105,101 research outputs found
Gauge-invariant field correlators in QCD at finite temperature
No full textWe determine, by numerical simulations on a lattice, the gauge-invariant two-point correlation functions of the gauge field strengths in the QCD vacuum at zero temperature, down to a distance of 0.1 fm. We also study the behaviour of the gauge-invariant field correlators in the theory at finite temperature, across the deconfinement phase transition
Theta dependence of SU(N) gauge theories in the presence of a topological term
No full textWe review results concerning the theta dependence of 4D SU(N) gauge theories
and QCD, where theta is the coefficient of the CP-violating topological term in
the Lagrangian. In particular, we discuss theta dependence in the large-N
limit.
Most results have been obtained within the lattice formulation of the theory
via numerical simulations, which allow to investigate the theta dependence of
the ground-state energy and the spectrum around theta=0 by determining the
moments of the topological charge distribution, and their correlations with
other observables. We discuss the various methods which have been employed to
determine the topological susceptibility, and higher-order terms of the theta
expansion. We review results at zero and finite temperature. We show that the
results support the scenario obtained by general large-N scaling arguments, and
in particular the Witten-Veneziano mechanism to explain the U(1)_A problem. We
also compare with results obtained by other approaches, especially in the
large-N limit, where the issue has been also addressed using, for example, the
AdS/CFT correspondence.
We discuss issues related to theta dependence in full QCD: the neutron
electric dipole moment, the dependence of the topological susceptibility on the
quark masses, the U(1)_A symmetry breaking at finite temperature.
We also consider the 2D CP(N) model, which is an interesting theoretical
laboratory to study issues related to topology. We review analytical results in
the large-N limit, and numerical results within its lattice formulation.
Finally, we discuss the main features of the two-point correlation function
of the topological charge density
Intellectual property protection for fast evolving technologies
No full textThis paper studies the effects of market competition and intellectual property protection in emerging technologies such as software. In doing so, this research aims at contributing to the ongoing discussion on the possibility of broadening the scope of patent protection, in the EU, in order to cover many of the newly evolving technologies. The model indicates that optimal patent protection is case specific, while its degree of protection should vary depending on the rate of growth of the particular technology, as well as the degree of market competition. The main argument of the paper is that intellectual property protection has a dual effect, allowing the innovator to fully appropriate his R&D, at the cost of limiting the number of innovators who will be able to innovate, reducing knowledge spillovers
Out-of-equilibrium scaling of the energy density along the critical relaxational flow after a quench of the temperature
No full textWe study the out-of-equilibrium behavior of statistical systems along critical relaxational flows arising from instantaneous quenches of the temperature T to the critical point Tc, starting from equilibrium conditions at time t=0. In the case of soft quenches, i.e., when the initial temperature T is assumed sufficiently close to Tc (to keep the system within the critical regime), the critical modes develop an out-of-equilibrium finite-size-scaling (FSS) behavior in terms of the rescaled time variable Θ=t/Lz, where t is the time interval after quenching, L is the size of the system, and z is the dynamic exponent associated with the dynamics. However, the realization of this picture is less clear when considering the energy density, whose equilibrium scaling behavior (corresponding to the starting point of the relaxational flow) is generally dominated by a temperature-dependent regular background term or mixing with the identity operator. These issues are investigated by numerical analyses within the three-dimensional lattice N-vector models, for N=3 and 4, which provide examples of critical behaviors with negative values of the specific-heat critical exponent α, implying that also the critical behavior of the specific heat gets hidden by the background term. The results show that, after subtraction of its asymptotic critical value at Tc, the energy density develops an asymptotic out-of-equilibrium FSS in terms of Θ as well, whose scaling function appears singular in the small-Θ limit
Resummation of Cactus Diagrams in the Clover Improved Lattice Formulation of QCD
No full textWe extend to the clover improved lattice formulation of QCD the resummation
of cactus diagrams, i.e. a certain class of tadpole-like gauge invariant
diagrams. Cactus resummation yields an improved perturbative expansion. We
apply it to the lattice renormalization of some two-fermion operators improving
their one-loop perturbative estimates
Resummation of Cactus Diagrams in Lattice QCD
No full textWe show how to perform a resummation, to all orders in perturbation theory,
of a certain class of gauge invariant diagrams in Lattice QCD. These diagrams
are often largely responsible for lattice artifacts. Our resummation leads to
an improved perturbative expansion. Applied to a number of cases of interest,
this expansion yields results remarkably close to corresponding nonperturbative
estimates
GAUGE-FERMION CONDENSATION IN SUPERSYMMETRIC GAUGE-THEORIES WITH GENERAL COMPACT LIE-GROUPS
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