4,067 research outputs found
Coherent Matter Wave Transport in Speckle Potentials
This article studies multiple scattering of matter waves by a disordered
optical potential in two and in three dimensions. We calculate fundamental
transport quantities such as the scattering mean free path , the
Boltzmann transport mean free path \elltrb, and the Boltzmann diffusion
constant , using a diagrammatic Green functions approach. Coherent
multiple scattering induces interference corrections known as weak localization
which entail a reduced diffusion constant. We derive the corresponding
expressions for matter wave transport in an correlated speckle potential and
provide the relevant parameter values for a possible experimental study of this
coherent transport regime, including the critical crossover to the regime of
strong or Anderson localization.Comment: 33 pages, minor corrections, published versio
Cosmic-ray antiproton constraints on light dark matter candidates
Some direct detection experiments have recently collected excess events that
could be interpreted as a dark matter (DM) signal, pointing to particles in the
10 GeV mass range. We show that scenarios in which DM can self-annihilate
with significant couplings to quarks are likely excluded by the cosmic-ray (CR)
antiproton data, provided the annihilation is S-wave dominated when DM
decouples in the early universe. These limits apply to most of supersymmetric
candidates, eg in the minimal supersymmetric standard model (MSSM) and in the
next-to-MSSM (NMSSM), and more generally to any thermal DM particle with
hadronizing annihilation final states.Comment: Contribution to the proceedings of TAUP-2011 (Munich, 5-9 IX 2011). 4
page
Invisible Higgs and Scalar Dark Matter
In this proceeding, we show that when we combined WMAP and the most recent
results of XENON100, the invisible width of the Higgs to scalar dark matter is
negligible(<10%), except in a small region with very light dark matter (< 10
GeV) not yet excluded by XENON100 or around 60 GeV where the ratio can reach
50% to 60%. The new results released by the Higgs searches of ATLAS and CMS set
very strong limits on the elastic scattering cross section.Comment: 4 pages, 2 figures, proceeding TAUP2011 References adde
RHESSI images and spectra of two small flares
We studied the evolution of two small flares (GOES class C2 and C1) that
developed in the same active region with different morphological
characteristics: one is extended and the other is compact. We analyzed the
accuracy and the consistency of different algorithms implemented in RHESSI
software to reconstruct the image of the emitting sources, for energies between
3 and 12 keV. We found that all tested algorithms give consistent results for
the peak position whil the other parameters can differ at most by a factor 2.
Pixon and Forward-fit generally converge to similar results but Pixon is more
reliable for reconstructing a complex source. We investigated the spectral
characteristics of the two flares during their evolution in the 3--25 keV
energy band. We found that a single thermal model of the photon spectrum is
inadequate to fit the observations and we needed to add either a non-thermal
model or a hot thermal one.The non-thermal and the double thermal fits are
comparable. If we assume a non-thermal model, the non-thermal energy is always
higher than the thermal one.Only during the very final decay phase a single
thermal model fits fairly well the observed spectrum.Comment: 26 pages, 11 figures, accepted by Solar Physic
Dairy Intake and Risk of Cognitive Decline and Dementia: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies
Dairy intake may influence cognition through several molecular pathways. However, epidemiologic studies yield inconsistent results, and no dose-response meta-analysis has been conducted yet. Therefore, we performed a systematic review with a dose-response meta-analysis about the association between dairy intake and cognitive decline or incidence of dementia. We investigated prospective studies with a follow-up â„6 mo on cognitive decline or dementia incidence in adults without known chronic conditions through a systematic search of Embase, Medline, Cochrane Library, Web of Science, and Google Scholar from inception to 11 July 2023. We evaluated the dose-response association using a random-effects model. We identified 15 eligible cohort studies with >300,000 participants and a median follow-up of 11.4 y. We observed a negative nonlinear association between cognitive decline/dementia incidence and dairy intake as assessed through the quantity of consumption, with the nadir at âŒ150 g/d (risk ratio: 0.88; 95% confidence interval: 0.78, 0.99). Conversely, we found an almost linear negative association when we considered the frequency of consumption (risk ratio for linear trend: 0.84; 95% confidence interval: 0.77, 0.92 for 1 time/d increase of dairy products). Stratified analysis by dairy products showed different shapes of the association with linear inverse relationship for milk intake, whereas possibly nonlinear for cheese. The inverse association was limited to Asian populations characterized by generally lower intake of dairy products, compared with the null association reported by European studies. In conclusion, our study suggests a nonlinear inverse association between dairy intake and cognitive decline or dementia, also depending on dairy types and population characteristics, although the heterogeneity was still high in overall and several subgroup analyses. Additional studies should be performed on this topic, including a wider range of intake and types of dairy products, to confirm a potential preventing role of dairy intake on cognitive decline and identify ideal intake doses. This review was registered at PROSPERO as CRD42020192395
Further Evidence for Chemical Fractionation from Ultraviolet Observations of Carbon Monoxide
Ultraviolet absorption from interstellar 12CO and 13CO was detected toward
rho Oph A and chi Oph. The measurements were obtained at medium resolution with
the Goddard High Resolution Spectrograph on the Hubble Space Telescope. Column
density ratios, N(12CO)/N(13CO), of 125 \pm 23 and 117 \pm 35 were derived for
the sight lines toward rho Oph A and chi Oph, respectively. A value of 1100 \pm
600 for the ratio N(12C16O)/N(12C18O) toward rho Oph A was also obtained.
Absorption from vibrationally excited H_2 (v" = 3) was clearly seen toward this
star as well.
The ratios are larger than the isotopic ratios for carbon and oxygen
appropriate for ambient interstellar material. Since for both carbon and oxygen
the more abundant isotopomer is enhanced, selective isotopic photodissociation
plays the key role in the fractionation process for these directions. The
enhancement arises because the more abundant isotopomer has lines that are more
optically thick, resulting in more self shielding from dissociating radiation.
A simple argument involving the amount of self shielding [from N(12CO)] and the
strength of the ultraviolet radiation field premeating the gas (from the amount
of vibrationally excited H_2) shows that selective isotopic photodissociation
controls the fractionation seen in these two sight lines, as well as the sight
line to zeta Oph.Comment: 40 pages, 8 figures, to appear in 10 July 2003 issue of Ap
Higgs to mu tau Decay in Supersymmetry without R Parity
In this letter, we report on lepton flavor violating Higgs decay into mu+tau
in the framework of the generic supersymmetric standard model without R parity
and list interesting combinations of R-parity violating parameters. We impose
other known experimental constraints on the parameters of the model and show
our results from the R-parity violating parameters. In our analysis, the
branching ratio of Higgs to mu+tau can exceed 10^{-5} within admissible
parameter space.Comment: 16 pages, 3 figures, 1 table. Version published in Europhysics
Letter
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