higgs - page 29

251. ‘‘Heterotic String Theory. 1. The Free Heterotic String,’’ D. J. Gross,
J. A. Harvey, E. Martinec, and R. Rohm, Nucl. Phys. B 256, 253–284
~1985!. ~A!
252. ‘‘Heterotic String Theory. 2. The Interacting Heterotic String,’’ D. J.
Gross, J. A. Harvey, E. Martinec, and R. Rohm, Nucl. Phys. B 267,
75–124 ~1986!. ~A!
253. ‘‘Vacuum Configurations for Superstrings,’’ P. Candelas, G. T.
Horowitz, A. Strominger, and E. Witten, Nucl. Phys. B 258, 46–74
~1985!. ~A!
H. Large extra dimensions
Although the usual superstring scenario envisions the six
extra dimensions in such theories as having spatial extent of
the order of the Planck scale, ( G N\/ c 3) 1/2. 102 33 cm, theo-
ries have been proposed in which some of the extra dimen-
sions are larger, leading to observable effects at accelerators
or in precise tests of Newton’s universal inverse square law
of gravitation.254–258 Reviews for the non-specialist have ap-
peared in Scientific American137 and Physics Today. 138
254. ‘‘A Possible New Dimension at a Few TeV,’’ I. Antoniadis, Phys.
Lett. B 246, 377–384 ~1990!. ~A!
255. ‘‘Weak Scale Superstrings,’’ J. D. Lykken, Phys. Rev. D 54, R3693–
R3697 ~1996!. ~A!
256. ‘‘The Hierarchy Problem and New Dimensions at a Millimeter,’’ N.
Arkani-Hamed, S. Dimopoulos, and G. R. Dvali, Phys. Lett. B 429,
263–272 ~1998!. ~A!
257. ‘‘New Dimensions at a Millimeter to a Fermi and Superstrings at a
TeV,’’ I. Antoniadis, N. Arkani-Hamed, S. Dimopoulos, and G. R.
Dvali, Phys. Lett. B 436, 257–263 ~1998!. ~A!
258. ‘‘Phenomenology, Astrophysics and Cosmology of Theories with
Sub-Millimeter Dimensions and TeV Scale Quantum Gravity,’’ N.
Arkani-Hamed, S. Dimopoulos, and and G. R. Dvali, Phys. Rev. D
59, 086004 ~1999!. ~A!
XI. HINTS OF NEW PHYSICS
A. Neutrino masses
The ability of neutrinos of one species to undergo oscilla-
tions into another is an indication of nonzero and nondegen-
erate neutrino masses.57,58 Several experiments find evidence
for such oscillations. Reviews have appeared in Refs. 59, 61,
131; the second of these also deals with precision elec-
troweak tests using neutrinos.
1. Solar neutrinos
Since the earliest attempts to detect neutrinos originating
from the Sun in the mid-1960s, the flux has been less than
predicted in the standard solar model.125 Recent experiments
at the Sudbury Neutrino Observatory ~SNO! in Ontario259,260
and the KamLAND Experiment in Japan261 strongly suggest
that this deficit is due to oscillations of the electron neutrinos
produced in the Sun into other species, most likely a combi-
nation of muon and tau neutrinos, induced by interaction
with the Sun in a manner ~now known as the MSW effect !
first proposed by Mikheev and Smirnov262 and
Wolfenstein.263 For reviews, see Refs. 35, 60.
2. Atmospheric neutrinos
Neutrinos produced by the interactions of cosmic rays in
the atmosphere are expected to be in the ratio n m: ne 5 2:1
~summing over neutrinos and antineutrinos!. 264 Instead, a ra-
tio more like 1:1 is observed. This phenomenon has been
traced to oscillations that are most likely n m→ n t , as a result
of definitive experiments performed by the Super-
Kamiokande collaboration in Japan.265,266 The mixing ap-
pears to be close to maximal, in contrast to the small mixings
of quarks described by off-diagonal elements of the CKM
matrix.
