63,723 research outputs found
Lower Mass Bound on the mass via Neutrinoless Double Beta Decay in a 3-3-1 Model
The discovery of neutrino masses has raised the importance of studies in the
context of neutrinoless double beta decay, which constitutes a landmark for
lepton number violation. The standard interpretation is that the light massive
neutrinos, that we observed oscillating in terrestrial experiments, mediate
double beta decay. In the minimal 3-3-1 model, object of our study, there is an
additional contribution that stems from the mixing between a new charged vector
boson, , and the Standard Model W boson. Even after setting this
mixing to be very small, we show that tight constraints arise from the
non-observation of neutrinoless double beta decay. Indeed, we derive bounds on
the mass of the gauge boson that might exceed those from collider
probes, and most importantly push the scale of symmetry breaking beyond its
validity, leading to the exclusion of the minimal 3-3-1 model.Comment: 16 pages, 5 figure
Impact of stellar companions on precise radial velocities
Context: With the announced arrival of instruments such as ESPRESSO one can
expect that several systematic noise sources on the measurement of precise
radial velocity will become the limiting factor instead of photon noise. A
stellar companion within the fiber is such a possible noise source. Aims: With
this work we aim at characterizing the impact of a stellar companion within the
fiber to radial velocity measurements made by fiber-fed spectrographs. We
consider the contaminant star either to be part of a binary system whose
primary star is the target star, or as a background/foreground star. Methods:
To carry out our study, we used HARPS spectra, co-added the target with
contaminant spectra, and then compared the resulting radial velocity with that
obtained from the original target spectrum. We repeated this procedure and used
different tunable knobs to reproduce the previously mentioned scenarios.
Results: We find that the impact on the radial velocity calculation is a
function of the difference between individual radial velocities, of the
difference between target and contaminant magnitude, and also of their spectral
types. For the worst-case scenario in which both target and contaminant star
are well centered on the fiber, the maximum contamination for a G or K star may
be higher than 10 cm/s, on average, if the difference between target and
contaminant magnitude is < 10, and higher than 1 m/s if <
8. If the target star is of spectral type M, < 8 produces the same
contamination of 10 cm/s, and a contamination may be higher than 1 m/sComment: Accepted for publication in A&A on 29/12/2019 - 14 page
Line-profile variations in radial-velocity measurements: Two alternative indicators for planetary searches
Aims. We introduce two methods to identify false-positive planetary signals
in the context of radial-velocity exoplanet searches. The first is the
bi-Gaussian cross-correlation function fitting, and the second is the
measurement of asymmetry in radial-velocity spectral line information content,
Vasy.
Methods. We make a systematic analysis of the most used common line profile
diagnosis, Bisector Inverse Slope and Velocity Span, along with the two
proposed ones. We evaluate all these diagnosis methods following a set of
well-defined common criteria and using both simulated and real data. We apply
them to simulated cross-correlation functions created with the program SOAP and
which are affected by the presence of stellar spots, and to real
cross-correlation functions, calculated from HARPS spectra, for stars with a
signal originating both in activity and created by a planet.
