485 research outputs found
Propagator for spinless and spin-1/2 Aharonov-Bohm-Coulomb systems
The propagator of the spinless Aharonov-Bohm-Coulomb system is derived by
following the Duru-Kleinert method. We use this propagator to explore the
spin-1/2 Aharonov-Bohm-Coulomb system which contains a point interaction as a
Zeeman term. Incorporation of the self-adjoint extension method into the
Green's function formalism properly allows us to derive the finite propagator
of the spin-1/2 Aharonov-Bohm-Coulomb system. As a by-product, the relation
between the self-adjoint extension parameter and the bare coupling constant is
obtained. Bound-state energy spectra of both spinless and spin-1/2
Aharonov-Bohm-Coulomb systems are examined.Comment: Slightly changed, to appear in Annals of Physics. 18 pages, Late
Non-Gaussianity in Cosmic Microwave Background Temperature Fluctuations from Cosmic (Super-)Strings
We compute analytically the small-scale temperature fluctuations of the
cosmic microwave background from cosmic (super-)strings and study the
dependence on the string intercommuting probability . We develop an
analytical model which describes the evolution of a string network and
calculate the numbers of string segments and kinks in a horizon volume. Then we
derive the probability distribution function (pdf) which takes account of
finite angular resolution of observation. The resultant pdf consists of a
Gaussian part due to frequent scatterings by long string segments and a
non-Gaussian tail due to close encounters with kinks. The dispersion of the
Gaussian part is reasonably consistent with that obtained by numerical
simulations by Fraisse et al.. On the other hand, the non-Gaussian tail
contains two phenomenological parameters which are determined by comparison
with the numerical results for P=1. Extrapolating the pdf to the cases with
, we predict that the non-Gaussian feature is suppressed for small .Comment: 6 pages, 2 figure, version accepted by JCA
Critical value of symmetry breaking parameter in the phase transition of decay rate
Phase transition of decay rate from quantum tunneling to thermal activity
regimes is investigated in (3+1)-dimensional field theories with symmetry
breaking term . By applying the two independent criteria for the sharp
first-order transition to the same model, the upper and lower bounds of
critical value of the symmetry breaking parameter are obtained. Unlike two
dimensional case continuum states of the fluctuation operator near sphaleron
solution play an important role to determine the type of transition.Comment: Several mistakes including figures are corrected. Accepted version in
Phys. Lett.
Single Spin Measurement using Single Electron Transistors to Probe Two Electron Systems
We present a method for measuring single spins embedded in a solid by probing
two electron systems with a single electron transistor (SET). Restrictions
imposed by the Pauli Principle on allowed two electron states mean that the
spin state of such systems has a profound impact on the orbital states
(positions) of the electrons, a parameter which SET's are extremely well suited
to measure. We focus on a particular system capable of being fabricated with
current technology: a Te double donor in Si adjacent to a Si/SiO2 interface and
lying directly beneath the SET island electrode, and we outline a measurement
strategy capable of resolving single electron and nuclear spins in this system.
We discuss the limitations of the measurement imposed by spin scattering
arising from fluctuations emanating from the SET and from lattice phonons. We
conclude that measurement of single spins, a necessary requirement for several
proposed quantum computer architectures, is feasible in Si using this strategy.Comment: 22 Pages, 8 Figures; revised version contains updated references and
small textual changes. Submitted to Phys. Rev.
Electronic localization at mesoscopic length scales: different definitions of localization and contact effects in a heuristic DNA model
In this work we investigate the electronic transport along model DNA
molecules using an effective tight-binding approach that includes the backbone
on site energies. The localization length and participation number are examined
as a function of system size, energy dependence, and the contact coupling
between the leads and the DNA molecule. On one hand, the transition from an
diffusive regime to a localized regime for short systems is identified,
suggesting the necessity of a further length scale revealing the system borders
sensibility. On the other hand, we show that the lenght localization and
participation number, do not depended of system size and contact coupling in
the thermodynamic limit. Finally we discuss possible length dependent origins
for the large discrepancies among experimental results for the electronic
transport in DNA sample
Novel and recurrent TRPV4 mutations and their association with distinct phenotypes within the TRPV4 dysplasia family
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
Search for single top quarks in the tau+jets channel using 4.8 fb of collision data
We present the first direct search for single top quark production using tau
leptons. The search is based on 4.8 fb of integrated luminosity
collected in collisions at =1.96 TeV with the D0 detector
at the Fermilab Tevatron Collider. We select events with a final state
including an isolated tau lepton, missing transverse energy, two or three jets,
one or two of them tagged. We use a multivariate technique to discriminate
signal from background. The number of events observed in data in this final
state is consistent with the signal plus background expectation. We set in the
tau+jets channel an upper limit on the single top quark cross section of
\TauLimObs pb at the 95% C.L. This measurement allows a gain of 4% in expected
sensitivity for the observation of single top production when combining it with
electron+jets and muon+jets channels already published by the D0 collaboration
with 2.3 fb of data. We measure a combined cross section of
\SuperCombineXSall pb, which is the most precise measurement to date.Comment: 12 pages, 5 figure
b-Jet Identification in the D0 Experiment
Algorithms distinguishing jets originating from b quarks from other jet
flavors are important tools in the physics program of the D0 experiment at the
Fermilab Tevatron p-pbar collider. This article describes the methods that have
been used to identify b-quark jets, exploiting in particular the long lifetimes
of b-flavored hadrons, and the calibration of the performance of these
algorithms based on collider data.Comment: submitted to Nuclear Instruments and Methods in Physics Research
Search for pair production of the scalar top quark in the electron-muon final state
We report the result of a search for the pair production of the lightest
supersymmetric partner of the top quark () in
collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron
collider corresponding to an integrated luminosity of 5.4 fb. The scalar
top quarks are assumed to decay into a quark, a charged lepton, and a
scalar neutrino (), and the search is performed in the electron
plus muon final state. No significant excess of events above the standard model
prediction is detected, and improved exclusion limits at the 95% C.L. are set
in the the (,) mass plane
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