4,214 research outputs found
Massive photons and Lorentz violation
All quadratic translation- and gauge-invariant photon operators for Lorentz
breakdown are included into the Stueckelberg Lagrangian for massive photons in
a generalized \xi-gauge. The corresponding dispersion relation and tree-level
propagator are determined exactly, and some leading-order results are derived.
The question of how to include such Lorentz-violating effects into a
perturbative quantum-field expansion is addressed. Applications of these
results within Lorentz-breaking quantum field theories include the
regularization of infrared divergences as well as the free propagation of
massive vector bosons.Comment: 12 pages, 1 figur
Mutual funds and the U.S. equity market
Mutual funds have become an important intermediary between households and financial markets, especially the equity market. About half of all households have a mutual fund account, and mutual funds hold about one-fifth of household financial assets. Because households have favored equity investments in their mutual fund accounts, mutual funds currently hold about one-fifth of all publicly traded U.S. equities. In addition to discussing the recent growth of mutual funds and their role in household finances, this article analyzes the relationship between households' investment decisions in equity mutual funds and equity market prices.Mutual funds ; Capital market ; Stock market
A First Experimental Limit on In-matter Torsion from Neutron Spin Rotation in Liquid He-4
We report the first experimental upper bound to our knowledge on possible
in-matter torsion interactions of the neutron from a recent search for parity
violation in neutron spin rotation in liquid He-4. Our experiment constrains a
coefficient consisting of a linear combination of parameters involving
the time components of the torsion fields and from the nucleons
and electrons in helium which violates parity. We report an upper bound of
GeV at 68% confidence level and indicate other physical
processes that could be analyzed to constrain in-matter torsion.Comment: 12 pages, typo correcte
Can galaxy growth be sustained through HI-rich minor mergers?
Local galaxies with specific star-formation rates (star-formation rate per
unit mass; sSFR~0.2-10/Gyr) as high as distant galaxies (z~1-3), are very rich
in HI. Those with low stellar masses, log M_star (M_sun)=8-9, for example, have
M_HI/M_star~5-30. Using continuity arguments of Peng et al. (2014), whereby the
specific merger rate is hypothesized to be proportional to the specific
star-formation rate, and HI gas mass measurements for local galaxies with high
sSFR, we estimate that moderate mass galaxies, log M_star (M_sun)=9-10.5, can
acquire sufficient gas through minor mergers (stellar mass ratios ~4-100) to
sustain their star formation rates at z~2. The relative fraction of the gas
accreted through minor mergers declines with increasing stellar mass and for
the most massive galaxies considered, log M_star (M_sun)=10.5-11, this
accretion rate is insufficient to sustain their star formation. We checked our
minor merger hypothesis at z=0 using the same methodology but now with
relations for local normal galaxies and find that minor mergers cannot account
for their specific growth rates, in agreement with observations of HI-rich
satellites around nearby spirals. We discuss a number of attractive features,
like a natural down-sizing effect, in using minor mergers with extended HI
disks to support star formation at high redshift. The answer to the question
posed by the title, "Can galaxy growth be sustained through \HI-rich minor
mergers?", is maybe, but only for relatively low mass galaxies and at high
redshift.Comment: 6 pages, 3 figures; in final acceptance by A&
Seals at sea: modelling seal distribution in the German bight based on aerial survey data
The Wadden Sea is an important habitat for harbour seals and grey seals. They regularly haul-out on sandbanks and islands along the coast. Comparably little is known about the time seals spend at sea and how they use the remainder of the North Sea. Yet, human activity in offshore waters is increasing and information on seal distribution in the North Sea is crucial for conservation and management. Aerial line transect surveys were conducted in the German bight from 2002 to 2007 to investigate the distribution and abundance of marine mammals. Distance sampling methodology was combined with density surface modelling for a spatially explicit analysis of seal distribution in the German North Sea. Depth and distance to coast were found to be relevant predictor variables for seal density. Density surface modelling allowed for a depiction of seal distribution in the study area as well as an abundance estimate. This is the first study to use aerial survey data to develop a density surface model (DSM) for a spatially explicit distribution estimate of seals at se
Dissecting the complex environment of a distant quasar with MUSE
High redshift quasars can be used to trace the early growth of massive
galaxies and may be triggered by galaxy-galaxy interactions. We present MUSE
science verification data on one such interacting system consisting of the
well-studied z=3.2 PKS1614+051 quasar, its AGN companion galaxy and bridge of
material radiating in Lyalpha between the quasar and its companion. We find a
total of four companion galaxies (at least two galaxies are new discoveries),
three of which reside within the likely virial radius of the quasar host,
suggesting that the system will evolve into a massive elliptical galaxy by the
present day. The MUSE data are of sufficient quality to split the extended
Lyalpha emission line into narrow velocity channels. In these the gas can be
seen extending towards each of the three neighbouring galaxies suggesting that
the emission-line gas originates in a gravitational interaction between the
galaxies and the quasar host. The photoionization source of this gas is less
clear but is probably dominated by the two AGN. The quasar's Lyalpha emission
spectrum is double-peaked, likely due to absorbing neutral material at the
quasar's systemic redshift with a low column density as no damping wings are
present. The spectral profiles of the AGN and bridge's Lyalpha emission are
also consistent with absorption at the same redshift indicating this neutral
material may extend over > 50 kpc. The fact that the neutral material is seen
in the line of sight to the quasar and transverse to it, and the fact that we
see the quasar and it also illuminates the emission-line bridge, suggests the
quasar radiates isotropically and any obscuring torus is small. These results
demonstrate the power of MUSE for investigating the dynamics of interacting
systems at high redshift.Comment: 9 pages, 6 figures, published in MNRA
The cluster environments of radio loud quasars
We have carried out multi-colour imaging of the fields of a statistically
complete sample of low-frequency selected radio loud quasars at 0.6<z<1.1, in
order to determine the characteristics of their environments. The largest radio
sources are located in the field, and smaller steep-spectrum sources are more
likely to be found in richer environments, from compact groups through to
clusters. This radio-based selection (including source size) of high redshift
groups and clusters is a highly efficient method of detecting rich environments
at these redshifts. Although our single filter clustering measures agree with
those of other workers, we show that these statistics cannot be used reliably
on fields individually, colour information is required for this.Comment: 5 pages, 3 figures, contribution to "Tracing Cosmic Evolution with
Galaxy Clusters" (Sesto 2001), ASP Conference Serie
- …