Sterile neutrino production via active-sterile oscillations: the quantum Zeno effect

We study several aspects of the kinetic approach to sterile neutrino production via active-sterile mixing. We obtain the neutrino propagator in the medium including self-energy corrections up to $\mathcal{O}(G^2_F)$, from which we extract the dispersion relations and damping rates of the propagating modes. The dispersion relations are the usual ones in terms of the index of refraction in the medium, and the damping rates are $\Gamma_1(k) = \Gamma_{aa}(k) \cos^2\theta_m(k); \Gamma_2(k) = \Gamma_{aa}(k) \sin^2\theta_m(k)$ where $\Gamma_{aa}(k)\propto G^2_F k T^4$ is the active neutrino scattering rate and $\theta_m(k)$ is the mixing angle in the medium. We provide a generalization of the transition probability in the \emph{medium from expectation values in the density matrix}: $P_{a\to s}(t) = \frac{\sin^22\theta_m}{4}[e^{-\Gamma_1t} + e^{-\Gamma_2 t}-2e^{-{1/2}(\Gamma_1+\Gamma_2)t} \cos\big(\Delta E t\big)]$ and study the conditions for its quantum Zeno suppression directly in real time. We find the general conditions for quantum Zeno suppression, which for $m_s\sim \textrm{keV}$ sterile neutrinos with $\sin2\theta \lesssim 10^{-3}$ \emph{may only be} fulfilled near an MSW resonance. We discuss the implications for sterile neutrino production and argue that in the early Universe the wide separation of relaxation scales far away from MSW resonances suggests the breakdown of the current kinetic approach.Comment: version to appear in JHE

Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei

In this article we examine the hypothesis that the highest energy cosmic rays are complex nuclei from extragalactic sources. Under reasonable physical assumptions, we show that the nearby metally rich starburst galaxies (M82 and NGC 253) can produce all the events observed above the ankle. This requires diffusion of particles below $10^{20}$ eV in extragalactic magnetic fields $B \approx 15$ nG. Above $10^{19}$ eV, the model predicts the presence of significant fluxes of medium mass and heavy nuclei with small rate of change of composition. Notwithstanding, the most salient feature of the starburst-hypothesis is a slight anisotropy induced by iron debris just before the spectrum-cutoff.Comment: To appear in Phys. Rev. D, reference adde

Ohm's Law for Plasma in General Relativity and Cowling's Theorem

The general-relativistic Ohm's law for a two-component plasma which includes the gravitomagnetic force terms even in the case of quasi-neutrality has been derived. The equations that describe the electromagnetic processes in a plasma surrounding a neutron star are obtained by using the general relativistic form of Maxwell equations in a geometry of slow rotating gravitational object. In addition to the general-relativistic effect first discussed by Khanna \& Camenzind (1996) we predict a mechanism of the generation of azimuthal current under the general relativistic effect of dragging of inertial frames on radial current in a plasma around neutron star. The azimuthal current being proportional to the angular velocity $\omega$ of the dragging of inertial frames can give valuable contribution on the evolution of the stellar magnetic field if $\omega$ exceeds $2.7\times 10^{17} (n/\sigma) \textrm{s}^{-1}$ ($n$ is the number density of the charged particles, $\sigma$ is the conductivity of plasma). Thus in general relativity a rotating neutron star, embedded in plasma, can in principle generate axial-symmetric magnetic fields even in axisymmetry. However, classical Cowling's antidynamo theorem, according to which a stationary axial-symmetric magnetic field can not be sustained against ohmic diffusion, has to be hold in the general-relativistic case for the typical plasma being responsible for the rotating neutron star.Comment: Accepted for publication in Astrophysics & Space Scienc

Clinical consequences of nonadherence to Barrett's esophagus surveillance recommendations:a Multicenter prospective cohort study

Half of Barrett's esophagus (BE) surveillance endoscopies do not adhere to guideline recommendations. In this multicenter prospective cohort study, we assessed the clinical consequences of nonadherence to recommended surveillance intervals and biopsy protocol. Data from BE surveillance patients were collected from endoscopy and pathology reports; questionnaires were distributed among endoscopists. We estimated the association between (non)adherence and (i) endoscopic curability of esophageal adenocarcinoma (EAC), (ii) mortality, and (iii) misclassification of histological diagnosis according to a multistate hidden Markov model. Potential explanatory parameters (patient, facility, endoscopist variables) for nonadherence, related to clinical impact, were analyzed. In 726 BE patients, 3802 endoscopies were performed by 167 endoscopists. Adherence to surveillance interval was 16% for non-dysplastic (ND)BE, 55% for low-grade dysplasia (LGD), and 54% of endoscopies followed the Seattle protocol. There was no evidence to support the following statements: longer surveillance intervals or fewer biopsies than recommended affect endoscopic curability of EAC or cause-specific mortality (P &gt; 0.20); insufficient biopsies affect the probability of NDBE (OR 1.0) or LGD (OR 2.3) being misclassified as high-grade dysplasia/EAC (P &gt; 0.05). Better adherence was associated with older patients (OR 1.1), BE segments ≤ 2 cm (OR 8.3), visible abnormalities (OR 1.8, all P ≤ 0.05), endoscopists with a subspecialty (OR 3.2), and endoscopists who deemed histological diagnosis an adequate marker (OR 2.0). Clinical consequences of nonadherence to guidelines appeared to be limited with respect to endoscopic curability of EAC and mortality. This indicates that BE surveillance recommendations should be optimized to minimize the burden of endoscopies.</p

Accuracy of 18F-FDG PET/CT in predicting residual disease after neoadjuvant chemoradiotherapy for esophageal cancer

Our purpose was to prospectively investigate optimal evaluation of qualitative and quantitative 18F-FDG PET/CT in response evaluations 12–14 wk after neoadjuvant chemoradiotherapy (nCRT) in esophageal cancer patients. Methods: This was a side study of the prospective diagnostic pre-SANO trial. 18F-FDG PET/CT scans at baseline and at 12–14 wk after nCRT were qualitatively assessed for the presence of tumor. Maximum SUVs normalized for lean body mass (SULmax) were measured in all scans. The primary endpoint was the proportion of false-negative patients with tumor regression grade (TRG) 3–4 (.10% vital residual tumor) in qualitative and quantitative analyses. Receiver-operating-characteristic curve analysis for TRG1 versus TRG3–4 using SULmax, SULmax tumor-to-esophagus ratio, and D%SULmax was performed to define optimal cutoffs. Secondary endpoints were sensitivity, specificity, negative predictive value, and positive predictive value for TRG1 versus TRG2–4. Results: In total, 129 of 219 patients were analyzed. Qualitative 18F-FDG PET/CT was unable to detect TRG3–4 in 15% of patients. Sensitivity, specificity, negative predictive value, and positive predictive value in qualitative analysis for detecting TRG1 versus TRG2–4 was 80%, 37%, 42%, and 77%, respectively. In 18 of 190 patients (10%) with follow-up scans after nCRT, 18F-FDG PET/CT identified new interval metastases. Quantitative parameters did not detect TRG3–4 tumor in 27%–61% of patients. The optimal cutoff for detecting TRG1 versus TRG2–4 was a post-nCRT SULmax of 2.93 (area under receiver-operating-characteristic curve, 0.70). Conclusion: Qualitative and quantitative analyses of 18F-FDG PET/CT are unable to accurately detect TRG3–4 and to discriminate substantial residual disease from benign inflammation-induced 18F-FDG uptake after nCRT. However, 18F-FDG PET/CT is useful for the detection of interval metastases and might become useful in an active surveillance strategy with serial 18F-FDG PET/CT scanning