30 research outputs found
Renormalons as Dilation Modes in the Functional Space
There are two possible sources of the factorial large-order behavior of a typical perturbative series. First, the number of different Feynman diagrams may be large; second, there may be abnormally large diagrams known as renormalons. It is well known that the large combinatorial number of diagrams is described by instanton-type solutions of the classical equations. We demonstrate that, from the functional-integral viewpoint, the renormalons do not correspond to a particular configuration but manifest themselves as dilatation modes in the functional space
Renormalons as dilatation modes in the functional space
There are two sources of the factorial large-order behavior of a typical
perturbative series. First, the number of the different Feynman diagrams may be
large; second, there are abnormally large diagrams known as renormalons. It is
well known that the large combinatorial number of diagrams is described by
instanton-type solutions of the classical equations. We demonstrate that from
the functional-integral viewpoint the renormalons do not correspond to a
particular configuration but manifest themselves as dilatation modes in the
functional space.Comment: 19 pages, latex, 5 eps figure
Induced vacuum energy-momentum tensor in the background of a d-2 - brane in d+1 - dimensional space-time
Charged scalar field is quantized in the background of a static d-2 - brane
which is a core of the magnetic flux lines in flat d+1 - dimensional
space-time. We find that vector potential of the magnetic core induces the
energy-momentum tensor in the vacuum. The tensor components are periodic
functions of the brane flux and holomorphic functions of space dimension. The
dependence on the distance from the brane and on the coupling to the space-time
curvature scalar is comprehensively analysed.Comment: 32 pages, 3 figures, journal version, some references adde
Asymptotic Energy Dependence of Hadronic Total Cross Sections from Lattice QCD
The nonperturbative approach to soft high-energy hadron-hadron scattering,
based on the analytic continuation of Wilson-loop correlation functions from
Euclidean to Minkowskian theory, allows to investigate the asymptotic energy
dependence of hadron-hadron total cross sections in lattice QCD. In this paper
we will show, using best fits of the lattice data with proper functional forms
satisfying unitarity and other physical constraints, how indications emerge in
favor of a universal asymptotic high-energy behavior of the kind B log^2 s for
hadronic total cross sections.Comment: Revised and extended version; 29 pages, 4 figure
Universality and the magnetic catalysis of chiral symmetry breaking
The hypothesis that the magnetic catalysis of chiral symmetry breaking is due
to interactions of massless fermions in their lowest Landau level is examined
in the context of chirally symmetric models with short ranged interactions. It
is argued that, when the magnetic field is sufficiently large, even an
infinitesimal attractive interaction in the appropriate channel will break
chiral symmetry.Comment: 24 pages, 6 figures, REVTeX. The final version with minor
corrections. To appear in Phys Rev D60 (1999
Chiral perturbation theory in a magnetic background - finite-temperature effects
We consider chiral perturbation theory for SU(2) at finite temperature in
a constant magnetic background . We compute the thermal mass of the pions
and the pion decay constant to leading order in chiral perturbation theory in
the presence of the magnetic field. The magnetic field gives rise to a
splitting between and as well as between
and . We also calculate the free energy and the
quark condensate to next-to-leading order in chiral perturbation theory. Both
the pion decay constants and the quark condensate are decreasing slower as a
function of temperature as compared to the case with vanishing magnetic field.
The latter result suggests that the critical temperature for the chiral
transition is larger in the presence of a constant magnetic field. The increase
of as a function of is in agreement with most model calculations but
in disagreement with recent lattice calculations.Comment: 24 pages and 9 fig
Lattice QCD Simulations in External Background Fields
We discuss recent results and future prospects regarding the investigation,
by lattice simulations, of the non-perturbative properties of QCD and of its
phase diagram in presence of magnetic or chromomagnetic background fields.
After a brief introduction to the formulation of lattice QCD in presence of
external fields, we focus on studies regarding the effects of external fields
on chiral symmetry breaking, on its restoration at finite temperature and on
deconfinement. We conclude with a few comments regarding the effects of
electromagnetic background fields on gluodynamics.Comment: 31 pages, 10 figures, minor changes and references added. To appear
in Lect. Notes Phys. "Strongly interacting matter in magnetic fields"
(Springer), edited by D. Kharzeev, K. Landsteiner, A. Schmitt, H.-U. Ye
Magnetic Oscillations in Dense Cold Quark Matter with Four-Fermion Interactions
The phase structures of Nambu-Jona-Lasinio models with one or two flavours
have been investigated at non-zero values of and , where is an
external magnetic field and is the chemical potential. In the phase
portraits of both models there arise infinitely many massless chirally
symmetric phases, as well as massive ones with spontaneously broken chiral
invariance, reflecting the existence of infinitely many Landau levels. Phase
transitions of first and second orders and a lot of tricritical points have
been shown to exist in phase diagrams. In the massless case, such a phase
structure leads unavoidably to the standard van Alphen-de Haas magnetic
oscillations of some thermodynamical quantities, including magnetization,
pressure and particle density. In the massive case we have found an oscillating
behaviour not only for thermodynamical quantities, but also for a dynamical
quantity as the quark mass. Besides, in this case we have non-standard, i.e.
non-periodic, magnetic oscillations, since the frequency of oscillations is an
-dependent quantity.Comment: latex, 29 pages, 8 figure