21,747 research outputs found
Estimating the large-scale angular power spectrum in the presence of systematics: a case study of Sloan Digital Sky Survey quasars
The angular power spectrum is a powerful statistic for analysing cosmological
signals imprinted in the clustering of matter. However, current galaxy and
quasar surveys cover limited portions of the sky, and are contaminated by
systematics that can mimic cosmological signatures and jeopardise the
interpretation of the measured power spectra. We provide a framework for
obtaining unbiased estimates of the angular power spectra of large-scale
structure surveys at the largest scales using quadratic estimators. The method
is tested by analysing the 600 CMASS mock catalogues constructed by Manera et
al. (2013) for the Baryon Oscillation Spectroscopic Survey (BOSS). We then
consider the Richards et al. (2009) catalogue of photometric quasars from the
Sixth Data Release (DR6) of the Sloan Digital Sky Survey (SDSS), which is known
to include significant stellar contamination and systematic uncertainties.
Focusing on the sample of ultraviolet-excess (UVX) sources, we show that the
excess clustering power present on the largest-scales can be largely mitigated
by making use of improved sky masks and projecting out the modes corresponding
to the principal systematics. In particular, we find that the sample of objects
with photometric redshift exhibits no evidence of
contamination when using our most conservative mask and mode projection. This
indicates that any residual systematics are well within the statistical
uncertainties. We conclude that, using our approach, this sample can be used
for cosmological studies.Comment: 18 pages, 18 figures. Version accepted by MNRA
Asymmetric Uncertainties: Sources, Treatment and Potential Dangers
The issue of asymmetric uncertainties resulting from fits, nonlinear
propagation and systematic effects is reviewed. It is shown that, in all cases,
whenever a published result is given with asymmetric uncertainties, the value
of the physical quantity of interest is biased with respect to what would be
obtained using at best all experimental and theoretical information that
contribute to evaluate the combined uncertainty. The probabilistic solution to
the problem is provided both in exact and in approximated forms.Comment: 21 pages, 5 figures. improved version with some corrections,
additional remarks and references (download of new version is recommended).
This paper and related work are also available at
http://www.roma1.infn.it/~dagos/prob+stat.htm
Optical response of small carbon clusters
We apply the time-dependent local density approximation (TDLDA) to calculate
dipole excitations in small carbon clusters. A strong low-frequency mode is
found which agrees well with observation for clusters C_n with n in the range
7-15. The size dependence of the mode may be understood simply as the classical
resonance of electrons in a conducting needle. For a ring geometry, the lowest
collective mode occurs at about twice the frequency of the collective mode in
the linear chain, and this may also be understood in simple terms.Comment: 19 pages, Latex(Revtex), and 7 figures Postscript; to be published in
Zeit. Phys. D; contact is [email protected]
A Systematic Approach to the SILH Lagrangian
We consider the electroweak chiral Lagrangian, including a light scalar
boson, in the limit of small . Here is the electroweak scale
and is the corresponding scale of the new strong dynamics. We show how the
conventional SILH Lagrangian, defined as the effective theory of a
strongly-interacting light Higgs (SILH) to first order in , can be
obtained as a limiting case of the complete electroweak chiral Lagrangian. The
approach presented here ensures the completeness of the operator basis at the
considered order, it clarifies the systematics of the effective Lagrangian,
guarantees a consistent and unambiguous power counting, and it shows how the
generalization of the effective field theory to higher orders in has to
be performed. We point out that terms of order , which are usually not
included in the SILH Lagrangian, are parametrically larger than terms of order
that are retained, as long as . Conceptual
issues such as custodial symmetry and its breaking are also discussed. For
illustration, the minimal composite Higgs model based on the coset
is considered at next-to-leading order in the chiral expansion.
It is shown how the effective Lagrangian for this model is contained as a
special case in the electroweak chiral Lagrangian based on .Comment: 22 pages, 1 figure; improved presentation of the results in section
The explicit form of the effective action for F1 and D-branes
In this work we consider the full interacting effective actions for
fundamental strings and D-branes in arbitrary bosonic type II supergravity
backgrounds. The explicit form of these actions is given in terms of component
fields, up to second order in the fermions. The results take a compact form
exhibiting -symmetry, as well as supersymmetry in a background with
Killing spinors. Also we give the explicit transformation rules for these
symmetries in all cases.Comment: 9 pages, based on the talk given at the RTN workshop of 2003
Copenhagen: 15/9-20/9/03. Published in the proceedings of the conferenc
Quadrupole Deformation of Barium Isotopes
The B(E2:0_1^+ -> 2_1^+) values of the Ba isotopes (Z=56) exhibit a sharp
increase in deformation as the neutron numbers approach the mid-shell value of
N=66. This behavior is anomalous because the 2_1^+ level energies are very
similar to those of the neighboring isotopes. By means of the axially-symmetric
deformed Woods-Saxon (WS) hamiltonian plus the BCS method, we investigated the
systematics of B(E2) of the Ba isotopes. We showed that 15% of the B(E2) values
at N=66 was due to the level crossing, occurring at the deformation with beta
being nearly 0.3, between the proton orbits originating from the orbits
Omega=1/2^-(h11/2) and 9/2^+(g9/2) at zero deformation. The latter of these two
was an intruder orbit originating from below the energy gap at Z=50, rising
higher in energy with the deformation and intruding the Z=50-82 shell. These
two orbits have the largest magnitude of the quadrupole moment with a different
sign among the orbits near and below the Fermi surface. Occupancy and
non-occupancy of these orbits by protons thus affect B(E2:0_1^+ -> 2_1^+)
significantly.Comment: 10 pages, 2 figures, to be published in Phys.Lett.
The Vector-Tensor Supermultiplet with Gauged Central Charge
The vector-tensor multiplet is coupled off-shell to an N=2 vector multiplet
such that its central charge transformations are realized locally. A gauged
central charge is a necessary prerequisite for a coupling to supergravity and
the strategy underlying our construction uses the potential for such a coupling
as a guiding principle. The results for the action and transformation rules
take a nonlinear form and necessarily include a Chern-Simons term. After a
duality transformation the action is encoded in a homogeneous holomorphic
function consistent with special geometry.Comment: 8 pages, LATE
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