1,375 research outputs found
Neutrinos and Future Concordance Cosmologies
We review the free parameters in the concordance cosmology, and those which
might be added to this set as the quality of astrophysical data improves. Most
concordance parameters encode information about otherwise unexplored aspects of
high energy physics, up to the GUT scale via the "inflationary sector," and
possibly even the Planck scale in the case of dark energy. We explain how
neutrino properties may be constrained by future astrophysical measurements.
Conversely, future neutrino physics experiments which directly measure these
parameters will remove uncertainty from fits to astrophysical data, and improve
our ability to determine the global properties of our universe.Comment: Proceedings of paper given at Neutrino 2008 meeting (by RE
Study of the leptonic decays of pseudoscalar and vector mesons and of the semileptonic and decays
We present results for different observables in weak decays of pseudoscalar
and vector mesons with a heavy or quark. The calculations are done in a
nonrelativistic constituent quark model improved at some instances by heavy
quark effective theory constraints. We determine pseudoscalar and vector meson
decay constants that within a few per cent satisfy , a
result expected in heavy quark symmetry when the heavy quark masses tend to
infinity. We also analyze the semileptonic and decays for
which we evaluate the different form factors. Here we impose heavy quark
effective theory constraints among form factors that are not satisfied by a
direct quark model calculation. The value of the form factors at zero recoil
allows us to determine, by comparison with experimental data, the value of the
Cabbibo-Kobayashi-Maskawa matrix element. From the
semileptonic decay we get in perfect agreement with
our previous determination based on the study of the semileptonic decay and also in excellent agreement with a recent experimental
determination by the DELPHI Collaboration. We further make use of the partial
conservation of axial current hypothesis to determine the strong coupling
constants and . The
ratio agrees with the heavy quark symmetry
prediction of 1.Comment: 19 Latex pages,6 figures, references added, corrected typos, content
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The Power Spectrum, Bias Evolution, and the Spatial Three-Point Correlation Function
We calculate perturbatively the normalized spatial skewness, , and full
three-point correlation function (3PCF), , induced by gravitational
instability of Gaussian primordial fluctuations for a biased tracer-mass
distribution in flat and open cold-dark-matter (CDM) models. We take into
account the dependence on the shape and evolution of the CDM power spectrum,
and allow the bias to be nonlinear and/or evolving in time, using an extension
of Fry's (1996) bias-evolution model. We derive a scale-dependent,
leading-order correction to the standard perturbative expression for in
the case of nonlinear biasing, as defined for the unsmoothed galaxy and
dark-matter fields, and find that this correction becomes large when probing
positive effective power-spectrum indices. This term implies that the inferred
nonlinear-bias parameter, as usually defined in terms of the smoothed density
fields, might depend on the chosen smoothing scale. In general, we find that
the dependence of on the biasing scheme can substantially outweigh that
on the adopted cosmology. We demonstrate that the normalized 3PCF, , is an
ill-behaved quantity, and instead investigate , the variance-normalized
3PCF. The configuration dependence of shows similarly strong
sensitivities to the bias scheme as , but also exhibits significant
dependence on the form of the CDM power spectrum. Though the degeneracy of
with respect to the cosmological parameters and constant linear- and
nonlinear-bias parameters can be broken by the full configuration dependence of
, neither statistic can distinguish well between evolving and non-evolving
bias scenarios. We show that this can be resolved, in principle, by considering
the redshift dependence of .Comment: 41 pages, including 12 Figures. To appear in The Astrophysical
Journal, Vol. 521, #
N-body simulations with generic non-Gaussian initial conditions I: Power Spectrum and halo mass function
We address the issue of setting up generic non-Gaussian initial conditions
for N-body simulations. We consider inflationary-motivated primordial
non-Gaussianity where the perturbations in the Bardeen potential are given by a
dominant Gaussian part plus a non-Gaussian part specified by its bispectrum.
The approach we explore here is suitable for any bispectrum, i.e. it does not
have to be of the so-called separable or factorizable form. The procedure of
generating a non-Gaussian field with a given bispectrum (and a given power
spectrum for the Gaussian component) is not univocal, and care must be taken so
that higher-order corrections do not leave a too large signature on the power
spectrum. This is so far a limiting factor of our approach. We then run N-body
simulations for the most popular inflationary-motivated non-Gaussian shapes.
