328 research outputs found
Exact response of the non-relativistic harmonic oscillator
Using Greens function and operator techniques we give a closed expression
for the response of a non-relativistic system interacting through confining,
harmonic forces. The expression for the incoherent part permits rapid
evaluation of coefficients in a 1/q expansion. A comparison is made with
standard approximation methods.Comment: 9p.; INFN-ISS 93/2; WIS-93/50/Jun-P
Fermionic functional renormalization group for first-order phase transitions: a mean-field model
First-order phase transitions in many-fermion systems are not detected in the
susceptibility analysis of common renormalization-group (RG) approaches. Here
we introduce a counterterm technique within the functional
renormalization-group (fRG) formalism which allows access to all stable and
metastable configurations. It becomes possible to study symmetry-broken states
which occur through first-order transitions as well as hysteresis phenomena.
For continuous transitions, the standard results are reproduced. As an example,
we study discrete-symmetry breaking in a mean-field model for a commensurate
charge-density wave. An additional benefit of the approach is that away from
the critical temperature for the breaking of discrete symmetries large
interactions can be avoided at all RG scales.Comment: 17 pages, 8 figures. v2 corrects typos, adds references and a
discussion of the literatur
Improved Coulomb Correction Formulae for Bose-Einstein Correlations
We present improved Coulomb correction formulae for Bose-Einstein
correlations including also exchange term and use them to calculate appropriate
correction factors for several source functions. It is found that Coulomb
correction to the exchange function in the Bose-Einstein correlations cannot be
neglected.Comment: LaTex file, 8 pages, hard copies of 6 (multiple) figures available on
request to [email protected] or [email protected]
Beyond the binary collision approximation for the large- response of liquid He
We discuss corrections to the linear response of a many-body system beyond
the binary collision approximation. We first derive for smooth pair
interactions an exact expression of the response , considerably
simplifying existing forms and present also the generalization for interactions
with a strong, short-range repulsion. We then apply the latter to the case of
liquid He. We display the numerical influence of the correction
around the quasi-elastic peak and in the low-intensity wings of the response,
far from that peak. Finally we resolve an apparent contradiction in previous
discussions around the fourth order cumulant expansion coefficient. Our results
prove that the large- response of liquid He can be accurately understood
on the basis of a dynamical theory.Comment: 19 p. Figs. available on reques
Bose-Einstein condensation in the presence of a uniform field and a point-like impurity
The behavior of an ideal -dimensional boson gas in the presence of a
uniform gravitational field is analyzed. It is explicitly shown that,
contrarily to an old standing folklore, the three-dimensional gas does not
undergo Bose-Einstein condensation at finite temperature. On the other hand,
Bose-Einstein condensation occurs at for if there is a
point-like impurity at the bottom of the vessel containing the gas.Comment: 14 pages, REVTEX. Revised version, accepted for publication in Phys.
Rev.
Confinement and scaling in deep inelastic scattering
We show that parton confinement in the final state generates large
corrections to Bjorken scaling, thus leaving less room for the logarithmic
corrections. In particular, the -scaling violations at large are
entirely described in terms of power corrections. For treatment of these
non-perturbative effects, we derive a new expansion in powers of for
the structure function that is free of infra-red singularities and which
reduces corrections to the leading term. The leading term represents scattering
from an off-mass-shell parton, which keeps the same virtual mass in the final
state. It is found that this quasi-free term is a function of a new variable
, which coincides with the Bjorken variable for . The
two variables are very different, however, at finite . In particular, the
variable depends on the invariant mass of the spectator particles.
Analysis of the data at large shows excellent scaling in the variable , and determines the value of the diquark mass to be close to zero. -scaling allows us to extract the structure function near the elastic
threshold. It is found to behave as . Predictions for the
structure functions based on -scaling are made.Comment: Discussion of target mass corrections is added. Accepted for
publication in Phys. Rev.
Uncorrelated Volatile Behavior during the 2011 Apparition of Comet C/2009 P1 Garradd
The High Resolution Instrument Infrared Spectrometer (HRI-IR) on board the Deep Impact Flyby spacecraft detected H2O, CO2, and CO in the coma of the dynamically young Oort Cloud comet C/2009 P1 (Garradd) post-perihelion at a heliocentric distance of 2 AU. Production rates were derived for the parent volatiles, Q_(H2O) = 4.6 ± 0.8 × 10^(28), Q_(CO2) = 3.9 ± 0.7 × 10^(27), and Q_(CO) = 2.9 ± 0.8 × 10^(28) molecules s^(–1), and are consistent with the trends seen by other observers and within the error bars of measurements acquired during a similar time period. When compiled with other observations of Garradd's dominant volatiles, unexpected behavior was seen in the release of CO. Garradd's H_2O outgassing, increasing and peaking pre-perihelion and then steadily decreasing, is more typical than that of CO, which monotonically increased throughout the entire apparition. Due to the temporal asymmetry in volatile release, Garradd exhibited the highest CO to H_2O abundance ratio ever observed for any comet inside the water snow line at ~60% during the HRI-IR observations. Also, the HRI-IR made the only direct measurement of CO_2, giving a typical cometary abundance ratio of CO_2 to H_2O of 8% but, with only one measurement, no sense of how it varied with orbital position
Level structure of 69Se
15 págs.; 9 figs.; 5 tabs. ; PACS number(s): 23.20.Lv, 21.10.Re, 27.50.1e, 21.60.2nExcited levels in 69Se have been studied using the 40Ca(32S,2pn)69Se reaction at 95- and 105-MeV beam energy, γ rays have been detected with the EUROBALL spectrometer operated in conjunction with the neutron wall and the charged-particle detector array EUCLIDES. New level sequences with positive and negative parities have been identified from n-γγ and n-γγγ coincidences. Spins have been assigned to many of the levels on the basis of angular distribution and directional correlation measurements. Excitation energies of the positive-parity yrast band and the branching ratios of its decay are compared with the predictions of the rigid triaxial rotor plus particle model. ©2004 The American Physical SocietyA. J. acknowledges financial support from the Deutsche Forschungsgemeinshaft (DPG)
within the Heisenberg program. This work was supported
by BMBF under Contract Nos. 06 OK 958 and 06 GÖ 951
and the EUROVIV Contract No. HPRI-CT-1999-000783.Peer Reviewe
Description of recent large- neutron inclusive scattering data from liquid He
We report dynamical calculations for large- structure functions of liquid
He at =1.6 and 2.3 K and compare those with recent MARI data. We extend
those calculations far beyond the experimental range q\le 29\Ain in order to
study the approach of the response to its asymptotic limit for a system with
interactions having a strong short-range repulsion. We find only small
deviations from theoretical behavior, valid for smooth . We repeat an
extraction by Glyde et al of cumulant coefficients from data. We argue that
fits determine the single atom momentum distribution, but express doubt as to
the extraction of meaningful Final State Interaction parameters.Comment: 37 pages, 13 postscript fig
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