23,028 research outputs found
Evidence for a dual population of neutron star mergers from short Gamma-Ray Burst observations
Short duration Gamma-Ray Bursts are thought to originate from the coalescence
of neutron stars in binary systems. They are detected as a brief ( 2s),
intense flash of gamma-ray radiation followed by a weaker, rapidly decreasing
afterglow. They are expected to be detected by Advanced LIGO and Virgo when
their sensitivity will be low enough. In a recent study we identified a
population of short Gamma-Ray Bursts that are intrinsically faint and nearby.
Here we provide evidence in favor of the existence of this new population that
can hardly be reproduced with a model of field neutron star binary
coalescences. We propose that these systems may be produced dynamically in
globular clusters, and may result from the merger of a black hole and a neutron
star. The advanced LIGO and Virgo observation of a high rate of NSBH mergers
compatible with the dynamical formation in globular clusters would be a
confirmation of this hypothesis and would enable for the derivation of the mass
function of black holes inside globular clusters, as well as the luminosity
function of faint short GRBs.Comment: 15 pages, 5 figures, 1 table, submitted to Ap
Spontaneous CP violation in the NJL model at theta = pi
As is well-known, spontaneous CP-violation in the strong interaction is
possible at theta = pi, which is commonly referred to as Dashen's phenomenon.
This phenomenon has been studied extensively using chiral Lagrangians. Here the
two-flavor NJL model at theta = pi is discussed. It turns out that the
occurrence of spontaneous CP-violation depends on the strength of the 't Hooft
determinant interaction, which describes the effect of instanton interactions.
The dependence of the phase structure, and in particular of the CP-violating
phase, on the quark masses, temperature, baryon and isospin chemical potential
is examined in detail. The latter dependence shows a modification of the
charged pion condensed phase first discussed by Son and Stephanov.Comment: 5 pages, 7 figures; talk given at the 8th Conference "Quark
Confinement and the Hadron Spectrum", Mainz, Germany, 1-6 September 200
Integrals over Products of Distributions and Coordinate Independence of Zero-Temperature Path Integrals
In perturbative calculations of quantum-statistical zero-temperature path
integrals in curvilinear coordinates one encounters Feynman diagrams involving
multiple temporal integrals over products of distributions, which are
mathematically undefined. In addition, there are terms proportional to powers
of Dirac delta-functions at the origin coming from the measure of path
integration. We give simple rules for integrating products of distributions in
such a way that the results ensure coordinate independence of the path
integrals. The rules are derived by using equations of motion and partial
integration, while keeping track of certain minimal features originating in the
unique definition of all singular integrals in dimensions. Our
rules yield the same results as the much more cumbersome calculations in 1-
epsilon dimensions where the limit epsilon --> 0 is taken at the end. They also
agree with the rules found in an independent treatment on a finite time
interval.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper (including all PS fonts) at
http://www.physik.fu-berlin.de/~kleinert/33
High-velocity gas towards the LMC resides in the Milky Way halo
To explore the origin of high-velocity gas in the direction of the Large
Magellanic Cloud (LMC) we analyze absorption lines in the ultraviolet spectrum
of a Galactic halo star that is located in front of the LMC at d=9.2 kpc
distance. We study the velocity-component structure of low and intermediate
metal ions in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic
Origins Spectrograph (COS) onboard HST, and measure equivalent widths and
column densities for these ions. We supplement our COS data with a
Far-Ultraviolet Spectroscopic Explorer spectrum of the nearby LMC star Sk-69 59
and with HI 21cm data from the Leiden-Argentina-Bonn (LAB) survey. Metal
absorption towards RXJ0439.8-6809 is unambiguously detected in three different
velocity components near v_LSR=0,+60, and +150 km/s. The presence of absorption
proves that all three gas components are situated in front of the star, thus
being located in the disk and inner halo of the Milky Way. For the
high-velocity cloud (HVC) at v_LSR=+150 km/s we derive an oxygen abundance of
[O/H]=-0.63 (~0.2 solar) from the neighbouring Sk-69 59 sightline, in
accordance with previous abundance measurements for this HVC. From the observed
kinematics we infer that the HVC hardly participates in the Galactic rotation.
Our study shows that the HVC towards the LMC represents a Milky Way halo cloud
that traces low-column density gas with relatively low metallicity. It rules
out scenarios in which the HVC represents material close to the LMC that stems
from a LMC outflow.Comment: 4 pages, 3 figures; submitted to A&A Letter
AND Protocols Using Only Uniform Shuffles
Secure multi-party computation using a deck of playing cards has been a
subject of research since the "five-card trick" introduced by den Boer in 1989.
One of the main problems in card-based cryptography is to design
committed-format protocols to compute a Boolean AND operation subject to
different runtime and shuffle restrictions by using as few cards as possible.
In this paper, we introduce two AND protocols that use only uniform shuffles.
The first one requires four cards and is a restart-free Las Vegas protocol with
finite expected runtime. The second one requires five cards and always
terminates in finite time.Comment: This paper has appeared at CSR 201
Inversion symmetry in the spin-Peierls compound NaV2O5
At room-temperature NaV2O5 was found to have the centrosymmetric space group
Pmmn. This space group implies the presence of only one kind of V site in
contrast with previous reports of the non-centrosymmetric counterpart P21mn.
This indicates a non-integer valence state of vanadium.
Furthermore, this symmetry has consequences for the interpretation of the
transition at 34 K, which was ascribed to a spin-Peierls transition of one
dimensional chains of V4+.Comment: Revtex, 3 pages, 2 postscript pictures embedded in the text.
Corrected a mistake in one pictur
Response to Invasion by Antigen and Effects of Threshold in an Immune Network Dynamical System Model with a Small Number of Degrees of Freedom
We study a dynamical system model of an idiotypic immune network with a small
number of degrees of freedom, mainly focusing on the effect of a threshold
above which antibodies can recognise antibodies. The response of the system to
invasions by antigens is investigated in the both models with and without the
threshold and it turns out that the system changes in a desirable direction for
moderate magnitude of perturbation. direction for moderate magnitude of
perturbation. Also, the propagation of disturbance by an antigen is
investigated in the system of one-dimensionally connected basic units taking
the closed 3-clone system as a unit, and it is clarified that the threshold of
the system has effects to enhance the stability of the network and to localise
the immune response.Comment: 6 pages, 6 figures. Submitted to Prog. Theor. Phy
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