12,011 research outputs found
Limits on Lorentz Violation from the Highest Energy Cosmic Rays
We place several new limits on Lorentz violating effects, which can modify
particles' dispersion relations, by considering the highest energy cosmic rays
observed. Since these are hadrons, this involves considering the partonic
content of such cosmic rays. We get a number of bounds on differences in
maximum propagation speeds, which are typically bounded at the 10^{-21} level,
and on momentum dependent dispersion corrections of the form v = 1 +-
p^2/Lambda^2, which typically bound Lambda > 10^{21} GeV, well above the Planck
scale. For (CPT violating) dispersion correction of the form v = 1 + p/Lambda,
the bounds are up to 15 orders of magnitude beyond the Planck scale.Comment: 24 pages, no figures. Added references, very slight changes. Version
published in Physical Review
Spin noise and Bell inequalities in a realistic superconductor-quantum dot entangler
Charge and spin current correlations are analyzed in a source of
spin-entangled electrons built from a superconductor and two quantum dots in
parallel. In addition to the ideal (crossed Andreev) channel, parasitic
channels (direct Andreev and cotunneling) and spin flip processes are fully
described in a density matrix framework. The way they reduce both the
efficiency and the fidelity of the entangler is quantitatively described by
analyzing the zero-frequency noise correlations of charge current as well as
spin current in the two output branches. Spin current noise is characterized by
a spin Fano factor, equal to 0 (total current noise) and -1 (crossed
correlations) for an ideal entangler. The violation of the Bell inequalities,
as a test of non-locality (entanglement) of split pairs, is formulated in terms
of the correlations of electron charge and spin numbers counted in a specific
time window . The efficiency of the test is analyzed, comparing to
the various time scales in the entangler operation.Comment: 8 pages, 5 figures, references added, to appear in Phys. Rev.
Phenological and molecular studies on the introduced seaweed Dictyota cyanoloma (Dictyotales, Phaeophyceae) along the Mediterranean coast of the Iberian Peninsula
Dictyota cyanoloma, a distinctive brown algal species characterized by a blue-iridescent margin, was recently reported as an introduced species in the Mediterranean Sea but little is known about its distribution dynamics, morphological plasticity and genetic structure. In this integrative study, we evaluate its past and present occurrence along the Mediterranean Iberian coast, assess the species' phenology in Palamos (Girona, Spain) and analyze the haplotype diversity by sequencing 49 individuals from nine sampling sites for different chloroplast and mitochondrial DNA regions. Although D. cyanoloma currently occurs along all the Mediterranean Iberian coasts (in 19 of 36 localities sampled, mostly in marinas and harbour environments), we were not able to find any herbarium material of this species (at BCN-Phyc and MA) predating the year 1987. In Palamos, D. cyanoloma is present all through the year, with a maximum development in winter and a minimum in summer. Fertile specimens are absent during summer (July and August). Sporophytes are dominant from January to June and gametophytes were found only in February, March and June. Information about the antheridia, which has never been described before, is provided. Two chloroplast and three mitochondrial haplotypes were observed, indicating that multiple introductions of D. cyanoloma occurred in the study area. Additionally, the genetic structure suggests that spread did not occur through simple advancing wave fronts but by several longdistance dispersal events. Further studies employing microsatellite markers could potentially offer a better resolution to unravel expansion and colonisation dynamics of D. cyanoloma in the Mediterranean Sea
Decoherence suppression via environment preparation
To protect a quantum system from decoherence due to interaction with its
environment, we investigate the existence of initial states of the environment
allowing for decoherence-free evolution of the system. For models in which a
two-state system interacts with a dynamical environment, we prove that such
states exist if and only if the interaction and self-evolution Hamiltonians
share an eigenstate. If decoherence by state preparation is not possible, we
show that initial states minimizing decoherence result from a delicate
compromise between the environment and interaction dynamics.Comment: 4 pages, 2 figure
Multi-species pair annihilation reactions
We consider diffusion-limited reactions A_i + A_j -> 0 (1 <= i < j <= q) in d
space dimensions. For q > 2 and d >= 2 we argue that the asymptotic density
decay for such mutual annihilation processes with equal rates and initial
densities is the same as for single-species pair annihilation A + A -> 0. In d
= 1, however, particle segregation occurs for all q < oo. The total density
decays according to a dependent power law, rho(t) ~ t^{-\alpha(q)}. Within
a simplified version of the model \alpha(q) = (q-1) / 2q can be determined
exactly. Our findings are supported through Monte Carlo simulations.Comment: 4 pages, revtex; two figures include
Selective amplification of scars in a chaotic optical fiber
In this letter we propose an original mechanism to select scar modes through
coherent gain amplification in a multimode D-shaped fiber. More precisely, we
numerically demonstrate how scar modes can be amplified by positioning a gain
region in the vicinity of specific points of a short periodic orbit known to
give rise to scar modes
An Ultrasoft X-ray Flare from 3XMM J152130.7+074916: a Tidal Disruption Event Candidate
We report on the discovery of an ultrasoft X-ray transient source, 3XMM
J152130.7+074916. It was serendipitously detected in an XMM-Newton observation
on 2000 August 23, and its location is consistent with the center of the galaxy
SDSS J152130.72+074916.5 (z=0.17901 and d_L=866 Mpc). The high-quality X-ray
spectrum can be fitted with a thermal disk with an apparent inner disk
temperature of 0.17 keV and a rest-frame 0.24-11.8 keV unabsorbed luminosity of
~5e43 erg/s, subject to a fast-moving warm absorber. Short-term variability was
also clearly observed, with the spectrum being softer at lower flux. The source
was covered but not detected in a Chandra observation on 2000 April 3, a Swift
observation on 2005 September 10, and a second XMM-Newton observation on 2014
January 19, implying a large variability (>260) of the X-ray flux. The optical
spectrum of the candidate host galaxy, taken ~11 yrs after the XMM-Newton
detection, shows no sign of nuclear activity. This, combined with its transient
and ultrasoft properties, leads us to explain the source as tidal disruption of
a star by the supermassive black hole in the galactic center. We attribute the
fast-moving warm absorber detected in the first XMM-Newton observation to the
super-Eddington outflow associated with the event and the short-term
variability to a disk instability that caused fast change of the inner disk
radius at a constant mass accretion rate.Comment: 9 pages, 5 figures. ApJ, in pres
Maternal separation induces anhedonia in female heterozygous serotonin transporter knockout rats
Funding Information: Funding was received from the NARSAD young investigator grant from the Brain & Behavioural Research foundation (grant nr 25206 ) and from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 660152 .Peer reviewe
Finite geometries and diffractive orbits in isospectral billiards
Several examples of pairs of isospectral planar domains have been produced in
the two-dimensional Euclidean space by various methods. We show that all these
examples rely on the symmetry between points and blocks in finite projective
spaces; from the properties of these spaces, one can derive a relation between
Green functions as well as a relation between diffractive orbits in isospectral
billiards.Comment: 10 page
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