32,458 research outputs found
Pion and Kaon Condensation at Finite Temperature and Density
In this paper, we study O(2N)-symmetric -theory at finite temperature
and density using the 2PI-1/N expansion. As specific examples, we consider pion
condensation at finite isospin chemical potential and kaon condensation at
finite chemical potential for hyper charge and isospin charge. We calculate the
phase diagrams and the quasiparticle masses for pions and kaons in the large-N
limit. It is shown that the effective potential and the gap equation can be
renormalized by using local counterterms for the coupling constant and mass
parameter, which are independent of temperature and chemical potentials.Comment: 10 pages. 7 Figures. v2: Better plots and figs. Added significant
number of refs v3: Accepted for publication in PRD. Added a figure and
improved part on renormalization as well as presentatio
Experimentally feasible quantum erasure-correcting code for continuous variables
We devise a scheme that protects quantum coherent states of light from
probabilistic losses, thus achieving the first continuous-variable quantum
erasure-correcting code. If the occurrence of erasures can be probed, then the
decoder enables, in principle, a perfect recovery of the original light states.
Otherwise, if supplemented with postselection based on homodyne detection, this
code can be turned into an efficient erasure-filtration scheme. The
experimental feasibility of the proposed protocol is carefully addressed
GMOR-like relation in IR-conformal gauge theories
A generalization of the GMOR relation to the case of infrared-conformal gauge
theories is discussed. The starting point is the chiral Ward identity
connecting the isovector pseudoscalar susceptibility to the chiral condensate,
in a mass-deformed theory. A renormalization-group analysis shows that the
pseudoscalar susceptibility is not saturated by the lightest state, but a
contribution from the continuum part of the spectrum survives in the chiral
limit. The computation also shows how infrared-conformal gauge theories behave
differently, depending on whether the anomalous dimension of the chiral
condensate be smaller or larger than 1.Comment: 28 pages, 1 PDF figur
New relations for scattering amplitudes in Yang-Mills theory at loop level
The calculation of scattering amplitudes in Yang-Mills theory at loop level
is important for the analysis of background processes at particle colliders as
well as our understanding of perturbation theory at the quantum level. We
present tools to derive relations for especially one loop amplitudes, as well
as several explicit examples for gauge theory coupled to a wide variety of
matter. These tools originate in certain scaling behavior of permutation and
cyclic sums of Yang-Mills tree amplitudes and loop integrands. In the latter
case evidence exists for relations at all loop orders.Comment: 12 pages, 4 figures. v3: typos corrected, figures and clarifications
adde
Experimental Demonstration of Continuous Variable Cloning with Phase-Conjugate Inputs
We report the experimental demonstration of continuous variable cloning of
phase conjugate coherent states as proposed by Cerf and Iblisdir (Phys. Rev.
Lett. 87, 247903 (2001)). In contrast to the proposal of Cerf and Iblisdir, the
cloning transformation is accomplished using only linear optical components,
homodyne detection and feedforward. Three clones are succesfully produced with
fidelities about 89%.Comment: 5 page
Exobiology on Mars
Descriptions of several instrument concepts that were generated during a workshop entitled, Exobiology Instrument Concepts for a Soviet Mars 94/94 Mission, held at NASA Ames Research Center in 1989 are presented. The objective was to define and describe instrument concepts for exobiology and related science that would be compatible with the mission types under discussion for the 1994 and 1996 Soviet Mars missions. Experiments that use existing technology were emphasized. The concepts discussed could also be used on U.S. missions that follow Mars Observer
Pattern Dynamics of Vortex Ripples in Sand: Nonlinear Modeling and Experimental Validation
Vortex ripples in sand are studied experimentally in a one-dimensional setup
with periodic boundary conditions. The nonlinear evolution, far from the onset
of instability, is analyzed in the framework of a simple model developed for
homogeneous patterns. The interaction function describing the mass transport
between neighboring ripples is extracted from experimental runs using a
recently proposed method for data analysis, and the predictions of the model
are compared to the experiment. An analytic explanation of the wavelength
selection mechanism in the model is provided, and the width of the stable band
of ripples is measured.Comment: 4 page
Linear response separation of a solid into atomic constituents: Li, Al, and their evolution under pressure
We present the first realization of the generalized pseudoatom concept
introduced by Ball, and adopt the name enatom to minimize confusion. This
enatom, which consists of a unique decomposition of the total charge density
(or potential) of any solid into a sum of overlapping atomiclike contributions
that move rigidly with the nuclei to first order, is calculated using
(numerical) linear response methods, and is analyzed for both fcc Li and Al at
pressures of 0, 35, and 50 GPa. These two simple fcc metals (Li is fcc and a
good superconductor in the 20-40 GPa range) show different physical behaviors
under pressure, which reflects the increasing covalency in Li and the lack of
it in Al. The nonrigid (deformation) parts of the enatom charge and potential
have opposite signs in Li and Al; they become larger under pressure only in Li.
