1,348 research outputs found
Monte Carlo study of the discontinuous quantum phase transition in the transverse-field Ising model on the pyrochlore lattice
The antiferromagnetic Ising model on the pyrochlore lattice exhibits a
quantum phase transition in an applied transverse field from the low-field
quantum spin-ice phase to the high-field polarized regime. Recent
field-theoretical analysis and series expansion results indicate this to be a
discontinuous, first-order transition. Here, we explore this transition using
quantum Monte Carlo simulations in order to assess this scenario and study the
thermodynamic properties in the vicinity of the quantum phase transition. For
this purpose, we also consider several variants of extended cluster-update
schemes for the transverse field Ising antiferromagnet on frustrated lattices
and compare their performance to the conventional bond-based algorithm for the
transverse field Ising model on the pyrochlore lattice.Comment: 13 pages, 15 figures, v2: as publishe
Gauss Law, Minimal Coupling and Fermionic PEPS for Lattice Gauge Theories
In these lecture notes, we review some recent works on Hamiltonian lattice
gauge theories, that involve, in particular, tensor network methods. The
results reviewed here are tailored together in a slightly different way from
the one used in the contexts where they were first introduced, by looking at
the Gauss law from two different points of view: for the gauge field it is a
differential equation, while from the matter point of view, on the other hand,
it is a simple, explicit algebraic equation. We will review and discuss what
these two points of view allow and do not allow us to do, in terms of unitarily
gauging a pure-matter theory and eliminating the matter from a gauge theory,
and relate that to the construction of PEPS (Projected Entangled Pair States)
for lattice gauge theories.Comment: Fourth version: minor revision of notes (third version) for SciPost.
Notes originally prepared for two lectures given in the Focus week "Tensor
Networks and Entanglement" of the workshop "Entanglement in Quantum System",
at the Galileo Galilei Institute for Theoretical Physics (GGI), Florence,
Italy in June 201
Classical radio source propagating into outer HI disc in NGC 3801
We present observations of a large-scale disc of neutral hydrogen (HI) in the
nearby Fanaroff & Riley type-I radio galaxy NGC 3801 with the Westerbork
Synthesis Radio Telescope. The HI disc (34 kpc in diameter and with M_HI = 1.3
x 10^9 M_sun) is aligned with the radio jet axis. This makes NGC 3801 an ideal
system for investigating the evolution of a small radio source through its host
galaxy's cold ISM. The large-scale HI disc is perpendicular to a known inner CO
disc and dust-lane. We argue that the formation history of the large-scale HI
disc is in agreement with earlier speculation that NGC 3801 was involved in a
past gas-rich galaxy-galaxy merger (although other formation histories are
discussed). The fact that NGC 3801 is located in an environment of several
HI-rich companions, and shows indications of ongoing interaction with the
nearby companion NGC 3802, strengthens this possibility. The large amounts of
ambient cold ISM, combined with X-ray results by Croston et al (2007) on the
presence of over-pressured radio jets and evidence for an obscuring torus, are
properties that are generally not, or no longer, associated with more evolved
FR-I radio sources. We do show, however, that the HI properties of NGC 3801 are
comparable to those of a significant fraction of nearby low-power compact radio
sources, suggesting that studies of NGC 3801 may reveal important insight into
a more general phase in the evolution of at least a significant fraction of
nearby radio galaxies.Comment: Accepted for publication in MNRAS (6 figure, 2 tables
Gas and stars in compact (young) radio sources
Gas can be used to trace the formation and evolution of galaxies as well as
the impact that the nuclear activity has on the surrounding medium. For nearby
compact radio sources, we have used observations of neutral hydrogen - that we
detected in emission distributed over very large scales - combined with the
study of the stellar population and deep optical images to investigate the
history of the formation of their host galaxy and the triggering of the
activity. For more distant and more powerful compact radio sources, we have
used optical spectra and HI - in absorption - to investigate the presence of
fast outflows that support the idea that compact radio sources are young radio
loud AGN observed during the early stages of their evolution and currently
shredding their natal cocoons through extreme circumnuclear outflows. We will
review the most recent results obtained from these projects.Comment: 4 pages, 2 figures, to appear in the proceedings of the '4th Workshop
on Compact Steep Spectrum and Gigahertz-Peaked Spectrum Radio Sources', AN in
pres
Cold gas & mergers: fundamental difference in HI properties of different types of radio galaxies?
We present results of a study of large-scale neutral hydrogen (HI) gas in
nearby radio galaxies. We find that the early-type host galaxies of different
types of radio sources (compact, FR-I and FR-II) appear to contain
fundamentally different large-scale HI properties: enormous regular rotating
disks and rings are present around the host galaxies of a significant fraction
of low power compact radio sources, while no large-scale HI is detected in low
power, edge-darkened FR-I radio galaxies. Preliminary results of a study of
nearby powerful, edge-brightened FR-II radio galaxies show that these systems
generally contain significant amounts of large-scale HI, often distributed in
tail- or bridge-like structures, indicative of a recent galaxy merger or
collision. Our results suggest that different types of radio galaxies may have
a different formation history, which could be related to a difference in the
triggering mechanism of the radio source. If confirmed by larger studies with
the next generation radio telescopes, this would be in agreement with previous
optical studies that suggest that powerful FR-II radio sources are likely
triggered by galaxy mergers and collisions, while the lower power FR-I sources
are fed in other ways (e.g. through the accretion of hot IGM). The giant HI
disks/rings associated with some compact sources could - at least in some cases
- be the relics of much more advanced mergers.Comment: 5 pages, 3 figures - to appear in PoS, "The Modern Radio Universe:
From Planets to Dark Energy Conference", Manchester UK, eds: Beswick, Diamond
& Schilizz
The location and impact of jet-driven outflows of cold gas: the case of 3C293
The nearby radio galaxy 3C293 is one of a small group of objects where
extreme outflows of neutral hydrogen have been detected. However, due to the
limited spatial resolution of previous observations, the exact location of the
outflow was not able to be determined. In this letter, we present new higher
resolution VLA observations of the central regions of this radio source and
detect a fast outflow of HI with a FWZI velocity of \Delta v~1200 km/s
associated with the inner radio jet, approximately 0.5 kpc west of the central
core. We investigate possible mechanisms which could produce the observed HI
outflow and conclude that it is driven by the radio-jet. However, this outflow
of neutral hydrogen is located on the opposite side of the nucleus to the
outflow of ionised gas previously detected in this object. We calculate a mass
outflow rate in the range of 8-50 solar masses/yr corresponding to a kinetic
energy power injected back into the ISM of 1.38x10^{42} - 1.00x10^{43} erg/s or
0.01 - 0.08 percent of the Eddington luminosity. This places it just outside
the range required by some galaxy evolution simulations for negative feedback
from the AGN to be effective in halting star-formation within the galaxy.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
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