430 research outputs found
Spin-Boson Hamiltonian and Optical Absorption of Molecular Dimers
An analysis of the eigenstates of a symmetry-broken spin-boson Hamiltonian is
performed by computing Bloch and Husimi projections. The eigenstate analysis is
combined with the calculation of absorption bands of asymmetric dimer
configurations constituted by monomers with nonidentical excitation energies
and optical transition matrix elements. Absorption bands with regular and
irregular fine structures are obtained and related to the transition from the
coexistence to a mixing of adiabatic branches in the spectrum. It is shown that
correlations between spin states allow for an interpolation between absorption
bands for different optical asymmetries.Comment: 15 pages, revTeX, 8 figures, accepted for publication in Phys. Rev.
Quantum Monte Carlo study of the one-dimensional Holstein model of spinless fermions
The Holstein model of spinless fermions interacting with dispersionless
phonons in one dimension is studied by a Green's function Monte Carlo
technique. The ground state energy, first fermionic excited state, density wave
correlations, and mean lattice displacement are calculated for lattices of up
to 16 sites, for one fermion per two sites, i.e., a half-filled band. Results
are obtained for values of the fermion hopping parameter of ,
, and where is the phonon frequency. At a finite
fermion-phonon coupling there is a transition from a metallic phase to an
insulating phase in which there is charge-density-wave order. Finite size
scaling is found to hold in the metallic phase and is used to extract the
coupling dependence of the Luttinger liquid parameters, and ,
the velocity of charge excitations and the correlation exponent, respectively.
For free fermions () and for strong coupling () our
results agree well with known analytic results. For and
our results are inconsistent with the metal-insulator transition being a
Kosterlitz-Thouless transition.\\Comment: 16 pages of ReVTeX, 11 figures in uuencoded compressed tar file.
Minor changes to text. Our results are inconsistent with the metal-insulator
transition studied being a Kosterlitz-Thouless transition. The figures are
now in the correct order. To appear in Physical Review B, April 15, 199
The impact of supportive nursing care on the needs of men with prostate cancer: a study across seven European countries
Background: prostate cancer is for many men a chronic disease with a long life expectancy after treatment. The impact of prostate cancer therapy on men has been well defined, however, explanation of the consequences of cancer treatment has not been modelled against the wider variables of long-term health-care provision. The aim of this study was to explore the parameters of unmet supportive care needs in men with prostate cancer in relation to the experience of nursing care. Methods: a survey was conducted among a volunteer sample of 1001 men with prostate cancer living in seven European countries. Results: at the time of the survey, 81% of the men had some unmet supportive care needs including psychological, sexual and health system and information needs. Logistic regression indicated that lack of post-treatment nursing care significantly predicted unmet need. Critically, men's contact with nurses and/or receipt of advice and support from nurses, for several different aspects of nursing care significantly had an impact on men's outcomes. Conclusion: Unmet need is related not only to disease and treatment factors but is also associated with the supportive care men received. Imperative to improving men's treatment outcomes is to also consider the access to nursing and the components of supportive care provided, especially after therapy
Nonadiabatic effects in a generalized Jahn-Teller lattice model: heavy and light polarons, pairing and metal-insulator transition
The ground state polaron potential of 1D lattice of two-level molecules with
spinless electrons and two Einstein phonon modes with quantum phonon-assisted
transitions between the levels is found anharmonic in phonon displacements. The
potential shows a crossover from two nonequivalent broad minima to a single
narrow minimum corresponding to the level positions in the ground state.
Generalized variational approach implies prominent nonadiabatic effects:(i) In
the limit of the symmetric E-e Jahn- Teller situation they cause transition
between the regime of the predominantly one-level "heavy" polaron and a "light"
polaron oscillating between the levels due to phonon assistance with almost
vanishing polaron displacement. It implies enhancement of the electron transfer
due to decrease of the "heavy" polaron mass (undressing) at the point of the
transition. Pairing of "light" polarons due to exchange of virtual phonons
occurs. Continuous transition to new energy ground state close to the
transition from "heavy" polaron phase to "light" (bi)polaron phase occurs. In
the "heavy" phase, there occurs anomalous (anharmonic) enhancements of quantum
fluctuations of the phonon coordinate, momentum and their product as functions
of the effective coupling. (ii) Dependence of the polaron mass on the optical
phonon frequency appears.(iii) Rabi oscillations significantly enhance quantum
shift of the insulator-metal transition line to higher values of the critical
effective e-ph coupling supporting so the metallic phase. In the E-e JT case,
insulator-metal transition coincide with the transition between the "heavy" and
the "light" (bi)polaron phase at certain (strong) effective e-ph interaction.Comment: Paper in LaTex format (file jtseptx.tex) and 9 GIF-figures
(ppic_1.gif,...ppic_9.gif
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Precise Measurement of the e+ e- --> pi+ pi- (gamma) Cross Section with the Initial-State Radiation Method at BABAR
A precise measurement of the cross section of the process
from threshold to an energy of 3GeV is obtained
with the initial-state radiation (ISR) method using 232fb of data
collected with the BaBar detector at center-of-mass energies near
10.6GeV. The ISR luminosity is determined from a study of the leptonic process
, which is found to agree with the
next-to-leading-order QED prediction to within 1.1%. The cross section for the
process is obtained with a systematic uncertainty
of 0.5% in the dominant resonance region. The leading-order hadronic
contribution to the muon magnetic anomaly calculated using the measured
cross section from threshold to 1.8GeV is .Comment: 58 pages, 56 figures, to be submitted to Phys. Rev.
