275 research outputs found
Remarks Concerning the Study of Four-Jet Events from Hadronic Decays of the Z0
The angular correlations of four-jet events from hadronic decays of the Z0
have been studied in the past mainly to extract from them the fundamental
constants of quantum chromodynamics called colour factors. Previous studies
have used all the available phase-space in order to maximize statistics. In
this note we want to point out the possibility that significant differences
between experiment and theory in restricted regions of phase-space might have
escaped detection. Such differences could be a harbinger of the existence of
new particles. Some preliminary results are presented.Comment: 9 pages, 3 figure
Dynamical Dark Energy model parameters with or without massive neutrinos
We use WMAP5 and other cosmological data to constrain model parameters in
quintessence cosmologies, focusing also on their shift when we allow for
non-vanishing neutrino masses. The Ratra-Peebles (RP) and SUGRA potentials are
used here, as examples of slowly or fastly varying state parameter w(a). Both
potentials depend on an energy scale \Lambda. Here we confirm the results of
previous analysis with WMAP3 data on the upper limits on \Lambda, which turn
out to be rather small (down to ~10^{-9} in RP cosmologies and ~10^{-5} for
SUGRA). Our constraints on \Lambda are not heavily affected by the inclusion of
neutrino mass as a free parameter. On the contrary, when the neutrino mass
degree of freedom is opened, significant shifts in the best-fit values of other
parameters occur.Comment: 9 pages, 3 figures, submitted to JCA
pi/K -> e nu branching ratios to O(e^2 p^4) in Chiral Perturbation Theory
We calculate the ratios R_{e/mu}^{(P)} = Gamma(P -> e nu)/Gamma (P -> mu nu)
(P=pi,K) in Chiral Perturbation Theory to order e^2 p^4. We complement the one-
and two-loop effective theory results with a matching calculation of the local
counterterm, performed within the large- expansion. We find
R_{e/mu}^{(\pi)} = (1.2352 \pm 0.0001)*10^{-4} and R_{e/mu}^{(K)} = (2.477 \pm
0.001)*10^{-5}, with uncertainty induced by the matching procedure and chiral
power counting. Given the sensitivity of upcoming new measurements, our results
provide a clean baseline to detect or constrain effects from weak-scale new
physics in these rare decays. As a by-product, we also update the theoretical
analysis of the individual pi/K -> \ell nu modes.Comment: 40 pages, 4 figures, 3 table
Constraining the cosmic radiation density due to lepton number with Big Bang Nucleosynthesis
The cosmic energy density in the form of radiation before and during Big Bang
Nucleosynthesis (BBN) is typically parameterized in terms of the effective
number of neutrinos N_eff. This quantity, in case of no extra degrees of
freedom, depends upon the chemical potential and the temperature characterizing
the three active neutrino distributions, as well as by their possible
non-thermal features. In the present analysis we determine the upper bounds
that BBN places on N_eff from primordial neutrino--antineutrino asymmetries,
with a careful treatment of the dynamics of neutrino oscillations. We consider
quite a wide range for the total lepton number in the neutrino sector, eta_nu=
eta_{nu_e}+eta_{nu_mu}+eta_{nu_tau} and the initial electron neutrino asymmetry
eta_{nu_e}^in, solving the corresponding kinetic equations which rule the
dynamics of neutrino (antineutrino) distributions in phase space due to
collisions, pair processes and flavor oscillations. New bounds on both the
total lepton number in the neutrino sector and the nu_e -bar{nu}_e asymmetry at
the onset of BBN are obtained fully exploiting the time evolution of neutrino
distributions, as well as the most recent determinations of primordial 2H/H
density ratio and 4He mass fraction. Note that taking the baryon fraction as
measured by WMAP, the 2H/H abundance plays a relevant role in constraining the
allowed regions in the eta_nu -eta_{nu_e}^in plane. These bounds fix the
maximum contribution of neutrinos with primordial asymmetries to N_eff as a
function of the mixing parameter theta_13, and point out the upper bound N_eff
< 3.4. Comparing these results with the forthcoming measurement of N_eff by the
Planck satellite will likely provide insight on the nature of the radiation
content of the universe.Comment: 17 pages, 9 figures, version to be published in JCA
Can residuals of the Solar system foreground explain low multipole anomalies of the CMB ?
