30 research outputs found
Electron g-2 in Light-Front Quantization
Basis Light-front Quantization has been proposed as a nonperturbative
framework for solving quantum field theory. We apply this approach to Quantum
Electrodynamics and explicitly solve for the light-front wave function of a
physical electron. Based on the resulting light-front wave function, we
evaluate the electron anomalous magnetic moment. Nonperturbative mass
renormalization is performed. Upon extrapolation to the infinite basis limit
our numerical results agree with the Schwinger result obtained in perturbation
theory to an accuracy of 0.06%.Comment: 6 pages, 4 figure
A search for the most massive galaxies: Double Trouble?
We describe the results of a search for galaxies with large (> 350 km/s)
velocity dispersions. The largest systems we have found appear to be the
extremes of the early-type galaxy population: compared to other galaxies with
similar luminosities, they have the largest velocity dispersions and the
smallest sizes. However, they are not distant outliers from the Fundamental
Plane and mass-to-light scaling relations defined by the bulk of the early-type
galaxy population. They may host the most massive black holes in the Universe,
and their abundance and properties can be used to constrain galaxy formation
models. Clear outliers from the scaling relations tend to be objects in
superposition (angular separations smaller than 1 arcsec), evidence for which
comes sometimes from the spectra, sometimes from the images, and sometimes from
both. The statistical properties of the superposed pairs, e.g., the
distribution of pair separations and velocity dispersions, can be used to
provide useful information about the expected distribution of image
multiplicities, separations and flux ratios due to gravitational lensing by
multiple lenses, and may also constrain models of their interaction rates.Comment: 20 pages, 8 figures. Accepted by AJ. The full set of figures in
Appendix B is available at
http://www.physics.upenn.edu/~bernardm/PAPERS/BIGEtypes/bernardi.FIG-B.ps.gz
Figure 8 did not show the set of galaxies described in the text of the
appendix. This has now been correcte
Candidate Isolated Neutron Stars and Other Optically Blank X-ray Fields Identified from the ROSAT All-Sky and Sloan Digital Sky Surveys
Only seven radio-quiet isolated neutron stars (INSs) emitting thermal X rays
are known, a sample that has yet to definitively address such fundamental
issues as the equation of state of degenerate neutron matter. We describe a
selection algorithm based on a cross-correlation of the ROSAT All-Sky Survey
(RASS) and the Sloan Digital Sky Survey (SDSS) that identifies X-ray error
circles devoid of plausible optical counterparts to the SDSS g~22 magnitudes
limit. We quantitatively characterize these error circles as optically blank;
they may host INSs or other similarly exotic X-ray sources such as radio-quiet
BL Lacs, obscured AGN, etc. Our search is an order of magnitude more selective
than previous searches for optically blank RASS error circles, and excludes the
99.9% of error circles that contain more common X-ray-emitting subclasses. We
find 11 candidates, nine of which are new. While our search is designed to find
the best INS candidates and not to produce a complete list of INSs in the RASS,
it is reassuring that our number of candidates is consistent with predictions
from INS population models. Further X-ray observations will obtain pinpoint
positions and determine whether these sources are entirely optically blank at
g~22, supporting the presence of likely isolated neutron stars and perhaps
enabling detailed follow-up studies of neutron star physics.Comment: Accepted for publication in the AJ; higher resolution figures
available at http://www.astro.washington.edu/agueros/pub
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Swift Detects a Remarkable Gamma-Ray Burst, GRB 060614, That Introduces a New Classification Scheme
Gamma ray bursts (GRBs) are known to come in two duration classes, separated at {approx}2 s. Long bursts originate from star forming regions in galaxies, have accompanying supernovae (SNe) when near enough to observe and are likely caused by massive-star collapsars. Recent observations show that short bursts originate in regions within their host galaxies with lower star formation rates, consistent with binary neutron star (NS) or NS - black hole (BH) mergers. Moreover, although their hosts are predominantly nearby galaxies, no SNe have been so far associated with short GRBs. We report here on the bright, nearby GRB 060614 that does not fit in either class. Its {approx}102 s duration groups it with long GRBs, while its temporal lag and peak luminosity fall entirely within the short GRB subclass. Moreover, very deep optical observations exclude an accompanying supernova, similar to short GRBs. This combination of a long duration event without accompanying SN poses a challenge to both a collapsar and merging NS interpretation and opens the door on a new GRB classification scheme that straddles both long and short bursts
NuSTAR Detection of the Blazar B2 1023+25 at Redshift 5.3
B2 1023+25 is an extremely radio-loud quasar at z = 5.3 that was first identified as a likely high-redshift blazar candidate in the SDSS+FIRST quasar catalog. Here, we use the Nuclear Spectroscopic Telescope Array (NuSTAR) to investigate its non-thermal jet emission, whose high-energy component we detected in the hard X-ray energy band. The X-ray flux is ~ 5.5 x 10^(-14)erg cm^(-2) s^(-1) (5-10 keV) and the photon spectral index is Γ_X ≃ 1.3-1.6. Modeling the full spectral energy distribution, we find that the jet is oriented close to the line of sight, with a viewing angle of ~3°, and has significant Doppler boosting, with a large bulk Lorentz factor ~13, which confirms the identification of B2 1023+25 as a blazar. B2 1023+25 is the first object at redshift larger than 5 detected by NuSTAR, demonstrating the ability of NuSTAR to investigate the early X-ray universe and to study extremely active supermassive black holes located at very high redshift
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Breaking the Attosecond, Angstrom and TV/M Field Barriers with Ultra-Fast Electron Beams
Recent initiatives at UCLA concerning ultra-short, GeV electron beam generation have been aimed at achieving sub-fs pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode. This use of very low Q beams may allow existing FEL injectors to produce few-100 attosecond pulses, with very high brightness. Towards this end, recent experiments at the LCLS have produced {approx}2 fs, 20 pC electron pulses. We discuss here extensions of this work, in which we seek to exploit the beam brightness in FELs, in tandem with new developments in cryogenic undulator technology, to create compact accelerator-undulator systems that can lase below 0.15 {angstrom}, or be used to permit 1.5 {angstrom} operation at 4.5 GeV. In addition, we are now developing experiments which use the present LCLS fs pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator for frontier high energy physics applications