208 research outputs found
Time dependent neutrino billiards
Quantum dynamica of a massless Dirac particle in time-dependent 1D box and
circular billiard with time-dependent radius is studied. An exact analytical
wave functions and eigenvalues are obtained for the case of linear
time-dependence of the boundary position
Creation of photons in an oscillating cavity with two moving mirrors
We study the creation of photons in a one dimensional oscillating cavity with
two perfectly conducting moving walls. By means of a conformal transformation
we derive a set of generalized Moore's equations whose solution contains the
whole information of the radiation field within the cavity. For the case of
resonant oscillations we solve these equations using a renormalization group
procedure that appropriately deals with the secular behaviour present in a
naive perturbative approach. We study the time evolution of the energy density
profile and of the number of created photons inside the cavity.Comment: LaTex file, 17 pages, 3 figures, uses epsf.st
The Biology Instrument for the Viking Mars Mission
Two Viking spacecraft have successfully soft landed on the surface of Mars. Each carries, along with other scientific instruments, one biology laboratory with three different experiments designed to search for evidence of living microorganisms in material sampled from the Martian surface. This 15.5-kg biology instrument which occupies a volume of almost 28.3 dm3 is the first to carry out an in situ search for extraterrestrial life on a planet. The three experiments are called the pyrolytic release, labeled release, and gas exchange. The pyrolytic release experiment has the capability to measure the fixation of carbon dioxide or carbon monoxide into organic matter. The labeled release experiment detects metabolic processes by monitoring the production of volatile carbon compounds from a radioactively labeled nutrient mixture. The gas exchange experiment monitors the gas changes in the head space above a soil sample which is either incubated in a humid environment or supplied with a rich organic nutrient solution. Each experiment can analyze a soil sample as it is received from the surface or, as a control, analyze a soil which has been heated to above 160C. Each instrument has the capability to receive four different soils dug from the Martian surface and perform a number of analysis cycles depending on the particular experiment. This paper describes in detail the design and operation of the three experiments and the supporting subsystems
Effects and Detectability of Quasi-Single Field Inflation in the Large-Scale Structure and Cosmic Microwave Background
Quasi-single field inflation predicts a peculiar momentum dependence in the
squeezed limit of the primordial bispectrum which smoothly interpolates between
the local and equilateral models. This dependence is directly related to the
mass of the isocurvatons in the theory which is determined by the
supersymmetry. Therefore, in the event of detection of a non-zero primordial
bispectrum, additional constraints on the parameter controlling the
momentum-dependence in the squeezed limit becomes an important question. We
explore the effects of these non-Gaussian initial conditions on large-scale
structure and the cosmic microwave background, with particular attention to the
galaxy power spectrum at large scales and scale-dependence corrections to
galaxy bias. We determine the simultaneous constraints on the two parameters
describing the QSF bispectrum that we can expect from upcoming large-scale
structure and cosmic microwave background observations. We find that for
relatively large values of the non-Gaussian amplitude parameters, but still
well within current uncertainties, galaxy power spectrum measurements will be
able to distinguish the QSF scenario from the predictions of the local model. A
CMB likelihood analysis, as well as Fisher matrix analysis, shows that there is
also a range of parameter values for which Planck data may be able distinguish
between QSF models and the related local and equilateral shapes. Given the
different observational weightings of the CMB and LSS results, degeneracies can
be significantly reduced in a joint analysis.Comment: 27 pages, 14 figure
Onset of Superfluidity in 4He Films Adsorbed on Disordered Substrates
We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor,
using high precision torsional oscillator and DC calorimetry techniques. Our
investigation focused on the onset of superfluidity at low temperatures as the
4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel
system were used to determine the superfluid density of films with transition
temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor
system probed the excitation spectrum of both non-superfluid and superfluid
films for temperatures down to 10 mK. Both sets of measurements suggest that
the critical coverage for the onset of superfluidity corresponds to a mobility
edge in the chemical potential, so that the onset transition is the bosonic
analog of a superconductor-insulator transition. The superfluid density
measurements, however, are not in agreement with the scaling theory of an onset
transition from a gapless, Bose glass phase to a superfluid. The heat capacity
measurements show that the non-superfluid phase is better characterized as an
insulator with a gap.Comment: 15 pages (RevTex), 21 figures (postscript
The performance of the jet trigger for the ATLAS detector during 2011 data taking
The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided protonâproton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleonânucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction
Measurement of the View the tt production cross-section using eÎŒ events with b-tagged jets in pp collisions at âs = 13 TeV with the ATLAS detector
This paper describes a measurement of the inclusive top quark pair production cross-section (ÏttÂŻ) with a data sample of 3.2 fbâ1 of protonâproton collisions at a centre-of-mass energy of âs = 13 TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electronâmuon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously ÏttÂŻ and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be:
ÏttÂŻ = 818 ± 8 (stat) ± 27 (syst) ± 19 (lumi) ± 12 (beam) pb,
where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented
- âŠ