10,254 research outputs found
Population synthesis of HII galaxies
We study the stellar population of galaxies with active star formation,
determining ages of the stellar components by means of spectral population
synthesis of their absorption spectra. The data consist of optical spectra of
185 nearby () emission line galaxies. They are mostly HII
galaxies, but we also include some Starbursts and Seyfert 2s, for comparison
purposes. They were grouped into 19 high signal-to-noise ratio template
spectra, according to their continuum distribution, absorption and emission
line characteristics. The templates were then synthesized with a star cluster
spectral base. The synthesis results indicate that HII galaxies are typically
age-composite stellar systems, presenting important contribution from
generations up to as old as 500 Myr. We detect a significant contribution of
populations with ages older than 1 Gyr in two groups of HII galaxies. The age
distributions of stellar populations among Starbursts can vary considerably
despite similarities in the emission line spectra. In the case of Seyfert 2
groups we obtain important contributions of old population, consistent with a
bulge. From the diversity of star formation histories, we conclude that typical
HII galaxies in the local universe are not systems presently forming their
first stellar generation.Comment: 12 pages, 4 figures, MNRAS in pres
Lagrangian approach to a symplectic formalism for singular systems
We develop a Lagrangian approach for constructing a symplectic structure for
singular systems. It gives a simple and unified framework for understanding the
origin of the pathologies that appear in the Dirac-Bergmann formalism, and
offers a more general approach for a symplectic formalism, even when there is
no Hamiltonian in a canonical sense. We can thus overcome the usual limitations
of the canonical quantization, and perform an algebraically consistent
quantization for a more general set of Lagrangian systems.Comment: 30 page
The Gelfand map and symmetric products
If A is an algebra of functions on X, there are many cases when X can be
regarded as included in Hom(A,C) as the set of ring homomorphisms. In this
paper the corresponding results for the symmetric products of X are introduced.
It is shown that the symmetric product Sym^n(X) is included in Hom(A,C) as the
set of those functions that satisfy equations generalising f(xy)=f(x)f(y).
These equations are related to formulae introduced by Frobenius and, for the
relevant A, they characterise linear maps on A that are the sum of ring
homomorphisms. The main theorem is proved using an identity satisfied by
partitions of finite sets.Comment: 14 pages, Late
Modeling self-organization of communication and topology in social networks
This paper introduces a model of self-organization between communication and
topology in social networks, with a feedback between different communication
habits and the topology. To study this feedback, we let agents communicate to
build a perception of a network and use this information to create strategic
links. We observe a narrow distribution of links when the communication is low
and a system with a broad distribution of links when the communication is high.
We also analyze the outcome of chatting, cheating, and lying, as strategies to
get better access to information in the network. Chatting, although only
adopted by a few agents, gives a global gain in the system. Contrary, a global
loss is inevitable in a system with too many liarsComment: 6 pages 7 figures, Java simulation available at
http://cmol.nbi.dk/models/inforew/inforew.htm
Signals of R-parity violating supersymmetry in neutrino scattering at muon storage rings
Neutrino oscillation signals at muon storage rings can be faked by
supersymmetric (SUSY) interactions in an R-parity violating scenario. We
investigate the -appearance signals for both long-baseline and near-site
experiments, and conclude that the latter is of great use in distinguishing
between oscillation and SUSY effects. On the other hand, SUSY can cause a
manifold increase in the event rate for wrong-sign muons at a long-baseline
setting, thereby providing us with signatures of new physics.Comment: 7 pages LaTeX, 4 ps figures, accepted for publication in Phys. Rev.
The Nature of the Optical Light in Seyfert 2 Galaxies with Polarized Continuum
We investigate the nature of the optical continuum and stellar population in
the central kpc of the Seyfert 2s Mrk 348, Mrk 573, NGC 1358 and Mrk 1210 using
long-slit spectra obtained along the radio or extended emission axis. These
galaxies are known to have polarized continuum-including polarized broad lines
in Mrk 348 and Mrk 1210--and previous studies indicate featureless continuum
(FC) contributions in the 20-50% range at 5500 A. Nevertheless, our
measurements of the equivalent widths of absorption lines and continuum ratios
as a function of distance from the nuclei show no dilution of the lines nor
bluening of the spectrum, as expected if a blue FC was present at the nucleus
in the above proportions. We investigate one possibility to account for this
effect: that the stellar population at the nucleus is the same as that from the
surrounding bulge and dominates the nuclear light. A spectral analysis confirms
that this hypothesis works for Mrk 348, NGC 1358 and Mrk 1210, for which we
find stellar contributions at the nucleus larger than 90% at all wavelengths.
We find that a larger stellar population contribution to the nuclear spectra
can play the role of the ``second FC'' source inferred from previous studies.
Stellar population synthesis shows that the nuclear regions of Mrk 348 and Mrk
1210 have important contributions of young to intermediate age stars (0--100
Myr), not present in templates of elliptical galaxies. In the case of Mrk 1210,
this is further confirmed by the detection of a ``Wolf-Rayet feature'' in the
nuclear emission-line spectrum.Comment: ApJ, accepted. Uses aaspp4.sty. [22 pages
Lepton number violating interactions and their effects on neutrino oscillation experiments
Mixing between bosons that transform differently under the standard model
gauge group, but identically under its unbroken subgroup, can induce
interactions that violate the total lepton number. We discuss four-fermion
operators that mediate lepton number violating neutrino interactions both in a
model-independent framework and within supersymmetry (SUSY) without R-parity.
The effective couplings of such operators are constrained by: i) the upper
bounds on the relevant elementary couplings between the bosons and the
fermions, ii) by the limit on universality violation in pion decays, iii) by
the data on neutrinoless double beta decay and, iv) by loop-induced neutrino
masses. We find that the present bounds imply that lepton number violating
neutrino interactions are not relevant for the solar and atmospheric neutrino
problems. Within SUSY without R-parity also the LSND anomaly cannot be
explained by such interactions, but one cannot rule out an effect
model-independently. Possible consequences for future terrestrial neutrino
oscillation experiments and for neutrinos from a supernova are discussed.Comment: 28 pages, 2 figures, Late
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