31,424 research outputs found
Spontaneous Symmetry Breaking in Tensor Theories
In this work we study spontaneous symmetry breaking patterns in tensor
models. We focus on the patterns which lead to effective matrix theories
transforming in the adjoint of . We find the explicit form of the
Goldstone bosons which are organized as matrix multiplets in the effective
theory. The choice of these symmetry breaking patterns is motivated by the fact
that, in some contexts, matrix theories are dual to gravity theories. Based on
this, we aim to build a bridge between tensor theories, quantum gravity and
holography.Comment: 40 pp, 1 fig. Update to match the published versio
Hyperon ordering in neutron star matter
We explore the possible formation of ordered phases in neutron star matter.
In the framework of a quantum hadrodynamics model where neutrons, protons and
Lambda hyperons interact via the exchange of mesons, we compare the energy of
the usually assumed uniform, liquid phase, to that of a configuration in which
di-lambda pairs immersed in an uniform nucleon fluid are localized on the nodes
of a regular lattice. The confining potential is calculated self-consistently
as resulting from the combined action of the nucleon fluid and the other
hyperons, under the condition of beta equilibrium. We are able to obtain stable
ordered phases for some reasonable sets of values of the model parameters. This
could have important consequences on the structure and cooling of neutron
stars.Comment: 6 pages, 2 figures. To appear in the proceedings of the 4th Catania
Relativistic Ion Studies: Exotic Clustering (CRIS 2002), Catania, Italy,
10-14 Jun 200
Weak lensing evidence for a filament between A222/A223
We present a weak lensing analysis and comparison to optical and X-ray maps
of the close pair of massive clusters A222/223. Indications for a filamentary
connection between the clusters are found and discussed.Comment: 6 pages, 1 figure. To appear in Proc. IAU Colloquium 195: Outskirts
of Galaxy Clusters - Intense Life in the Suburbs. Version with higher
resolution available at
http://www.astro.uni-bonn.de/~dietrich/torino_proc.ps.g
On the use of the Fourier Transform to determine the projected rotational velocity of line-profile variable B stars
The Fourier Transform method is a popular tool to derive the rotational
velocities of stars from their spectral line profiles. However, its domain of
validity does not include line-profile variables with time-dependent profiles.
We investigate the performance of the method for such cases, by interpreting
the line-profile variations of spotted B stars, and of pulsating B tars, as if
their spectral lines were caused by uniform surface rotation along with
macroturbulence. We perform time-series analysis and harmonic least-squares
fitting of various line diagnostics and of the outcome of several
implementations of the Fourier Transform method. We find that the projected
rotational velocities derived from the Fourier Transform vary appreciably
during the pulsation cycle whenever the pulsational and rotational velocity
fields are of similar magnitude. The macroturbulent velocities derived while
ignoring the pulsations can vary with tens of km/s during the pulsation cycle.
The temporal behaviour of the deduced rotational and macroturbulent velocities
are in antiphase with each other. The rotational velocity is in phase with the
second moment of the line profiles. The application of the Fourier method to
stars with considerable pulsational line broadening may lead to an appreciable
spread in the values of the rotation velocity, and, by implication, of the
deduced value of the macroturbulence. These two quantities should therefore not
be derived from single snapshot spectra if the aim is to use them as a solid
diagnostic for the evaluation of stellar evolution models of slow to moderate
rotators.Comment: 13 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Nuclear Activity in Circumnuclear Ring Galaxies
We have analyzed the frequency and properties of the nuclear activity in a
sample of galaxies with circumnuclear rings and spirals (CNRs). This sample was
compared with a control sample of galaxies with very similar global properties
but without circumnuclear rings. We discuss the relevance of the results in
regard to the AGN feeding processes and present the following results: (i)
bright companion galaxies seem not to be important for the appearance of CNRs,
which appear to be more related to intrinsic properties of the host galaxies or
to minor merger processes; (ii) the proportion of strong bars in galaxies with
an AGN and a CNR is somewhat higher than the expected ratio of strongly barred
AGN galaxies from the results of Ho and co-workers; (iii) the incidence of
Seyfert activity coeval with CNRs is clearly larger than the rate expected from
the morphological distribution of the host galaxies; (iv) the rate of Sy 2 to
Sy 1 type galaxies with CNRs is about three times larger than the expected
ratio for galaxies without CNRs and is opposite to that predicted by the
geometric paradigm of the classical unified model for AGNs, although it does
support the hy-pothesis that Sy 2 activity is linked to circumnuclear star
formation. The possible selection effects of the sample are discussed, and we
conclude that the detected trends are strong enough to justify high quality
observations of as large as possible sets of galaxies with circumnuclear rings
and their matched control samples.Comment: Submitted to International Journal of Astronomy and Astrophysic
Switchable ultrastrong coupling in circuit QED
Superconducting quantum circuits possess the ingredients for quantum
information processing and for developing on-chip microwave quantum optics.
From the initial manipulation of few-level superconducting systems (qubits)
to their strong coupling to microwave resonators, the time has come to consider
the generation and characterization of propagating quantum microwaves. In this
paper, we design a key ingredient that will prove essential in the general
frame: a swtichable coupling between qubit(s) and transmission line(s) that can
work in the ultrastrong coupling regime, where the coupling strength approaches
the qubit transition frequency. We propose several setups where two or more
loops of Josephson junctions are directly connected to a closed (cavity) or
open transmission line. We demonstrate that the circuit induces a coupling that
can be modulated in strength and type. Given recent studies showing the
accessibility to the ultrastrong regime, we expect our ideas to have an
immediate impact in ongoing experiments
Hyperonic crystallization in hadronic matter
Published in Hadrons, Nuclei and Applications, World Scientific, Singapore,
Proc.of the Conference Bologna2000. Structure of the Nucleus at the Dawn of the
Century, G. Bonsignori, M. Bruno, A. Ventura, D. Vretenar Editors, pag. 319.Comment: 4 pages, 2figure
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