Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Tuesday
however large and cannot be mimicked by taking only the slopes of the
polarisabilities at zero energy into account. An analysis using dynamical
polarisabilities from either Heavy Baryon Chiral Perturbation Theory
including the ∆(1232) as dynamical degree of freedom or using dispersion
theory predicts however values in agreement with experiment at all
energies. We comment on recent data from Lund at ω ≈ 50 MeV.
Supported in part by DFG under grant GR 1887/1-2 and by BMBF.
[1.] H.W. Grießhammer and T.R. Hemmert: nucl-th/0110006.
HK 9.2 Tue 10:30 Foyer Chemie
Debye Screening At Finite Temperature, Revisited — •Roland
A. Schneider — Physik-Department, Technische Universität München,
Garching, Germany
We present a new, alternative way to calculate the screening of the
static potential between two charges in (non)abelian gauge theories at
high temperatures by looking at the magnetic properties of the vacuum.
The Hard Thermal Loop (HTL) gluon and photon Debye masses are
recovered in a first, though incomplete approximation. In QED, the
complete calculation to order α exhibits an interesting cancellation of
terms, resulting in a logarithmic running α(T ). Debye screening is then
caused by the modified index of refraction of the vacuum. In QCD, an
unphysical Landau pole occurs that arises, as in more sophisticated thermal
renormalization group calculations, from the wrong sign of the gluon
contribution.
Supported in part by BMBF and GSI.
HK 9.3 Tue 10:30 Foyer Chemie
Thermodynamics of fireball expansion — •Thorsten Renk 1 ,
Roland A. Schneider 1 ,andWolfram Weise 1,2 — 1 Technische Universität
München — 2 ECT ∗ ,Trento
The fireball created in an ultrarelativistic heavy ion collision is the
environment in which all processes providing clues about the possible
formation of the quark-gluon plasma (QGP) happen. It is therefore crucial
to understand the dynamics of this hot and dense system. We set
up a model in which the fireball evolution is reconstructed between two
stages, the freeze-out, which is accessible by hadronic observables, and
the initial conditions for which the overlap geometry can be calculated.
Using the equation of state (EoS) provided by a quasiparticle model of
the QGP, we are able to calculate thermodynamical properties in volume
slices of constant proper time and determine the volume expansion selfconsistently.
The resulting evolution model can then be tested against
other observables.
Work supportet in part by BMBF and GSI.
HK 9.4 Tue 10:30 Foyer Chemie
Simple High Accuracy Calculations of the Three Nucleon System
at Very Low Energies — •Harald W. Grießhammer —
Institut für Theoretische Physik (T39), TU München, D-85747 Garching
At very low energies, pions do not have to be treated as explicit degrees
of freedom in an Effective Field Theory of few nucleon systems. The resulting
power counting allows for simple, model independent, systematic
and rigorous computations of the properties of nuclear systems with an
error estimate. Usually, high precision calculations are performed with
relative ease. In the triton channel of the three nucleon system, it has
however been demonstrated [1] that an unusual, non-perturbative renormalisation
phenomenon leads to a three body force which is needed even
at leading order in order to absorb cut-off dependence. This yields a
limit cycle for the three body force, and explanations of the Efimov and
Thomas effects as well as of the Phillips line of nuclear physics. Here,
it is shown that this phenomenon is limited to the doublet Swave only,
so that computations in the other channels can be performed with ease
to high accuracy. Demonstrating a new technique to obtain results of
increasing accuracy in the Effective Field Theory approach, corrections
to the Phillips line obtained at LO as well as phase shifts in the triton
channel of nd scattering are discussed both above and below the deuteron
breakup point. The calculations converge rapidly.
Supported in part by DFG under grant GR 1887/1-2 and by BMBF.
[1.] P. Bedaque, H.-W. Hammer and U. van Kolck: Nucl. Phys. A676,
357 (2000).
