D.N. Spergel,
et al.,
"Three-year
Wilkinson Microwave
Anisotropy Probe
(WMAP)
observations:
Implications for
cosmology,"
Astrophys. J.
Suppl. Ser.,
170(2): 377-408, June
2007. [13 U.S. and
Canadian institutions]
*178TD
170
1
2
X.H. Chen, et
al.,
Superconductivity at
43K in SmFeAs
O1-xFx,
Nature,
453(7196): 761-2, 5
June 2008. [U. Sci.
& Tech., Hefei,
China] *308UK
43
†
3
A.G. Riess, et
al., "New
Hubble Space
Telescope
discoveries of type Ia
supernovae at
z = 1:
Narrowing constraints
on the early behavior
of dark energy,"
Astrophys. J.,
659(1): 98-121, 10
April 2007. [10 U.S.
institutions] *158EF
37
4
4
J. Bagger, N.
Lambert, "Gauge
symmetry and
supersymmetry of
multiple M2-branes,"
Phys. Rev. D,
77(6): no. 065008, 15
March 2008. [Johns
Hopkins U., Baltimore,
MD; King's Coll.
London, U.K.] *282CF
37
†
5
Z.A. Ren, et
al.,
"Superconductivity at
55 K in iron-based
F-doped layered
quaternary compound
Sm[O1-xF
x]FeAs,"
Chinese Phys.
Lett., 25(6):
2215-6, June 2008.
[Chinese Acad. Sci,
Beijing] *306MN
36
†
6
J. Bagger, N. Lambert,
"Comments on multiple
M2-branes," J. High
Energy Phys., 2:
no. 105, February 2008.
[Johns Hopkins U.,
Baltimore; King's Coll.
London, U.K.] *285GD
33
†
7
J.Y. Kim, et
al., "Efficient
tandem polymer solar
cells fabricated by
all-solution
processing,"
Science,
317(5835): 222-5, 13
July 2007. [U. Calif.,
Santa Barbara; Gwangju
Inst. Sci. Tech.,
Korea] *189DC
32
8
8
M.
Tegmark, et
al.,
"Cosmological
constraints from
the SDSS luminous
red galaxies,"
Phys. Rev.
D, 74(12): no.
123507, December
2006. [36
institutions
worldwide] *121QJ
31
3
9
P.M. Ho, Y. Imamura, Y.
Matsuo, "M2 to D2
revisited," J. High
Energy Phys., 7:
no. 003, July 2008.
[Natl. Taiwan U,
Taipei; U. Tokyo,
Japan] *333HR
26
†
10
J. Distler, et
al., "M2-branes on
M-folds," J. High
Energy Phys., 5:
no. 38, May 2008. [U.
Texas, Austin; Tata
Inst., Mumbai, India;
U. British Columbia,
Vancouver, Canada]
*312JA
Every so often the Hot Papers table of Science
Watch captures a revolution in science. In the early
1990s buckyballs held center stage for a while, followed by
light-emitting diodes. Then we had a flood of Hot Papers on
high-temperature superconductivity, a field that is still
with us at positions #2 and #5. Physics Hot Papers of the
last ten years beautifully captured the emergence of a
consensus cosmology, and the reshaping of that subject as
precision science.
In the present selection, cosmology still dominates: #1
gives the latest values for several cosmological
parameters, #3 describes what can be learned about dark
energy by studying distant supernovae, and #8 dwells on the
cosmological implications. This latest selection has an
intriguing quartet of papers on string theory, describing
properties of M2-branes (#4, #6, #9, and #10). Not for ten
years has string theory featured this strongly. Are we
seeing a revolution?
Historically, string theory is a child of the 1960s, when
attempts were made to understand the strong nuclear force,
which was eventually explained by quantum chromodynamics.
String theory made a comeback in the 1970s-80s as a
candidate for producing a unified field theory. The
mid-1980s mark the first revolution in which theorists
convinced themselves that five different string theories,
each requiring 10 dimensions, offered a road to
unification. Suddenly a curious intellectual puzzle became
mainstream physics, in which vibrating strings represented
elementary particles. The theory required that the extra 6
spatial dimensions must wrap into a tiny geometrical space,
which is why we do not experience them.
The second superstring revolution dates from the mid-1990s,
with the discovery of new and powerful symmetries, known as
dualities. The key papers from that period show how the
five apparently different string theories are all related.
They are the limiting cases of an underlying theory known
as M-theory, which requires 11 dimensions. Although we lack
a full account of M-theory, plenty of progress has been
made in understanding its properties. The fundamental
objects of M-theory are membranes and higher dimensional
entities collectively known as p-branes. M-theory produced
the rich physics of D-branes, the objects on which the ends
of open strings terminate. Mathematicians have used
D-branes to probe spacetime and gauge curvature, and some
have speculated that the entire visible universe is a
D3-brane floating in 11 dimensions.
We can use the four Hot Papers on string theory to see if a
third revolution is taking place. The high citation rates
of this cluster on M2-branes suggests that it is. According
to
Jonathan Bagger (Johns Hopkins University) and
Neil Lambert (King’s College, London), "M-branes
are mysterious objects, and virtually nothing is known about their
underlying dynamics" (#4), which contrasts with the
D-brane scenario, where a great deal of progress has
been made. Bagger-Lambert theory looks at the
interactions of multiple M2-branes ending on a
5-dimensional M5 brane. The formalism is highly
mathematical, and the research involves the invention of
new algebra. The game involves finding a Lagrangian
formulism that is consistent with the symmetries of
M2-branes. In modern theoretical physics the Lagrangian
is an energy density function that sums up the dynamics
of the whole system, and that’s why it is a
starting point for investigating dynamics in M-theory.
(See Research Front Map of
the
"Bagger-Lambert Theory.")
Hot Paper #4 develops the Bagger-Lambert field theory by
first gauging the theory and then making it supersymmetric.
In a companion paper, #6, they set out physical predictions
for multiple M2-branes. Paper #9 makes a further advance by
showing how results known for D2-branes can now be derived
from Bagger-Lambert theory. Finally #10 explores a new
class of algebraic puzzles that M-theory has uncovered.
This Science Watch compilation shows that the
string-theory circus is back in town with a whole new show,
but physicists on the sidewalk continue to be deeply
skeptical, questioning whether these mathematical conjuring
tricks involve physics at all. On the positive side, the
history of physics teaches us that the greatest
breakthroughs required an enormous prior effort to develop
new mathematical tools. Thus it was that Newton invented
calculus, Maxwell introduced vector algebra, while Einstein
adopted 4-dimensional geometry and tensor algebra. For
Newtonian mechanics and general relativity, initially only
a few practitioners could get their heads around the math.
Just like today, really.
Dr. Simon Mitton is a Fellow of St. Edmund’s
College, Cambridge, U.K.