53,706 research outputs found
Ultraluminous X-ray Sources forming in low metallicity natal environments
In the last few years multiwavelength observations have boosted our
understanding of Ultraluminous X-ray Sources (ULXs). Yet, the most fundamental
questions on ULXs still remain to be definitively answered: do they contain
stellar or intermediate mass black holes? How do they form? We investigate the
possibility that the black holes hosted in ULXs originate from massive (40-120
) stars in low metallicity natal environments. Such black holes have a
typical mass in the range and may account for the
properties of bright (above erg s) ULXs. More than massive black holes might have been generated in this way in the metal
poor Cartwheel galaxy during the last years and might power most of the
ULXs observed in it. Support to our interpretation comes from NGC 1313 X-2, the
first ULX with a tentative identification of the orbital period in the optical
band, for which binary evolution calculations show that the system is most
likely made by a massive donor dumping matter on a black hole.Comment: 4 pages. To appear in the Proceedings of the Conference "X-Ray
Astronomy 2009: Present Status, Multiwavelength Approach and Future
Perspectives", Bologna, Italy, September 2009, Eds. A. Comastri, M. Cappi, L.
Angelini, 2010 AIP (in press)
K -> pi pi and a light scalar meson
We explore the Delta-I= 1/2 rule and epsilon'/epsilon in K -> pi pi
transitions using a Dyson-Schwinger equation model. Exploiting the feature that
QCD penguin operators direct K^0_S transitions through 0^{++} intermediate
states, we find an explanation of the enhancement of I=0 K -> pi pi transitions
in the contribution of a light sigma-meson. This mechanism also affects
epsilon'/epsilon.Comment: 7 pages, REVTE
The Calculation of Vacuum Properties from the Global Color Symmetry Model
A modified method for calculating the non-perturbative quark vacuum
condensates from the global color symmetry model is derived. Within this
approach it is shown that the vacuum condensates are free of ultraviolet
divergence which is different from previous studies. As a special, the
two-quark condensate and the mixed quark-gluon condensate are calculated. A
comparision with the results of the other nonperturbative QCD approaches is
given.Comment: 17 page
Herding cats: observing live coding in the wild
After a momentous decade of live coding activities, this paper seeks to explore the practice with the aim of situating it in the history of contemporary arts and music. The article introduces several key points of investigation in live coding research and discusses some examples of how live coding practitioners engage with these points in their system design and performances. In the light of the extremely diverse manifestations of live coding activities, the problem of defining the practice is discussed, and the question raised whether live coding will actually be necessary as an independent category
New stability results for Einstein scalar gravity
We consider asymptotically anti de Sitter gravity coupled to a scalar field
with mass slightly above the Breitenlohner-Freedman bound. This theory admits a
large class of consistent boundary conditions characterized by an arbitrary
function . An important open question is to determine which admit stable
ground states. It has previously been shown that the total energy is bounded
from below if is bounded from below and the bulk scalar potential
admits a suitable superpotential. We extend this result and show that the
energy remains bounded even in some cases where can become arbitrarily
negative. As one application, this leads to the possibility that in
gauge/gravity duality, one can add a double trace operator with negative
coefficient to the dual field theory and still have a stable vacuum
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