12,623 research outputs found
Kinematic sensitivity to the Fierz term of -decay differential spectra
The current most stringent constraints on exotic scalar or tensor couplings
in neutron and nuclear decay, involving left-handed neutrinos, are
obtained from the Fierz interference term. The sensitivity to this term in a
correlation coefficient is usually driven by an energy-averaged kinematic
factor that increases monotonically toward smaller values of the
endpoint energies. We first point out here that this property does not hold for
certain differential observables that are directly sensitive to the Fierz term,
such as the or the recoil energy spectrum. This observation is relevant
for the selection of sensitive transitions in searches for exotic couplings
through spectrum shape measurements. We then point out previous errors in the
exploitation of measurements of the angular correlation coefficient
and discuss their impact on the extraction of constraints on exotic couplings.Comment: 7 pages, 5 figure
Chiral low-energy constants from tau data
We analyze how the recent precise hadronic tau-decay data on the V-A spectral
function and general properties of QCD such as analyticity, the operator
product expansion and chiral perturbation theory (ChPT), can be used to improve
the knowledge of some of the low-energy constants of ChPT. In particular we
find the most precise values of L_{9,10} (or equivalently l_{5,6}) at order p^4
and p^6 and the first phenomenological determination of C_87 (c_50).Comment: Proceedings of the 6th International Workshop on Chiral Dynamics
(Bern, Switzerland, July 6-10, 2009). 9 pages, 3 figure
Pinched weights and Duality Violation in QCD Sum Rules: a critical analysis
We analyze the so-called pinched weights, that are generally thought to
reduce the violation of quark-hadron duality in Finite-Energy Sum Rules. After
showing how this is not true in general, we explain how to address this
question for the LR correlator and any particular pinched weight taking
advantage of our previous work [1], where the possible high-energy behavior of
the LR spectral function was studied. In particular we show that the use of
pinched weights allows to determine with high accuracy the dimension six and
eight contributions in the operator product expansion,
O6=(-4.3^[+0.9}_{-0.7})*10^-3 GeV^6 and O8=(-7.2^{+4.2}_{-5.3})*10^-3 GeV^8.Comment: 11 pages. A few references added and discussion slightly enlarged.
Results unchanged
Effective temperatures and radii of planet-hosting stars from IR photometry
In this paper we present and analyse determinations of effective temperatures
of planet-hosting stars using infrared (IR) photometry. One of our goals is the
comparison with spectroscopic temperatures to evaluate the presence of
systematic effects that could alter the determination of metal abundances. To
estimate the stellar temperatures we have followed a new approach based on
fitting the observed 2MASS IR photometry with accurately calibrated synthetic
photometry. Special care has been put in evaluating all sources of possible
errors and incorporating them in the analysis. A comparison of our temperature
determinations with spectroscopic temperatures published by different groups
reveals the presence of no systematic trends and a scatter compatible with the
quoted uncertainties of 0.5-1.3%. This mutual agreement strengthens the results
of both the spectroscopic and IR photometry analyses. Comparisons with other
photometric temperature calibrations, generally with poorer performances, are
also presented. In addition, the method employed of fitting IR photometry
naturally yields determinations of the stellar semi-angular diameters, which,
when combined with the distances, results in estimations of the stellar radii
with remarkable accuracies of ~2-4%. A comparison with the only star in the
sample with an empirically determined radius (HD 209458 -- from transit
photometry) indicates excellent agreement.Comment: 4 pages, 1 figure, accepted for publication as a letter in A&
Global constraints on anomalous triple gauge couplings in effective field theory approach
We present a combined analysis of LHC Higgs data (signal strengths) together
with LEP-2 WW production measurements. To characterize possible deviations from
the Standard Model (SM) predictions, we employ the framework of an Effective
Field Theory (EFT) where the SM is extended by higher-dimensional operators
suppressed by the mass scale of new physics . The analysis is
performed consistently at the order in the EFT expansion keeping
all the relevant operators. While the two data sets suffer from flat
directions, together they impose stringent model-independent constraints on the
anomalous triple gauge couplings. As a side product, we provide the results of
the combined fit in different EFT bases.Comment: 7 pages. v2: References and clarifications adde
The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418
The 9.7-micron silicate absorption profile in the interstellar medium
provides important information on the physical and chemical composition of
interstellar dust grains. Measurements in the Milky Way have shown that the
profile in the diffuse interstellar medium is very similar to the amorphous
silicate profiles found in circumstellar dust shells around late M stars, and
narrower than the silicate profile in denser star-forming regions. Here, we
investigate the silicate absorption profile towards the very heavily obscured
nucleus of NGC 4418, the galaxy with the deepest known silicate absorption
feature, and compare it to the profiles seen in the Milky Way. Comparison
between the 8-13 micron spectrum obtained with TReCS on Gemini and the larger
aperture spectrum obtained from the Spitzer archive indicates that the former
isolates the nuclear emission, while Spitzer detects low surface brightness
circumnuclear diffuse emission in addition. The silicate absorption profile
towards the nucleus is very similar to that in the diffuse ISM in the Milky Way
with no evidence of spectral structure from crystalline silicates or silicon
carbide grains.Comment: 7 Pages, 3 figures. MNRAS in pres
Conceptos extraños
En primer lugar consideramos la posibilidad de tomar la idea de Dios como un producto puramente cultural y por tanto superable en algún sentido. Se examina el concepto de teorema de limitación para analizar la posibilidad de prescindir de la idea de �origen del universo� mediante un refinamiento sustancial de ciertas nociones fuertemente asentadas en nuestra tradiciónFirstly I will defend the possibility of considering the idea of a creator God as a purely cultural and therefore surpassable idea. Then, I examine the concept of impossibility theorem to study the possibility of finally overcoming the idea of an origin of the universe through a substantial refinement of certain notions strongly established in our cultural tradition
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