3,583 research outputs found
A Skyrme-type proposal for baryonic matter
The Skyrme model is a low-energy effective field theory for QCD, where the
baryons emerge as soliton solutions. It is, however, not so easy within the
standard Skyrme model to reproduce the almost exact linear growth of the
nuclear masses with the baryon number (topological charge), due to the lack of
Bogomolny solutions in this model, which has also hindered analytical progress.
Here we identify a submodel within the Skyrme-type low energy effective action
which does have a Bogomolny bound and exact Bogomolny solutions, and therefore,
at least at the classical level, reproduces the nuclear masses by construction.
Due to its high symmetry, this model qualitatively reproduces the main features
of the liquid droplet model of nuclei. Finally, we discuss under which
circumstances the proposed sextic term, which is of an essentially geometric
and topological nature, can be expected to give a reasonable description of
properties of nuclei.Comment: 11 pages, 2 figures, latex. v3: Extended and revised version, some
clarifications added. Some references and 2 figures added. v4: matches
published versio
Cherenkov radio pulses from electromagnetic showers in the time-domain
The electric field of the Cherenkov radio pulse produced by a single charged
particle track in a dielectric medium is derived from first principles. An
algorithm is developed to obtain the pulse in the time domain for numerical
calculations. The algorithm is implemented in a Monte Carlo simulation of
electromagnetic showers in dense media (specifically designed for coherent
radio emission applications) as might be induced by interactions of ultra-high
energy neutrinos. The coherent Cherenkov radio emission produced by such
showers is obtained simultaneously both in the time and frequency domains. A
consistency check performed by Fourier-transforming the pulse in time and
comparing it to the frequency spectrum obtained directly in the simulations
yields, as expected, fully consistent results. The reversal of the time
structure inside the Cherenkov cone and the signs of the corresponding pulses
are addressed in detail. The results, besides testing algorithms used for
reference calculations in the frequency domain, shed new light into the
properties of the radio pulse in the time domain. The shape of the pulse in the
time domain is directly related to the depth development of the excess charge
in the shower and its width to the observation angle with respect to the
Cherenkov direction. This information can be of great practical importance for
interpreting actual data.Comment: 10 pages, 4 figure
A Phenomenological Analysis of Non-resonant Charm Meson Decays
We analyse the consequences of the usual assumption of a constant function to
fit non-resonant decays from experimental Dalitz plot describing charmed meson
decays. We first show, using the decay channel as
an example, how an inadequate extraction of the non-resonant contribution could
yield incorrect measurements for the resonant channels. We analyse how the
correct study of this decay will provide a test for the validity of
factorization in D meson decays. Finally, we show how form factors could be
extracted from non-resonant decays. We particularly discuss about the form
factor that can be measured from the decay. We
emphasize on its relevance for the study of the decay and the extraction of the meson width.Comment: 14 pages, Latex including 6 eps figure
The RMS Survey: Distribution and properties of a sample of massive young stars
The Red MSX Source (RMS) survey has identified a large sample of massive
young stellar objects (MYSOs) and ultra compact (UC) HII regions from a sample
of ~2000 MSX and 2MASS colour selected sources. Using a recent catalogue of
molecular clouds derived from the Boston University-Five College Radio
Astronomy Observatory Galactic Ring Survey (GRS), and by applying a Galactic
scaleheight cut off of 120 pc, we solve the distance ambiguity for RMS sources
located within 18\degr 54\degr. These two steps yield kinematic
distances to 291 sources out of a possible 326 located within the GRS longitude
range. Combining distances and integrated fluxes derived from spectral energy
distributions, we estimate luminosities to these sources and find that > 90%
are indicative of the presence of a massive star. We find the completeness
limit of our sample is ~10^4 Lsun, which corresponds to a zero age main
sequence (ZAMS) star with a mass of ~12 Msun. Selecting only these sources, we
construct a complete sample of 196 sources. Comparing the properties of the
sample of young massive stars with the general population, we find the
RMS-clouds are generally larger, more massive, and more turbulent. We examine
the distribution of this sub-sample with respect to the location of the spiral
arms and the Galactic bar and find them to be spatially correlated. We identify
three significant peaks in the source surface density at Galactocentric radii
of approximately 4, 6 and 8 kpc, which correspond to the proposed positions of
the Scutum, Sagittarius and Perseus spiral arms, respectively. Fitting a scale
height to the data we obtain an average value of ~29+-0.5 pc, which agrees well
with other reported values in the literature, however, we note a dependence of
the scale height on galactocentric radius with it increases from 30 pc to 45 pc
between 2.5 and 8.5 kpc.Comment: Accepted for publication by MNRAS. Paper consists of 15 pages
including 12 figures and four tables. Full versions of Tables 2 and 3 will
only be available online. The resolution of Figure 9 has been reduced - a
full resolution version of the paper can be download from here:
http://www.ast.leeds.ac.uk/cgi-bin/RMS/RMS_PUBLICATIONS.cg
Interaction between macroions mediated by divalent rod-like ions
Attractive interactions between identical like-charged macroions
in aqueous multivalent salt solution arise due to ion-ion
correlations. The mean-field level Poisson-Boltzmann (PB) theory
does not predict such behavior for point-like structureless ions.
