis lost a bet during a game
of darts. His penalty required that he use the word “penguin”
in a journal article.
"For some time, it was not clear to me how to get the word
into this b quark paper that we were writing at the time,”
Ellis wrote. “Then, one evening?I stopped on my way
back to my apartment to visit some friends living in Meyrin,
where I smoked some illegal substance. Later, when I got
back to my apartment and continued working on our paper,
I had a sudden flash that the famous diagrams looked like
penguins. So we put the name into our paper, and the rest,
as they say, is history.”
The threshold of existence
During the 1970s, the three researchers also focused on
QCD sum rules, the method used to find the mass and other
properties of hadrons, a type of strongly interacting particle.
This problem had challenged theoretical high-energy physicists
for decades.
The approach taken by Shifman, Vainshtein, and Zakharov
traces the evolution of quarks and gluons in the vacuum.
From the perspective of modern science, Shifman explains,
the vacuum is a very complicated medium, full of fluctuating
fields that are responsible for the basic properties of
hadrons.
This new approach—dubbed the SVZ sum rules in honor
of the authors—later was formulated in three papers
that comprised the entire 1979 issue of Nuclear Physics.
Vainshtein vividly recalls the days they spent preparing
for publication. Using manual typewriters, the three men
painstakingly retyped multiple copies of their manuscripts,
some required for prepublication review and others needed
for KGB approval.
After the papers were finally dispatched, the three were
exhausted, “not just from thinking about physics itself,
but [from] physically writing out all the equations,”
Vainshtein says.
A profound discovery
According to Shifman, supersymmetry is one of the hottest
areas of physics research, involving hundreds of physicists
around the world, including TPI researchers.
But it wasn't always so.
"We started working on aspects of supersymmetry in the
early 1980s, at the time when it seemed rather exotic,”
he says. “Very few people in the world worked in this
direction. Now, 15 years later, the results we obtained
then turned out to be very important. They are intertwined
in the fabric of the recent breakthrough developments in
high-energy physics by Seiberg and Witten of Princeton University,
today's leading researchers in high-energy physics.”
Every particle in nature is one of two subatomic varieties,
either a boson or a fermion. During the 1970s, researchers
in Russia and Switzerland uncovered a symmetrical relationship
between the two species, known as supersymmetry. Studies
have determined that the relative quantity of bosons and
fermions may have major ramifications for the physical sciences.
"The discovery of supersymmetry is comparable to what Einstein
did in the early part of this century,” says Shifman.
Supersymmetry picks up where the revolutionary ideas of
quantum mechanics left off. According to quantum mechanics,
fields of subatomic particles—such as electrons—can
never stop moving completely.
"When fields fluctuate, they store some energy in themselves,”
Shifman says. Because there is so much matter in the universe,
all of which stores energy, there should be an abundance
of energy floating around. In fact, space should be lit
up with energy, like a billboard along an interstate at
night.
But that level of energy is ruled out by direct experimental
measurements.
Astrophysicists are pretty good at calculating energy levels
present in the far reaches of space, known as vacuum energy
density. But when they calculated that density—the
cosmological constant—and compared it with quantum
mechanics calculations, they discovered a mind-boggling
numerical discrepancy.
“We don't have a name for this number,” Shifman
says. “It's billions of billions of billions.”
Clearly, something was wrong, but no one knew what.
"Before supersymmetry,” Shifman says, “there
was no hint [of] how to deal with it.”
Physicists eventually reasoned that the balance of bosons
and fermions may eliminate the discrepancy. Supersymmetry
theorizes that because bosons contribute positive density
and fermions contribute negative density, the densities
neutralize each other. The remaining energy level is much
closer to astrophysicists' original calculations.
"This is going to be the theory of the 21st century,”
Shifman asserts. “It's such a hot topic that in many
places it's the only thing people are working on.
An oasis of physics
During the academic year, TPI teems with activity, as visiting
scholars, graduate students, and postdoctoral researchers
mingle with faculty. Russian is the preferred language spoken
here, for six of the institute's eight full-time faculty
members are Russian.
Tucked away in the back of Tate laboratory, TPI may seem
isolated from the outside world, but a unique combination
of international geopolitical factors made TPI what it is
today.
Without perestroika, TPI's staff roster would likely be
completely different. “Before 1989, I don't think
I would have been able to come here,” Vainshtein says.
“During a period of more than 20 years, the KGB only
granted permission for me to travel to the West twice. 1989
was a different year, you could feel it.”
About the same time, thousands of miles away, several factors
converged to create a world-class advanced physics institute
at the University. Physics professor Stephen Gasiorowicz
and William Fine, a Minneapolis real estate developer and
former attorney, had been working for three years to stir
up interest in such an institute at the University. Those
efforts were finally starting to pay off.
The drive to create TPI met resistance at first, but eventually
found a supporter in Professor Ken Keller, then University
president. TPI was launched in 1986 with a $2 million gift
from Fine that established three endowed chairs and with
a strong commitment of additional funds from the University.
Today, TPI physicists are advancing the science in three
main areas: astroparticle physics, including supersymmetry;
high-energy physics such as QCD; and condensed-matter physics.
Fine currently sits with Gasiorowicz and six others on
TPI's oversight committee. Fine may seem to be an unlikely
donor for a theoretical physics institute, but he explains
his interest in the science quite simply: “Physics
is the most fundamental of the sciences.”
He adds, “I don't know the language of physics, which
is mathematics, but I do have enough of an inkling to appreciate
its advancement.”
Experts and professors from all over the world often write
to this group of Russian physicists, expressing their desire
to work at the institute. They want to participate in what
Shifman calls “a critical mass of physics minds”
at TPI.
"We're having young people from all over the world writing
letters,” Shifman says of TPI's many bright-eyed visitors.
“They come not for the money, but for the atmosphere,
the knowledge.”
