97,339 research outputs found
The bright optical companion to the eclipsing millisecond pulsar in NGC 6397
We report the possible optical identification of the companion to the
eclipsing millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397. A
bright variable star with an anomalous red colour and optical variability which
nicely correlates to the orbital period of the pulsar has been found close to
the pulsar position. If confirmed, the optical light curve, reminiscent of
tidal distorsions similar to those observed in detached and contact binaries,
support the idea that this is the first case of a Roche lobe filling companion
to a millisecond pulsar.Comment: 9 pages, 4 embedded figures, submitted to ApJ Letter
A spacetime realization of kappa-Poincare algebra
We study a Hamiltonian realization of the phase space of kappa-Poincare
algebra that yields a definition of velocity consistent with the deformed
Lorentz symmetry. We are also able to determine the laws of transformation of
spacetime coordinates and to define an invariant spacetime metric, and discuss
some possible experimental consequences.Comment: 5 pages, plain TeX. Some misprints corrected. A discussion on the
possibility of experimental verifications adde
General helicity formalism for Single and Double Spin Asymmetries in p p --> pion + X
We consider within a generalized QCD factorization approach, the high energy
inclusive polarized process p p --> pion + X, including all intrinsic partonic
motions. Several new spin and k_T-dependent soft functions appear and
contribute to cross sections and spin asymmetries. We present here formal
expressions for transverse single spin asymmetries and double longitudinal
ones. The transverse single spin asymmetry, A_N, is considered in detail, and
all contributions are evaluated numerically. It is shown that the azimuthal
phase integrations strongly suppress most contributions, leaving at work mainly
the Sivers effect.Comment: LaTeX, 5 pages, 1 eps figure, uses epsfig, wrapfig. Talk delivered by
S. Melis at the ``XI Workshop on High Energy Spin Physics'', SPIN 05,
September 27 - October 1, 2005, Dubna, Russi
The Parkes Multibeam Pulsar Survey: PSR J1811-1736 - a pulsar in a highly eccentric binary system
We are undertaking a high-frequency survey of the Galactic plane for radio
pulsars, using the 13-element multibeam receiver on the 64-m Parkes radio
telescope. We describe briefly the survey system and some of the initial
results. PSR J1811-1736, one of the first pulsars discovered with this system,
has a rotation period of 104 ms. Subsequent timing observations using the 76-m
radio telescope at Jodrell Bank show that it is in an 18.8-day,
highly-eccentric binary orbit. We have measured the rate of advance of
periastron which indicates a total system mass of 2.6 +- 0.9 Msun, and the
minimum companion mass is about 0.7 Msun. This, the high orbital eccentricity
and the recycled nature of the pulsar suggests that this system is composed of
two neutron stars, only the fourth or fifth such system known in the disk of
the Galaxy.Comment: 6 pages, 3 embedded EPS figures, to be published in MNRA
First minimum bias physics results at LHCb
We report on the first measurements of the LHCb experiment, as obtained from
collisions at TeV and 7 TeV recorded using a minimum bias
trigger. In particular measurements of the absolute production cross
section at TeV and of the ratio both
at TeV and 7 TeV are discussed and preliminary results are
presented.Comment: To appear in the Proceedings of the 15th International QCD Conference
(QCD10) submitted to Nuc. Phys. (Proc. Suppl.
Lattice Boltzmann models for non-ideal fluids with arrested phase-separation
The effects of mid-range repulsion in Lattice Boltzmann models on the
coalescence/breakup behaviour of single-component, non-ideal fluids are
investigated. It is found that mid-range repulsive interactions allow the
formation of spray-like, multi-droplet configurations, with droplet size
directly related to the strength of the repulsive interaction. The simulations
show that just a tiny ten-percent of mid-range repulsive pseudo-energy can
boost the surface/volume ratio of the phase- separated fluid by nearly two
orders of magnitude. Drawing upon a formal analogy with magnetic Ising systems,
a pseudo-potential energy is defined, which is found to behave like a
quasi-conserved quantity for most of the time-evolution. This offers a useful
quantitative indicator of the stability of the various configurations, thus
helping the task of their interpretation and classification. The present
approach appears to be a promising tool for the computational modelling of
complex flow phenomena, such as atomization, spray formation and
micro-emulsions, break-up phenomena and possibly glassy-like systems as well.Comment: 12 pages, 9 figure
The geometry of symplectic pairs
We study the geometry of manifolds carrying symplectic pairs consisting of
two closed 2-forms of constant ranks, whose kernel foliations are
complementary. Using a variation of the construction of Boothby and Wang we
build contact-symplectic and contact pairs from symplectic pairs.Comment: to appear in Transactions of the American Mathematical Societ
Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−
The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Microscopic unitary description of tidal excitations in high-energy string-brane collisions
The eikonal operator was originally introduced to describe the effect of
tidal excitations on higher-genus elastic string amplitudes at high energy. In
this paper we provide a precise interpretation for this operator through the
explicit tree-level calculation of generic inelastic transitions between closed
strings as they scatter off a stack of parallel Dp-branes. We perform this
analysis both in the light-cone gauge, using the Green-Schwarz vertex, and in
the covariant formalism, using the Reggeon vertex operator. We also present a
detailed discussion of the high energy behaviour of the covariant string
amplitudes, showing how to take into account the energy factors that enhance
the contribution of the longitudinally polarized massive states in a simple
way.Comment: 58 page
Black hole solutions of gravity theories with nonminimal coupling between matter and curvature
We study black hole solutions in an extension of General Relativity (GR) with
an explicit non-minimal coupling between matter and curvature. General black
hole solutions satisfying the known energy conditions are derived including the
ones with anti-de Sitter background. These solutions differ from those of GR
just by a coupling function dependent rescaling of the mass and charge of the
black hole and by a "dressing" of the cosmological constant. The existence of
black hole solutions of the nonminimally coupled theory as well as the
conditions for a suitable weak field limit are considered as a constraint on
the coupling function responsible for the nonminimal coupling between matter
and curvature. The "dressing" of the cosmological constant is then used to
address the cosmological constant problem.Comment: 24 pages, no figure
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