Is Turing's Thesis the Consequence of a More General Physical Principle?

We discuss historical attempts to formulate a physical hypothesis from which Turing's thesis may be derived, and also discuss some related attempts to establish the computability of mathematical models in physics. We show that these attempts are all related to a single, unified hypothesis.Comment: 10 pages, 0 figures; section 1 revised, other minor change

Inflation near a metastable de Sitter vacuum from moduli stabilisation

We study the cosmological properties of a metastable de Sitter vacuum obtained recently in the framework of type IIB flux compactifications in the presence of three D7-brane stacks, based on perturbative quantum corrections at both world-sheet and string loop level that are dominant at large volume and weak coupling. In the simplest case, the model has one effective parameter controlling the shape of the potential of the inflaton which is identified with the volume modulus. The model provides a phenomenological successful small-field inflation for a value of the parameter that makes the minimum very shallow and near the maximum. The horizon exit is close to the inflection point while most of the required e-folds of the Universe expansion are generated near the minimum, with a prediction for the ratio of tensor-to-scalar primordial fluctuations $r \sim 4 \times 10^{-4}$. Despite its shallowness, the minimum turns out to be practically stable. We show that it can decay only through the Hawking-Moss instanton leading to an extremely long decay rate. Obviously, in order to end inflation and obtain a realistic model, new low-energy physics is needed around the minimum, at intermediate energy scales of order $10^{12}$ GeV. An attractive possibility is by introducing a "waterfall"' field within the framework of hybrid inflation.Comment: 25 pages, 9 figures; v2: published version, minor correction

On the nature of the residual meson-meson interaction from simulations with a QED2+1{}_{2+1} model

A potential between mesons is extracted from 4-point functions within lattice gauge theory taking 2+1 dimensional QED as an example. This theory possesses confinement and dynamical fermions. The resulting meson-meson potential has a short-ranged hard repulsive core and the expected dipole-dipole forces lead to attraction at intermediate distances. Sea quarks lead to a softer form of the total potential.Comment: 4 pages, uuencoded tar-compressed postscript file, contribution to Lattice'9

Baryon-Baryon Potentials on the Lattice

The interaction of spatially extended heavy baryons is investigated in the framework of lattice QCD with dynamical quarks. It is shown that the expected dipole forces have a very short range and that the baryon-antibaryon interaction is more attractive than the baryon-baryon interaction. Sea quarks play a minor important role.Comment: 8 pages, uuencoded postscript file; Physics Letters B, in pres

Content validation of a new measure of patient-reported barriers to antiretroviral therapy adherence, the I-Score: results from a Delphi study

