Research highlights: Theoretical Elementary Particle Physics, Astrophysics, and Cosmology
Neutrino physics and astrophysics offer
an opportunity to study both the fundamental laws of nature and the
workings of some of the most energetic objects in the universe.
Through Neutrino Eyes:
Ghostly Particles Become Astronomical Tools.
By G. Gelmini, A. Kusenko and T.
Recent discovery by the IceCube observatory of astrophysical
neutrinos with PeV energies opens a new window on the
universe. The origin of these neutrinos is still
unclear. For example, distant blazars were expected to produce a
spectrum peaked at 1 PeV. However, these neutrinos could also
come from decays of dark matter
Read an article in Los
Read research papers about PeV neutrinos
produced by blazars [PRL
(2013)]; and by dark matter [PRD 2013].
Dark matter. Most of the matter in the universe is dark
matter, which is not made of ordinary atoms. The identity of dark
matter particles remains a puzzle. A number of
well-motivated dark-matter candidates have been considered. For
example, if supersymmetry exists, than the lightest supersymmetric
particle, or gravitino, or supersymmetric Q-balls can make up the dark
matter. Another well-motivated candidate for such
a particle is the right-handed or sterile
neutrino. This idea is
supported by compelling theoretical arguments and by intriguing astrophysical
hints. The first dedicated search
for dark matter using X-ray telescopes is under
way [read research papers or a review
article in Physics
Connections: from cosmic rays to gamma rays, to
cosmic backgrounds and intergalactic magnetic fields.
Supermassive black holes in the centers of distant galaxies can
swallow large amounts of gas and stellar matter. Part of the
energy is released in the form of a powerful jet which emits
high-energy cosmic rays and gamma rays. The highest
energy gamma rays cannot travel very far because they lose energy in
interactions with starlight and infrared light re-emitted by
dust. Yet, some very energetic gamma rays have been observed from some very
distant objects. This created a puzzle, whose resolution pointed
to a possible contributions of cosmic rays. Now there is a growing
evidence that gamma rays arriving from distant sources (z>0.15) did
not originate at the source, but were produced in the cosmic ray
interactions along the line of sight. This surprising connection
between cosmic rays and gamma rays resolves several puzzles,
proves that cosmic rays of the
highest energies are, indeed, produced in active galactic nuclei,
and it opens some new ways to measure
extragalactic background light, as well as intergalactic magnetic
fields, which permeate deep space between
galaxies, possibly, since the time of the Big Bang.
papers in ApJ,
ApJ Letters, AP, and Phys. Rev. Lett.
Read an article in Science
and also in UCLA
Read about sterile neutrinos, dark matter, and the pulsar kicks: Scientific
American (2011), Nature
American (2010), Nature
(2006), Economist (2006),
(2006), CERN Courier (2006)
Physics News Update, Sky and
Telescope (1997), New
present a number of puzzles. It is difficult to understand why a single
cosmic particle should carry as much energy as a bullet! Moreover,
recent results from Pierre
Observatory indicate that many of these particles are nuclei, not
protons. This implies that natural nuclear accelerators, such as Gamma
Ray Bursts and other unusual stellar explosions, have taken place in
our own Galaxy in the past.
Read a research paper in Phys.
Read about cosmic accelerators in UCLA
News or in CERN
Courier (2010), and about Inexplicable
nuclei in Nature (2010)
Supersymmetric Q-balls are non-topological solitons that
owe their stability to a
conservation of some global charge. Baryonic
Q-balls appear in every
supersymmetric extension of the Standard Model. If
supersymmetry exists, stable Q-balls could be copiously produced at the
end of inflation and may now exist
as a form of dark matter
[read a research paper or a review
article in Rev.
Scientist article, and also a story in AIP
Physics News Update.
Although every particle has its antiparticle, there is no
antimatter in the observed universe. The process in which the
was produced in the early universe, called baryogenesis,
remains a mystery. An appealing scenario is the Affleck-Dine
baryogenesis, which can generate both ordinary
matter and dark
a review article in Rev. Mod. Phys.].
Professor Kusenko grew up in Simferopol, Crimea, Ukraine. He received his undergraduate and graduate
education at Moscow State
University and YITP, Stony Brook,
respectively, and he obtained a Ph.D. degree in 1994.
He held positions at University of Pennsylvania
and at CERN Theory
Division prior to joining UCLA.
Professor Kusenko is a
Fellow of American Physical Society and an active member of
Aspen Center for Physics.
Recent honors, awards
Fellow of American Physical Society
(elected in 2008)
of the Phys. Rev. and Phys. Rev. Lett. (2012)
List of publications from SPIRES
(drawing by Edward I. Kirich)
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