21,069 research outputs found
Frontiers of Astrophysics - Workshop Summary
We summarize recent results presented in the astrophysics session during a
conference on ``Frontiers of Contemporary Physics''. We will discuss three main
fields (High-Energy Astrophysics, Relativistic Astrophysics, and Cosmology),
where Astrophysicists are pushing the limits of our knowledge of the physics of
the universe to new frontiers. Since the highlights of early 1997 were the
first detection of a redshift and the optical and X-ray afterglows of gamma-ray
bursts, as well as the first well-documented flares of TeV-Blazars across a
large fraction of the electromagnetic spectrum, we will concentrate on these
topics. Other topics covered are black holes and relativistic jets, high-energy
cosmic rays, Neutrino-Astronomy, extragalactic magnetic fields, and
cosmological models.Comment: Proceedings of the Workshop "Frontiers in Contemporary Physics",
Nashville, May 11-16, 1997, AIP-conference series, Ed. T. Weiler & R.
Panvini, LaTex(aip2col), 13 pages, preprint also available at
http://www.astro.umd.edu/~hfalcke/publications.html#frontier
Particle Astrophysics and Cosmology: Cosmic Laboratories for New Physics (Summary of the Snowmass 2001 P4 Working Group)
The past few years have seen dramatic breakthroughs and spectacular and
puzzling discoveries in astrophysics and cosmology. In many cases, the new
observations can only be explained with the introduction of new fundamental
physics. Here we summarize some of these recent advances. We then describe
several problem in astrophysics and cosmology, ripe for major advances, whose
resolution will likely require new physics.Comment: 27 pages, 14 figure
Potential of EBL and cosmology studies with the Cherenkov Telescope Array
Very high energy (VHE, E >100 GeV) gamma-rays are absorbed via interaction
with low-energy photons from the extragalactic background light (EBL) if the
involved photon energies are above the threshold for electron-positron pair
creation. The VHE gamma-ray absorption, which is energy dependent and increases
strongly with redshift, distorts the VHE spectra observed from distant objects.
The observed energy spectra of the AGNs carry, therefore, an imprint of the
EBL. The detection of VHE gamma-ray spectra of distant sources (z = 0.11 -
0.54) by current generation Imaging Atmospheric Cherenkov Telescopes (IACTs)
enabled to set strong upper limits on the EBL density, using certain basic
assumptions about blazar physics. In this paper it is studied how the improved
sensitivity of the Cherenkov Telescope Array (CTA) and its enlarged energy
coverage will enlarge our knowledge about the EBL and its sources. CTA will
deliver a large sample of AGN at different redshifts with detailed measured
spectra. In addition, it will provide the exciting opportunity to use gamma ray
bursts (GRBs) as probes for the EBL density at high redshifts.Comment: 12 pages, 9 figures, to appear in Astroparticle Physics. arXiv admin
note: text overlap with arXiv:1005.119
How Dark Matter Came to Matter
The history of the dark matter problem can be traced back to at least the
1930s, but it was not until the early 1970s that the issue of 'missing matter'
was widely recognized as problematic. In the latter period, previously separate
issues involving missing mass were brought together in a single anomaly. We
argue that reference to a straightforward 'accumulation of evidence' alone is
inadequate to comprehend this episode. Rather, the rise of cosmological
research, the accompanying renewed interest in the theory of relativity and
changes in the manpower division of astronomy in the 1960s are key to
understanding how dark matter came to matter. At the same time, this story may
also enlighten us on the methodological dimensions of past practices of physics
and cosmology.Comment: Accepted for publication in Nature Astronomy. Corrected typ
From Equivalence Principles to Cosmology: Cosmic Polarization Rotation, CMB Observation, Neutrino Number Asymmetry, Lorentz Invariance and CPT
In this paper, we review the approach leading to cosmic polarization rotation
observation and present the current status with an outlook. In the study of the
relations among equivalence principles, we found that long-range
pseudoscalar-photon interaction is allowed. Pseudoscalar-photon interaction
would induce a rotation of linear polarization of electromagnetic wave
propagating with cosmological/astrophysical distance. In 2002, DASI
successfully observed the polarization of the cosmological microwave background
radiation. In 2003, WMAP observed the correlation of polarization with
temperature anisotropy at more than 10 sigma in the cosmological microwave
background. From this high polarization-temperature correlation in WMAP
observation, we put a limit of 0.1 rad on the rotation of linear polarization
of cosmological microwave background (CMB) propagation. Pseudoscalar-photon
interaction is proportional to the gradient of the pseudoscalar field. From
phenomenological point of view, this gradient could be neutrino number
asymmetry current, other density current, or a constant vector. In these
situations, Lorentz invariance or CPT may or may not effectively be violated.
In this paper, we review and compile various results. Better accuracy in CMB
polarization observation is expected from PLANCK mission to be launched next
year. A dedicated CMB polarization observer in the future would probe this
fundamental issue more deeply.Comment: 9 pages, 2 figures, a few references with corresponding text change
added in this version, invited talk given in VIII Asia-Pacific International
Conference on Gravitation and Astophysics (ICGA8), August 29 - September 1,
2007, Nara Women's University, Japan, submitted to Progress of Theoretical
Physics Supplemen
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