These results establish a method of construction of the enatom, whose potential
can be used to obtain a real-space understanding of the vibrational properties
and electron-phonon interaction in solids.Comment: 13 pages, 9 figures, 1 table, V2: fixed problem with Fig. 7, V3:
minor correction
The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars
The detailed chemical composition of most metal-poor halo stars has been
found to be highly uniform, but a minority of stars exhibit dramatic
enhancements in their abundances of heavy neutron-capture elements and/or of
carbon. The key question for Galactic chemical evolution models is whether
these peculiarities reflect the composition of the natal clouds, or if they are
due to later mass transfer of processed material from a binary companion. If
the former case applies, the observed excess of certain elements was implanted
within selected clouds in the early ISM from a production site at interstellar
distances. Our aim is to determine the frequency and orbital properties of
binaries among these chemically peculiar stars. This information provides the
basis for deciding whether mass transfer from a binary companion is necessary
and sufficient to explain their unusual compositions. This paper discusses our
study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element
enhanced VMP and EMP stars. High-resolution, low signal-to-noise spectra of the
stars were obtained at roughly monthly intervals over 8 years with the FIES
spectrograph at the Nordic Optical Telescope. From these spectra, radial
velocities with an accuracy of ~100 m/s were determined by cross-correlation
against an optimized template. 14 of the programme stars exhibit no significant
RV variation over this period, while 3 are binaries with orbits of typical
eccentricity for their periods, resulting in a normal binary frequency of
~18+-6% for the sample. Our results confirm our preliminary conclusion from
2011, based on partial data, that the chemical peculiarity of the r-I and r-II
stars is not caused by any putative binary companions. Instead, it was
imprinted on the natal molecular clouds of these stars by an external, distant
source. Models of the ISM in early galaxies should account for such mechanisms.Comment: 14 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Local Ranking Problem on the BrowseGraph
The "Local Ranking Problem" (LRP) is related to the computation of a
centrality-like rank on a local graph, where the scores of the nodes could
significantly differ from the ones computed on the global graph. Previous work
has studied LRP on the hyperlink graph but never on the BrowseGraph, namely a
graph where nodes are webpages and edges are browsing transitions. Recently,
this graph has received more and more attention in many different tasks such as
ranking, prediction and recommendation. However, a web-server has only the
browsing traffic performed on its pages (local BrowseGraph) and, as a
consequence, the local computation can lead to estimation errors, which hinders
the increasing number of applications in the state of the art. Also, although
the divergence between the local and global ranks has been measured, the
possibility of estimating such divergence using only local knowledge has been
mainly overlooked. These aspects are of great interest for online service
providers who want to: (i) gauge their ability to correctly assess the
importance of their resources only based on their local knowledge, and (ii)
take into account real user browsing fluxes that better capture the actual user
interest than the static hyperlink network. We study the LRP problem on a
BrowseGraph from a large news provider, considering as subgraphs the
aggregations of browsing traces of users coming from different domains. We show
that the distance between rankings can be accurately predicted based only on
structural information of the local graph, being able to achieve an average
rank correlation as high as 0.8
- …