Various multivalent ions, such as certain DNA condensing agents
or short stiff polyelectrolytes, do have an internal, often
rod-like, structure. Applying PB theory to the
generic case of divalent rod-like salt ions, we find attraction
between like-charged macroions above a critical distance between
the two individual charges of the rod-like ions. We calculate
this distance analytically within linearized PB theory.
Numerical results for the non-linear PB theory indicate strong
enhancement of the tendency to mediate attractive interactions
Radiation Damping of a BPS Monopole; an Implication to S-duality
The radiation reaction of a BPS monopole in the presence of incident
electromagnetic waves as well as massless Higgs waves is analyzed classically.
The reactive forces are compared to those of boson that is interpreted as a
dual partner of the BPS monopole. It is shown that the damping of acceleration
is dual to each other, while in the case of finite size effects the duality is
broken explicitly. Their implications on the duality are discussed.Comment: 20 pages, uses revtex, changes in reference
Practical and accurate calculations of Askaryan radiation
An in-depth characterization of coherent radio Cherenkov pulses from particle
showers in dense dielectric media, referred to as the Askaryan effect, is
presented. The time-domain calculation developed in this article is based on a
form factor to account for the lateral dimensions of the shower. It is
computationally efficient and able to reproduce the results of detailed
particle shower simulations with high fidelity in most regions of practical
interest including Fresnel effects due to the longitudinal development of the
shower. In addition, an intuitive interpretation of the characteristics of the
Askaryan pulse is provided. We expect our approach to benefit the analysis of
radio pulses in experiments exploiting the radio technique.Comment: Replaced with version published Phys. Rev.
Mechanism of Pion Production in p Scattering at 1 GeV/nucleon
The one-pion and two-pion production in the p(alpha, alpha prime)X reaction
at an energy of E{alpha} = 4.2 GeV has been studied by simultaneous
registration of the scattered alpha particles and the secondary pion or proton.
The obtained results demonstrate that the inelastic alpha-particle scattering
on the proton at the energy of the experiment proceeds either through
excitation and decay of Delta resonance in the projectile or through excitation
in the target proton of the Roper resonance, which decays mainly on a nucleon
and a pion or a nucleon and a sigma meson - system of two pions in the isospin
I = 0, S-wave.Comment: 16 pages, 10 figures. Submitted to Proceedings of the XX
International Baldin Seminar on High - Energy Physics Problems, Dubna,
October 4 - 9, 201
The RMS Survey: H2O masers towards a sample of southern hemisphere massive YSO candidates and ultra compact HII regions
Context: The Red MSX Source (RMS) survey has identified a large sample of
candidate massive young stellar objects (MYSOs) and ultra compact (UC) HII
regions from a sample of ~2000 MSX and 2MASS colour selected sources. Aims: To
search for H2O masers towards a large sample of young high mass stars and to
investigate the statistical correlation of H2O masers with the earliest stages
of massive star formation. Methods: We have used the Mopra Radio telescope to
make position-switched observations towards ~500 UCHII regions and MYSOs
candidates identified from the RMS survey and located between 190\degr < l <
30\degr. These observations have a 4 sensitivity of ~1 Jy and a
velocity resolution of ~0.4 km/s.} Results: We have detected 163 H2O masers,
approximately 75% of which were previously unknown. Comparing the maser
velocities with the velocities of the RMS sources, determined from 13CO
observations, we have identified 135 RMS-H2O maser associations, which
corresponds to a detection rate of ~27%. Taking into account the differences in
sensitivity and source selection we find our detection rate is in general
agreement with previously reported surveys. Conclusions: We find similar
detection rates for UCHII regions and MYSOs candidates, suggesting that the
conditions needed for maser activity are equally likely in these two stages of
the star formation process. Looking at the detection rate as a function of
distance from the Galactic centre we find it significantly enhanced within the
solar circle, peaking at ~37% between 6-7 kpc, which is consistent with
previous surveys of UC HII regions, possibly indicating the presence of a high
proportion of more luminous YSOs and HII regions.Comment: Accepted for publication in Astronomy and Astrophysics. 10 pages, 7
figures. Full versions of Figure 2 and Tables 1 and 2 will only be available
at the CDS or from the lead autho
Finite size effects near the onset of the oscillatory instability
A system of two complex Ginzburg - Landau equations is considered that applies at the onset of the oscillatory instability in spatial domains whose size is large (but finite) in one direction; the dependent variables are the slowly modulated complex amplitudes of two counterpropagating wavetrains. In order to obtain a well posed problem, four boundary conditions must be imposed at the boundaries. Two of them were already known, and the other two are first derived in this paper. In the generic case when the group velocity is of order unity, the resulting problem has terms that are not of the same order of magnitude. This fact allows us to consider two distinguished limits and to derive two associated (simpler) sub-models, that are briefly discussed. Our results predict quite a rich variety of complex dynamics that is due to both the modulational instability and finite size effects
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