HK 9.5 Tue 10:30 Foyer Chemie
Note on finite temperature sum rules for vector and axialvector
spectral functions — •Eugenio Marco 1 , Ralf Hofmann 2 ,
and Wolfram Weise 1,3 — 1 Physik-Department, Technische Universität
München — 2 Max-Planck-Institut für Physik (Werner-Heisenberg-
Institut), — 3 ECT ∗ , Villazzano (Trento), Italy
An updated analysis of vector and axial-vector spectral functions is
presented. The resonant contributions to the spectral integrals are shown
to be expressible as multiples of 4π2f 2 π , encoding the scale of spontaneous
chiral symmetry breaking in QCD. Up to order T 2 this behavior carries
over to the case of finite temperature.
Work supported in part by BMBF, GSI and the Alexander von Humboldt
Foundation.
HK 9.6 Tue 10:30 Foyer Chemie
Chiral Magnetism of the Nucleon — •Thomas R. Hemmert 1
and Wolfram Weise 1,2 — 1 Physik Department T39, TU München
— 2 ECT*, Trento, Italy
We are analysing the quark-mass dependence of the isovector anomalous
magnetic moment of the nucleon [1]. Quenched Lattice data for this
quantity from the Adelaide group [2] are only available for quark-masses
heavier than 20 times the physical light quark masses, making extrapolation
schemes necessary to bridge the gap between lattice data and the
physical magnetic moments of the nucleon. We report on recent work
of such an extrapolation performed with the help of chiral effective field
theories, resulting in a simple extrapolation formula for the case of the
magnetic moments. We also compare our extrapolation formula with the
Pade-formula recently suggested by the Adelaide group [2].
[1] T.R. Hemmert and W. Weise, “Chiral Magnetism of the Nucleon”,
forthcoming. Preliminary results are reported in nucl-th/0105051.
[2] D.B. Leinweber, D.H. Lu and A.W. Thomas, Phys.Rev.D60:034014
(1999).
WorksupportedinpartbyDFGandBMBF
HK 9.7 Tue 10:30 Foyer Chemie
Baryon chiral perturbation theory with a cutoff regularization:
Inclusion of decuplet states — •Bu¯gra Borasoy 1 , Barry Holstein
2 , Randy Lewis 3 , and Pierre Ouimet 3 — 1 Physik Department,
Technische Universität München — 2 University Of Massachusetts,
Amherst, USA — 3 University of Regina, Regina, Canada
In SU(3) chiral perturbation theory short distance effects, arising from
the propagation of Goldstone bosons over distances smaller than a typical
hadronic size, are model-dependent and can lead to a lack of convergence
in the SU(3) chiral expansion if they are included in loop diagrams. Such
effects can be removed in a chirally consistent fashion by use of a cutoff
ameliorating problems which have arisen in previous calculations due to
large loop effects. In this investigation, we employ cutoff regularization
and focus on the inclusion of decuplet states which may yield significant
contributions since the mass difference between the nucleon and decuplet
is less than twice the pion mass and octet and decuplet states become
even degenerate in the large Nc limit. We discuss the octet baryon
masses, axial couplings, s-wave hyperon decay, and magnetic moments
taking contributions from internal decuplet states into account. The realistic
treatment of chiral baryon corrections is just what is needed in
order to extrapolate state of the art lattice calculations, which are done
for quark masses (and therefore pion masses) considerably heavier than
the values given experimentally, down to realistic values.
Work supported in part by the DFG.
HK 9.8 Tue 10:30 Foyer Chemie
Study of relativistic bound states in a scalar model using diagonalization/Monte
Carlo methods — •Bu¯gra Borasoy 1 and
Dean Lee 2 — 1 Physik Department, Technische Universität München
— 2 North Carolina State University, Raleigh, USA
A recently proposed diagonalization/Monte Carlo computational
scheme is used to study relativistic two-body and three-body bound
states in (φ 6 − φ 4 )1+1 theory. Diagonalization makes it possible to
extract detailed information about wavefunctions and excited states,
while Monte Carlo allows one to handle the exponential increase in the
number of basis states for large volume systems. The first half of the
method involves finding and diagonalizing the Hamiltonian restricted to
an optimal subspace which includes the most important basis vectors
of the lowest energy eigenstates. Once the most important basis
vectors are found and their interactions treated exactly, Monte Carlo
is used to sample the contribution of the remaining basis vectors. In