3. Indications in an accelerator experiment
An experiment performed at Los Alamos National
Laboratory267 in the Liquid Scintillator Neutrino Detector
~LSND! finds evidence for n ¯
m→ n ¯ e oscillations. An experi-
ment known as MiniBooNE which has begun to operate at
Fermilab will check this possibility.268
259. ‘‘Measurement of the Charged Current Interactions Produced by 8B
Solar Neutrinos at the Sudbury Neutrino Observatory,’’ SNO Collab.,
Q. R. Ahmad et al., Phys. Rev. Lett. 87, 071301 ~2001!. ~I!
260. ‘‘Direct Evidence for Neutrino Flavor Transformation from Neutral-
Current Interactions in the Sudbury Neutrino Observatory,’’ SNO
Collab., Q. R. Ahmad et al., Phys. Rev. Lett. 89, 011301 ~2002!;
‘‘Measurement of Day and Night Neutrino Energy Spectra at SNO
and Constraints on Neutrino Mixing Parameters,’’ SNO Collab., Q.
R. Ahmad et al., Phys. Rev. Lett. 89, 011302 ~2002!. ~I!
261. ‘‘First Results from KamLAND: Evidence for Reactor Anti-Neutrino
Disappearance,’’ KamLAND Collaboration, K. Eguchi et al., Phys.
Rev. Lett. 90, 021802 ~2003!.
262. ‘‘Resonance Enhancement of Oscillations in Matter and Solar
Neutrino Spectroscopy,’’ S. P. Mikheev and A. Yu. Smirnov, Yad. Fiz.
42 , 1441–1448 ~1985! @Sov. J. Nucl. Phys. 42, 913–917 ~1985!#. ~I!
263. ‘‘Neutrino Oscillations in Matter,’’ L. Wolfenstein, Phys. Rev. D 17,
2369–2374 ~1978!. ~I!
264. ‘‘Flux of Atmospheric Neutrinos,’’ T. K. Gaisser and M. Honda, Ann.
Rev. Nucl. Part. Sci. 52, 153–199 ~2002!.
265. ‘‘Evidence for Oscillation of Atmospheric Neutrinos,’’ Super-
Kamiokande Collaboration, Y. Fukuda et al., Phys. Rev. Lett. 81,
1562–1567 ~1998!. ~I!
266. ‘‘ t Neutrinos Favored Over Sterile Neutrinos in Atmospheric Muon
Neutrino Oscillations,’’ Super-Kamiokande Collaboration, S. Fukuda
et al., Phys. Rev. Lett. 85, 3999–4003 ~2000!. ~I!
267. ‘‘Evidence for Neutrino Oscillations from the Observation of n ¯ e Ap-
pearance in a n ¯ m Beam,’’ LSND Collaboration, A. Aguilar et al.,
Phys. Rev. D 64, 112007 ~2001!. ~I!
268. ‘‘The Status of MiniBooNE,’’ E. A. Hawker, Int. J. Mod. Phys. A 16
„S1B!, 755–757 ~2001!. ~I! For an up-to-date web page see:
http://www-boone.fnal.gov/.
B. Cosmic microwave background radiation
The 2.7 K radiation left over from the Big Bang contains a
wealth of information about both the early Universe and par-
ticle physics. In particular, the spatial pattern of its fluctua-
tions indicates that the Universe is exactly on the border
between open and closed, and strongly supports the idea that
the Universe underwent a period of exponential inflation
early in its history.134,135,269–271 For a review of the cosmo-
logical parameters, see Ref. 272.
269. ‘‘Big-Bang Cosmology,’’ K. A. Olive and J. A. Peacock, in Review of
Particle Physics, K. Hagiwara et al., Ref. 73, pp. 152–161. ~I!
270. ‘‘Global Cosmological Parameters: H 0 , V M , and L,’’ M. Fukugita
and C. J. Hogan, in Review of Particle Physics, K. Hagiwara et al.,
Ref. 73, pp. 166–172. ~I!
271. ‘‘Cosmic Background Radiation,’’ G. F. Smoot and D. Scott, in Re-
view of Particle Physics, K. Hagiwara et al., Ref. 73, pp. 177–181.
~I!
272. ‘‘The Cosmic Triangle: Revealing the State of the Universe,’’ N. Bah-
call, J. P. Ostriker, S. Perlmutter, and P. J. Steinhardt, Science 284,
1481-1488 ~1999!. ~I!
C. Baryon asymmetry of the Universe
To explain why the visible Universe seems to contain so
many more baryons than antibaryons, Sakharov273 proposed
314 314 Am. J. Phys., Vol. 71, No. 4, April 2003 Jonathan L. Rosner