387 research outputs found
Effective Field Theory Dimensional Regularization
A Lorentz-covariant regularization scheme for effective field theories with
an arbitrary number of propagating heavy and light particles is given. This
regularization scheme leaves the low-energy analytic structure of Greens
functions intact and preserves all the symmetries of the underlying Lagrangian.
The power divergences of regularized loop integrals are controlled by the
low-energy kinematic variables. Simple diagrammatic rules are derived for the
regularization of arbitrary one-loop graphs and the generalization to higher
loops is discussed.Comment: 22 pages, 11 figures and 1 tabl
Low-energy gluon contributions to the vacuum polarization of heavy quarks
We calculate a correction to the electromagnetic current induced by a heavy
quark loop. The contribution of this correction to the vacuum polarization
function appears at the O(alpha_s^3) order of perturbation theory and has a
qualitatively new feature -- its absorptive part starts at zero energy in
contrast to other contributions where the absorptive parts start at the
two-particle threshold. Our result imposes a constraint on the order n of the
moments used in the heavy-quark sum rules, n<4.Comment: 8 pages in LaTeX, 1 PostScript figure included in the tex
Exchange interaction effects in the thermodynamic properties of quantum dots
We study electron-electron interaction effects in the thermodynamic
properties of quantum-dot systems. We obtain the direct and exchange
contributions to the specific heat C_v in the self-consistent Hartree-Fock
approximation at finite temperatures. An exchange-induced phase transition is
observed and the transition temperature is shown to be inversely proportional
to the size of the system. The exchange contribution to C_v dominates over the
direct and kinetic contributions in the intermediate regime of interaction
strength (r_s ~ 1). Furthermore, the electron-electron interaction modifies
both the amplitude and the period of magnetic field induced oscillations in
C_v.Comment: 4 pages, 4 figures; To appear in Phys. Rev.
Finite calculation of divergent selfenergy diagrams
Using dispersive techniques, it is possible to avoid ultraviolet divergences
in the calculation of Feynman diagrams, making subsequent regularization of
divergent diagrams unnecessary. We give a simple introduction to the most
important features of such dispersive techniques in the framework of the
so-called finite causal perturbation theory. The method is also applied to the
'divergent' general massive two-loop sunrise selfenergy diagram, where it leads
directly to an analytic expression for the imaginary part of the diagram in
accordance with the literature, whereas the real part can be obtained by a
single integral dispersion relation. It is pointed out that dispersive methods
have been known for decades and have been applied to several nontrivial Feynman
diagram calculations.Comment: 15 pages, Latex, one figure, added reference
Mixed quark-nucleon phase in neutron stars and nuclear symmetry energy
The influence of the nuclear symmetry energy on the formation of a mixed
quark-nucleon phase in neutron star cores is studied. We use simple
parametrizations of the nuclear matter equation of state, and the bag model for
the quark phase. The behavior of nucleon matter isobars, which is responsible
for the existence of the mixed phase, is investigated. The role of the nuclear
symmetry energy changes with the value of the bag constant B. For lower values
of B the properties of the mixed phase do not depend strongly on the symmetry
energy. For larger B we find that a critical pressure for the first quark
droplets to form is strongly dependent on the nuclear symmetry energy, but the
pressure at which last nucleons disappear is independent of it.Comment: 12 pages, 16 figures, Phys. Rev. C in pres
corrections to the correlator of finite mass baryon currents
We present analytical next-to-leading order results for the correlator of
baryonic currents at the three loop level with one finite mass quark. We obtain
the massless and the HQET limit of the correlator from the general formula as
particular cases. We also give explicit expressions for the moments of the
spectral density.Comment: 12 pages, 2 Postscript figure
Decay-assisted collinear resonance ionization spectroscopy: Application to neutron-deficient francium
This paper reports on the hyperfine-structure and radioactive-decay studies
of the neutron-deficient francium isotopes Fr performed with the
Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE
facility, CERN. The high resolution innate to collinear laser spectroscopy is
combined with the high efficiency of ion detection to provide a
highly-sensitive technique to probe the hyperfine structure of exotic isotopes.
The technique of decay-assisted laser spectroscopy is presented, whereby the
isomeric ion beam is deflected to a decay spectroscopy station for alpha-decay
tagging of the hyperfine components. Here, we present the first
hyperfine-structure measurements of the neutron-deficient francium isotopes
Fr, in addition to the identification of the low-lying states of
Fr performed at the CRIS experiment.Comment: Accepted for publication with Physical Review
Laser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry
The magnetic dipole moments and changes in mean-square charge radii of the
neutron-rich isotopes were measured with the
newly-installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at
ISOLDE, CERN, probing the to atomic
transition. The values for
and follow the observed increasing
slope of the charge radii beyond . The charge radii odd-even
staggering in this neutron-rich region is discussed, showing that
has a weakly inverted odd-even staggering while
has normal staggering. This suggests that both isotopes
reside at the borders of a region of inverted staggering, which has been
associated with reflection-asymmetric shapes. The value supports a shell model configuration for the
ground state. The values support the tentative
spin, and point to a intruder ground state configuration.Comment: Accepted for publication with Physical Review
Top quark mass definition and top quark pair production near threshold at the NLC
We suggest an infrared-insensitive quark mass, defined by subtracting the
soft part of the quark self energy from the pole mass. We demonstrate the deep
relation of this definition with the static quark-antiquark potential. At
leading order in 1/m this mass coincides with the PS mass which is defined in a
completely different manner. Going beyond static limit, the small normalization
point introduces recoil corrections which are calculated here as well. Using
this mass concept and other concepts for the quark mass we calculate the cross
section of e+ e- -> t t-bar near threshold at NNLO accuracy adopting three
alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS
mass, and (3) fixing the new mass which we call the PS-bar mass. We demonstrate
that perturbative predictions for the cross section become much more stable if
we use the PS or the PS-bar mass for the calculations. A careful analysis
suggests that the top quark mass can be extracted from a threshold scan at NLC
with an accuracy of about 100-200 MeV.Comment: published version, 21 pages in LaTeX including 11 PostScript figure
Radiolysis of NaCl at high and low temperatures: development of size distribution of bubbles and colloids
New experimental results are presented on low temperature irradiation (18 °C) of rock-salt samples which had been exposed to initial doses up to 320 GRad at 100 °C. Differential scanning calorimetry (DSC) shows that the latent heat of melting (LHM) of sodium colloids decreases during subsequent low-temperature irradiation, whereas the stored energy (SE) increases slowly, indicating that the process of radiolysis continues. The decrease of the LHM is due to dissolution of large colloids, because the intensities of the melting peaks decrease during the second stage irradiation at low temperature. The model is formulated to describe the nucleation kinetics and the evolution of the size distribution of chlorine precipitates and sodium colloids in NaCl under high dose irradiation. It is shown that the mechanism of dissolution of large Na colloids during low temperature irradiation can be related to melting of sodium colloids.
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