99,604 research outputs found
The HI Chronicles of LITTLE THINGS BCDs: Evidence for External Perturbations in the Morphology and Kinematics of Haro 29 and Haro 36
We analyze high angular and velocity resolution HI-line data of two LITTLE
THINGS (1) blue compact dwarfs (BCDs): Haro 29 and Haro 36. Both of these BCDs
are disturbed morphologically and kinematically. Haro 29's HI data reveal a
kinematic major axis that is offset from the optical major axis, and a
disturbed outer HI component, indicating that Haro 29 may have had a past
interaction. Position-velocity diagrams of Haro 36 indicate that it has two
kinematically separate components at its center and a likely tidal tail in
front of the galaxy. We find that Haro 36 most likely had an interaction in the
past, is currently interacting with an unknown companion, or is a merger
remnant. (1) "Local Irregulars That Trace Luminosity Extremes The HI Nearby
Galaxy Survey" http://www2.lowell.edu/users/dah/littlethings/index.htmlComment: To be published in The Astronomical Journa
What is liquid in random porous media: the Barker-Henderson perturbation theory
We apply the Barker-Henderson (BH) perturbation theory to the study of a
Lennard-Jones fluid confined in a random porous matrix formed by hard sphere
particles. In order to describe the reference system needed in this
perturbation scheme, the extension of the scaled particle theory (SPT) is used.
The recent progress in the development of SPT approach for a hard sphere fluid
in a hard sphere matrix allows us to obtain very accurate results for
thermodynamic properties in such a system. Hence, we combine the BH
perturbation theory with the SPT approach to derive expressions for the
chemical potential and the pressure of a confined fluid. Using the obtained
expressions, the liquid-vapour phase diagrams of a LJ fluid in HS matrix are
built from the phase equilibrium conditions. Therefore, the effect of matrix
porosity and a size of matrix particles is considered. It is shown that a
decrease of matrix porosity lowers both the critical temperature and the
critical density, while the phase diagram becomes narrower. An increase of a
size of matrix particles leads to an increase of the critical temperature. From
the comparison it is observed that the results obtained from the theory are in
agreement with computer simulations. The approach proposed in the present study
can be extended to the case of anisotropic fluid particles in HS matrices.Comment: 17 pages, 9 figure
Noncommutative Induced Gauge Theories on Moyal Spaces
Noncommutative field theories on Moyal spaces can be conveniently handled
within a framework of noncommutative geometry. Several renormalisable matter
field theories that are now identified are briefly reviewed. The construction
of renormalisable gauge theories on these noncommutative Moyal spaces, which
remains so far a challenging problem, is then closely examined. The computation
in 4-D of the one-loop effective gauge theory generated from the integration
over a scalar field appearing in a renormalisable theory minimally coupled to
an external gauge potential is presented. The gauge invariant effective action
is found to involve, beyond the expected noncommutative version of the pure
Yang-Mills action, additional terms that may be interpreted as the gauge theory
counterpart of the harmonic term, which for the noncommutative -theory
on Moyal space ensures renormalisability. A class of possible candidates for
renormalisable gauge theory actions defined on Moyal space is presented and
discussed.Comment: 24 pages, 6 figures. Talk given at the "International Conference on
Noncommutative Geometry and Physics", April 2007, Orsay (France). References
updated. To appear in J. Phys. Conf. Se
Windows over a New Low Energy Axion
We outline some general features of possible extensions of the Standard Model
that include anomalous U(1) gauge symmetries, a certain number of axions and
their mixings with the CP-odd Higgs sector. As previously shown, after the
mixing one of the axions becomes a physical pseudoscalar (the axi-Higgs) that
can take the role of a modified QCD axion. It can be driven to be very light by
the same non-perturbative effects that are held responsible for the solution of
the strong CP-problem. At the same time the axi-Higgs has a sizeable gauge
interaction, which is not allowed to the Peccei-Quinn axion, possibly
explaining the PVLAS results. We point out that the Wess-Zumino term, typical
of these models, can be both interpreted as an anomaly inflow from higher
dimensional theories (second window) but also as a result of partial decoupling
of an extra Higgs sector (and of a fermion) that leaves behind an effective
anomalous abelian theory (first window) in a broken St\"{u}ckelberg phase. The
possibility that the axi-Higgs can be heavy, of the order of the Higgs mass or
larger, however, can't be excluded. The potentialities for the discovery of
this particle and of anomaly effects in the neutral current sector at the LHC
are briefly discussed in the context of a superstring inspired model (second
window), but with results that remain valid also if any of the two
possibilities is realized in Nature.Comment: 17 pages, 8 Figs, replaced with revised final version, to appear on
Phys.Lett.
Stuckelberg Axions and the Effective Action of Anomalous Abelian Models 1. A unitarity analysis of the Higgs-axion mixing
We analyze the quantum consistency of anomalous abelian models and of their
effective field theories, rendered anomaly-free by a Wess-Zumino term, in the
case of multiple abelian symmetries. These models involve the combined
Higgs-Stuckelberg mechanism and predict a pseudoscalar axion-like field that
mixes with the goldstones of the ordinary Higgs sector. We focus our study on
the issue of unitarity of these models both before and after spontaneous
symmetry breaking and detail the set of Ward identities and the organization of
the loop expansion in the effective theory. The analysis is performed on simple
models where we show, in general, the emergence of new effective vertices
determined by certain anomalous interactions.Comment: 67 pages, 26 figures, replaced with revised final version, to appear
on JHE
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