53 research outputs found

    Hilbert space of Quantum Field Theory in de Sitter spacetime

    Full text link
    We study the decomposition of the Hilbert space of quantum field theory in (d+1)(d+1) dimensional de Sitter spacetime into Unitary Irreducible Representations (UIRs) of its isometry group \SO(1,d+1)(1,d+1). Firstly, we consider multi-particle states in free theories starting from the tensor product of single-particle UIRs. Secondly, we study conformal multiplets of a bulk Conformal Field Theory with symmetry group \SO(2,d+1)(2,d+1). Our main tools are the Harish-Chandra characters and the numerical diagonalization of the (truncated) quadratic Casimir of \SO(1,d+1)(1,d+1). We introduce a continuous density that encodes the spectrum of irreducible representations contained in a reducible one of \SO(1,d+1). Our results are complete for d=1d=1 and d=2d=2. In higher dimensions, we rederive and extend several results previously known in the literature. Our work provides the foundation for future nonperturbative bootstrap studies of Quantum Field Theory in de Sitter spacetime.Comment: 58 pages + appendices, 44 figures and 4 table

    The K\"all\'en-Lehmann representation in de Sitter spacetime

    Full text link
    We study two-point functions of symmetric traceless local operators in the bulk of de Sitter spacetime. We derive the K\"all\'en-Lehmann spectral decomposition for any spin and show that unitarity implies its spectral densities are nonnegative. In addition, we recover the K\"all\'en-Lehmann decomposition in Minkowski space by taking the flat space limit. Using harmonic analysis and the Wick rotation to Euclidean Anti de Sitter, we derive an inversion formula to compute the spectral densities. Using the inversion formula, we relate the analytic structure of the spectral densities to the late-time boundary operator content. We apply our technical tools to study two-point functions of composite operators in free and weakly coupled theories. In the weakly coupled case, we show how the K\"all\'en-Lehmann decomposition is useful to find the anomalous dimensions of the late-time boundary operators. We also derive the K\"all\'en-Lehmann representation of two-point functions of spinning primary operators of a Conformal Field Theory on de Sitter.Comment: 62 pages + appendices, 10 figure

    To be published in Health Physics

    Get PDF
    ABSTRACT In June 2007, the United States Department of Energy incorporated revised values of neutron weighting factors into its occupational radiation protection regulation Title 10, Code of Federal Regulations Part 835 as part of updating its radiation dosimetry system. This has led to a reassessment of neutron radiation fields at high energy accelerators such as those at the Fermi National Accelerator Laboratory (Fermilab) in the context of the amended regulation and contemporary guidance of the International Commission on Radiological Protection. Values of dose per fluence factors appropriate for accelerator radiation fields calculated elsewhere are collated and radiation weighting factors compared. The results of this revision to the dosimetric system are applied to americium-beryllium neutron energy spectra commonly used for instrument calibrations. Also, a set of typical accelerator neutron energy spectra previously measured at Fermilab are reassessed in light of the new dosimetry system. The implications of this revision and of recent ICRP publications are found to be of moderate significance

    Knowledge and perception toward colorectal cancer screening in east of Iran

    Get PDF
    Background: Colorectal Cancer (CRC) is the third most common cancer in Iran and its early detection is necessary. This study is based on perception of people in the east of Iran toward CRC screening. Methods: In a cross-sectional study, 1060 randomly selected individuals who referred to Razavi Hospital of Mashhad, Iran, between September the 1 st , 2012 and February the 28 th , 2013 as patients or their visitors involved in an interview to fill a questionnaire on CRC screening. Results: The participants’ age ranged from 40 to 88 years (mean= 55). More than 90% had no knowledge of CRC and screening tests. The most cited reasons for not having screening tests were “did not have any problem” and “did not think it was needed”. Although, older people had more knowledge of CRC ( P = 0.033), there was no relationship between gender, health insurance status, family history of individuals and their knowledge about CRC ( P > 0.050). Employment, education and higher income had positive effect on the perception of people toward CRC screening ( P < 0.050). Conclusion: Lack of knowledge in people in lower socio-economical class with limited literacy is the most important barrier to CRC screening. As such, designing educational programs involving physicians and media is important to improve CRC screening rates

    Activation detector measurements at the hadron absorber of the NuMI neutrino beamline at Fermilab

    Get PDF
    Two-dimensional distributions of the production rates of radionuclides in aluminum and gold activation detectors, placed behind the hadron absorber of the NuMI beamline at Fermilab were obtained in an experiment for shielding data as a dump in a proton-beam-energy domain above 100 GeV. The production rates of 7 Be, 22 Na, and 24 Na in the aluminum activation detectors and those of 185 Os, 194 Au, and 196 Au in the gold activation detectors were obtained from the Îł-ray spectra of HPGe counters. It was concluded that in these distributions showed some peaks that can be attributed to a lack of shielding caused by the gaps for arraignment and cooling in the hadron absorber. The radionuclides in the activation detectors were mainly produced by neutrons, protons and pions, according to analyses of calculated results by the PHITS code
    • …