The halo mass function and the non-linear power spectrum agree with theoretical
analytical approximations proposed in the literature, even if they were so far
developed and tested only for a particular shape (the local one). We plan to
make the simulations outputs available to the community via the non-Gaussian
simulations comparison project web site
http://icc.ub.edu/~liciaverde/NGSCP.html.Comment: 23 pages, 10 figure
First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Angular Power Spectrum
We present the angular power spectrum derived from the first-year Wilkinson
Microwave Anisotropy Probe (WMAP) sky maps. We study a variety of power
spectrum estimation methods and data combinations and demonstrate that the
results are robust. The data are modestly contaminated by diffuse Galactic
foreground emission, but we show that a simple Galactic template model is
sufficient to remove the signal. Point sources produce a modest contamination
in the low frequency data. After masking ~700 known bright sources from the
maps, we estimate residual sources contribute ~3500 uK^2 at 41 GHz, and ~130
uK^2 at 94 GHz, to the power spectrum l*(l+1)*C_l/(2*pi) at l=1000. Systematic
errors are negligible compared to the (modest) level of foreground emission.
Our best estimate of the power spectrum is derived from 28 cross-power spectra
of statistically independent channels. The final spectrum is essentially
independent of the noise properties of an individual radiometer. The resulting
spectrum provides a definitive measurement of the CMB power spectrum, with
uncertainties limited by cosmic variance, up to l~350. The spectrum clearly
exhibits a first acoustic peak at l=220 and a second acoustic peak at l~540 and
it provides strong support for adiabatic initial conditions. Kogut et al.
(2003) analyze the C_l^TE power spectrum, and present evidence for a relatively
high optical depth, and an early period of cosmic reionization. Among other
things, this implies that the temperature power spectrum has been suppressed by
\~30% on degree angular scales, due to secondary scattering.Comment: One of thirteen companion papers on first-year WMAP results submitted
to ApJ; 44 pages, 14 figures; a version with higher quality figures is also
available at http://lambda.gsfc.nasa.gov/product/map/map_bibliography.htm
Prospects in Constraining the Dark Energy Potential
We generalize to non-flat geometries the formalism of Simon et al. (2005) to
reconstruct the dark energy potential. This formalism makes use of quantities
similar to the Horizon-flow parameters in inflation, can, in principle, be made
non-parametric and is general enough to be applied outside the simple, single
scalar field quintessence. Since presently available and forthcoming data do
not allow a non-parametric and exact reconstruction of the potential, we
consider a general parametric description in term of Chebyshev polynomials. We
then consider present and future measurements of H(z), Baryon Acoustic
Oscillations surveys and Supernovae type 1A surveys, and investigate their
constraints on the dark energy potential. We find that, relaxing the flatness
assumption increases the errors on the reconstructed dark energy evolution but
does not open up significant degeneracies, provided that a modest prior on
geometry is imposed. Direct measurements of H(z), such as those provided by BAO
surveys, are crucially important to constrain the evolution of the dark energy
potential and the dark energy equation of state, especially for non-trivial
deviations from the standard LambdaCDM model.Comment: 22 pages, 7 figures. 2 references correcte
Coulomb chronometry to probe the decay mechanism of hot nuclei
In 129 Xe+ nat Sn central collisions from 8 to 25 MeV/A, the three-fragment
exit channel occurs with a significant cross section. We show that these
fragments arise from two successive binary splittings of a heavy composite
system. The sequence of fragment production is determined. Strong Coulomb
proximity effects are observed in the three-fragment final state. A comparison
with Coulomb trajec-tory calculations shows that the time scale between the
consecutive break-ups decreases with increasing bombarding energy, becoming
quasi-simultaneous above excitation energy E * = 4.00.5 MeV/A. This
transition from sequential to simultaneous break-up was interpreted as the
signature of the onset of multifragmentation for the three-fragment exit
channel in this system.Comment: 12 pages; 13 Figures; 4 Table; Accepted for publication in Physical
Review
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