The low multipole anomalies of the Cosmic Microwave Background has received
much attention during the last few years. It is still not ascertained whether
these anomalies are indeed primordial or the result of systematics or
foregrounds. An example of a foreground, which could generate some non-Gaussian
and statistically anisotropic features at low multipole range, is the very
symmetric Kuiper Belt in the outer solar system. In this paper, expanding upon
the methods presented by Maris et al. (2011), we investigate the contributions
from the Kuiper Belt objects (KBO) to the WMAP ILC 7 map, whereby we can
minimize the contrast in power between even and odd multipoles in the CMB,
discussed discussed by Kim & Naselsky (2010). We submit our KBO de-correlated
CMB signal to several tests, to analyze its validity, and find that
incorporation of the KBO emission can decrease the quadrupole-octupole
alignment and parity asymmetry problems, provided that the KBO signals has a
non-cosmological dipole modulation, associated with the statistical anisotropy
of the ILC 7 map. Additionally, we show that the amplitude of the dipole
modulation, within a 2 sigma interval, is in agreement with the corresponding
amplitudes, discussed by Lew (2008).Comment: 24 pages, 9 figures, 5 tables. Matches version in JCA
Multi-field open inflation model and multi-field dynamics in tunneling
We consider a multi-field open inflation model, in which one of the fields
dominates quantum tunneling from a false vacuum while the other field governs
slow-roll inflation within the bubble nucleated from false vacuum decay. We
call the former the tunneling field and the latter the inflaton field. In the
limit of a negligible interaction between the two fields, the false vacuum
decay is described by a Coleman-De Luccia instanton. Here we take into account
the coupling between the two fields and construct explicitly a multi-field
instanton for a simple quartic potential model. We also solve the evolution of
the scalar fields within the bubble. We find our model realizes open inflation
successfully. This is the first concrete, viable model of open inflation
realized with a simple potential. We then study the effect of the multi-field
dynamics on the false vacuum decay, specifically on the tunneling rate. We find
the tunneling rate increases in general in comparison with the single field
case, though the increase is small unless the inflaton affects the instanton
solution substantially.Comment: 13 pages, 4 figure
The CMB Bispectrum
We use a separable mode expansion estimator with WMAP data to estimate the
bispectrum for all the primary families of non-Gaussian models. We review the
late-time mode expansion estimator methodology which can be applied to any
non-separable primordial and CMB bispectrum model, and we demonstrate how the
method can be used to reconstruct the CMB bispectrum from an observational map.
We extend the previous validation of the general estimator using local map
simulations. We apply the estimator to the coadded WMAP 5-year data,
reconstructing the WMAP bispectrum using multipoles and
orthonormal 3D eigenmodes. We constrain all popular nearly scale-invariant
models, ensuring that the theoretical bispectrum is well-described by a
convergent mode expansion. Constraints from the local model \fnl=54.4\pm
29.4 and the equilateral model \fnl=143.5\pm 151.2 (\Fnl = 25.1\pm 26.4)
are consistent with previously published results. (Here, we use a nonlinearity
parameter \Fnl normalised to the local case, to allow more direct comparison
between different models.) Notable new constraints from our method include
those for the constant model \Fnl = 35.1 \pm 27.4 , the flattened model \Fnl
= 35.4\pm 29.2, and warm inflation \Fnl = 10.3\pm 27.2. We investigate
feature models surveying a wide parameter range in both the scale and phase,
and we find no significant evidence of non-Gaussianity in the models surveyed.
