135 research outputs found
Analytic Gravitational-Force Calculations for Models of the Kuiper Belt, with Application to the Pioneer Anomaly
We use analytic techniques to study the gravitational force that would be
produced by different Kuiper-Belt mass distributions. In particular, we study
the 3-dimensional rings (and wedge) whose densities vary as the inverse of the
distance, as a constant, as the inverse-squared of the distance, as well as
that which varies according to the Boss-Peale model. These analytic
calculations yield physical insight into the physics of the problem. They also
verify that physically viable models of this type can produce neither the
magnitude nor the constancy of the Pioneer anomaly.Comment: 11 pages, 8 figures, final corrections for publicatio
5D gravity and the discrepant G measurements
It is shown that 5D Kaluza-Klein theory stabilized by an external bulk scalar
field may solve the discrepant laboratory G measurements. This is achieved by
an effective coupling between gravitation and the geomagnetic field.
Experimental considerations are also addressed.Comment: 13 pages, to be published in: Proceedings of the 18th Course of the
School on Cosmology and Gravitation: The gravitational Constant. Generalized
gravitational theories and experiments (30 April-10 May 2003, Erice). Ed. by
G. T. Gillies, V. N. Melnikov and V. de Sabbata, (Kluwer), 13pp. (in print)
(2003
Hydrogen and Helium Atoms and Molecules in an Intense Magnetic Field
We calculate the atomic structure of hydrogen and helium, atoms and molecules
in an intense magnetic field, analytically and numerically with a judiciously
chosen basis.Comment: 16 pages, 5 figures, to appear in Phys. Rev.
The Las Campanas Infrared Survey. IV. The Photometric Redshift Survey and the Rest-frame R-band Galaxy Luminosity Function at 0.5 <= z <= 1.5
(Abridged) We present rest-frame R-band galaxy luminosity function
measurements for three different redshift ranges: 0.5<=z<=0.75, 0.75<=z<=1.0,
and 1.0<=z<=1.5. Our measurements are based on photometric redshifts for ~3000
H-band selected galaxies with apparent magnitudes 17<=H<=20 from the Las
Campanas Infrared Survey. We show that our photometric redshifts are accurate
with an RMS dispersion between the photometric and spectroscopic redshifts of
\sigma_z/(1+z)~0.08. Using galaxies identified in the Hubble Deep Field South
and Chandra Deep Field South regions, we find, respectively, that (7.3\pm 0.2)
% and (16.7\pm 0.4)% of the H=1. We first demonstrate
that the systematic uncertainty inherent in the luminosity function
measurements due to uncertainties in photometric redshifts is non-negligible
and therefore must be accounted for. We then develop a technique to correct for
this systematic error by incorporating the redshift error functions of
individual galaxies in the luminosity function analysis. The redshift error
functions account for the non-gaussian characteristics of photometric redshift
uncertainties. They are the products of a convolution between the corresponding
redshift likelihood functions of individual galaxies and a Gaussian
distribution function that characterizes template-mismatch variance. We
demonstrate, based on a Monte Carlo simulation, that we are able to completely
recover the bright end of the intrinsic galaxy luminosity function using this
technique. Finally, we calculate the luminosity function separately for the
total H-band selected sample and for a sub-sample of early-type galaxies that
have a best-fit spectral type of E/S0 or Sab from the photometric redshift
analysis.Comment: 42 pages and 12 figures; Accepted for publication in the
Astrophysical Journa
Quantum Vacuum Experiments Using High Intensity Lasers
The quantum vacuum constitutes a fascinating medium of study, in particular
since near-future laser facilities will be able to probe the nonlinear nature
of this vacuum. There has been a large number of proposed tests of the
low-energy, high intensity regime of quantum electrodynamics (QED) where the
nonlinear aspects of the electromagnetic vacuum comes into play, and we will
here give a short description of some of these. Such studies can shed light,
not only on the validity of QED, but also on certain aspects of nonperturbative
effects, and thus also give insights for quantum field theories in general.Comment: 9 pages, 8 figur
Polarization control of isolated high-harmonic pulses
High-harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, thus far, the shortest isolated attosecond pulses have only been produced with linear polarization, which limits the range of physics that can be explored. Here, we demonstrate robust polarization control of isolated extreme-ultraviolet pulses by exploiting non-collinear high-harmonic generation driven by two counter-rotating few-cycle laser beams. The circularly polarized supercontinuum is produced at a central photon energy of 33âeV with a transform limit of 190âas and a predicted linear chirp of 330âas. By adjusting the ellipticity of the two counter-rotating driving pulses simultaneously, we control the polarization state of isolated extreme-ultraviolet pulsesâfrom circular through elliptical to linear polarizationâwithout sacrificing conversion efficiency. Access to the purely circularly polarized supercontinuum, combined with full helicity and ellipticity control, paves the way towards attosecond metrology of circular dichroism.The experimental work was carried out at National Tsing Hua University, Institute of Photonics Technologies, supported by the Ministry of Science and Technology, Taiwan (grants 105-2112-M-007-030-MY3, 105-2112-M-001-030 and 104-2112-M-007-012-MY3). The concept of isolated circularly polarized attosecond pulses was developed by C.H.-G., D.D.H., M.M.M., C.G.D., H.C.K., A.B. and A.J.-B.. C.H.