623 research outputs found
Quartic Mass Corrections to
The influence of nonvanishing quark masses on the total cross section in
electron positron collisions and on the decay rate is calculated. The
corrections are expanded in and \as. Methods similar to those applied
for the quadratic mass terms allow to derive the corrections of order \as
m^4/s^2 and \as^2m^4/s^2. Coefficients which depend logarithmically on
and which cannot be absorbed in a running quark mass arise in order
\as^2. The implications of these results on electron positron annihilation
cross sections at LEP and at lower energies in particular between the charm and
the bottom threshold and for energies several GeV above the threshold
are discussed.Comment: 17 pages, LaTex (uses epsf.sty, figures appended as uuencoded ps- and
eps-files). A complete postscript file, including figures, is available via
anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as
/pub/ttp94-08/ttp94-08.ps, Local preprint# TTP94-0
Quark and pion condensation in a chromomagnetic background field
The general features of quark and pion condensation in dense quark matter
with flavor asymmetry have been considered at finite temperature in the
presence of a chromomagnetic background field modelling the gluon condensate.
In particular, pion condensation in the case of a constant abelian
chromomagnetic field and zero temperature has been studied both analytically
and numerically. Under the influence of the chromomagnetic background field the
effective potential of the system is found to have a global minimum for a
finite pion condensate even for small values of the effective quark coupling
constant. In the strong field limit, an effective dimensional reduction has
been found to take place.Comment: 17 pages, 6 figure
The Influence of an External Chromomagnetic Field on Color Superconductivity
We study the competition of quark-antiquark and diquark condensates under the
influence of an external chromomagnetic field modelling the gluon condensate
and in dependence on the chemical potential and temperature. As our results
indicate, an external chromomagnetic field might produce remarkable qualitative
changes in the picture of the color superconducting (CSC) phase formation. This
concerns, in particular, the possibility of a transition to the CSC phase and
diquark condensation at finite temperature.Comment: 27 pages, RevTex, 8 figures; the version accepted for the publication
in PRD (few references added; new numerical results added; main conclusions
are not changed
Higgs Decay into Gluons up to O(\alpha_s^3 G_F m_t^2)
The decay of the Standard Model Higgs boson in the intermediate-mass range
into gluons is considered where special emphasis is put on the influence of the
leading electroweak corrections proportional to G_F m_t^2. An effective
Lagrangian approach is used where the top quark is integrated out. The
evaluation of the coefficient function is performed using two different
methods. The first one is concerned with the direct evaluation of the vertex
diagrams and the second method is based on a low-energy theorem. In a first
step the tools needed for the computation are provided namely the
renormalization constants of the QCD Lagrangian are computed up to O(\alpha_s^2
G_F m_t^2). Also the decoupling constants for the strong coupling constant
\alpha_s and the light quark masses relating the quantities of the full theory
to the corresponding quantities of the effective one are evaluated up to order
\alpha_s^2 G_F m_t^2.Comment: 20 pages (revtex), 3 figure
Wilson Fermions on a Transverse Lattice
In the light-front formulation of field theory, it is possible to write down
a chirally invariant mass term. It thus appears as if one could solve the
species doubling problem on a light-front quantized transverse lattice in a
chirally invariant way. However, upon introducing link fields and after
renormalizing, one finds exactly the same LF Hamiltonian as if one had started
from the standard Wilson action in the first place. The (light-front) chirally
invariant transverse lattice regularization is thus not chirally invariant in
the conventional sense. As an application of the Wilson formulation for
fermions on a lattice, we calculate spectrum, distribution functions
and distribution amplitudes for mesons below in a truncated Fock space.Comment: 14 pages, RevTe
The Case for Quantum Key Distribution
Quantum key distribution (QKD) promises secure key agreement by using quantum
mechanical systems. We argue that QKD will be an important part of future
cryptographic infrastructures. It can provide long-term confidentiality for
encrypted information without reliance on computational assumptions. Although
QKD still requires authentication to prevent man-in-the-middle attacks, it can
make use of either information-theoretically secure symmetric key
authentication or computationally secure public key authentication: even when
using public key authentication, we argue that QKD still offers stronger
security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009
Workshop on Quantum and Classical Information Security; version 2 minor
content revision
Low-Energy Universality in Atomic and Nuclear Physics
An effective field theory developed for systems interacting through
short-range interactions can be applied to systems of cold atoms with a large
scattering length and to nucleons at low energies. It is therefore the ideal
tool to analyze the universal properties associated with the Efimov effect in
three- and four-body systems. In this "progress report", we will discuss recent
results obtained within this framework and report on progress regarding the
inclusion of higher order corrections associated with the finite range of the
underlying interaction.Comment: Commissioned article for Few-Body Systems, 47 pp, 16 fig
A lattice formulation of chiral gauge theories
We present a method for implementing gauge theories of chiral fermions on the
lattice.Comment: 3 pages LaTeX, espcrc2 style file. Talk presented at LATTICE96(chiral
gauge
Abelian-Projected Effective Gauge Theory of QCD with Asymptotic Freedom and Quark Confinement
We give an outline of a recent proof that the low-energy effective gauge
theory exhibiting quark confinement due to magnetic monopole condensation can
be derived from QCD without any specific assumption. We emphasize that the
low-energy effective abelian gauge theories obtained here give the dual
description of the same physics in the low-energy region. They show that the
QCD vacuum is nothing but the dual (type II) superconductor.Comment: 15 pages, Latex, no figures, Talk given at YKIS'97, Non-perturbative
QCD, Kyot
Abelian-Projected Effective Gauge Theory of QCD with Asymptotic Freedom and Quark Confinement
Starting from SU(2) Yang-Mills theory in 3+1 dimensions, we prove that the
abelian-projected effective gauge theories are written in terms of the maximal
abelian gauge field and the dual abelian gauge field interacting with monopole
current. This is performed by integrating out all the remaining non-Abelian
gauge field belonging to SU(2)/U(1). We show that the resulting abelian gauge
theory recovers exactly the same one-loop beta function as the original
Yang-Mills theory. Moreover, the dual abelian gauge field becomes massive if
the monopole condensation occurs. This result supports the dual superconductor
scenario for quark confinement in QCD. We give a criterion of dual
superconductivity and point out that the monopole condensation can be estimated
from the classical instanton configuration. Therefore there can exist the
effective abelian gauge theory which shows both asymptotic freedom and quark
confinement based on the dual Meissner mechanism. Inclusion of arbitrary number
of fermion flavors is straightforward in this approach. Some implications to
lower dimensional case will also be discussed.Comment: 39 pages, Latex, no figures, (2.2, 4.1, 4.3 are modified; 4.4,
Appendices A,B,C and references are added. No change in conclusion
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