We propose a measure \barFnl for the total integrated bispectrum and find
that the measured value is consistent with the null hypothesis that CMB
anisotropies obey Gaussian statistics. We argue that this general bispectrum
survey with the WMAP data represents the best evidence for Gaussianity to date
and we discuss future prospects, notably from the Planck satellite
The Vacuole Model: New Terms in the Second Order Deflection of Light
The present paper is an extension of a recent work (Bhattacharya et al. 2010)
to the Einstein-Strauss vacuole model with a cosmological constant, where we
work out the light deflection by considering perturbations up to order M^3 and
confirm the light bending obtained previously in their vacuole model by Ishak
et al. (2008). We also obtain another local coupling term
-((5{\pi}M^2{\Lambda})/8) related to {\Lambda}, in addition to the one obtained
by Sereno (2008, 2009). We argue that the vacuole method for light deflection
is exclusively suited to cases where the cosmological constant {\Lambda}
disappears from the path equation. However, the original Rindler-Ishak method
(2007) still applies even if a certain parameter {\gamma} of Weyl gravity does
not disappear. Here, using an alternative prescription, we obtain the known
term -(({\gamma}R)/2), as well as another new local term ((3{\pi}{\gamma}M)/2)
between M and {\gamma}. Physical implications are compared, where we argue that
the repulsive term -(({\gamma}R)/2) can be masked by the Schwarzschild term
((2M)/R) in the halo regime supporting attractive property of the dark matter.Comment: 15 page
Galactic-Centre Gamma Rays in CMSSM Dark Matter Scenarios
We study the production of gamma rays via LSP annihilations in the core of
the Galaxy as a possible experimental signature of the constrained minimal
supersymmetric extension of the Standard Model (CMSSM), in which
supersymmetry-breaking parameters are assumed to be universal at the GUT scale,
assuming also that the LSP is the lightest neutralino chi. The part of the
CMSSM parameter space that is compatible with the measured astrophysical
density of cold dark matter is known to include a stau_1 - chi coannihilation
strip, a focus-point strip where chi has an enhanced Higgsino component, and a
funnel at large tanb where the annihilation rate is enhanced by the poles of
nearby heavy MSSM Higgs bosons, A/H. We calculate the total annihilation rates,
the fractions of annihilations into different Standard Model final states and
the resulting fluxes of gamma rays for CMSSM scenarios along these strips. We
observe that typical annihilation rates are much smaller in the coannihilation
strip for tanb = 10 than along the focus-point strip or for tanb = 55, and that
the annihilation branching ratios differ greatly between the different dark
matter strips. Whereas the current Fermi-LAT data are not sensitive to any of
the CMSSM scenarios studied, and the calculated gamma-ray fluxes are probably
unobservably low along the coannihilation strip for tanb = 10, we find that
substantial portions of the focus-point strips and rapid-annihilation funnel
regions could be pressured by several more years of Fermi-LAT data, if
understanding of the astrophysical background and/or systematic uncertainties
can be improved in parallel.Comment: 33 pages, 12 figures, comments and references added, version to
appear in JCA
Mapping systematic errors in helium abundance determinations using Markov Chain Monte Carlo
Monte Carlo techniques have been used to evaluate the statistical and
systematic uncertainties in the helium abundances derived from extragalactic
H~II regions. The helium abundance is sensitive to several physical parameters
associated with the H~II region. In this work, we introduce Markov Chain Monte
Carlo (MCMC) methods to efficiently explore the parameter space and determine
the helium abundance, the physical parameters, and the uncertainties derived
from observations of metal poor nebulae. Experiments with synthetic data show
that the MCMC method is superior to previous implementations (based on flux
perturbation) in that it is not affected by biases due to non-physical
parameter space. The MCMC analysis allows a detailed exploration of
degeneracies, and, in particular, a false minimum that occurs at large values
of optical depth in the He~I emission lines. We demonstrate that introducing
the electron temperature derived from the [O~III] emission lines as a prior, in
a very conservative manner, produces negligible bias and effectively eliminates
the false minima occurring at large optical depth. We perform a frequentist
analysis on data from several "high quality" systems. Likelihood plots
illustrate degeneracies, asymmetries, and limits of the determination. In
agreement with previous work, we find relatively large systematic errors,
limiting the precision of the primordial helium abundance for currently
available spectra.Comment: 25 pages, 11 figure
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