30,009 research outputs found
An Accelerated Multiboson Algorithm for Coulomb Gases with Dynamical Dielectric Effects
A recent reformulation [1] of the problem of Coulomb gases in the presence of
a dynamical dielectric medium showed that finite temperature simulations of
such systems can be accomplished on the basis of completely local Hamiltonians
on a spatial lattice by including additional bosonic fields. For large systems,
the Monte Carlo algorithm proposed in Ref. [1] becomes inefficient due to a low
acceptance rate for particle moves in a fixed background multiboson field. We
show here how this problem can be circumvented by use of a coupled
particle-multiboson update procedure that improves acceptance rates on large
lattices by orders of magnitude. The method is tested on a one-component plasma
with neutral dielectric particles for a variety of system sizes.Comment: 13 pages, 2 figures, fixed typos, added reference
A New Method for Estimating Dark Matter Halo Masses using Globular Cluster Systems
All galaxies are thought to reside within large halos of dark matter, whose
properties can only be determined from indirect observations. The formation and
assembly of galaxies is determined from the interplay between these dark matter
halos and the baryonic matter they host. Although statistical relations can be
used to approximate how massive a galaxy's halo is, very few individual
galaxies have direct measurements of their halo masses. We present a method to
directly estimate the total mass of a galaxy's dark halo using its system of
globular clusters. The link between globular cluster systems and halo masses is
independent of a galaxy's type and environment, in contrast to the relationship
between galaxy halo and stellar masses. This trend is expected in models where
globular clusters form in early, rare density peaks in the cold dark matter
density field and the epoch of reionisation was roughly coeval throughout the
Universe. We illustrate the general utility of this relation by demonstrating
that a galaxy's supermassive black hole mass and global X-ray luminosity are
directly proportional to their host dark halo masses, as inferred from our new
method.Comment: 6 pages, 4 colour figures. Accepted by MNRAS Letters. Data catalogue
available from the first autho
Improved Pseudofermion Approach for All-Point Propagators
Quark propagators with arbitrary sources and sinks can be obtained more
efficiently using a pseudofermion method with a mode-shifted action.
Mode-shifting solves the problem of critical slowing down (for light quarks)
induced by low eigenmodes of the Dirac operator. The method allows the full
physical content of every gauge configuration to be extracted, and should be
especially helpful for unquenched QCD calculations. The method can be applied
for all the conventional quark actions: Wilson, Sheikoleslami-Wohlert,
Kogut-Susskind, as well as Ginsparg-Wilson compliant overlap actions. The
statistical properties of the method are examined and examples of physical
processes under study are presented.Comment: LateX, 26 pages, 10 eps figure
Modular Forms on the Double Half-Plane
We formulate a notion of modular form on the double half-plane for
half-integral weights and explain its relationship to the usual notion of
modular form. The construction we provide is compatible with certain physical
considerations due to the second author.Comment: 17 pages: Minor corrections in text (due to a helpful referee),
updated affiliations. Accepted for publication in the International Journal
for Number Theory (IJNT
Extending the baseline: Spitzer Mid-Infrared Photometry of Globular Cluster Systems in the Centaurus A and Sombrero Galaxies
Spitzer IRAC mid-infrared photometry is presented for the globular cluster
(GC) systems of the NGC 5128 ("Centaurus A") and NGC 4594 ("Sombrero")
galaxies. Existing optical photometric and spectroscopic are combined with this
new data in a comprehensive optical to mid-IR colour catalogue of 260 GCs.
Empirical colour-metallicity relationships are derived for all optical to
mid-IR colour combinations.
These colours prove to be very effective quantities to test the photometric
predictions of simple stellar population (SSP) models. In general, four SSP
models show larger discrepancies between each other and the data at bluer
wavelengths, especially at high metallicities. Such differences become very
important when attempting to use colour-colour model predictions to constrain
the ages of stellar populations. Furthermore, the age-substructure determined
from colour-colour diagrams and 91 NGC 5128 GCs with spectroscopic ages from
Beasley et al. (2008) are inconsistent, suggesting any apparent GC system
age-substructure implied by a colour-colour analysis must be verified
independently.
Unlike blue wavebands, certain optical to mid-IR colours are insensitive to
the flux from hot horizontal branch stars and thus provide an excellent
metallicity proxy. The NGC 5128 GC system shows strong bimodality in the
optical R-band to mid-IR colour distributions, hence proving it is bimodal in
metallicity. In this new colour space, a colour-magnitude trend, a "blue tilt",
is found in the NGC 5128 metal-poor GC data. The NGC 5128 young GCs do not
contribute to this trend. [abridged]Comment: 16 pages, 12 colour figures. To be published in MNRAS. Catalogue
available from the first author. Full resolution copy available here
http://lee.spitler.googlepages.com/spitzer_spitler.pd
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