Background Over a third of people living with HIV (PLHIV) have suboptimal adherence to antiretroviral therapy (ART). Measures of barriers to ART adherence often lack comprehensiveness. To help manage ART adherence barriers in HIV care, we are developing a new patient-reported outcome measure (PROM) of these barriers (the I-Score). Methods We assessed the content validity of 100 items (distinct barriers) to retain only those most relevant to both PLHIV and HIV health/social service providers. A web-based Delphi was conducted in Canada and France, collecting data from December 2018 to October 2019. Items were evaluated on relevance (the combined rated importance and actionability for HIV care of items among both PLHIV and providers); comprehensibility (rated item clarity); comprehensiveness (examined against our conceptual framework); cross-cultural equivalence (based on comparisons by questionnaire language (English, French) and country of residence). Pearson’s chi-square tests were used for comparisons by language, country, gender, and stakeholder group (PLHIV, providers). Results Panelists included 40 PLHIV and 57 providers (66% response rate). Thirty-one items were retained based on consensus thresholds for relevance (minimum: 50% for PLHIV, 60% for providers) and showed good comprehensibility and comprehensiveness, when compared to our conceptual framework (representation of: 6/6 domains, 15/20 subdomains). No significant difference in relevance based on language or country was found among retained items, suggestive of cross-cultural equivalence. Among all 100 items, only 6 significant differences on relevance were observed for gender. For 62 items, the relevance ratings of PLHIV and providers differed significantly, with providers showing greater endorsement of all items but one. Discussion The Delphi led to a much-needed item reduction. Remaining items highlight the panel’s multidimensional priorities for the PROM on ART adherence barriers, with few, if any, differences by language, country, and gender. While the analyses may lack generalizability and power, the sample size is considered adequate for a PROM validation study. Conclusion Retained items showed good content validity. The different patterns of item endorsement observed underscore the utility of engaging multiple stakeholder groups in PROM development for use in clinical practice. The greater endorsement of items by providers versus patients merits further investigation, including the implications of such differentials for measure development.KE is partially supported by a SPOR Mentorship Chair in Innovative Clinical Trials awarded by the CIHR to BL (Grant No. 383427). BL is supported by a career award, LE 250, from the Quebec Ministry of Health for researchers in Family Medicine. The Delphi benefited from methodological expertise and funding from the Quebec SPOR Support Unit -McGill Methodological Developments Platform (Grant No. M006). The Delphi is a subproject of the PROM development study, the I-Score Study, which is supported, in part, by the CIHR HIV Clinical Trials Network (CTN 283) and by a research Grant from the Investigator Initiated Studies Program of Merck Canada Inc. (Grant No. IISP-53538), neither of which had a hand in the design, conduct, or writing up of this work. The opinions expressed in this study are those of the authors and do not necessarily represent those of Merck Canada Inc or its affiliates or related companies

Extraction of hadron-hadron potentials on the lattice within 2+1 dimensional QED

A potential between mesons is extracted from 4-point functions within lattice gauge theory taking 2+1 dimensional QED as an example. This theory possesses confinement and dynamical fermions. The resulting meson-meson potential has a short-ranged hard repulsive core due to antisymmetrization. The expected dipole-dipole forces lead to attraction at intermediate distances. Sea quarks lead to a softer form of the total potential.Comment: 12 pages, uuencoded tar-compressed postscript fil

Gamma-rays from Galactic Black Hole Candidates with Stochastic Particle Acceleration

We consider stochastic particle acceleration in plasmas around stellar mass black holes to explain the emissions above 1 MeV from Galactic black hole candidates. We show that for certain parameter regimes, electrons can overcome Coulomb losses and be accelerated beyond the thermal distribution to form a new population, whose distribution is broad and usually not a power law; the peak energy of the distribution is determined by the balance between acceleration and cooling, with particles piling up around it. Radiation by inverse Compton scattering off the thermal (from background) and non-thermal (produced by acceleration) particles can in principle explain the hard X-ray to gamma-ray emissions from black hole candidates. We present model fits of Cyg X-1 and GRO J0422 in 50 keV -- 5 MeV region observed with OSSE and COMPTEL.Comment: 2 figures, to appear in March 20 of ApJ

Nonlocal Kinetic Equation and Simulations of Heavy Ion Reactions

A kinetic equation which combines the quasiparticle drift of Landau's equation with a dissipation governed by a nonlocal and noninstantaneous scattering integral in the spirit of Enskog corrections is discussed. Numerical values of the off-shell contribution to the Wigner distribution, of the collision duration and of the collision nonlocality are presented for different realistic potentials. On preliminary results we show that simulations of quantum molecular dynamics extended by the nonlocal treatment of collisions leads to a broader proton distribution bringing the theoretical spectra closer towards the experimental values than the local approach.Comment: Proceedings of the Erice School, published as Vol. 42 of "Progress in Particle and Nuclear Physics" by ELSEVIE

The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM

The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based multi-band astronomical Variable Objects Monitor), a French-Chinese mission with Italian contribution. Observations are expected to start in 2013. It has been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent sources of the sky, thanks to its wide field of view (about 2 sr) and its remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging sensitivity in the 4-70 keV energy band. These characteristics are well suited to detect highly redshifted GRBs, and consequently to provide fast and accurate triggers to other onboard or ground-based instruments able to follow-up the detected events in a very short time from the optical wavelength bands up to the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008, Nanjing, Chin