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Measurement of B(B-->X_s {\gamma}), the B-->X_s {\gamma} photon energy spectrum, and the direct CP asymmetry in B-->X_{s+d} {\gamma} decays
The photon spectrum in B --> X_s {\gamma} decay, where X_s is any strange
hadronic state, is studied using a data sample of (382.8\pm 4.2) \times 10^6
e^+ e^- --> \Upsilon(4S) --> BBbar events collected by the BABAR experiment at
the PEP-II collider. The spectrum is used to measure the branching fraction B(B
--> X_s \gamma) = (3.21 \pm 0.15 \pm 0.29 \pm 0.08)\times 10^{-4} and the
first, second, and third moments = 2.267 \pm 0.019 \pm 0.032 \pm
0.003 GeV,, )^2> = 0.0484 \pm 0.0053 \pm 0.0077 \pm
0.0005 GeV^2, and )^3> = -0.0048 \pm 0.0011 \pm 0.0011
\pm 0.0004 GeV^3, for the range E_\gamma > 1.8 GeV, where E_{\gamma} is the
photon energy in the B-meson rest frame. Results are also presented for
narrower E_{\gamma} ranges. In addition, the direct CP asymmetry A_{CP}(B -->
X_{s+d} \gamma) is measured to be 0.057 \pm 0.063. The spectrum itself is also
unfolded to the B-meson rest frame; that is the frame in which theoretical
predictions for its shape are made.Comment: 37 pages, 19 postscript figures, submitted to Phys. Rev. D. No
analysis or results have changed from previous version. Some changes to
improve clarity based on interactions with Phys. Rev. D referees, including
one new Figure (Fig. 13), and some minor wording/punctuation/spelling
mistakes fixe
Measurement of ISR-FSR interference in the processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi- gamma
Charge asymmetry in processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi-
gamma is measured using 232 fb-1 of data collected with the BABAR detector at
center-of-mass energies near 10.58 GeV. An observable is introduced and shown
to be very robust against detector asymmetries while keeping a large
sensitivity to the physical charge asymmetry that results from the interference
between initial and final state radiation. The asymmetry is determined as
afunction of the invariant mass of the final-state tracks from production
threshold to a few GeV/c2. It is compared to the expectation from QED for e+ e-
--> mu+ mu- gamma and from theoretical models for e+ e- --> pi+ pi- gamma. A
clear interference pattern is observed in e+ e- --> pi+ pi- gamma, particularly
in the vicinity of the f_2(1270) resonance. The inferred rate of lowest order
FSR production is consistent with the QED expectation for e+ e- --> mu+ mu-
gamma, and is negligibly small for e+ e- --> pi+ pi- gamma.Comment: 32 pages,29 figures, to be submitted to Phys. Rev.
Observation of time-reversal violation in the B0 meson system
The individually named authors work collectively as The BABAR Collaboration. Copyright @ 2012 American Physical Society.Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time-reversal violation. The decays of entangled neutral B mesons into definite flavor states (B0 or BÂŻÂŻÂŻ0), and J/ÏK0L or ccÂŻK0S final states (referred to as B+ or Bâ), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, BÂŻÂŻÂŻ0âBâ and BââBÂŻÂŻÂŻ0, as a function of the time difference between the two B decays. Using 468Ă106 BBÂŻÂŻÂŻ pairs produced in ΄(4S) decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding ÎS+T=â1.37±0.14(stat)±0.06(syst) and ÎSâT=1.17±0.18(stat)±0.11(syst). These nonzero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.DOE and NSF (USA), NSERC (Canada), CEA and CNRS-IN2P3 (France), BMBF and
DFG(Germany), INFN (Italy), FOM (The Netherlands),
NFR (Norway), MES (Russia), MINECO (Spain), STFC
(United Kingdom). Individuals have received support from
the Marie Curie EIF (European Union), the A. P. Sloan
Foundation (USA) and the Binational Science Foundation
(USA-Israel)
Measurement of Branching Fractions and Rate Asymmetries in the Rare Decays B -> K(*) l+ l-
In a sample of 471 million BB events collected with the BABAR detector at the
PEP-II e+e- collider we study the rare decays B -> K(*) l+ l-, where l+ l- is
either e+e- or mu+mu-. We report results on partial branching fractions and
isospin asymmetries in seven bins of di-lepton mass-squared. We further present
CP and lepton-flavor asymmetries for di-lepton masses below and above the J/psi
resonance. We find no evidence for CP or lepton-flavor violation. The partial
branching fractions and isospin asymmetries are consistent with the Standard
Model predictions and with results from other experiments.Comment: 16 pages, 14 figures, accepted by Phys. Rev.
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