Results. We demonstrate that the bi-Gaussian method allows a more precise
characterization of the deformation of line profiles than the standard bisector
inverse slope. The calculation of the deformation indicator is simpler and its
interpretation more straightforward. More importantly, its amplitude can be up
to 30% larger than that of the bisector span, allowing the detection of
smaller-amplitude correlations with radial-velocity variations. However, a
particular parametrization of the bisector inverse slope is shown to be more
efficient on high-signal-to-noise data than both the standard bisector and the
bi-Gaussian. The results of the Vasy method show that this indicator is more
effective than any of the previous ones, being correlated with the
radial-velocity with more significance for signals resulting from a line
deformation. Moreover, it provides a qualitative advantage over the bisector,
showing significant correlations with RV for active stars for which bisector
analysis is inconclusive. (abridged)Comment: 12 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics, comments welcom
A Bayesian estimate of the CMB-large-scale structure cross-correlation
Evidences for late-time acceleration of the Universe are provided by multiple
probes, such as Type Ia supernovae, the cosmic microwave background (CMB) and
large-scale structure (LSS). In this work, we focus on the integrated
Sachs--Wolfe (ISW) effect, i.e., secondary CMB fluctuations generated by
evolving gravitational potentials due to the transition between, e.g., the
matter and dark energy (DE) dominated phases. Therefore, assuming a flat
universe, DE properties can be inferred from ISW detections. We present a
Bayesian approach to compute the CMB--LSS cross-correlation signal. The method
is based on the estimate of the likelihood for measuring a combined set
consisting of a CMB temperature and a galaxy contrast maps, provided that we
have some information on the statistical properties of the fluctuations
affecting these maps. The likelihood is estimated by a sampling algorithm,
therefore avoiding the computationally demanding techniques of direct
evaluation in either pixel or harmonic space. As local tracers of the matter
distribution at large scales, we used the Two Micron All Sky Survey (2MASS)
galaxy catalog and, for the CMB temperature fluctuations, the ninth-year data
release of the Wilkinson Microwave Anisotropy Probe (WMAP9). The results show a
dominance of cosmic variance over the weak recovered signal, due mainly to the
shallowness of the catalog used, with systematics associated with the sampling
algorithm playing a secondary role as sources of uncertainty. When combined
with other complementary probes, the method presented in this paper is expected
to be a useful tool to late-time acceleration studies in cosmology.Comment: 21 pages, 15 figures, 4 tables. We extended the previous analyses
including WMAP9 Q, V and W channels, besides the ILC map. Updated to match
accepted ApJ versio
K X-Ray Energies and Transition Probabilities for He-, Li- and Be-like Praseodymium ions
Theoretical transition energies and probabilities for He-, Li- and Be-like
Praseodymium ions are calculated in the framework of the multi-configuration
Dirac-Fock method (MCDF), including QED corrections. These calculated values
are compared to recent experimental data obtained in the Livermore SuperEBIT
electron beam ion trap facility
Interplay between chiral and axial symmetries in a SU(2) Nambu--Jona-Lasinio Model with the Polyakov loop
We consider a two flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model where the
Lagrangian includes an interaction term that explicitly breaks the U
anomaly. At finite temperature, the restoration of chiral and axial symmetries,
signaled by the behavior of several observables, is investigated. We compare
the effects of two regularizations at finite temperature, one of them, that
allows high momentum quarks states, leading to the full recovery of chiral
symmetry. From the analysis of the behavior of the topological susceptibility
and of the mesonic masses of the axial partners, it is found in the SU(2) model
that, unlike the SU(3) results, the recovery of the axial symmetry is not a
consequence of the full recovery of the chiral symmetry. Thus, one needs to use
an additional idea, by means of a temperature dependence of the anomaly
coefficient, that simulates instanton suppression effects.Comment: 21 pages, 5 figures; PRD versio
Tracking Vector Magnetograms with the Magnetic Induction Equation
The differential affine velocity estimator (DAVE) developed in Schuck (2006)
for estimating velocities from line-of-sight magnetograms is modified to
directly incorporate horizontal magnetic fields to produce a differential
affine velocity estimator for vector magnetograms (DAVE4VM). The DAVE4VM's
performance is demonstrated on the synthetic data from the anelastic
pseudospectral ANMHD simulations that were used in the recent comparison of
velocity inversion techniques by Welsch (2007). The DAVE4VM predicts roughly
95% of the helicity rate and 75% of the power transmitted through the
simulation slice. Inter-comparison between DAVE4VM and DAVE and further
analysis of the DAVE method demonstrates that line-of-sight tracking methods
capture the shearing motion of magnetic footpoints but are insensitive to flux
emergence -- the velocities determined from line-of-sight methods are more
consistent with horizontal plasma velocities than with flux transport
velocities. These results suggest that previous studies that rely on velocities
determined from line-of-sight methods such as the DAVE or local correlation
tracking may substantially misrepresent the total helicity rates and power
through the photosphere.Comment: 30 pages, 13 figure
Topological Defects in Contracting Universes
We study the behaviour and consequences of cosmic string networks in
contracting universes. They approximately behave during the collapse phase as a
radiation fluids. Scaling solutions describing this are derived and tested
against high-resolution numerical simulations. A string network in a
contracting universe, together with the gravitational radiation it generates,
can affect the dynamics of the universe both locally and globally, and be an
important source of radiation, entropy and inhomogeneity. We discuss possible
implications for bouncing and cyclic models.Comment: Shorter version of astro-ph/0206287. To appear in Phys. Rev. Let
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