-G. acknowledges support from the Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007â2013), under Research Executive Agency grant agreement no. 328334. C.H.-G. and L.P. acknowledge support from Junta de Castilla y LeĂłn (SA046U16) and the Ministerio de EconomĂa y Competitividad (FIS2013-44174-P, FIS2016-75652-P). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators (BBVA Foundation). M.M.M. and H.C.K. acknowledge support from the Department of Energy Basic Energy Sciences (award no. DE-FG02-99ER14982) for the concepts and experimental set-up. For part of the theory, A.B., A.J.-B., C.G.D., M.M.M. and H.C.K. acknowledge support from a Multidisciplinary University Research Initiatives grant from the Air Force Office of Scientific Research (award no. FA9550-16-1-0121). A.J.-B. also acknowledges support from the US National Science Foundation (grant no. PHY-1734006). This work utilized the Janus supercomputer, which is supported by the US National Science Foundation (grant no. CNS-0821794) and the University of Colorado, Boulder. This research made use of the high-performance computing resources of the Castilla y LeĂłn Supercomputing Center (SCAYLE, www.scayle.es), financed by the European Regional Development Fund (ERDF). J.L.E. acknowledges support from the National Science Foundation Graduate Research Fellowship (DGE-1144083). L.R. acknowledges support from the Ministerio de EducaciĂłn, Cultura y Deporte (FPU16/02591)
The VMC survey - XVIII : Radial dependence of the low-mass, 0.57-0.82 Msun stellar mass function in the galactic globular cluster 47 Tucanae
We use near-infrared observations obtained as part of the Visible and Infrared Survey Telescope for Astronomy (VISTA) Survey of the Magellanic Clouds (VMC), as well as two complementary Hubble Space Telescope (HST) data sets, to study the luminosity and mass functions (MFs) as a function of clustercentric radius of the main-sequence stars in the Galactic globular cluster 47 Tucanae. The HST observations indicate a relative deficit in the numbers of faint stars in the central region of the cluster compared with its periphery, for 18.75 †mF606W †20.9 mag (corresponding to a stellar mass range of 0.55 < m*/Mâ < 0.73). The stellar number counts at 6.â§7 from the cluster core show a deficit for 17.62 †mF606W †19.7 mag (i.e., 0.65 < m*/Mâ < 0.82), which is consistent with expectations from mass segregation. The VMC-based stellar MFs exhibit power-law shapes for masses in the range 0.55 < m*/Mâ < 0.82. These power laws are characterized by an almost constant slope, α. The radial distribution of the power-law slopes α thus shows evidence of the importance of both mass segregation and tidal stripping, for both the first- and second-generation stars in 47 Tuc.Peer reviewedFinal Accepted Versio
Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
We report on \ixpe observations of the Be-transient X-ray pulsar LS V +44
17/RX J0440.9+4431 at two luminosity levels during the giant outburst in
January--February 2023. Considering the observed spectral variability and
changes in the pulse profiles, the source was likely caught in super- and
sub-critical states with significantly different emission region geometry,
associated with the presence of accretion columns and hot spots, respectively.
We focus here on the pulse-phase resolved polarimetric analysis and find that
the observed dependencies of the polarization degree and polarization angle
(PA) on pulse phase are indeed drastically different for the two observations.
The observed differences, if interpreted within the framework of the rotating
vector model (RVM), imply dramatic variations of the spin axis inclination and
the position angle and the magnetic colatitude by tens of degrees within just a
few days separating the observations. We suggest that the apparent changes in
the observed PA phase dependence are predominantly related to the presence of a
polarized unpulsed component in addition to the polarized radiation associated
with the pulsar itself. We show that the observed PA phase dependence in both
observations can then be explained with a single set of RVM parameters defining
the pulsar's geometry. We also suggest that the additional polarized component
is likely produced by scattering of the pulsar radiation off the equatorial
disk wind.Comment: 9 pages, 5 figures, submitted to A&
Matter in Strong Magnetic Fields
The properties of matter are significantly modified by strong magnetic
fields, Gauss (), as are typically
found on the surfaces of neutron stars. In such strong magnetic fields, the
Coulomb force on an electron acts as a small perturbation compared to the
magnetic force. The strong field condition can also be mimicked in laboratory
semiconductors. Because of the strong magnetic confinement of electrons
perpendicular to the field, atoms attain a much greater binding energy compared
to the zero-field case, and various other bound states become possible,
including molecular chains and three-dimensional condensed matter. This article
reviews the electronic structure of atoms, molecules and bulk matter, as well
as the thermodynamic properties of dense plasma, in strong magnetic fields,
. The focus is on the basic physical pictures and
approximate scaling relations, although various theoretical approaches and
numerical results are also discussed. For the neutron star surface composed of
light elements such as hydrogen or helium, the outermost layer constitutes a
nondegenerate, partially ionized Coulomb plasma if , and may be in
the form of a condensed liquid if the magnetic field is stronger (and
temperature K). For the iron surface, the outermost layer of the
neutron star can be in a gaseous or a condensed phase depending on the cohesive
property of the iron condensate.Comment: 45 pages with 9 figures. Many small additions/changes. Accepted for
publication in Rev. Mod. Phy
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